diff options
author | bapt <bapt@FreeBSD.org> | 2015-01-04 00:58:30 +0000 |
---|---|---|
committer | bapt <bapt@FreeBSD.org> | 2015-01-04 00:58:30 +0000 |
commit | 6947e68c2d0b3f89be0bdf9b0ef84502bf18027d (patch) | |
tree | 8a96c88ad6e18cb490442897926a87f349d66802 /contrib/binutils/ld | |
parent | fdb01c77003977d286c195a7d5c8d4d0e0277df6 (diff) | |
download | FreeBSD-src-6947e68c2d0b3f89be0bdf9b0ef84502bf18027d.zip FreeBSD-src-6947e68c2d0b3f89be0bdf9b0ef84502bf18027d.tar.gz |
Add pregenerated documentation for as(1) and ld(1)
Diffstat (limited to 'contrib/binutils/ld')
-rw-r--r-- | contrib/binutils/ld/configdoc.texi | 25 | ||||
-rw-r--r-- | contrib/binutils/ld/ld.txt | 6564 |
2 files changed, 6589 insertions, 0 deletions
diff --git a/contrib/binutils/ld/configdoc.texi b/contrib/binutils/ld/configdoc.texi new file mode 100644 index 0000000..03ab558 --- /dev/null +++ b/contrib/binutils/ld/configdoc.texi @@ -0,0 +1,25 @@ +@c ------------------------------ CONFIGURATION VARS: +@c 1. Inclusiveness of this manual +@set GENERIC + +@c 2. Specific target machines +@set ARM +@set H8300 +@set HPPA +@set I960 +@set M68HC11 +@set MMIX +@set MSP430 +@set POWERPC +@set POWERPC64 +@set Renesas +@set SPU +@set TICOFF +@set WIN32 +@set XTENSA + +@c 3. Properties of this configuration +@clear SingleFormat +@set UsesEnvVars +@c ------------------------------ end CONFIGURATION VARS + diff --git a/contrib/binutils/ld/ld.txt b/contrib/binutils/ld/ld.txt new file mode 100644 index 0000000..e4aa1f1 --- /dev/null +++ b/contrib/binutils/ld/ld.txt @@ -0,0 +1,6564 @@ +START-INFO-DIR-ENTRY +* Ld: (ld). The GNU linker. +END-INFO-DIR-ENTRY + +LD +1 Overview +2 Invocation + 2.1 Command Line Options + 2.1.1 Options Specific to i386 PE Targets + 2.1.2 Options specific to Motorola 68HC11 and 68HC12 targets + 2.2 Environment Variables +3 Linker Scripts + 3.1 Basic Linker Script Concepts + 3.2 Linker Script Format + 3.3 Simple Linker Script Example + 3.4 Simple Linker Script Commands + 3.4.1 Setting the Entry Point + 3.4.2 Commands Dealing with Files + 3.4.3 Commands Dealing with Object File Formats + 3.4.4 Other Linker Script Commands + 3.5 Assigning Values to Symbols + 3.5.1 Simple Assignments + 3.5.2 PROVIDE + 3.5.3 PROVIDE_HIDDEN + 3.5.4 Source Code Reference + 3.6 SECTIONS Command + 3.6.1 Output Section Description + 3.6.2 Output Section Name + 3.6.3 Output Section Address + 3.6.4 Input Section Description + 3.6.4.1 Input Section Basics + 3.6.4.2 Input Section Wildcard Patterns + 3.6.4.3 Input Section for Common Symbols + 3.6.4.4 Input Section and Garbage Collection + 3.6.4.5 Input Section Example + 3.6.5 Output Section Data + 3.6.6 Output Section Keywords + 3.6.7 Output Section Discarding + 3.6.8 Output Section Attributes + 3.6.8.1 Output Section Type + 3.6.8.2 Output Section LMA + 3.6.8.3 Forced Output Alignment + 3.6.8.4 Forced Input Alignment + 3.6.8.5 Output Section Region + 3.6.8.6 Output Section Phdr + 3.6.8.7 Output Section Fill + 3.6.9 Overlay Description + 3.7 MEMORY Command + 3.8 PHDRS Command + 3.9 VERSION Command + 3.10 Expressions in Linker Scripts + 3.10.1 Constants + 3.10.2 Symbol Names + 3.10.3 Orphan Sections + 3.10.4 The Location Counter + 3.10.5 Operators + 3.10.6 Evaluation + 3.10.7 The Section of an Expression + 3.10.8 Builtin Functions + 3.11 Implicit Linker Scripts +4 Machine Dependent Features + 4.1 'ld' and the H8/300 + 4.2 'ld' and the Intel 960 Family + 4.3 'ld' and the Motorola 68HC11 and 68HC12 families + 4.3.1 Linker Relaxation + 4.3.2 Trampoline Generation + 4.4 'ld' and the ARM family + 4.5 'ld' and HPPA 32-bit ELF Support + 4.6 'ld' and MMIX + 4.7 'ld' and MSP430 + 4.8 'ld' and PowerPC 32-bit ELF Support + 4.9 'ld' and PowerPC64 64-bit ELF Support + 4.10 'ld' and SPU ELF Support + 4.11 'ld''s Support for Various TI COFF Versions + 4.12 'ld' and WIN32 (cygwin/mingw) + 4.13 'ld' and Xtensa Processors +5 BFD + 5.1 How It Works: An Outline of BFD + 5.1.1 Information Loss + 5.1.2 The BFD canonical object-file format +6 Reporting Bugs + 6.1 Have You Found a Bug? + 6.2 How to Report Bugs +Appendix A MRI Compatible Script Files +Appendix B GNU Free Documentation License + ADDENDUM: How to use this License for your documents +LD Index +LD +** + +This file documents the GNU linker ld version "2.17.50 [FreeBSD] +2007-07-03". + + This document is distributed under the terms of the GNU Free +Documentation License. A copy of the license is included in the section +entitled "GNU Free Documentation License". + +1 Overview +********** + +'ld' combines a number of object and archive files, relocates their data +and ties up symbol references. Usually the last step in compiling a +program is to run 'ld'. + + 'ld' accepts Linker Command Language files written in a superset of +AT&T's Link Editor Command Language syntax, to provide explicit and +total control over the linking process. + + This version of 'ld' uses the general purpose BFD libraries to +operate on object files. This allows 'ld' to read, combine, and write +object files in many different formats--for example, COFF or 'a.out'. +Different formats may be linked together to produce any available kind +of object file. *Note BFD::, for more information. + + Aside from its flexibility, the GNU linker is more helpful than other +linkers in providing diagnostic information. Many linkers abandon +execution immediately upon encountering an error; whenever possible, +'ld' continues executing, allowing you to identify other errors (or, in +some cases, to get an output file in spite of the error). + +2 Invocation +************ + +The GNU linker 'ld' is meant to cover a broad range of situations, and +to be as compatible as possible with other linkers. As a result, you +have many choices to control its behavior. + +2.1 Command Line Options +======================== + +The linker supports a plethora of command-line options, but in actual +practice few of them are used in any particular context. For instance, +a frequent use of 'ld' is to link standard Unix object files on a +standard, supported Unix system. On such a system, to link a file +'hello.o': + + ld -o OUTPUT /lib/crt0.o hello.o -lc + + This tells 'ld' to produce a file called OUTPUT as the result of +linking the file '/lib/crt0.o' with 'hello.o' and the library 'libc.a', +which will come from the standard search directories. (See the +discussion of the '-l' option below.) + + Some of the command-line options to 'ld' may be specified at any +point in the command line. However, options which refer to files, such +as '-l' or '-T', cause the file to be read at the point at which the +option appears in the command line, relative to the object files and +other file options. Repeating non-file options with a different +argument will either have no further effect, or override prior +occurrences (those further to the left on the command line) of that +option. Options which may be meaningfully specified more than once are +noted in the descriptions below. + + Non-option arguments are object files or archives which are to be +linked together. They may follow, precede, or be mixed in with +command-line options, except that an object file argument may not be +placed between an option and its argument. + + Usually the linker is invoked with at least one object file, but you +can specify other forms of binary input files using '-l', '-R', and the +script command language. If _no_ binary input files at all are +specified, the linker does not produce any output, and issues the +message 'No input files'. + + If the linker cannot recognize the format of an object file, it will +assume that it is a linker script. A script specified in this way +augments the main linker script used for the link (either the default +linker script or the one specified by using '-T'). This feature permits +the linker to link against a file which appears to be an object or an +archive, but actually merely defines some symbol values, or uses 'INPUT' +or 'GROUP' to load other objects. Note that specifying a script in this +way merely augments the main linker script; use the '-T' option to +replace the default linker script entirely. *Note Scripts::. + + For options whose names are a single letter, option arguments must +either follow the option letter without intervening whitespace, or be +given as separate arguments immediately following the option that +requires them. + + For options whose names are multiple letters, either one dash or two +can precede the option name; for example, '-trace-symbol' and +'--trace-symbol' are equivalent. Note--there is one exception to this +rule. Multiple letter options that start with a lower case 'o' can only +be preceded by two dashes. This is to reduce confusion with the '-o' +option. So for example '-omagic' sets the output file name to 'magic' +whereas '--omagic' sets the NMAGIC flag on the output. + + Arguments to multiple-letter options must either be separated from +the option name by an equals sign, or be given as separate arguments +immediately following the option that requires them. For example, +'--trace-symbol foo' and '--trace-symbol=foo' are equivalent. Unique +abbreviations of the names of multiple-letter options are accepted. + + Note--if the linker is being invoked indirectly, via a compiler +driver (e.g. 'gcc') then all the linker command line options should be +prefixed by '-Wl,' (or whatever is appropriate for the particular +compiler driver) like this: + + gcc -Wl,--startgroup foo.o bar.o -Wl,--endgroup + + This is important, because otherwise the compiler driver program may +silently drop the linker options, resulting in a bad link. + + Here is a table of the generic command line switches accepted by the +GNU linker: + +'@FILE' + Read command-line options from FILE. The options read are inserted + in place of the original @FILE option. If FILE does not exist, or + cannot be read, then the option will be treated literally, and not + removed. + + Options in FILE are separated by whitespace. A whitespace + character may be included in an option by surrounding the entire + option in either single or double quotes. Any character (including + a backslash) may be included by prefixing the character to be + included with a backslash. The FILE may itself contain additional + @FILE options; any such options will be processed recursively. + +'-aKEYWORD' + This option is supported for HP/UX compatibility. The KEYWORD + argument must be one of the strings 'archive', 'shared', or + 'default'. '-aarchive' is functionally equivalent to '-Bstatic', + and the other two keywords are functionally equivalent to + '-Bdynamic'. This option may be used any number of times. + +'-AARCHITECTURE' +'--architecture=ARCHITECTURE' + In the current release of 'ld', this option is useful only for the + Intel 960 family of architectures. In that 'ld' configuration, the + ARCHITECTURE argument identifies the particular architecture in the + 960 family, enabling some safeguards and modifying the + archive-library search path. *Note 'ld' and the Intel 960 family: + i960, for details. + + Future releases of 'ld' may support similar functionality for other + architecture families. + +'-b INPUT-FORMAT' +'--format=INPUT-FORMAT' + 'ld' may be configured to support more than one kind of object + file. If your 'ld' is configured this way, you can use the '-b' + option to specify the binary format for input object files that + follow this option on the command line. Even when 'ld' is + configured to support alternative object formats, you don't usually + need to specify this, as 'ld' should be configured to expect as a + default input format the most usual format on each machine. + INPUT-FORMAT is a text string, the name of a particular format + supported by the BFD libraries. (You can list the available binary + formats with 'objdump -i'.) *Note BFD::. + + You may want to use this option if you are linking files with an + unusual binary format. You can also use '-b' to switch formats + explicitly (when linking object files of different formats), by + including '-b INPUT-FORMAT' before each group of object files in a + particular format. + + The default format is taken from the environment variable + 'GNUTARGET'. *Note Environment::. You can also define the input + format from a script, using the command 'TARGET'; see *note Format + Commands::. + +'-c MRI-COMMANDFILE' +'--mri-script=MRI-COMMANDFILE' + For compatibility with linkers produced by MRI, 'ld' accepts script + files written in an alternate, restricted command language, + described in *note MRI Compatible Script Files: MRI. Introduce MRI + script files with the option '-c'; use the '-T' option to run + linker scripts written in the general-purpose 'ld' scripting + language. If MRI-CMDFILE does not exist, 'ld' looks for it in the + directories specified by any '-L' options. + +'-d' +'-dc' +'-dp' + These three options are equivalent; multiple forms are supported + for compatibility with other linkers. They assign space to common + symbols even if a relocatable output file is specified (with '-r'). + The script command 'FORCE_COMMON_ALLOCATION' has the same effect. + *Note Miscellaneous Commands::. + +'-e ENTRY' +'--entry=ENTRY' + Use ENTRY as the explicit symbol for beginning execution of your + program, rather than the default entry point. If there is no + symbol named ENTRY, the linker will try to parse ENTRY as a number, + and use that as the entry address (the number will be interpreted + in base 10; you may use a leading '0x' for base 16, or a leading + '0' for base 8). *Note Entry Point::, for a discussion of defaults + and other ways of specifying the entry point. + +'--exclude-libs LIB,LIB,...' + Specifies a list of archive libraries from which symbols should not + be automatically exported. The library names may be delimited by + commas or colons. Specifying '--exclude-libs ALL' excludes symbols + in all archive libraries from automatic export. This option is + available only for the i386 PE targeted port of the linker and for + ELF targeted ports. For i386 PE, symbols explicitly listed in a + .def file are still exported, regardless of this option. For ELF + targeted ports, symbols affected by this option will be treated as + hidden. + +'-E' +'--export-dynamic' + When creating a dynamically linked executable, add all symbols to + the dynamic symbol table. The dynamic symbol table is the set of + symbols which are visible from dynamic objects at run time. + + If you do not use this option, the dynamic symbol table will + normally contain only those symbols which are referenced by some + dynamic object mentioned in the link. + + If you use 'dlopen' to load a dynamic object which needs to refer + back to the symbols defined by the program, rather than some other + dynamic object, then you will probably need to use this option when + linking the program itself. + + You can also use the dynamic list to control what symbols should be + added to the dynamic symbol table if the output format supports it. + See the description of '--dynamic-list'. + +'-EB' + Link big-endian objects. This affects the default output format. + +'-EL' + Link little-endian objects. This affects the default output + format. + +'-f' +'--auxiliary NAME' + When creating an ELF shared object, set the internal DT_AUXILIARY + field to the specified name. This tells the dynamic linker that + the symbol table of the shared object should be used as an + auxiliary filter on the symbol table of the shared object NAME. + + If you later link a program against this filter object, then, when + you run the program, the dynamic linker will see the DT_AUXILIARY + field. If the dynamic linker resolves any symbols from the filter + object, it will first check whether there is a definition in the + shared object NAME. If there is one, it will be used instead of + the definition in the filter object. The shared object NAME need + not exist. Thus the shared object NAME may be used to provide an + alternative implementation of certain functions, perhaps for + debugging or for machine specific performance. + + This option may be specified more than once. The DT_AUXILIARY + entries will be created in the order in which they appear on the + command line. + +'-F NAME' +'--filter NAME' + When creating an ELF shared object, set the internal DT_FILTER + field to the specified name. This tells the dynamic linker that + the symbol table of the shared object which is being created should + be used as a filter on the symbol table of the shared object NAME. + + If you later link a program against this filter object, then, when + you run the program, the dynamic linker will see the DT_FILTER + field. The dynamic linker will resolve symbols according to the + symbol table of the filter object as usual, but it will actually + link to the definitions found in the shared object NAME. Thus the + filter object can be used to select a subset of the symbols + provided by the object NAME. + + Some older linkers used the '-F' option throughout a compilation + toolchain for specifying object-file format for both input and + output object files. The GNU linker uses other mechanisms for this + purpose: the '-b', '--format', '--oformat' options, the 'TARGET' + command in linker scripts, and the 'GNUTARGET' environment + variable. The GNU linker will ignore the '-F' option when not + creating an ELF shared object. + +'-fini NAME' + When creating an ELF executable or shared object, call NAME when + the executable or shared object is unloaded, by setting DT_FINI to + the address of the function. By default, the linker uses '_fini' + as the function to call. + +'-g' + Ignored. Provided for compatibility with other tools. + +'-GVALUE' +'--gpsize=VALUE' + Set the maximum size of objects to be optimized using the GP + register to SIZE. This is only meaningful for object file formats + such as MIPS ECOFF which supports putting large and small objects + into different sections. This is ignored for other object file + formats. + +'-hNAME' +'-soname=NAME' + When creating an ELF shared object, set the internal DT_SONAME + field to the specified name. When an executable is linked with a + shared object which has a DT_SONAME field, then when the executable + is run the dynamic linker will attempt to load the shared object + specified by the DT_SONAME field rather than the using the file + name given to the linker. + +'-i' + Perform an incremental link (same as option '-r'). + +'-init NAME' + When creating an ELF executable or shared object, call NAME when + the executable or shared object is loaded, by setting DT_INIT to + the address of the function. By default, the linker uses '_init' + as the function to call. + +'-lNAMESPEC' +'--library=NAMESPEC' + Add the archive or object file specified by NAMESPEC to the list of + files to link. This option may be used any number of times. If + NAMESPEC is of the form ':FILENAME', 'ld' will search the library + path for a file called FILENAME, otherise it will search the + library path for a file called 'libNAMESPEC.a'. + + On systems which support shared libraries, 'ld' may also search for + files other than 'libNAMESPEC.a'. Specifically, on ELF and SunOS + systems, 'ld' will search a directory for a library called + 'libNAMESPEC.so' before searching for one called 'libNAMESPEC.a'. + (By convention, a '.so' extension indicates a shared library.) + Note that this behavior does not apply to ':FILENAME', which always + specifies a file called FILENAME. + + The linker will search an archive only once, at the location where + it is specified on the command line. If the archive defines a + symbol which was undefined in some object which appeared before the + archive on the command line, the linker will include the + appropriate file(s) from the archive. However, an undefined symbol + in an object appearing later on the command line will not cause the + linker to search the archive again. + + See the '-(' option for a way to force the linker to search + archives multiple times. + + You may list the same archive multiple times on the command line. + + This type of archive searching is standard for Unix linkers. + However, if you are using 'ld' on AIX, note that it is different + from the behaviour of the AIX linker. + +'-LSEARCHDIR' +'--library-path=SEARCHDIR' + Add path SEARCHDIR to the list of paths that 'ld' will search for + archive libraries and 'ld' control scripts. You may use this + option any number of times. The directories are searched in the + order in which they are specified on the command line. Directories + specified on the command line are searched before the default + directories. All '-L' options apply to all '-l' options, + regardless of the order in which the options appear. + + If SEARCHDIR begins with '=', then the '=' will be replaced by the + "sysroot prefix", a path specified when the linker is configured. + + The default set of paths searched (without being specified with + '-L') depends on which emulation mode 'ld' is using, and in some + cases also on how it was configured. *Note Environment::. + + The paths can also be specified in a link script with the + 'SEARCH_DIR' command. Directories specified this way are searched + at the point in which the linker script appears in the command + line. + +'-mEMULATION' + Emulate the EMULATION linker. You can list the available + emulations with the '--verbose' or '-V' options. + + If the '-m' option is not used, the emulation is taken from the + 'LDEMULATION' environment variable, if that is defined. + + Otherwise, the default emulation depends upon how the linker was + configured. + +'-M' +'--print-map' + Print a link map to the standard output. A link map provides + information about the link, including the following: + + * Where object files are mapped into memory. + * How common symbols are allocated. + * All archive members included in the link, with a mention of + the symbol which caused the archive member to be brought in. + * The values assigned to symbols. + + Note - symbols whose values are computed by an expression + which involves a reference to a previous value of the same + symbol may not have correct result displayed in the link map. + This is because the linker discards intermediate results and + only retains the final value of an expression. Under such + circumstances the linker will display the final value enclosed + by square brackets. Thus for example a linker script + containing: + + foo = 1 + foo = foo * 4 + foo = foo + 8 + + will produce the following output in the link map if the '-M' + option is used: + + 0x00000001 foo = 0x1 + [0x0000000c] foo = (foo * 0x4) + [0x0000000c] foo = (foo + 0x8) + + See *note Expressions:: for more information about expressions + in linker scripts. + +'-n' +'--nmagic' + Turn off page alignment of sections, and mark the output as + 'NMAGIC' if possible. + +'-N' +'--omagic' + Set the text and data sections to be readable and writable. Also, + do not page-align the data segment, and disable linking against + shared libraries. If the output format supports Unix style magic + numbers, mark the output as 'OMAGIC'. Note: Although a writable + text section is allowed for PE-COFF targets, it does not conform to + the format specification published by Microsoft. + +'--no-omagic' + This option negates most of the effects of the '-N' option. It + sets the text section to be read-only, and forces the data segment + to be page-aligned. Note - this option does not enable linking + against shared libraries. Use '-Bdynamic' for this. + +'-o OUTPUT' +'--output=OUTPUT' + Use OUTPUT as the name for the program produced by 'ld'; if this + option is not specified, the name 'a.out' is used by default. The + script command 'OUTPUT' can also specify the output file name. + +'-O LEVEL' + If LEVEL is a numeric values greater than zero 'ld' optimizes the + output. This might take significantly longer and therefore + probably should only be enabled for the final binary. + +'-q' +'--emit-relocs' + Leave relocation sections and contents in fully linked executables. + Post link analysis and optimization tools may need this information + in order to perform correct modifications of executables. This + results in larger executables. + + This option is currently only supported on ELF platforms. + +'--force-dynamic' + Force the output file to have dynamic sections. This option is + specific to VxWorks targets. + +'-r' +'--relocatable' + Generate relocatable output--i.e., generate an output file that can + in turn serve as input to 'ld'. This is often called "partial + linking". As a side effect, in environments that support standard + Unix magic numbers, this option also sets the output file's magic + number to 'OMAGIC'. If this option is not specified, an absolute + file is produced. When linking C++ programs, this option _will + not_ resolve references to constructors; to do that, use '-Ur'. + + When an input file does not have the same format as the output + file, partial linking is only supported if that input file does not + contain any relocations. Different output formats can have further + restrictions; for example some 'a.out'-based formats do not support + partial linking with input files in other formats at all. + + This option does the same thing as '-i'. + +'-R FILENAME' +'--just-symbols=FILENAME' + Read symbol names and their addresses from FILENAME, but do not + relocate it or include it in the output. This allows your output + file to refer symbolically to absolute locations of memory defined + in other programs. You may use this option more than once. + + For compatibility with other ELF linkers, if the '-R' option is + followed by a directory name, rather than a file name, it is + treated as the '-rpath' option. + +'-s' +'--strip-all' + Omit all symbol information from the output file. + +'-S' +'--strip-debug' + Omit debugger symbol information (but not all symbols) from the + output file. + +'-t' +'--trace' + Print the names of the input files as 'ld' processes them. + +'-T SCRIPTFILE' +'--script=SCRIPTFILE' + Use SCRIPTFILE as the linker script. This script replaces 'ld''s + default linker script (rather than adding to it), so COMMANDFILE + must specify everything necessary to describe the output file. + *Note Scripts::. If SCRIPTFILE does not exist in the current + directory, 'ld' looks for it in the directories specified by any + preceding '-L' options. Multiple '-T' options accumulate. + +'-dT SCRIPTFILE' +'--default-script=SCRIPTFILE' + Use SCRIPTFILE as the default linker script. *Note Scripts::. + + This option is similar to the '--script' option except that + processing of the script is delayed until after the rest of the + command line has been processed. This allows options placed after + the '--default-script' option on the command line to affect the + behaviour of the linker script, which can be important when the + linker command line cannot be directly controlled by the user. (eg + because the command line is being constructed by another tool, such + as 'gcc'). + +'-u SYMBOL' +'--undefined=SYMBOL' + Force SYMBOL to be entered in the output file as an undefined + symbol. Doing this may, for example, trigger linking of additional + modules from standard libraries. '-u' may be repeated with + different option arguments to enter additional undefined symbols. + This option is equivalent to the 'EXTERN' linker script command. + +'-Ur' + For anything other than C++ programs, this option is equivalent to + '-r': it generates relocatable output--i.e., an output file that + can in turn serve as input to 'ld'. When linking C++ programs, + '-Ur' _does_ resolve references to constructors, unlike '-r'. It + does not work to use '-Ur' on files that were themselves linked + with '-Ur'; once the constructor table has been built, it cannot be + added to. Use '-Ur' only for the last partial link, and '-r' for + the others. + +'--unique[=SECTION]' + Creates a separate output section for every input section matching + SECTION, or if the optional wildcard SECTION argument is missing, + for every orphan input section. An orphan section is one not + specifically mentioned in a linker script. You may use this option + multiple times on the command line; It prevents the normal merging + of input sections with the same name, overriding output section + assignments in a linker script. + +'-v' +'--version' +'-V' + Display the version number for 'ld'. The '-V' option also lists + the supported emulations. + +'-x' +'--discard-all' + Delete all local symbols. + +'-X' +'--discard-locals' + Delete all temporary local symbols. (These symbols start with + system-specific local label prefixes, typically '.L' for ELF + systems or 'L' for traditional a.out systems.) + +'-y SYMBOL' +'--trace-symbol=SYMBOL' + Print the name of each linked file in which SYMBOL appears. This + option may be given any number of times. On many systems it is + necessary to prepend an underscore. + + This option is useful when you have an undefined symbol in your + link but don't know where the reference is coming from. + +'-Y PATH' + Add PATH to the default library search path. This option exists + for Solaris compatibility. + +'-z KEYWORD' + The recognized keywords are: + + 'combreloc' + Combines multiple reloc sections and sorts them to make + dynamic symbol lookup caching possible. + + 'defs' + Disallows undefined symbols in object files. Undefined + symbols in shared libraries are still allowed. + + 'execstack' + Marks the object as requiring executable stack. + + 'initfirst' + This option is only meaningful when building a shared object. + It marks the object so that its runtime initialization will + occur before the runtime initialization of any other objects + brought into the process at the same time. Similarly the + runtime finalization of the object will occur after the + runtime finalization of any other objects. + + 'interpose' + Marks the object that its symbol table interposes before all + symbols but the primary executable. + + 'lazy' + When generating an executable or shared library, mark it to + tell the dynamic linker to defer function call resolution to + the point when the function is called (lazy binding), rather + than at load time. Lazy binding is the default. + + 'loadfltr' + Marks the object that its filters be processed immediately at + runtime. + + 'muldefs' + Allows multiple definitions. + + 'nocombreloc' + Disables multiple reloc sections combining. + + 'nocopyreloc' + Disables production of copy relocs. + + 'nodefaultlib' + Marks the object that the search for dependencies of this + object will ignore any default library search paths. + + 'nodelete' + Marks the object shouldn't be unloaded at runtime. + + 'nodlopen' + Marks the object not available to 'dlopen'. + + 'nodump' + Marks the object can not be dumped by 'dldump'. + + 'noexecstack' + Marks the object as not requiring executable stack. + + 'norelro' + Don't create an ELF 'PT_GNU_RELRO' segment header in the + object. + + 'now' + When generating an executable or shared library, mark it to + tell the dynamic linker to resolve all symbols when the + program is started, or when the shared library is linked to + using dlopen, instead of deferring function call resolution to + the point when the function is first called. + + 'origin' + Marks the object may contain $ORIGIN. + + 'relro' + Create an ELF 'PT_GNU_RELRO' segment header in the object. + + 'max-page-size=VALUE' + Set the emulation maximum page size to VALUE. + + 'common-page-size=VALUE' + Set the emulation common page size to VALUE. + + Other keywords are ignored for Solaris compatibility. + +'-( ARCHIVES -)' +'--start-group ARCHIVES --end-group' + The ARCHIVES should be a list of archive files. They may be either + explicit file names, or '-l' options. + + The specified archives are searched repeatedly until no new + undefined references are created. Normally, an archive is searched + only once in the order that it is specified on the command line. + If a symbol in that archive is needed to resolve an undefined + symbol referred to by an object in an archive that appears later on + the command line, the linker would not be able to resolve that + reference. By grouping the archives, they all be searched + repeatedly until all possible references are resolved. + + Using this option has a significant performance cost. It is best + to use it only when there are unavoidable circular references + between two or more archives. + +'--accept-unknown-input-arch' +'--no-accept-unknown-input-arch' + Tells the linker to accept input files whose architecture cannot be + recognised. The assumption is that the user knows what they are + doing and deliberately wants to link in these unknown input files. + This was the default behaviour of the linker, before release 2.14. + The default behaviour from release 2.14 onwards is to reject such + input files, and so the '--accept-unknown-input-arch' option has + been added to restore the old behaviour. + +'--as-needed' +'--no-as-needed' + This option affects ELF DT_NEEDED tags for dynamic libraries + mentioned on the command line after the '--as-needed' option. + Normally, the linker will add a DT_NEEDED tag for each dynamic + library mentioned on the command line, regardless of whether the + library is actually needed. '--as-needed' causes DT_NEEDED tags to + only be emitted for libraries that satisfy some symbol reference + from regular objects which is undefined at the point that the + library was linked. '--no-as-needed' restores the default + behaviour. + +'--add-needed' +'--no-add-needed' + This option affects the treatment of dynamic libraries from ELF + DT_NEEDED tags in dynamic libraries mentioned on the command line + after the '--no-add-needed' option. Normally, the linker will add + a DT_NEEDED tag for each dynamic library from DT_NEEDED tags. + '--no-add-needed' causes DT_NEEDED tags will never be emitted for + those libraries from DT_NEEDED tags. '--add-needed' restores the + default behaviour. + +'-assert KEYWORD' + This option is ignored for SunOS compatibility. + +'-Bdynamic' +'-dy' +'-call_shared' + Link against dynamic libraries. This is only meaningful on + platforms for which shared libraries are supported. This option is + normally the default on such platforms. The different variants of + this option are for compatibility with various systems. You may + use this option multiple times on the command line: it affects + library searching for '-l' options which follow it. + +'-Bgroup' + Set the 'DF_1_GROUP' flag in the 'DT_FLAGS_1' entry in the dynamic + section. This causes the runtime linker to handle lookups in this + object and its dependencies to be performed only inside the group. + '--unresolved-symbols=report-all' is implied. This option is only + meaningful on ELF platforms which support shared libraries. + +'-Bstatic' +'-dn' +'-non_shared' +'-static' + Do not link against shared libraries. This is only meaningful on + platforms for which shared libraries are supported. The different + variants of this option are for compatibility with various systems. + You may use this option multiple times on the command line: it + affects library searching for '-l' options which follow it. This + option also implies '--unresolved-symbols=report-all'. This option + can be used with '-shared'. Doing so means that a shared library + is being created but that all of the library's external references + must be resolved by pulling in entries from static libraries. + +'-Bsymbolic' + When creating a shared library, bind references to global symbols + to the definition within the shared library, if any. Normally, it + is possible for a program linked against a shared library to + override the definition within the shared library. This option is + only meaningful on ELF platforms which support shared libraries. + +'-Bsymbolic-functions' + When creating a shared library, bind references to global function + symbols to the definition within the shared library, if any. This + option is only meaningful on ELF platforms which support shared + libraries. + +'--dynamic-list=DYNAMIC-LIST-FILE' + Specify the name of a dynamic list file to the linker. This is + typically used when creating shared libraries to specify a list of + global symbols whose references shouldn't be bound to the + definition within the shared library, or creating dynamically + linked executables to specify a list of symbols which should be + added to the symbol table in the executable. This option is only + meaningful on ELF platforms which support shared libraries. + + The format of the dynamic list is the same as the version node + without scope and node name. See *note VERSION:: for more + information. + +'--dynamic-list-data' + Include all global data symbols to the dynamic list. + +'--dynamic-list-cpp-new' + Provide the builtin dynamic list for C++ operator new and delete. + It is mainly useful for building shared libstdc++. + +'--dynamic-list-cpp-typeinfo' + Provide the builtin dynamic list for C++ runtime type + identification. + +'--check-sections' +'--no-check-sections' + Asks the linker _not_ to check section addresses after they have + been assigned to see if there are any overlaps. Normally the + linker will perform this check, and if it finds any overlaps it + will produce suitable error messages. The linker does know about, + and does make allowances for sections in overlays. The default + behaviour can be restored by using the command line switch + '--check-sections'. + +'--cref' + Output a cross reference table. If a linker map file is being + generated, the cross reference table is printed to the map file. + Otherwise, it is printed on the standard output. + + The format of the table is intentionally simple, so that it may be + easily processed by a script if necessary. The symbols are printed + out, sorted by name. For each symbol, a list of file names is + given. If the symbol is defined, the first file listed is the + location of the definition. The remaining files contain references + to the symbol. + +'--no-define-common' + This option inhibits the assignment of addresses to common symbols. + The script command 'INHIBIT_COMMON_ALLOCATION' has the same effect. + *Note Miscellaneous Commands::. + + The '--no-define-common' option allows decoupling the decision to + assign addresses to Common symbols from the choice of the output + file type; otherwise a non-Relocatable output type forces assigning + addresses to Common symbols. Using '--no-define-common' allows + Common symbols that are referenced from a shared library to be + assigned addresses only in the main program. This eliminates the + unused duplicate space in the shared library, and also prevents any + possible confusion over resolving to the wrong duplicate when there + are many dynamic modules with specialized search paths for runtime + symbol resolution. + +'--defsym SYMBOL=EXPRESSION' + Create a global symbol in the output file, containing the absolute + address given by EXPRESSION. You may use this option as many times + as necessary to define multiple symbols in the command line. A + limited form of arithmetic is supported for the EXPRESSION in this + context: you may give a hexadecimal constant or the name of an + existing symbol, or use '+' and '-' to add or subtract hexadecimal + constants or symbols. If you need more elaborate expressions, + consider using the linker command language from a script (*note + Assignment: Symbol Definitions: Assignments.). _Note:_ there + should be no white space between SYMBOL, the equals sign ("<=>"), + and EXPRESSION. + +'--demangle[=STYLE]' +'--no-demangle' + These options control whether to demangle symbol names in error + messages and other output. When the linker is told to demangle, it + tries to present symbol names in a readable fashion: it strips + leading underscores if they are used by the object file format, and + converts C++ mangled symbol names into user readable names. + Different compilers have different mangling styles. The optional + demangling style argument can be used to choose an appropriate + demangling style for your compiler. The linker will demangle by + default unless the environment variable 'COLLECT_NO_DEMANGLE' is + set. These options may be used to override the default. + +'--dynamic-linker FILE' + Set the name of the dynamic linker. This is only meaningful when + generating dynamically linked ELF executables. The default dynamic + linker is normally correct; don't use this unless you know what you + are doing. + +'--fatal-warnings' + Treat all warnings as errors. + +'--force-exe-suffix' + Make sure that an output file has a .exe suffix. + + If a successfully built fully linked output file does not have a + '.exe' or '.dll' suffix, this option forces the linker to copy the + output file to one of the same name with a '.exe' suffix. This + option is useful when using unmodified Unix makefiles on a + Microsoft Windows host, since some versions of Windows won't run an + image unless it ends in a '.exe' suffix. + +'--gc-sections' +'--no-gc-sections' + Enable garbage collection of unused input sections. It is ignored + on targets that do not support this option. This option is not + compatible with '-r' or '--emit-relocs'. The default behaviour (of + not performing this garbage collection) can be restored by + specifying '--no-gc-sections' on the command line. + +'--print-gc-sections' +'--no-print-gc-sections' + List all sections removed by garbage collection. The listing is + printed on stderr. This option is only effective if garbage + collection has been enabled via the '--gc-sections') option. The + default behaviour (of not listing the sections that are removed) + can be restored by specifying '--no-print-gc-sections' on the + command line. + +'--help' + Print a summary of the command-line options on the standard output + and exit. + +'--target-help' + Print a summary of all target specific options on the standard + output and exit. + +'-Map MAPFILE' + Print a link map to the file MAPFILE. See the description of the + '-M' option, above. + +'--no-keep-memory' + 'ld' normally optimizes for speed over memory usage by caching the + symbol tables of input files in memory. This option tells 'ld' to + instead optimize for memory usage, by rereading the symbol tables + as necessary. This may be required if 'ld' runs out of memory + space while linking a large executable. + +'--no-undefined' +'-z defs' + Report unresolved symbol references from regular object files. + This is done even if the linker is creating a non-symbolic shared + library. The switch '--[no-]allow-shlib-undefined' controls the + behaviour for reporting unresolved references found in shared + libraries being linked in. + +'--allow-multiple-definition' +'-z muldefs' + Normally when a symbol is defined multiple times, the linker will + report a fatal error. These options allow multiple definitions and + the first definition will be used. + +'--allow-shlib-undefined' +'--no-allow-shlib-undefined' + Allows (the default) or disallows undefined symbols in shared + libraries. This switch is similar to '--no-undefined' except that + it determines the behaviour when the undefined symbols are in a + shared library rather than a regular object file. It does not + affect how undefined symbols in regular object files are handled. + + The reason that '--allow-shlib-undefined' is the default is that + the shared library being specified at link time may not be the same + as the one that is available at load time, so the symbols might + actually be resolvable at load time. Plus there are some systems, + (eg BeOS) where undefined symbols in shared libraries is normal. + (The kernel patches them at load time to select which function is + most appropriate for the current architecture. This is used for + example to dynamically select an appropriate memset function). + Apparently it is also normal for HPPA shared libraries to have + undefined symbols. + +'--no-undefined-version' + Normally when a symbol has an undefined version, the linker will + ignore it. This option disallows symbols with undefined version + and a fatal error will be issued instead. + +'--default-symver' + Create and use a default symbol version (the soname) for + unversioned exported symbols. + +'--default-imported-symver' + Create and use a default symbol version (the soname) for + unversioned imported symbols. + +'--no-warn-mismatch' + Normally 'ld' will give an error if you try to link together input + files that are mismatched for some reason, perhaps because they + have been compiled for different processors or for different + endiannesses. This option tells 'ld' that it should silently + permit such possible errors. This option should only be used with + care, in cases when you have taken some special action that ensures + that the linker errors are inappropriate. + +'--no-warn-search-mismatch' + Normally 'ld' will give a warning if it finds an incompatible + library during a library search. This option silences the warning. + +'--no-whole-archive' + Turn off the effect of the '--whole-archive' option for subsequent + archive files. + +'--noinhibit-exec' + Retain the executable output file whenever it is still usable. + Normally, the linker will not produce an output file if it + encounters errors during the link process; it exits without writing + an output file when it issues any error whatsoever. + +'-nostdlib' + Only search library directories explicitly specified on the command + line. Library directories specified in linker scripts (including + linker scripts specified on the command line) are ignored. + +'--oformat OUTPUT-FORMAT' + 'ld' may be configured to support more than one kind of object + file. If your 'ld' is configured this way, you can use the + '--oformat' option to specify the binary format for the output + object file. Even when 'ld' is configured to support alternative + object formats, you don't usually need to specify this, as 'ld' + should be configured to produce as a default output format the most + usual format on each machine. OUTPUT-FORMAT is a text string, the + name of a particular format supported by the BFD libraries. (You + can list the available binary formats with 'objdump -i'.) The + script command 'OUTPUT_FORMAT' can also specify the output format, + but this option overrides it. *Note BFD::. + +'-pie' +'--pic-executable' + Create a position independent executable. This is currently only + supported on ELF platforms. Position independent executables are + similar to shared libraries in that they are relocated by the + dynamic linker to the virtual address the OS chooses for them + (which can vary between invocations). Like normal dynamically + linked executables they can be executed and symbols defined in the + executable cannot be overridden by shared libraries. + +'-qmagic' + This option is ignored for Linux compatibility. + +'-Qy' + This option is ignored for SVR4 compatibility. + +'--relax' + An option with machine dependent effects. This option is only + supported on a few targets. *Note 'ld' and the H8/300: H8/300. + *Note 'ld' and the Intel 960 family: i960. *Note 'ld' and Xtensa + Processors: Xtensa. *Note 'ld' and the 68HC11 and 68HC12: + M68HC11/68HC12. *Note 'ld' and PowerPC 32-bit ELF Support: PowerPC + ELF32. + + On some platforms, the '--relax' option performs global + optimizations that become possible when the linker resolves + addressing in the program, such as relaxing address modes and + synthesizing new instructions in the output object file. + + On some platforms these link time global optimizations may make + symbolic debugging of the resulting executable impossible. This is + known to be the case for the Matsushita MN10200 and MN10300 family + of processors. + + On platforms where this is not supported, '--relax' is accepted, + but ignored. + +'--retain-symbols-file FILENAME' + Retain _only_ the symbols listed in the file FILENAME, discarding + all others. FILENAME is simply a flat file, with one symbol name + per line. This option is especially useful in environments (such + as VxWorks) where a large global symbol table is accumulated + gradually, to conserve run-time memory. + + '--retain-symbols-file' does _not_ discard undefined symbols, or + symbols needed for relocations. + + You may only specify '--retain-symbols-file' once in the command + line. It overrides '-s' and '-S'. + +'-rpath DIR' + Add a directory to the runtime library search path. This is used + when linking an ELF executable with shared objects. All '-rpath' + arguments are concatenated and passed to the runtime linker, which + uses them to locate shared objects at runtime. The '-rpath' option + is also used when locating shared objects which are needed by + shared objects explicitly included in the link; see the description + of the '-rpath-link' option. If '-rpath' is not used when linking + an ELF executable, the contents of the environment variable + 'LD_RUN_PATH' will be used if it is defined. + + The '-rpath' option may also be used on SunOS. By default, on + SunOS, the linker will form a runtime search patch out of all the + '-L' options it is given. If a '-rpath' option is used, the + runtime search path will be formed exclusively using the '-rpath' + options, ignoring the '-L' options. This can be useful when using + gcc, which adds many '-L' options which may be on NFS mounted file + systems. + + For compatibility with other ELF linkers, if the '-R' option is + followed by a directory name, rather than a file name, it is + treated as the '-rpath' option. + +'-rpath-link DIR' + When using ELF or SunOS, one shared library may require another. + This happens when an 'ld -shared' link includes a shared library as + one of the input files. + + When the linker encounters such a dependency when doing a + non-shared, non-relocatable link, it will automatically try to + locate the required shared library and include it in the link, if + it is not included explicitly. In such a case, the '-rpath-link' + option specifies the first set of directories to search. The + '-rpath-link' option may specify a sequence of directory names + either by specifying a list of names separated by colons, or by + appearing multiple times. + + This option should be used with caution as it overrides the search + path that may have been hard compiled into a shared library. In + such a case it is possible to use unintentionally a different + search path than the runtime linker would do. + + The linker uses the following search paths to locate required + shared libraries: + 1. Any directories specified by '-rpath-link' options. + 2. Any directories specified by '-rpath' options. The difference + between '-rpath' and '-rpath-link' is that directories + specified by '-rpath' options are included in the executable + and used at runtime, whereas the '-rpath-link' option is only + effective at link time. Searching '-rpath' in this way is + only supported by native linkers and cross linkers which have + been configured with the '--with-sysroot' option. + 3. On an ELF system, if the '-rpath' and 'rpath-link' options + were not used, search the contents of the environment variable + 'LD_RUN_PATH'. It is for the native linker only. + 4. On SunOS, if the '-rpath' option was not used, search any + directories specified using '-L' options. + 5. For a native linker, the contents of the environment variable + 'LD_LIBRARY_PATH'. + 6. For a native ELF linker, the directories in 'DT_RUNPATH' or + 'DT_RPATH' of a shared library are searched for shared + libraries needed by it. The 'DT_RPATH' entries are ignored if + 'DT_RUNPATH' entries exist. + 7. The default directories, normally '/lib' and '/usr/lib'. + 8. For a native linker on an ELF system, if the file + '/etc/ld.so.conf' exists, the list of directories found in + that file. + + If the required shared library is not found, the linker will issue + a warning and continue with the link. + +'-shared' +'-Bshareable' + Create a shared library. This is currently only supported on ELF, + XCOFF and SunOS platforms. On SunOS, the linker will automatically + create a shared library if the '-e' option is not used and there + are undefined symbols in the link. + +'--sort-common' + This option tells 'ld' to sort the common symbols by size when it + places them in the appropriate output sections. First come all the + one byte symbols, then all the two byte, then all the four byte, + and then everything else. This is to prevent gaps between symbols + due to alignment constraints. + +'--sort-section name' + This option will apply 'SORT_BY_NAME' to all wildcard section + patterns in the linker script. + +'--sort-section alignment' + This option will apply 'SORT_BY_ALIGNMENT' to all wildcard section + patterns in the linker script. + +'--split-by-file [SIZE]' + Similar to '--split-by-reloc' but creates a new output section for + each input file when SIZE is reached. SIZE defaults to a size of 1 + if not given. + +'--split-by-reloc [COUNT]' + Tries to creates extra sections in the output file so that no + single output section in the file contains more than COUNT + relocations. This is useful when generating huge relocatable files + for downloading into certain real time kernels with the COFF object + file format; since COFF cannot represent more than 65535 + relocations in a single section. Note that this will fail to work + with object file formats which do not support arbitrary sections. + The linker will not split up individual input sections for + redistribution, so if a single input section contains more than + COUNT relocations one output section will contain that many + relocations. COUNT defaults to a value of 32768. + +'--stats' + Compute and display statistics about the operation of the linker, + such as execution time and memory usage. + +'--sysroot=DIRECTORY' + Use DIRECTORY as the location of the sysroot, overriding the + configure-time default. This option is only supported by linkers + that were configured using '--with-sysroot'. + +'--traditional-format' + For some targets, the output of 'ld' is different in some ways from + the output of some existing linker. This switch requests 'ld' to + use the traditional format instead. + + For example, on SunOS, 'ld' combines duplicate entries in the + symbol string table. This can reduce the size of an output file + with full debugging information by over 30 percent. Unfortunately, + the SunOS 'dbx' program can not read the resulting program ('gdb' + has no trouble). The '--traditional-format' switch tells 'ld' to + not combine duplicate entries. + +'--section-start SECTIONNAME=ORG' + Locate a section in the output file at the absolute address given + by ORG. You may use this option as many times as necessary to + locate multiple sections in the command line. ORG must be a single + hexadecimal integer; for compatibility with other linkers, you may + omit the leading '0x' usually associated with hexadecimal values. + _Note:_ there should be no white space between SECTIONNAME, the + equals sign ("<=>"), and ORG. + +'-Tbss ORG' +'-Tdata ORG' +'-Ttext ORG' + Same as -section-start, with '.bss', '.data' or '.text' as the + SECTIONNAME. + +'--unresolved-symbols=METHOD' + Determine how to handle unresolved symbols. There are four + possible values for 'method': + + 'ignore-all' + Do not report any unresolved symbols. + + 'report-all' + Report all unresolved symbols. This is the default. + + 'ignore-in-object-files' + Report unresolved symbols that are contained in shared + libraries, but ignore them if they come from regular object + files. + + 'ignore-in-shared-libs' + Report unresolved symbols that come from regular object files, + but ignore them if they come from shared libraries. This can + be useful when creating a dynamic binary and it is known that + all the shared libraries that it should be referencing are + included on the linker's command line. + + The behaviour for shared libraries on their own can also be + controlled by the '--[no-]allow-shlib-undefined' option. + + Normally the linker will generate an error message for each + reported unresolved symbol but the option + '--warn-unresolved-symbols' can change this to a warning. + +'--dll-verbose' +'--verbose' + Display the version number for 'ld' and list the linker emulations + supported. Display which input files can and cannot be opened. + Display the linker script being used by the linker. + +'--version-script=VERSION-SCRIPTFILE' + Specify the name of a version script to the linker. This is + typically used when creating shared libraries to specify additional + information about the version hierarchy for the library being + created. This option is only meaningful on ELF platforms which + support shared libraries. *Note VERSION::. + +'--warn-common' + Warn when a common symbol is combined with another common symbol or + with a symbol definition. Unix linkers allow this somewhat sloppy + practise, but linkers on some other operating systems do not. This + option allows you to find potential problems from combining global + symbols. Unfortunately, some C libraries use this practise, so you + may get some warnings about symbols in the libraries as well as in + your programs. + + There are three kinds of global symbols, illustrated here by C + examples: + + 'int i = 1;' + A definition, which goes in the initialized data section of + the output file. + + 'extern int i;' + An undefined reference, which does not allocate space. There + must be either a definition or a common symbol for the + variable somewhere. + + 'int i;' + A common symbol. If there are only (one or more) common + symbols for a variable, it goes in the uninitialized data area + of the output file. The linker merges multiple common symbols + for the same variable into a single symbol. If they are of + different sizes, it picks the largest size. The linker turns + a common symbol into a declaration, if there is a definition + of the same variable. + + The '--warn-common' option can produce five kinds of warnings. + Each warning consists of a pair of lines: the first describes the + symbol just encountered, and the second describes the previous + symbol encountered with the same name. One or both of the two + symbols will be a common symbol. + + 1. Turning a common symbol into a reference, because there is + already a definition for the symbol. + FILE(SECTION): warning: common of `SYMBOL' + overridden by definition + FILE(SECTION): warning: defined here + + 2. Turning a common symbol into a reference, because a later + definition for the symbol is encountered. This is the same as + the previous case, except that the symbols are encountered in + a different order. + FILE(SECTION): warning: definition of `SYMBOL' + overriding common + FILE(SECTION): warning: common is here + + 3. Merging a common symbol with a previous same-sized common + symbol. + FILE(SECTION): warning: multiple common + of `SYMBOL' + FILE(SECTION): warning: previous common is here + + 4. Merging a common symbol with a previous larger common symbol. + FILE(SECTION): warning: common of `SYMBOL' + overridden by larger common + FILE(SECTION): warning: larger common is here + + 5. Merging a common symbol with a previous smaller common symbol. + This is the same as the previous case, except that the symbols + are encountered in a different order. + FILE(SECTION): warning: common of `SYMBOL' + overriding smaller common + FILE(SECTION): warning: smaller common is here + +'--warn-constructors' + Warn if any global constructors are used. This is only useful for + a few object file formats. For formats like COFF or ELF, the + linker can not detect the use of global constructors. + +'--warn-multiple-gp' + Warn if multiple global pointer values are required in the output + file. This is only meaningful for certain processors, such as the + Alpha. Specifically, some processors put large-valued constants in + a special section. A special register (the global pointer) points + into the middle of this section, so that constants can be loaded + efficiently via a base-register relative addressing mode. Since + the offset in base-register relative mode is fixed and relatively + small (e.g., 16 bits), this limits the maximum size of the constant + pool. Thus, in large programs, it is often necessary to use + multiple global pointer values in order to be able to address all + possible constants. This option causes a warning to be issued + whenever this case occurs. + +'--warn-once' + Only warn once for each undefined symbol, rather than once per + module which refers to it. + +'--warn-section-align' + Warn if the address of an output section is changed because of + alignment. Typically, the alignment will be set by an input + section. The address will only be changed if it not explicitly + specified; that is, if the 'SECTIONS' command does not specify a + start address for the section (*note SECTIONS::). + +'--warn-shared-textrel' + Warn if the linker adds a DT_TEXTREL to a shared object. + +'--warn-unresolved-symbols' + If the linker is going to report an unresolved symbol (see the + option '--unresolved-symbols') it will normally generate an error. + This option makes it generate a warning instead. + +'--error-unresolved-symbols' + This restores the linker's default behaviour of generating errors + when it is reporting unresolved symbols. + +'--whole-archive' + For each archive mentioned on the command line after the + '--whole-archive' option, include every object file in the archive + in the link, rather than searching the archive for the required + object files. This is normally used to turn an archive file into a + shared library, forcing every object to be included in the + resulting shared library. This option may be used more than once. + + Two notes when using this option from gcc: First, gcc doesn't know + about this option, so you have to use '-Wl,-whole-archive'. + Second, don't forget to use '-Wl,-no-whole-archive' after your list + of archives, because gcc will add its own list of archives to your + link and you may not want this flag to affect those as well. + +'--wrap SYMBOL' + Use a wrapper function for SYMBOL. Any undefined reference to + SYMBOL will be resolved to '__wrap_SYMBOL'. Any undefined + reference to '__real_SYMBOL' will be resolved to SYMBOL. + + This can be used to provide a wrapper for a system function. The + wrapper function should be called '__wrap_SYMBOL'. If it wishes to + call the system function, it should call '__real_SYMBOL'. + + Here is a trivial example: + + void * + __wrap_malloc (size_t c) + { + printf ("malloc called with %zu\n", c); + return __real_malloc (c); + } + + If you link other code with this file using '--wrap malloc', then + all calls to 'malloc' will call the function '__wrap_malloc' + instead. The call to '__real_malloc' in '__wrap_malloc' will call + the real 'malloc' function. + + You may wish to provide a '__real_malloc' function as well, so that + links without the '--wrap' option will succeed. If you do this, + you should not put the definition of '__real_malloc' in the same + file as '__wrap_malloc'; if you do, the assembler may resolve the + call before the linker has a chance to wrap it to 'malloc'. + +'--eh-frame-hdr' + Request creation of '.eh_frame_hdr' section and ELF + 'PT_GNU_EH_FRAME' segment header. + +'--enable-new-dtags' +'--disable-new-dtags' + This linker can create the new dynamic tags in ELF. But the older + ELF systems may not understand them. If you specify + '--enable-new-dtags', the dynamic tags will be created as needed. + If you specify '--disable-new-dtags', no new dynamic tags will be + created. By default, the new dynamic tags are not created. Note + that those options are only available for ELF systems. + +'--hash-size=NUMBER' + Set the default size of the linker's hash tables to a prime number + close to NUMBER. Increasing this value can reduce the length of + time it takes the linker to perform its tasks, at the expense of + increasing the linker's memory requirements. Similarly reducing + this value can reduce the memory requirements at the expense of + speed. + +'--hash-style=STYLE' + Set the type of linker's hash table(s). STYLE can be either 'sysv' + for classic ELF '.hash' section, 'gnu' for new style GNU + '.gnu.hash' section or 'both' for both the classic ELF '.hash' and + new style GNU '.gnu.hash' hash tables. The default is 'sysv'. + +'--reduce-memory-overheads' + This option reduces memory requirements at ld runtime, at the + expense of linking speed. This was introduced to select the old + O(n^2) algorithm for link map file generation, rather than the new + O(n) algorithm which uses about 40% more memory for symbol storage. + + Another effect of the switch is to set the default hash table size + to 1021, which again saves memory at the cost of lengthening the + linker's run time. This is not done however if the '--hash-size' + switch has been used. + + The '--reduce-memory-overheads' switch may be also be used to + enable other tradeoffs in future versions of the linker. + +2.1.1 Options Specific to i386 PE Targets +----------------------------------------- + +The i386 PE linker supports the '-shared' option, which causes the +output to be a dynamically linked library (DLL) instead of a normal +executable. You should name the output '*.dll' when you use this +option. In addition, the linker fully supports the standard '*.def' +files, which may be specified on the linker command line like an object +file (in fact, it should precede archives it exports symbols from, to +ensure that they get linked in, just like a normal object file). + + In addition to the options common to all targets, the i386 PE linker +support additional command line options that are specific to the i386 PE +target. Options that take values may be separated from their values by +either a space or an equals sign. + +'--add-stdcall-alias' + If given, symbols with a stdcall suffix (@NN) will be exported + as-is and also with the suffix stripped. [This option is specific + to the i386 PE targeted port of the linker] + +'--base-file FILE' + Use FILE as the name of a file in which to save the base addresses + of all the relocations needed for generating DLLs with 'dlltool'. + [This is an i386 PE specific option] + +'--dll' + Create a DLL instead of a regular executable. You may also use + '-shared' or specify a 'LIBRARY' in a given '.def' file. [This + option is specific to the i386 PE targeted port of the linker] + +'--enable-stdcall-fixup' +'--disable-stdcall-fixup' + If the link finds a symbol that it cannot resolve, it will attempt + to do "fuzzy linking" by looking for another defined symbol that + differs only in the format of the symbol name (cdecl vs stdcall) + and will resolve that symbol by linking to the match. For example, + the undefined symbol '_foo' might be linked to the function + '_foo@12', or the undefined symbol '_bar@16' might be linked to the + function '_bar'. When the linker does this, it prints a warning, + since it normally should have failed to link, but sometimes import + libraries generated from third-party dlls may need this feature to + be usable. If you specify '--enable-stdcall-fixup', this feature + is fully enabled and warnings are not printed. If you specify + '--disable-stdcall-fixup', this feature is disabled and such + mismatches are considered to be errors. [This option is specific + to the i386 PE targeted port of the linker] + +'--export-all-symbols' + If given, all global symbols in the objects used to build a DLL + will be exported by the DLL. Note that this is the default if there + otherwise wouldn't be any exported symbols. When symbols are + explicitly exported via DEF files or implicitly exported via + function attributes, the default is to not export anything else + unless this option is given. Note that the symbols 'DllMain@12', + 'DllEntryPoint@0', 'DllMainCRTStartup@12', and 'impure_ptr' will + not be automatically exported. Also, symbols imported from other + DLLs will not be re-exported, nor will symbols specifying the DLL's + internal layout such as those beginning with '_head_' or ending + with '_iname'. In addition, no symbols from 'libgcc', 'libstd++', + 'libmingw32', or 'crtX.o' will be exported. Symbols whose names + begin with '__rtti_' or '__builtin_' will not be exported, to help + with C++ DLLs. Finally, there is an extensive list of + cygwin-private symbols that are not exported (obviously, this + applies on when building DLLs for cygwin targets). These + cygwin-excludes are: '_cygwin_dll_entry@12', + '_cygwin_crt0_common@8', '_cygwin_noncygwin_dll_entry@12', + '_fmode', '_impure_ptr', 'cygwin_attach_dll', 'cygwin_premain0', + 'cygwin_premain1', 'cygwin_premain2', 'cygwin_premain3', and + 'environ'. [This option is specific to the i386 PE targeted port + of the linker] + +'--exclude-symbols SYMBOL,SYMBOL,...' + Specifies a list of symbols which should not be automatically + exported. The symbol names may be delimited by commas or colons. + [This option is specific to the i386 PE targeted port of the + linker] + +'--file-alignment' + Specify the file alignment. Sections in the file will always begin + at file offsets which are multiples of this number. This defaults + to 512. [This option is specific to the i386 PE targeted port of + the linker] + +'--heap RESERVE' +'--heap RESERVE,COMMIT' + Specify the amount of memory to reserve (and optionally commit) to + be used as heap for this program. The default is 1Mb reserved, 4K + committed. [This option is specific to the i386 PE targeted port + of the linker] + +'--image-base VALUE' + Use VALUE as the base address of your program or dll. This is the + lowest memory location that will be used when your program or dll + is loaded. To reduce the need to relocate and improve performance + of your dlls, each should have a unique base address and not + overlap any other dlls. The default is 0x400000 for executables, + and 0x10000000 for dlls. [This option is specific to the i386 PE + targeted port of the linker] + +'--kill-at' + If given, the stdcall suffixes (@NN) will be stripped from symbols + before they are exported. [This option is specific to the i386 PE + targeted port of the linker] + +'--large-address-aware' + If given, the appropriate bit in the "Characteristics" field of the + COFF header is set to indicate that this executable supports + virtual addresses greater than 2 gigabytes. This should be used in + conjunction with the /3GB or /USERVA=VALUE megabytes switch in the + "[operating systems]" section of the BOOT.INI. Otherwise, this bit + has no effect. [This option is specific to PE targeted ports of + the linker] + +'--major-image-version VALUE' + Sets the major number of the "image version". Defaults to 1. + [This option is specific to the i386 PE targeted port of the + linker] + +'--major-os-version VALUE' + Sets the major number of the "os version". Defaults to 4. [This + option is specific to the i386 PE targeted port of the linker] + +'--major-subsystem-version VALUE' + Sets the major number of the "subsystem version". Defaults to 4. + [This option is specific to the i386 PE targeted port of the + linker] + +'--minor-image-version VALUE' + Sets the minor number of the "image version". Defaults to 0. + [This option is specific to the i386 PE targeted port of the + linker] + +'--minor-os-version VALUE' + Sets the minor number of the "os version". Defaults to 0. [This + option is specific to the i386 PE targeted port of the linker] + +'--minor-subsystem-version VALUE' + Sets the minor number of the "subsystem version". Defaults to 0. + [This option is specific to the i386 PE targeted port of the + linker] + +'--output-def FILE' + The linker will create the file FILE which will contain a DEF file + corresponding to the DLL the linker is generating. This DEF file + (which should be called '*.def') may be used to create an import + library with 'dlltool' or may be used as a reference to + automatically or implicitly exported symbols. [This option is + specific to the i386 PE targeted port of the linker] + +'--out-implib FILE' + The linker will create the file FILE which will contain an import + lib corresponding to the DLL the linker is generating. This import + lib (which should be called '*.dll.a' or '*.a' may be used to link + clients against the generated DLL; this behaviour makes it possible + to skip a separate 'dlltool' import library creation step. [This + option is specific to the i386 PE targeted port of the linker] + +'--enable-auto-image-base' + Automatically choose the image base for DLLs, unless one is + specified using the '--image-base' argument. By using a hash + generated from the dllname to create unique image bases for each + DLL, in-memory collisions and relocations which can delay program + execution are avoided. [This option is specific to the i386 PE + targeted port of the linker] + +'--disable-auto-image-base' + Do not automatically generate a unique image base. If there is no + user-specified image base ('--image-base') then use the platform + default. [This option is specific to the i386 PE targeted port of + the linker] + +'--dll-search-prefix STRING' + When linking dynamically to a dll without an import library, search + for '<string><basename>.dll' in preference to 'lib<basename>.dll'. + This behaviour allows easy distinction between DLLs built for the + various "subplatforms": native, cygwin, uwin, pw, etc. For + instance, cygwin DLLs typically use '--dll-search-prefix=cyg'. + [This option is specific to the i386 PE targeted port of the + linker] + +'--enable-auto-import' + Do sophisticated linking of '_symbol' to '__imp__symbol' for DATA + imports from DLLs, and create the necessary thunking symbols when + building the import libraries with those DATA exports. Note: Use + of the 'auto-import' extension will cause the text section of the + image file to be made writable. This does not conform to the + PE-COFF format specification published by Microsoft. + + Using 'auto-import' generally will 'just work' - but sometimes you + may see this message: + + "variable '<var>' can't be auto-imported. Please read the + documentation for ld's '--enable-auto-import' for details." + + This message occurs when some (sub)expression accesses an address + ultimately given by the sum of two constants (Win32 import tables + only allow one). Instances where this may occur include accesses + to member fields of struct variables imported from a DLL, as well + as using a constant index into an array variable imported from a + DLL. Any multiword variable (arrays, structs, long long, etc) may + trigger this error condition. However, regardless of the exact + data type of the offending exported variable, ld will always detect + it, issue the warning, and exit. + + There are several ways to address this difficulty, regardless of + the data type of the exported variable: + + One way is to use -enable-runtime-pseudo-reloc switch. This leaves + the task of adjusting references in your client code for runtime + environment, so this method works only when runtime environment + supports this feature. + + A second solution is to force one of the 'constants' to be a + variable - that is, unknown and un-optimizable at compile time. + For arrays, there are two possibilities: a) make the indexee (the + array's address) a variable, or b) make the 'constant' index a + variable. Thus: + + extern type extern_array[]; + extern_array[1] --> + { volatile type *t=extern_array; t[1] } + + or + + extern type extern_array[]; + extern_array[1] --> + { volatile int t=1; extern_array[t] } + + For structs (and most other multiword data types) the only option + is to make the struct itself (or the long long, or the ...) + variable: + + extern struct s extern_struct; + extern_struct.field --> + { volatile struct s *t=&extern_struct; t->field } + + or + + extern long long extern_ll; + extern_ll --> + { volatile long long * local_ll=&extern_ll; *local_ll } + + A third method of dealing with this difficulty is to abandon + 'auto-import' for the offending symbol and mark it with + '__declspec(dllimport)'. However, in practise that requires using + compile-time #defines to indicate whether you are building a DLL, + building client code that will link to the DLL, or merely + building/linking to a static library. In making the choice between + the various methods of resolving the 'direct address with constant + offset' problem, you should consider typical real-world usage: + + Original: + --foo.h + extern int arr[]; + --foo.c + #include "foo.h" + void main(int argc, char **argv){ + printf("%d\n",arr[1]); + } + + Solution 1: + --foo.h + extern int arr[]; + --foo.c + #include "foo.h" + void main(int argc, char **argv){ + /* This workaround is for win32 and cygwin; do not "optimize" */ + volatile int *parr = arr; + printf("%d\n",parr[1]); + } + + Solution 2: + --foo.h + /* Note: auto-export is assumed (no __declspec(dllexport)) */ + #if (defined(_WIN32) || defined(__CYGWIN__)) && \ + !(defined(FOO_BUILD_DLL) || defined(FOO_STATIC)) + #define FOO_IMPORT __declspec(dllimport) + #else + #define FOO_IMPORT + #endif + extern FOO_IMPORT int arr[]; + --foo.c + #include "foo.h" + void main(int argc, char **argv){ + printf("%d\n",arr[1]); + } + + A fourth way to avoid this problem is to re-code your library to + use a functional interface rather than a data interface for the + offending variables (e.g. set_foo() and get_foo() accessor + functions). [This option is specific to the i386 PE targeted port + of the linker] + +'--disable-auto-import' + Do not attempt to do sophisticated linking of '_symbol' to + '__imp__symbol' for DATA imports from DLLs. [This option is + specific to the i386 PE targeted port of the linker] + +'--enable-runtime-pseudo-reloc' + If your code contains expressions described in -enable-auto-import + section, that is, DATA imports from DLL with non-zero offset, this + switch will create a vector of 'runtime pseudo relocations' which + can be used by runtime environment to adjust references to such + data in your client code. [This option is specific to the i386 PE + targeted port of the linker] + +'--disable-runtime-pseudo-reloc' + Do not create pseudo relocations for non-zero offset DATA imports + from DLLs. This is the default. [This option is specific to the + i386 PE targeted port of the linker] + +'--enable-extra-pe-debug' + Show additional debug info related to auto-import symbol thunking. + [This option is specific to the i386 PE targeted port of the + linker] + +'--section-alignment' + Sets the section alignment. Sections in memory will always begin + at addresses which are a multiple of this number. Defaults to + 0x1000. [This option is specific to the i386 PE targeted port of + the linker] + +'--stack RESERVE' +'--stack RESERVE,COMMIT' + Specify the amount of memory to reserve (and optionally commit) to + be used as stack for this program. The default is 2Mb reserved, 4K + committed. [This option is specific to the i386 PE targeted port + of the linker] + +'--subsystem WHICH' +'--subsystem WHICH:MAJOR' +'--subsystem WHICH:MAJOR.MINOR' + Specifies the subsystem under which your program will execute. The + legal values for WHICH are 'native', 'windows', 'console', 'posix', + and 'xbox'. You may optionally set the subsystem version also. + Numeric values are also accepted for WHICH. [This option is + specific to the i386 PE targeted port of the linker] + +2.1.2 Options specific to Motorola 68HC11 and 68HC12 targets +------------------------------------------------------------ + +The 68HC11 and 68HC12 linkers support specific options to control the +memory bank switching mapping and trampoline code generation. + +'--no-trampoline' + This option disables the generation of trampoline. By default a + trampoline is generated for each far function which is called using + a 'jsr' instruction (this happens when a pointer to a far function + is taken). + +'--bank-window NAME' + This option indicates to the linker the name of the memory region + in the 'MEMORY' specification that describes the memory bank + window. The definition of such region is then used by the linker + to compute paging and addresses within the memory window. + +2.2 Environment Variables +========================= + +You can change the behaviour of 'ld' with the environment variables +'GNUTARGET', 'LDEMULATION' and 'COLLECT_NO_DEMANGLE'. + + 'GNUTARGET' determines the input-file object format if you don't use +'-b' (or its synonym '--format'). Its value should be one of the BFD +names for an input format (*note BFD::). If there is no 'GNUTARGET' in +the environment, 'ld' uses the natural format of the target. If +'GNUTARGET' is set to 'default' then BFD attempts to discover the input +format by examining binary input files; this method often succeeds, but +there are potential ambiguities, since there is no method of ensuring +that the magic number used to specify object-file formats is unique. +However, the configuration procedure for BFD on each system places the +conventional format for that system first in the search-list, so +ambiguities are resolved in favor of convention. + + 'LDEMULATION' determines the default emulation if you don't use the +'-m' option. The emulation can affect various aspects of linker +behaviour, particularly the default linker script. You can list the +available emulations with the '--verbose' or '-V' options. If the '-m' +option is not used, and the 'LDEMULATION' environment variable is not +defined, the default emulation depends upon how the linker was +configured. + + Normally, the linker will default to demangling symbols. However, if +'COLLECT_NO_DEMANGLE' is set in the environment, then it will default to +not demangling symbols. This environment variable is used in a similar +fashion by the 'gcc' linker wrapper program. The default may be +overridden by the '--demangle' and '--no-demangle' options. + +3 Linker Scripts +**************** + +Every link is controlled by a "linker script". This script is written +in the linker command language. + + The main purpose of the linker script is to describe how the sections +in the input files should be mapped into the output file, and to control +the memory layout of the output file. Most linker scripts do nothing +more than this. However, when necessary, the linker script can also +direct the linker to perform many other operations, using the commands +described below. + + The linker always uses a linker script. If you do not supply one +yourself, the linker will use a default script that is compiled into the +linker executable. You can use the '--verbose' command line option to +display the default linker script. Certain command line options, such +as '-r' or '-N', will affect the default linker script. + + You may supply your own linker script by using the '-T' command line +option. When you do this, your linker script will replace the default +linker script. + + You may also use linker scripts implicitly by naming them as input +files to the linker, as though they were files to be linked. *Note +Implicit Linker Scripts::. + +3.1 Basic Linker Script Concepts +================================ + +We need to define some basic concepts and vocabulary in order to +describe the linker script language. + + The linker combines input files into a single output file. The +output file and each input file are in a special data format known as an +"object file format". Each file is called an "object file". The output +file is often called an "executable", but for our purposes we will also +call it an object file. Each object file has, among other things, a +list of "sections". We sometimes refer to a section in an input file as +an "input section"; similarly, a section in the output file is an +"output section". + + Each section in an object file has a name and a size. Most sections +also have an associated block of data, known as the "section contents". +A section may be marked as "loadable", which mean that the contents +should be loaded into memory when the output file is run. A section +with no contents may be "allocatable", which means that an area in +memory should be set aside, but nothing in particular should be loaded +there (in some cases this memory must be zeroed out). A section which +is neither loadable nor allocatable typically contains some sort of +debugging information. + + Every loadable or allocatable output section has two addresses. The +first is the "VMA", or virtual memory address. This is the address the +section will have when the output file is run. The second is the "LMA", +or load memory address. This is the address at which the section will +be loaded. In most cases the two addresses will be the same. An +example of when they might be different is when a data section is loaded +into ROM, and then copied into RAM when the program starts up (this +technique is often used to initialize global variables in a ROM based +system). In this case the ROM address would be the LMA, and the RAM +address would be the VMA. + + You can see the sections in an object file by using the 'objdump' +program with the '-h' option. + + Every object file also has a list of "symbols", known as the "symbol +table". A symbol may be defined or undefined. Each symbol has a name, +and each defined symbol has an address, among other information. If you +compile a C or C++ program into an object file, you will get a defined +symbol for every defined function and global or static variable. Every +undefined function or global variable which is referenced in the input +file will become an undefined symbol. + + You can see the symbols in an object file by using the 'nm' program, +or by using the 'objdump' program with the '-t' option. + +3.2 Linker Script Format +======================== + +Linker scripts are text files. + + You write a linker script as a series of commands. Each command is +either a keyword, possibly followed by arguments, or an assignment to a +symbol. You may separate commands using semicolons. Whitespace is +generally ignored. + + Strings such as file or format names can normally be entered +directly. If the file name contains a character such as a comma which +would otherwise serve to separate file names, you may put the file name +in double quotes. There is no way to use a double quote character in a +file name. + + You may include comments in linker scripts just as in C, delimited by +'/*' and '*/'. As in C, comments are syntactically equivalent to +whitespace. + +3.3 Simple Linker Script Example +================================ + +Many linker scripts are fairly simple. + + The simplest possible linker script has just one command: 'SECTIONS'. +You use the 'SECTIONS' command to describe the memory layout of the +output file. + + The 'SECTIONS' command is a powerful command. Here we will describe +a simple use of it. Let's assume your program consists only of code, +initialized data, and uninitialized data. These will be in the '.text', +'.data', and '.bss' sections, respectively. Let's assume further that +these are the only sections which appear in your input files. + + For this example, let's say that the code should be loaded at address +0x10000, and that the data should start at address 0x8000000. Here is a +linker script which will do that: + SECTIONS + { + . = 0x10000; + .text : { *(.text) } + . = 0x8000000; + .data : { *(.data) } + .bss : { *(.bss) } + } + + You write the 'SECTIONS' command as the keyword 'SECTIONS', followed +by a series of symbol assignments and output section descriptions +enclosed in curly braces. + + The first line inside the 'SECTIONS' command of the above example +sets the value of the special symbol '.', which is the location counter. +If you do not specify the address of an output section in some other way +(other ways are described later), the address is set from the current +value of the location counter. The location counter is then incremented +by the size of the output section. At the start of the 'SECTIONS' +command, the location counter has the value '0'. + + The second line defines an output section, '.text'. The colon is +required syntax which may be ignored for now. Within the curly braces +after the output section name, you list the names of the input sections +which should be placed into this output section. The '*' is a wildcard +which matches any file name. The expression '*(.text)' means all +'.text' input sections in all input files. + + Since the location counter is '0x10000' when the output section +'.text' is defined, the linker will set the address of the '.text' +section in the output file to be '0x10000'. + + The remaining lines define the '.data' and '.bss' sections in the +output file. The linker will place the '.data' output section at +address '0x8000000'. After the linker places the '.data' output +section, the value of the location counter will be '0x8000000' plus the +size of the '.data' output section. The effect is that the linker will +place the '.bss' output section immediately after the '.data' output +section in memory. + + The linker will ensure that each output section has the required +alignment, by increasing the location counter if necessary. In this +example, the specified addresses for the '.text' and '.data' sections +will probably satisfy any alignment constraints, but the linker may have +to create a small gap between the '.data' and '.bss' sections. + + That's it! That's a simple and complete linker script. + +3.4 Simple Linker Script Commands +================================= + +In this section we describe the simple linker script commands. + +3.4.1 Setting the Entry Point +----------------------------- + +The first instruction to execute in a program is called the "entry +point". You can use the 'ENTRY' linker script command to set the entry +point. The argument is a symbol name: + ENTRY(SYMBOL) + + There are several ways to set the entry point. The linker will set +the entry point by trying each of the following methods in order, and +stopping when one of them succeeds: + * the '-e' ENTRY command-line option; + * the 'ENTRY(SYMBOL)' command in a linker script; + * the value of the symbol 'start', if defined; + * the address of the first byte of the '.text' section, if present; + * The address '0'. + +3.4.2 Commands Dealing with Files +--------------------------------- + +Several linker script commands deal with files. + +'INCLUDE FILENAME' + Include the linker script FILENAME at this point. The file will be + searched for in the current directory, and in any directory + specified with the '-L' option. You can nest calls to 'INCLUDE' up + to 10 levels deep. + +'INPUT(FILE, FILE, ...)' +'INPUT(FILE FILE ...)' + The 'INPUT' command directs the linker to include the named files + in the link, as though they were named on the command line. + + For example, if you always want to include 'subr.o' any time you do + a link, but you can't be bothered to put it on every link command + line, then you can put 'INPUT (subr.o)' in your linker script. + + In fact, if you like, you can list all of your input files in the + linker script, and then invoke the linker with nothing but a '-T' + option. + + In case a "sysroot prefix" is configured, and the filename starts + with the '/' character, and the script being processed was located + inside the "sysroot prefix", the filename will be looked for in the + "sysroot prefix". Otherwise, the linker will try to open the file + in the current directory. If it is not found, the linker will + search through the archive library search path. See the + description of '-L' in *note Command Line Options: Options. + + If you use 'INPUT (-lFILE)', 'ld' will transform the name to + 'libFILE.a', as with the command line argument '-l'. + + When you use the 'INPUT' command in an implicit linker script, the + files will be included in the link at the point at which the linker + script file is included. This can affect archive searching. + +'GROUP(FILE, FILE, ...)' +'GROUP(FILE FILE ...)' + The 'GROUP' command is like 'INPUT', except that the named files + should all be archives, and they are searched repeatedly until no + new undefined references are created. See the description of '-(' + in *note Command Line Options: Options. + +'AS_NEEDED(FILE, FILE, ...)' +'AS_NEEDED(FILE FILE ...)' + This construct can appear only inside of the 'INPUT' or 'GROUP' + commands, among other filenames. The files listed will be handled + as if they appear directly in the 'INPUT' or 'GROUP' commands, with + the exception of ELF shared libraries, that will be added only when + they are actually needed. This construct essentially enables + '--as-needed' option for all the files listed inside of it and + restores previous '--as-needed' resp. '--no-as-needed' setting + afterwards. + +'OUTPUT(FILENAME)' + The 'OUTPUT' command names the output file. Using + 'OUTPUT(FILENAME)' in the linker script is exactly like using '-o + FILENAME' on the command line (*note Command Line Options: + Options.). If both are used, the command line option takes + precedence. + + You can use the 'OUTPUT' command to define a default name for the + output file other than the usual default of 'a.out'. + +'SEARCH_DIR(PATH)' + The 'SEARCH_DIR' command adds PATH to the list of paths where 'ld' + looks for archive libraries. Using 'SEARCH_DIR(PATH)' is exactly + like using '-L PATH' on the command line (*note Command Line + Options: Options.). If both are used, then the linker will search + both paths. Paths specified using the command line option are + searched first. + +'STARTUP(FILENAME)' + The 'STARTUP' command is just like the 'INPUT' command, except that + FILENAME will become the first input file to be linked, as though + it were specified first on the command line. This may be useful + when using a system in which the entry point is always the start of + the first file. + +3.4.3 Commands Dealing with Object File Formats +----------------------------------------------- + +A couple of linker script commands deal with object file formats. + +'OUTPUT_FORMAT(BFDNAME)' +'OUTPUT_FORMAT(DEFAULT, BIG, LITTLE)' + The 'OUTPUT_FORMAT' command names the BFD format to use for the + output file (*note BFD::). Using 'OUTPUT_FORMAT(BFDNAME)' is + exactly like using '--oformat BFDNAME' on the command line (*note + Command Line Options: Options.). If both are used, the command + line option takes precedence. + + You can use 'OUTPUT_FORMAT' with three arguments to use different + formats based on the '-EB' and '-EL' command line options. This + permits the linker script to set the output format based on the + desired endianness. + + If neither '-EB' nor '-EL' are used, then the output format will be + the first argument, DEFAULT. If '-EB' is used, the output format + will be the second argument, BIG. If '-EL' is used, the output + format will be the third argument, LITTLE. + + For example, the default linker script for the MIPS ELF target uses + this command: + OUTPUT_FORMAT(elf32-bigmips, elf32-bigmips, elf32-littlemips) + This says that the default format for the output file is + 'elf32-bigmips', but if the user uses the '-EL' command line + option, the output file will be created in the 'elf32-littlemips' + format. + +'TARGET(BFDNAME)' + The 'TARGET' command names the BFD format to use when reading input + files. It affects subsequent 'INPUT' and 'GROUP' commands. This + command is like using '-b BFDNAME' on the command line (*note + Command Line Options: Options.). If the 'TARGET' command is used + but 'OUTPUT_FORMAT' is not, then the last 'TARGET' command is also + used to set the format for the output file. *Note BFD::. + +3.4.4 Other Linker Script Commands +---------------------------------- + +There are a few other linker scripts commands. + +'ASSERT(EXP, MESSAGE)' + Ensure that EXP is non-zero. If it is zero, then exit the linker + with an error code, and print MESSAGE. + +'EXTERN(SYMBOL SYMBOL ...)' + Force SYMBOL to be entered in the output file as an undefined + symbol. Doing this may, for example, trigger linking of additional + modules from standard libraries. You may list several SYMBOLs for + each 'EXTERN', and you may use 'EXTERN' multiple times. This + command has the same effect as the '-u' command-line option. + +'FORCE_COMMON_ALLOCATION' + This command has the same effect as the '-d' command-line option: + to make 'ld' assign space to common symbols even if a relocatable + output file is specified ('-r'). + +'INHIBIT_COMMON_ALLOCATION' + This command has the same effect as the '--no-define-common' + command-line option: to make 'ld' omit the assignment of addresses + to common symbols even for a non-relocatable output file. + +'NOCROSSREFS(SECTION SECTION ...)' + This command may be used to tell 'ld' to issue an error about any + references among certain output sections. + + In certain types of programs, particularly on embedded systems when + using overlays, when one section is loaded into memory, another + section will not be. Any direct references between the two + sections would be errors. For example, it would be an error if + code in one section called a function defined in the other section. + + The 'NOCROSSREFS' command takes a list of output section names. If + 'ld' detects any cross references between the sections, it reports + an error and returns a non-zero exit status. Note that the + 'NOCROSSREFS' command uses output section names, not input section + names. + +'OUTPUT_ARCH(BFDARCH)' + Specify a particular output machine architecture. The argument is + one of the names used by the BFD library (*note BFD::). You can + see the architecture of an object file by using the 'objdump' + program with the '-f' option. + +3.5 Assigning Values to Symbols +=============================== + +You may assign a value to a symbol in a linker script. This will define +the symbol and place it into the symbol table with a global scope. + +3.5.1 Simple Assignments +------------------------ + +You may assign to a symbol using any of the C assignment operators: + +'SYMBOL = EXPRESSION ;' +'SYMBOL += EXPRESSION ;' +'SYMBOL -= EXPRESSION ;' +'SYMBOL *= EXPRESSION ;' +'SYMBOL /= EXPRESSION ;' +'SYMBOL <<= EXPRESSION ;' +'SYMBOL >>= EXPRESSION ;' +'SYMBOL &= EXPRESSION ;' +'SYMBOL |= EXPRESSION ;' + + The first case will define SYMBOL to the value of EXPRESSION. In the +other cases, SYMBOL must already be defined, and the value will be +adjusted accordingly. + + The special symbol name '.' indicates the location counter. You may +only use this within a 'SECTIONS' command. *Note Location Counter::. + + The semicolon after EXPRESSION is required. + + Expressions are defined below; see *note Expressions::. + + You may write symbol assignments as commands in their own right, or +as statements within a 'SECTIONS' command, or as part of an output +section description in a 'SECTIONS' command. + + The section of the symbol will be set from the section of the +expression; for more information, see *note Expression Section::. + + Here is an example showing the three different places that symbol +assignments may be used: + + floating_point = 0; + SECTIONS + { + .text : + { + *(.text) + _etext = .; + } + _bdata = (. + 3) & ~ 3; + .data : { *(.data) } + } +In this example, the symbol 'floating_point' will be defined as zero. +The symbol '_etext' will be defined as the address following the last +'.text' input section. The symbol '_bdata' will be defined as the +address following the '.text' output section aligned upward to a 4 byte +boundary. + +3.5.2 PROVIDE +------------- + +In some cases, it is desirable for a linker script to define a symbol +only if it is referenced and is not defined by any object included in +the link. For example, traditional linkers defined the symbol 'etext'. +However, ANSI C requires that the user be able to use 'etext' as a +function name without encountering an error. The 'PROVIDE' keyword may +be used to define a symbol, such as 'etext', only if it is referenced +but not defined. The syntax is 'PROVIDE(SYMBOL = EXPRESSION)'. + + Here is an example of using 'PROVIDE' to define 'etext': + SECTIONS + { + .text : + { + *(.text) + _etext = .; + PROVIDE(etext = .); + } + } + + In this example, if the program defines '_etext' (with a leading +underscore), the linker will give a multiple definition error. If, on +the other hand, the program defines 'etext' (with no leading +underscore), the linker will silently use the definition in the program. +If the program references 'etext' but does not define it, the linker +will use the definition in the linker script. + +3.5.3 PROVIDE_HIDDEN +-------------------- + +Similar to 'PROVIDE'. For ELF targeted ports, the symbol will be hidden +and won't be exported. + +3.5.4 Source Code Reference +--------------------------- + +Accessing a linker script defined variable from source code is not +intuitive. In particular a linker script symbol is not equivalent to a +variable declaration in a high level language, it is instead a symbol +that does not have a value. + + Before going further, it is important to note that compilers often +transform names in the source code into different names when they are +stored in the symbol table. For example, Fortran compilers commonly +prepend or append an underscore, and C++ performs extensive 'name +mangling'. Therefore there might be a discrepancy between the name of a +variable as it is used in source code and the name of the same variable +as it is defined in a linker script. For example in C a linker script +variable might be referred to as: + + extern int foo; + + But in the linker script it might be defined as: + + _foo = 1000; + + In the remaining examples however it is assumed that no name +transformation has taken place. + + When a symbol is declared in a high level language such as C, two +things happen. The first is that the compiler reserves enough space in +the program's memory to hold the _value_ of the symbol. The second is +that the compiler creates an entry in the program's symbol table which +holds the symbol's _address_. ie the symbol table contains the address +of the block of memory holding the symbol's value. So for example the +following C declaration, at file scope: + + int foo = 1000; + + creates a entry called 'foo' in the symbol table. This entry holds +the address of an 'int' sized block of memory where the number 1000 is +initially stored. + + When a program references a symbol the compiler generates code that +first accesses the symbol table to find the address of the symbol's +memory block and then code to read the value from that memory block. +So: + + foo = 1; + + looks up the symbol 'foo' in the symbol table, gets the address +associated with this symbol and then writes the value 1 into that +address. Whereas: + + int * a = & foo; + + looks up the symbol 'foo' in the symbol table, gets it address and +then copies this address into the block of memory associated with the +variable 'a'. + + Linker scripts symbol declarations, by contrast, create an entry in +the symbol table but do not assign any memory to them. Thus they are an +address without a value. So for example the linker script definition: + + foo = 1000; + + creates an entry in the symbol table called 'foo' which holds the +address of memory location 1000, but nothing special is stored at +address 1000. This means that you cannot access the _value_ of a linker +script defined symbol - it has no value - all you can do is access the +_address_ of a linker script defined symbol. + + Hence when you are using a linker script defined symbol in source +code you should always take the address of the symbol, and never attempt +to use its value. For example suppose you want to copy the contents of +a section of memory called .ROM into a section called .FLASH and the +linker script contains these declarations: + + start_of_ROM = .ROM; + end_of_ROM = .ROM + sizeof (.ROM) - 1; + start_of_FLASH = .FLASH; + + Then the C source code to perform the copy would be: + + extern char start_of_ROM, end_of_ROM, start_of_FLASH; + + memcpy (& start_of_FLASH, & start_of_ROM, & end_of_ROM - & start_of_ROM); + + Note the use of the '&' operators. These are correct. + +3.6 SECTIONS Command +==================== + +The 'SECTIONS' command tells the linker how to map input sections into +output sections, and how to place the output sections in memory. + + The format of the 'SECTIONS' command is: + SECTIONS + { + SECTIONS-COMMAND + SECTIONS-COMMAND + ... + } + + Each SECTIONS-COMMAND may of be one of the following: + + * an 'ENTRY' command (*note Entry command: Entry Point.) + * a symbol assignment (*note Assignments::) + * an output section description + * an overlay description + + The 'ENTRY' command and symbol assignments are permitted inside the +'SECTIONS' command for convenience in using the location counter in +those commands. This can also make the linker script easier to +understand because you can use those commands at meaningful points in +the layout of the output file. + + Output section descriptions and overlay descriptions are described +below. + + If you do not use a 'SECTIONS' command in your linker script, the +linker will place each input section into an identically named output +section in the order that the sections are first encountered in the +input files. If all input sections are present in the first file, for +example, the order of sections in the output file will match the order +in the first input file. The first section will be at address zero. + +3.6.1 Output Section Description +-------------------------------- + +The full description of an output section looks like this: + SECTION [ADDRESS] [(TYPE)] : + [AT(LMA)] [ALIGN(SECTION_ALIGN)] [SUBALIGN(SUBSECTION_ALIGN)] + { + OUTPUT-SECTION-COMMAND + OUTPUT-SECTION-COMMAND + ... + } [>REGION] [AT>LMA_REGION] [:PHDR :PHDR ...] [=FILLEXP] + + Most output sections do not use most of the optional section +attributes. + + The whitespace around SECTION is required, so that the section name +is unambiguous. The colon and the curly braces are also required. The +line breaks and other white space are optional. + + Each OUTPUT-SECTION-COMMAND may be one of the following: + + * a symbol assignment (*note Assignments::) + * an input section description (*note Input Section::) + * data values to include directly (*note Output Section Data::) + * a special output section keyword (*note Output Section Keywords::) + +3.6.2 Output Section Name +------------------------- + +The name of the output section is SECTION. SECTION must meet the +constraints of your output format. In formats which only support a +limited number of sections, such as 'a.out', the name must be one of the +names supported by the format ('a.out', for example, allows only +'.text', '.data' or '.bss'). If the output format supports any number +of sections, but with numbers and not names (as is the case for Oasys), +the name should be supplied as a quoted numeric string. A section name +may consist of any sequence of characters, but a name which contains any +unusual characters such as commas must be quoted. + + The output section name '/DISCARD/' is special; *note Output Section +Discarding::. + +3.6.3 Output Section Address +---------------------------- + +The ADDRESS is an expression for the VMA (the virtual memory address) of +the output section. If you do not provide ADDRESS, the linker will set +it based on REGION if present, or otherwise based on the current value +of the location counter. + + If you provide ADDRESS, the address of the output section will be set +to precisely that. If you provide neither ADDRESS nor REGION, then the +address of the output section will be set to the current value of the +location counter aligned to the alignment requirements of the output +section. The alignment requirement of the output section is the +strictest alignment of any input section contained within the output +section. + + For example, + .text . : { *(.text) } +and + .text : { *(.text) } +are subtly different. The first will set the address of the '.text' +output section to the current value of the location counter. The second +will set it to the current value of the location counter aligned to the +strictest alignment of a '.text' input section. + + The ADDRESS may be an arbitrary expression; *note Expressions::. For +example, if you want to align the section on a 0x10 byte boundary, so +that the lowest four bits of the section address are zero, you could do +something like this: + .text ALIGN(0x10) : { *(.text) } +This works because 'ALIGN' returns the current location counter aligned +upward to the specified value. + + Specifying ADDRESS for a section will change the value of the +location counter. + +3.6.4 Input Section Description +------------------------------- + +The most common output section command is an input section description. + + The input section description is the most basic linker script +operation. You use output sections to tell the linker how to lay out +your program in memory. You use input section descriptions to tell the +linker how to map the input files into your memory layout. + +3.6.4.1 Input Section Basics +............................ + +An input section description consists of a file name optionally followed +by a list of section names in parentheses. + + The file name and the section name may be wildcard patterns, which we +describe further below (*note Input Section Wildcards::). + + The most common input section description is to include all input +sections with a particular name in the output section. For example, to +include all input '.text' sections, you would write: + *(.text) +Here the '*' is a wildcard which matches any file name. To exclude a +list of files from matching the file name wildcard, EXCLUDE_FILE may be +used to match all files except the ones specified in the EXCLUDE_FILE +list. For example: + (*(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors)) + will cause all .ctors sections from all files except 'crtend.o' and +'otherfile.o' to be included. + + There are two ways to include more than one section: + *(.text .rdata) + *(.text) *(.rdata) +The difference between these is the order in which the '.text' and +'.rdata' input sections will appear in the output section. In the first +example, they will be intermingled, appearing in the same order as they +are found in the linker input. In the second example, all '.text' input +sections will appear first, followed by all '.rdata' input sections. + + You can specify a file name to include sections from a particular +file. You would do this if one or more of your files contain special +data that needs to be at a particular location in memory. For example: + data.o(.data) + + If you use a file name without a list of sections, then all sections +in the input file will be included in the output section. This is not +commonly done, but it may by useful on occasion. For example: + data.o + + When you use a file name which does not contain any wild card +characters, the linker will first see if you also specified the file +name on the linker command line or in an 'INPUT' command. If you did +not, the linker will attempt to open the file as an input file, as +though it appeared on the command line. Note that this differs from an +'INPUT' command, because the linker will not search for the file in the +archive search path. + +3.6.4.2 Input Section Wildcard Patterns +....................................... + +In an input section description, either the file name or the section +name or both may be wildcard patterns. + + The file name of '*' seen in many examples is a simple wildcard +pattern for the file name. + + The wildcard patterns are like those used by the Unix shell. + +'*' + matches any number of characters +'?' + matches any single character +'[CHARS]' + matches a single instance of any of the CHARS; the '-' character + may be used to specify a range of characters, as in '[a-z]' to + match any lower case letter +'\' + quotes the following character + + When a file name is matched with a wildcard, the wildcard characters +will not match a '/' character (used to separate directory names on +Unix). A pattern consisting of a single '*' character is an exception; +it will always match any file name, whether it contains a '/' or not. +In a section name, the wildcard characters will match a '/' character. + + File name wildcard patterns only match files which are explicitly +specified on the command line or in an 'INPUT' command. The linker does +not search directories to expand wildcards. + + If a file name matches more than one wildcard pattern, or if a file +name appears explicitly and is also matched by a wildcard pattern, the +linker will use the first match in the linker script. For example, this +sequence of input section descriptions is probably in error, because the +'data.o' rule will not be used: + .data : { *(.data) } + .data1 : { data.o(.data) } + + Normally, the linker will place files and sections matched by +wildcards in the order in which they are seen during the link. You can +change this by using the 'SORT_BY_NAME' keyword, which appears before a +wildcard pattern in parentheses (e.g., 'SORT_BY_NAME(.text*)'). When +the 'SORT_BY_NAME' keyword is used, the linker will sort the files or +sections into ascending order by name before placing them in the output +file. + + 'SORT_BY_ALIGNMENT' is very similar to 'SORT_BY_NAME'. The +difference is 'SORT_BY_ALIGNMENT' will sort sections into ascending +order by alignment before placing them in the output file. + + 'SORT' is an alias for 'SORT_BY_NAME'. + + When there are nested section sorting commands in linker script, +there can be at most 1 level of nesting for section sorting commands. + + 1. 'SORT_BY_NAME' ('SORT_BY_ALIGNMENT' (wildcard section pattern)). + It will sort the input sections by name first, then by alignment if + 2 sections have the same name. + 2. 'SORT_BY_ALIGNMENT' ('SORT_BY_NAME' (wildcard section pattern)). + It will sort the input sections by alignment first, then by name if + 2 sections have the same alignment. + 3. 'SORT_BY_NAME' ('SORT_BY_NAME' (wildcard section pattern)) is + treated the same as 'SORT_BY_NAME' (wildcard section pattern). + 4. 'SORT_BY_ALIGNMENT' ('SORT_BY_ALIGNMENT' (wildcard section + pattern)) is treated the same as 'SORT_BY_ALIGNMENT' (wildcard + section pattern). + 5. All other nested section sorting commands are invalid. + + When both command line section sorting option and linker script +section sorting command are used, section sorting command always takes +precedence over the command line option. + + If the section sorting command in linker script isn't nested, the +command line option will make the section sorting command to be treated +as nested sorting command. + + 1. 'SORT_BY_NAME' (wildcard section pattern ) with '--sort-sections + alignment' is equivalent to 'SORT_BY_NAME' ('SORT_BY_ALIGNMENT' + (wildcard section pattern)). + 2. 'SORT_BY_ALIGNMENT' (wildcard section pattern) with '--sort-section + name' is equivalent to 'SORT_BY_ALIGNMENT' ('SORT_BY_NAME' + (wildcard section pattern)). + + If the section sorting command in linker script is nested, the +command line option will be ignored. + + If you ever get confused about where input sections are going, use +the '-M' linker option to generate a map file. The map file shows +precisely how input sections are mapped to output sections. + + This example shows how wildcard patterns might be used to partition +files. This linker script directs the linker to place all '.text' +sections in '.text' and all '.bss' sections in '.bss'. The linker will +place the '.data' section from all files beginning with an upper case +character in '.DATA'; for all other files, the linker will place the +'.data' section in '.data'. + SECTIONS { + .text : { *(.text) } + .DATA : { [A-Z]*(.data) } + .data : { *(.data) } + .bss : { *(.bss) } + } + +3.6.4.3 Input Section for Common Symbols +........................................ + +A special notation is needed for common symbols, because in many object +file formats common symbols do not have a particular input section. The +linker treats common symbols as though they are in an input section +named 'COMMON'. + + You may use file names with the 'COMMON' section just as with any +other input sections. You can use this to place common symbols from a +particular input file in one section while common symbols from other +input files are placed in another section. + + In most cases, common symbols in input files will be placed in the +'.bss' section in the output file. For example: + .bss { *(.bss) *(COMMON) } + + Some object file formats have more than one type of common symbol. +For example, the MIPS ELF object file format distinguishes standard +common symbols and small common symbols. In this case, the linker will +use a different special section name for other types of common symbols. +In the case of MIPS ELF, the linker uses 'COMMON' for standard common +symbols and '.scommon' for small common symbols. This permits you to +map the different types of common symbols into memory at different +locations. + + You will sometimes see '[COMMON]' in old linker scripts. This +notation is now considered obsolete. It is equivalent to '*(COMMON)'. + +3.6.4.4 Input Section and Garbage Collection +............................................ + +When link-time garbage collection is in use ('--gc-sections'), it is +often useful to mark sections that should not be eliminated. This is +accomplished by surrounding an input section's wildcard entry with +'KEEP()', as in 'KEEP(*(.init))' or 'KEEP(SORT_BY_NAME(*)(.ctors))'. + +3.6.4.5 Input Section Example +............................. + +The following example is a complete linker script. It tells the linker +to read all of the sections from file 'all.o' and place them at the +start of output section 'outputa' which starts at location '0x10000'. +All of section '.input1' from file 'foo.o' follows immediately, in the +same output section. All of section '.input2' from 'foo.o' goes into +output section 'outputb', followed by section '.input1' from 'foo1.o'. +All of the remaining '.input1' and '.input2' sections from any files are +written to output section 'outputc'. + + SECTIONS { + outputa 0x10000 : + { + all.o + foo.o (.input1) + } + outputb : + { + foo.o (.input2) + foo1.o (.input1) + } + outputc : + { + *(.input1) + *(.input2) + } + } + +3.6.5 Output Section Data +------------------------- + +You can include explicit bytes of data in an output section by using +'BYTE', 'SHORT', 'LONG', 'QUAD', or 'SQUAD' as an output section +command. Each keyword is followed by an expression in parentheses +providing the value to store (*note Expressions::). The value of the +expression is stored at the current value of the location counter. + + The 'BYTE', 'SHORT', 'LONG', and 'QUAD' commands store one, two, +four, and eight bytes (respectively). After storing the bytes, the +location counter is incremented by the number of bytes stored. + + For example, this will store the byte 1 followed by the four byte +value of the symbol 'addr': + BYTE(1) + LONG(addr) + + When using a 64 bit host or target, 'QUAD' and 'SQUAD' are the same; +they both store an 8 byte, or 64 bit, value. When both host and target +are 32 bits, an expression is computed as 32 bits. In this case 'QUAD' +stores a 32 bit value zero extended to 64 bits, and 'SQUAD' stores a 32 +bit value sign extended to 64 bits. + + If the object file format of the output file has an explicit +endianness, which is the normal case, the value will be stored in that +endianness. When the object file format does not have an explicit +endianness, as is true of, for example, S-records, the value will be +stored in the endianness of the first input object file. + + Note--these commands only work inside a section description and not +between them, so the following will produce an error from the linker: + SECTIONS { .text : { *(.text) } LONG(1) .data : { *(.data) } } + whereas this will work: + SECTIONS { .text : { *(.text) ; LONG(1) } .data : { *(.data) } } + + You may use the 'FILL' command to set the fill pattern for the +current section. It is followed by an expression in parentheses. Any +otherwise unspecified regions of memory within the section (for example, +gaps left due to the required alignment of input sections) are filled +with the value of the expression, repeated as necessary. A 'FILL' +statement covers memory locations after the point at which it occurs in +the section definition; by including more than one 'FILL' statement, you +can have different fill patterns in different parts of an output +section. + + This example shows how to fill unspecified regions of memory with the +value '0x90': + FILL(0x90909090) + + The 'FILL' command is similar to the '=FILLEXP' output section +attribute, but it only affects the part of the section following the +'FILL' command, rather than the entire section. If both are used, the +'FILL' command takes precedence. *Note Output Section Fill::, for +details on the fill expression. + +3.6.6 Output Section Keywords +----------------------------- + +There are a couple of keywords which can appear as output section +commands. + +'CREATE_OBJECT_SYMBOLS' + The command tells the linker to create a symbol for each input + file. The name of each symbol will be the name of the + corresponding input file. The section of each symbol will be the + output section in which the 'CREATE_OBJECT_SYMBOLS' command + appears. + + This is conventional for the a.out object file format. It is not + normally used for any other object file format. + +'CONSTRUCTORS' + When linking using the a.out object file format, the linker uses an + unusual set construct to support C++ global constructors and + destructors. When linking object file formats which do not support + arbitrary sections, such as ECOFF and XCOFF, the linker will + automatically recognize C++ global constructors and destructors by + name. For these object file formats, the 'CONSTRUCTORS' command + tells the linker to place constructor information in the output + section where the 'CONSTRUCTORS' command appears. The + 'CONSTRUCTORS' command is ignored for other object file formats. + + The symbol '__CTOR_LIST__' marks the start of the global + constructors, and the symbol '__CTOR_END__' marks the end. + Similarly, '__DTOR_LIST__' and '__DTOR_END__' mark the start and + end of the global destructors. The first word in the list is the + number of entries, followed by the address of each constructor or + destructor, followed by a zero word. The compiler must arrange to + actually run the code. For these object file formats GNU C++ + normally calls constructors from a subroutine '__main'; a call to + '__main' is automatically inserted into the startup code for + 'main'. GNU C++ normally runs destructors either by using + 'atexit', or directly from the function 'exit'. + + For object file formats such as 'COFF' or 'ELF' which support + arbitrary section names, GNU C++ will normally arrange to put the + addresses of global constructors and destructors into the '.ctors' + and '.dtors' sections. Placing the following sequence into your + linker script will build the sort of table which the GNU C++ + runtime code expects to see. + + __CTOR_LIST__ = .; + LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2) + *(.ctors) + LONG(0) + __CTOR_END__ = .; + __DTOR_LIST__ = .; + LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2) + *(.dtors) + LONG(0) + __DTOR_END__ = .; + + If you are using the GNU C++ support for initialization priority, + which provides some control over the order in which global + constructors are run, you must sort the constructors at link time + to ensure that they are executed in the correct order. When using + the 'CONSTRUCTORS' command, use 'SORT_BY_NAME(CONSTRUCTORS)' + instead. When using the '.ctors' and '.dtors' sections, use + '*(SORT_BY_NAME(.ctors))' and '*(SORT_BY_NAME(.dtors))' instead of + just '*(.ctors)' and '*(.dtors)'. + + Normally the compiler and linker will handle these issues + automatically, and you will not need to concern yourself with them. + However, you may need to consider this if you are using C++ and + writing your own linker scripts. + +3.6.7 Output Section Discarding +------------------------------- + +The linker will not create output sections with no contents. This is +for convenience when referring to input sections that may or may not be +present in any of the input files. For example: + .foo : { *(.foo) } +will only create a '.foo' section in the output file if there is a +'.foo' section in at least one input file, and if the input sections are +not all empty. Other link script directives that allocate space in an +output section will also create the output section. + + The linker will ignore address assignments (*note Output Section +Address::) on discarded output sections, except when the linker script +defines symbols in the output section. In that case the linker will +obey the address assignments, possibly advancing dot even though the +section is discarded. + + The special output section name '/DISCARD/' may be used to discard +input sections. Any input sections which are assigned to an output +section named '/DISCARD/' are not included in the output file. + +3.6.8 Output Section Attributes +------------------------------- + +We showed above that the full description of an output section looked +like this: + SECTION [ADDRESS] [(TYPE)] : + [AT(LMA)] [ALIGN(SECTION_ALIGN)] [SUBALIGN(SUBSECTION_ALIGN)] + { + OUTPUT-SECTION-COMMAND + OUTPUT-SECTION-COMMAND + ... + } [>REGION] [AT>LMA_REGION] [:PHDR :PHDR ...] [=FILLEXP] + We've already described SECTION, ADDRESS, and OUTPUT-SECTION-COMMAND. +In this section we will describe the remaining section attributes. + +3.6.8.1 Output Section Type +........................... + +Each output section may have a type. The type is a keyword in +parentheses. The following types are defined: + +'NOLOAD' + The section should be marked as not loadable, so that it will not + be loaded into memory when the program is run. +'DSECT' +'COPY' +'INFO' +'OVERLAY' + These type names are supported for backward compatibility, and are + rarely used. They all have the same effect: the section should be + marked as not allocatable, so that no memory is allocated for the + section when the program is run. + + The linker normally sets the attributes of an output section based on +the input sections which map into it. You can override this by using +the section type. For example, in the script sample below, the 'ROM' +section is addressed at memory location '0' and does not need to be +loaded when the program is run. The contents of the 'ROM' section will +appear in the linker output file as usual. + SECTIONS { + ROM 0 (NOLOAD) : { ... } + ... + } + +3.6.8.2 Output Section LMA +.......................... + +Every section has a virtual address (VMA) and a load address (LMA); see +*note Basic Script Concepts::. The address expression which may appear +in an output section description sets the VMA (*note Output Section +Address::). + + The expression LMA that follows the 'AT' keyword specifies the load +address of the section. + + Alternatively, with 'AT>LMA_REGION' expression, you may specify a +memory region for the section's load address. *Note MEMORY::. Note +that if the section has not had a VMA assigned to it then the linker +will use the LMA_REGION as the VMA region as well. + + If neither 'AT' nor 'AT>' is specified for an allocatable section, +the linker will set the LMA such that the difference between VMA and LMA +for the section is the same as the preceding output section in the same +region. If there is no preceding output section or the section is not +allocatable, the linker will set the LMA equal to the VMA. *Note Output +Section Region::. + + This feature is designed to make it easy to build a ROM image. For +example, the following linker script creates three output sections: one +called '.text', which starts at '0x1000', one called '.mdata', which is +loaded at the end of the '.text' section even though its VMA is +'0x2000', and one called '.bss' to hold uninitialized data at address +'0x3000'. The symbol '_data' is defined with the value '0x2000', which +shows that the location counter holds the VMA value, not the LMA value. + + SECTIONS + { + .text 0x1000 : { *(.text) _etext = . ; } + .mdata 0x2000 : + AT ( ADDR (.text) + SIZEOF (.text) ) + { _data = . ; *(.data); _edata = . ; } + .bss 0x3000 : + { _bstart = . ; *(.bss) *(COMMON) ; _bend = . ;} + } + + The run-time initialization code for use with a program generated +with this linker script would include something like the following, to +copy the initialized data from the ROM image to its runtime address. +Notice how this code takes advantage of the symbols defined by the +linker script. + + extern char _etext, _data, _edata, _bstart, _bend; + char *src = &_etext; + char *dst = &_data; + + /* ROM has data at end of text; copy it. */ + while (dst < &_edata) { + *dst++ = *src++; + } + + /* Zero bss */ + for (dst = &_bstart; dst< &_bend; dst++) + *dst = 0; + +3.6.8.3 Forced Output Alignment +............................... + +You can increase an output section's alignment by using ALIGN. + +3.6.8.4 Forced Input Alignment +.............................. + +You can force input section alignment within an output section by using +SUBALIGN. The value specified overrides any alignment given by input +sections, whether larger or smaller. + +3.6.8.5 Output Section Region +............................. + +You can assign a section to a previously defined region of memory by +using '>REGION'. *Note MEMORY::. + + Here is a simple example: + MEMORY { rom : ORIGIN = 0x1000, LENGTH = 0x1000 } + SECTIONS { ROM : { *(.text) } >rom } + +3.6.8.6 Output Section Phdr +........................... + +You can assign a section to a previously defined program segment by +using ':PHDR'. *Note PHDRS::. If a section is assigned to one or more +segments, then all subsequent allocated sections will be assigned to +those segments as well, unless they use an explicitly ':PHDR' modifier. +You can use ':NONE' to tell the linker to not put the section in any +segment at all. + + Here is a simple example: + PHDRS { text PT_LOAD ; } + SECTIONS { .text : { *(.text) } :text } + +3.6.8.7 Output Section Fill +........................... + +You can set the fill pattern for an entire section by using '=FILLEXP'. +FILLEXP is an expression (*note Expressions::). Any otherwise +unspecified regions of memory within the output section (for example, +gaps left due to the required alignment of input sections) will be +filled with the value, repeated as necessary. If the fill expression is +a simple hex number, ie. a string of hex digit starting with '0x' and +without a trailing 'k' or 'M', then an arbitrarily long sequence of hex +digits can be used to specify the fill pattern; Leading zeros become +part of the pattern too. For all other cases, including extra +parentheses or a unary '+', the fill pattern is the four least +significant bytes of the value of the expression. In all cases, the +number is big-endian. + + You can also change the fill value with a 'FILL' command in the +output section commands; (*note Output Section Data::). + + Here is a simple example: + SECTIONS { .text : { *(.text) } =0x90909090 } + +3.6.9 Overlay Description +------------------------- + +An overlay description provides an easy way to describe sections which +are to be loaded as part of a single memory image but are to be run at +the same memory address. At run time, some sort of overlay manager will +copy the overlaid sections in and out of the runtime memory address as +required, perhaps by simply manipulating addressing bits. This approach +can be useful, for example, when a certain region of memory is faster +than another. + + Overlays are described using the 'OVERLAY' command. The 'OVERLAY' +command is used within a 'SECTIONS' command, like an output section +description. The full syntax of the 'OVERLAY' command is as follows: + OVERLAY [START] : [NOCROSSREFS] [AT ( LDADDR )] + { + SECNAME1 + { + OUTPUT-SECTION-COMMAND + OUTPUT-SECTION-COMMAND + ... + } [:PHDR...] [=FILL] + SECNAME2 + { + OUTPUT-SECTION-COMMAND + OUTPUT-SECTION-COMMAND + ... + } [:PHDR...] [=FILL] + ... + } [>REGION] [:PHDR...] [=FILL] + + Everything is optional except 'OVERLAY' (a keyword), and each section +must have a name (SECNAME1 and SECNAME2 above). The section definitions +within the 'OVERLAY' construct are identical to those within the general +'SECTIONS' contruct (*note SECTIONS::), except that no addresses and no +memory regions may be defined for sections within an 'OVERLAY'. + + The sections are all defined with the same starting address. The +load addresses of the sections are arranged such that they are +consecutive in memory starting at the load address used for the +'OVERLAY' as a whole (as with normal section definitions, the load +address is optional, and defaults to the start address; the start +address is also optional, and defaults to the current value of the +location counter). + + If the 'NOCROSSREFS' keyword is used, and there any references among +the sections, the linker will report an error. Since the sections all +run at the same address, it normally does not make sense for one section +to refer directly to another. *Note NOCROSSREFS: Miscellaneous +Commands. + + For each section within the 'OVERLAY', the linker automatically +provides two symbols. The symbol '__load_start_SECNAME' is defined as +the starting load address of the section. The symbol +'__load_stop_SECNAME' is defined as the final load address of the +section. Any characters within SECNAME which are not legal within C +identifiers are removed. C (or assembler) code may use these symbols to +move the overlaid sections around as necessary. + + At the end of the overlay, the value of the location counter is set +to the start address of the overlay plus the size of the largest +section. + + Here is an example. Remember that this would appear inside a +'SECTIONS' construct. + OVERLAY 0x1000 : AT (0x4000) + { + .text0 { o1/*.o(.text) } + .text1 { o2/*.o(.text) } + } +This will define both '.text0' and '.text1' to start at address 0x1000. +'.text0' will be loaded at address 0x4000, and '.text1' will be loaded +immediately after '.text0'. The following symbols will be defined if +referenced: '__load_start_text0', '__load_stop_text0', +'__load_start_text1', '__load_stop_text1'. + + C code to copy overlay '.text1' into the overlay area might look like +the following. + + extern char __load_start_text1, __load_stop_text1; + memcpy ((char *) 0x1000, &__load_start_text1, + &__load_stop_text1 - &__load_start_text1); + + Note that the 'OVERLAY' command is just syntactic sugar, since +everything it does can be done using the more basic commands. The above +example could have been written identically as follows. + + .text0 0x1000 : AT (0x4000) { o1/*.o(.text) } + PROVIDE (__load_start_text0 = LOADADDR (.text0)); + PROVIDE (__load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0)); + .text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) { o2/*.o(.text) } + PROVIDE (__load_start_text1 = LOADADDR (.text1)); + PROVIDE (__load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1)); + . = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1)); + +3.7 MEMORY Command +================== + +The linker's default configuration permits allocation of all available +memory. You can override this by using the 'MEMORY' command. + + The 'MEMORY' command describes the location and size of blocks of +memory in the target. You can use it to describe which memory regions +may be used by the linker, and which memory regions it must avoid. You +can then assign sections to particular memory regions. The linker will +set section addresses based on the memory regions, and will warn about +regions that become too full. The linker will not shuffle sections +around to fit into the available regions. + + A linker script may contain at most one use of the 'MEMORY' command. +However, you can define as many blocks of memory within it as you wish. +The syntax is: + MEMORY + { + NAME [(ATTR)] : ORIGIN = ORIGIN, LENGTH = LEN + ... + } + + The NAME is a name used in the linker script to refer to the region. +The region name has no meaning outside of the linker script. Region +names are stored in a separate name space, and will not conflict with +symbol names, file names, or section names. Each memory region must +have a distinct name. + + The ATTR string is an optional list of attributes that specify +whether to use a particular memory region for an input section which is +not explicitly mapped in the linker script. As described in *note +SECTIONS::, if you do not specify an output section for some input +section, the linker will create an output section with the same name as +the input section. If you define region attributes, the linker will use +them to select the memory region for the output section that it creates. + + The ATTR string must consist only of the following characters: +'R' + Read-only section +'W' + Read/write section +'X' + Executable section +'A' + Allocatable section +'I' + Initialized section +'L' + Same as 'I' +'!' + Invert the sense of any of the preceding attributes + + If a unmapped section matches any of the listed attributes other than +'!', it will be placed in the memory region. The '!' attribute reverses +this test, so that an unmapped section will be placed in the memory +region only if it does not match any of the listed attributes. + + The ORIGIN is an numerical expression for the start address of the +memory region. The expression must evaluate to a constant and it cannot +involve any symbols. The keyword 'ORIGIN' may be abbreviated to 'org' +or 'o' (but not, for example, 'ORG'). + + The LEN is an expression for the size in bytes of the memory region. +As with the ORIGIN expression, the expression must be numerical only and +must evaluate to a constant. The keyword 'LENGTH' may be abbreviated to +'len' or 'l'. + + In the following example, we specify that there are two memory +regions available for allocation: one starting at '0' for 256 kilobytes, +and the other starting at '0x40000000' for four megabytes. The linker +will place into the 'rom' memory region every section which is not +explicitly mapped into a memory region, and is either read-only or +executable. The linker will place other sections which are not +explicitly mapped into a memory region into the 'ram' memory region. + + MEMORY + { + rom (rx) : ORIGIN = 0, LENGTH = 256K + ram (!rx) : org = 0x40000000, l = 4M + } + + Once you define a memory region, you can direct the linker to place +specific output sections into that memory region by using the '>REGION' +output section attribute. For example, if you have a memory region +named 'mem', you would use '>mem' in the output section definition. +*Note Output Section Region::. If no address was specified for the +output section, the linker will set the address to the next available +address within the memory region. If the combined output sections +directed to a memory region are too large for the region, the linker +will issue an error message. + + It is possible to access the origin and length of a memory in an +expression via the 'ORIGIN(MEMORY)' and 'LENGTH(MEMORY)' functions: + + _fstack = ORIGIN(ram) + LENGTH(ram) - 4; + +3.8 PHDRS Command +================= + +The ELF object file format uses "program headers", also knows as +"segments". The program headers describe how the program should be +loaded into memory. You can print them out by using the 'objdump' +program with the '-p' option. + + When you run an ELF program on a native ELF system, the system loader +reads the program headers in order to figure out how to load the +program. This will only work if the program headers are set correctly. +This manual does not describe the details of how the system loader +interprets program headers; for more information, see the ELF ABI. + + The linker will create reasonable program headers by default. +However, in some cases, you may need to specify the program headers more +precisely. You may use the 'PHDRS' command for this purpose. When the +linker sees the 'PHDRS' command in the linker script, it will not create +any program headers other than the ones specified. + + The linker only pays attention to the 'PHDRS' command when generating +an ELF output file. In other cases, the linker will simply ignore +'PHDRS'. + + This is the syntax of the 'PHDRS' command. The words 'PHDRS', +'FILEHDR', 'AT', and 'FLAGS' are keywords. + + PHDRS + { + NAME TYPE [ FILEHDR ] [ PHDRS ] [ AT ( ADDRESS ) ] + [ FLAGS ( FLAGS ) ] ; + } + + The NAME is used only for reference in the 'SECTIONS' command of the +linker script. It is not put into the output file. Program header +names are stored in a separate name space, and will not conflict with +symbol names, file names, or section names. Each program header must +have a distinct name. + + Certain program header types describe segments of memory which the +system loader will load from the file. In the linker script, you +specify the contents of these segments by placing allocatable output +sections in the segments. You use the ':PHDR' output section attribute +to place a section in a particular segment. *Note Output Section +Phdr::. + + It is normal to put certain sections in more than one segment. This +merely implies that one segment of memory contains another. You may +repeat ':PHDR', using it once for each segment which should contain the +section. + + If you place a section in one or more segments using ':PHDR', then +the linker will place all subsequent allocatable sections which do not +specify ':PHDR' in the same segments. This is for convenience, since +generally a whole set of contiguous sections will be placed in a single +segment. You can use ':NONE' to override the default segment and tell +the linker to not put the section in any segment at all. + + You may use the 'FILEHDR' and 'PHDRS' keywords appear after the +program header type to further describe the contents of the segment. +The 'FILEHDR' keyword means that the segment should include the ELF file +header. The 'PHDRS' keyword means that the segment should include the +ELF program headers themselves. + + The TYPE may be one of the following. The numbers indicate the value +of the keyword. + +'PT_NULL' (0) + Indicates an unused program header. + +'PT_LOAD' (1) + Indicates that this program header describes a segment to be loaded + from the file. + +'PT_DYNAMIC' (2) + Indicates a segment where dynamic linking information can be found. + +'PT_INTERP' (3) + Indicates a segment where the name of the program interpreter may + be found. + +'PT_NOTE' (4) + Indicates a segment holding note information. + +'PT_SHLIB' (5) + A reserved program header type, defined but not specified by the + ELF ABI. + +'PT_PHDR' (6) + Indicates a segment where the program headers may be found. + +EXPRESSION + An expression giving the numeric type of the program header. This + may be used for types not defined above. + + You can specify that a segment should be loaded at a particular +address in memory by using an 'AT' expression. This is identical to the +'AT' command used as an output section attribute (*note Output Section +LMA::). The 'AT' command for a program header overrides the output +section attribute. + + The linker will normally set the segment flags based on the sections +which comprise the segment. You may use the 'FLAGS' keyword to +explicitly specify the segment flags. The value of FLAGS must be an +integer. It is used to set the 'p_flags' field of the program header. + + Here is an example of 'PHDRS'. This shows a typical set of program +headers used on a native ELF system. + + PHDRS + { + headers PT_PHDR PHDRS ; + interp PT_INTERP ; + text PT_LOAD FILEHDR PHDRS ; + data PT_LOAD ; + dynamic PT_DYNAMIC ; + } + + SECTIONS + { + . = SIZEOF_HEADERS; + .interp : { *(.interp) } :text :interp + .text : { *(.text) } :text + .rodata : { *(.rodata) } /* defaults to :text */ + ... + . = . + 0x1000; /* move to a new page in memory */ + .data : { *(.data) } :data + .dynamic : { *(.dynamic) } :data :dynamic + ... + } + +3.9 VERSION Command +=================== + +The linker supports symbol versions when using ELF. Symbol versions are +only useful when using shared libraries. The dynamic linker can use +symbol versions to select a specific version of a function when it runs +a program that may have been linked against an earlier version of the +shared library. + + You can include a version script directly in the main linker script, +or you can supply the version script as an implicit linker script. You +can also use the '--version-script' linker option. + + The syntax of the 'VERSION' command is simply + VERSION { version-script-commands } + + The format of the version script commands is identical to that used +by Sun's linker in Solaris 2.5. The version script defines a tree of +version nodes. You specify the node names and interdependencies in the +version script. You can specify which symbols are bound to which +version nodes, and you can reduce a specified set of symbols to local +scope so that they are not globally visible outside of the shared +library. + + The easiest way to demonstrate the version script language is with a +few examples. + + VERS_1.1 { + global: + foo1; + local: + old*; + original*; + new*; + }; + + VERS_1.2 { + foo2; + } VERS_1.1; + + VERS_2.0 { + bar1; bar2; + extern "C++" { + ns::*; + "int f(int, double)"; + } + } VERS_1.2; + + This example version script defines three version nodes. The first +version node defined is 'VERS_1.1'; it has no other dependencies. The +script binds the symbol 'foo1' to 'VERS_1.1'. It reduces a number of +symbols to local scope so that they are not visible outside of the +shared library; this is done using wildcard patterns, so that any symbol +whose name begins with 'old', 'original', or 'new' is matched. The +wildcard patterns available are the same as those used in the shell when +matching filenames (also known as "globbing"). However, if you specify +the symbol name inside double quotes, then the name is treated as +literal, rather than as a glob pattern. + + Next, the version script defines node 'VERS_1.2'. This node depends +upon 'VERS_1.1'. The script binds the symbol 'foo2' to the version node +'VERS_1.2'. + + Finally, the version script defines node 'VERS_2.0'. This node +depends upon 'VERS_1.2'. The scripts binds the symbols 'bar1' and +'bar2' are bound to the version node 'VERS_2.0'. + + When the linker finds a symbol defined in a library which is not +specifically bound to a version node, it will effectively bind it to an +unspecified base version of the library. You can bind all otherwise +unspecified symbols to a given version node by using 'global: *;' +somewhere in the version script. + + The names of the version nodes have no specific meaning other than +what they might suggest to the person reading them. The '2.0' version +could just as well have appeared in between '1.1' and '1.2'. However, +this would be a confusing way to write a version script. + + Node name can be omitted, provided it is the only version node in the +version script. Such version script doesn't assign any versions to +symbols, only selects which symbols will be globally visible out and +which won't. + + { global: foo; bar; local: *; }; + + When you link an application against a shared library that has +versioned symbols, the application itself knows which version of each +symbol it requires, and it also knows which version nodes it needs from +each shared library it is linked against. Thus at runtime, the dynamic +loader can make a quick check to make sure that the libraries you have +linked against do in fact supply all of the version nodes that the +application will need to resolve all of the dynamic symbols. In this +way it is possible for the dynamic linker to know with certainty that +all external symbols that it needs will be resolvable without having to +search for each symbol reference. + + The symbol versioning is in effect a much more sophisticated way of +doing minor version checking that SunOS does. The fundamental problem +that is being addressed here is that typically references to external +functions are bound on an as-needed basis, and are not all bound when +the application starts up. If a shared library is out of date, a +required interface may be missing; when the application tries to use +that interface, it may suddenly and unexpectedly fail. With symbol +versioning, the user will get a warning when they start their program if +the libraries being used with the application are too old. + + There are several GNU extensions to Sun's versioning approach. The +first of these is the ability to bind a symbol to a version node in the +source file where the symbol is defined instead of in the versioning +script. This was done mainly to reduce the burden on the library +maintainer. You can do this by putting something like: + __asm__(".symver original_foo,foo@VERS_1.1"); +in the C source file. This renames the function 'original_foo' to be an +alias for 'foo' bound to the version node 'VERS_1.1'. The 'local:' +directive can be used to prevent the symbol 'original_foo' from being +exported. A '.symver' directive takes precedence over a version script. + + The second GNU extension is to allow multiple versions of the same +function to appear in a given shared library. In this way you can make +an incompatible change to an interface without increasing the major +version number of the shared library, while still allowing applications +linked against the old interface to continue to function. + + To do this, you must use multiple '.symver' directives in the source +file. Here is an example: + + __asm__(".symver original_foo,foo@"); + __asm__(".symver old_foo,foo@VERS_1.1"); + __asm__(".symver old_foo1,foo@VERS_1.2"); + __asm__(".symver new_foo,foo@@VERS_2.0"); + + In this example, 'foo@' represents the symbol 'foo' bound to the +unspecified base version of the symbol. The source file that contains +this example would define 4 C functions: 'original_foo', 'old_foo', +'old_foo1', and 'new_foo'. + + When you have multiple definitions of a given symbol, there needs to +be some way to specify a default version to which external references to +this symbol will be bound. You can do this with the 'foo@@VERS_2.0' +type of '.symver' directive. You can only declare one version of a +symbol as the default in this manner; otherwise you would effectively +have multiple definitions of the same symbol. + + If you wish to bind a reference to a specific version of the symbol +within the shared library, you can use the aliases of convenience (i.e., +'old_foo'), or you can use the '.symver' directive to specifically bind +to an external version of the function in question. + + You can also specify the language in the version script: + + VERSION extern "lang" { version-script-commands } + + The supported 'lang's are 'C', 'C++', and 'Java'. The linker will +iterate over the list of symbols at the link time and demangle them +according to 'lang' before matching them to the patterns specified in +'version-script-commands'. + + Demangled names may contains spaces and other special characters. As +described above, you can use a glob pattern to match demangled names, or +you can use a double-quoted string to match the string exactly. In the +latter case, be aware that minor differences (such as differing +whitespace) between the version script and the demangler output will +cause a mismatch. As the exact string generated by the demangler might +change in the future, even if the mangled name does not, you should +check that all of your version directives are behaving as you expect +when you upgrade. + +3.10 Expressions in Linker Scripts +================================== + +The syntax for expressions in the linker script language is identical to +that of C expressions. All expressions are evaluated as integers. All +expressions are evaluated in the same size, which is 32 bits if both the +host and target are 32 bits, and is otherwise 64 bits. + + You can use and set symbol values in expressions. + + The linker defines several special purpose builtin functions for use +in expressions. + +3.10.1 Constants +---------------- + +All constants are integers. + + As in C, the linker considers an integer beginning with '0' to be +octal, and an integer beginning with '0x' or '0X' to be hexadecimal. +The linker considers other integers to be decimal. + + In addition, you can use the suffixes 'K' and 'M' to scale a constant +by '1024' or '1024*1024' respectively. For example, the following all +refer to the same quantity: + _fourk_1 = 4K; + _fourk_2 = 4096; + _fourk_3 = 0x1000; + +3.10.2 Symbol Names +------------------- + +Unless quoted, symbol names start with a letter, underscore, or period +and may include letters, digits, underscores, periods, and hyphens. +Unquoted symbol names must not conflict with any keywords. You can +specify a symbol which contains odd characters or has the same name as a +keyword by surrounding the symbol name in double quotes: + "SECTION" = 9; + "with a space" = "also with a space" + 10; + + Since symbols can contain many non-alphabetic characters, it is +safest to delimit symbols with spaces. For example, 'A-B' is one +symbol, whereas 'A - B' is an expression involving subtraction. + +3.10.3 Orphan Sections +---------------------- + +Orphan sections are sections present in the input files which are not +explicitly placed into the output file by the linker script. The linker +will still copy these sections into the output file, but it has to guess +as to where they should be placed. The linker uses a simple heuristic +to do this. It attempts to place orphan sections after non-orphan +sections of the same attribute, such as code vs data, loadable vs +non-loadable, etc. If there is not enough room to do this then it +places at the end of the file. + + For ELF targets, the attribute of the section includes section type +as well as section flag. + +3.10.4 The Location Counter +--------------------------- + +The special linker variable "dot" '.' always contains the current output +location counter. Since the '.' always refers to a location in an +output section, it may only appear in an expression within a 'SECTIONS' +command. The '.' symbol may appear anywhere that an ordinary symbol is +allowed in an expression. + + Assigning a value to '.' will cause the location counter to be moved. +This may be used to create holes in the output section. The location +counter may not be moved backwards inside an output section, and may not +be moved backwards outside of an output section if so doing creates +areas with overlapping LMAs. + + SECTIONS + { + output : + { + file1(.text) + . = . + 1000; + file2(.text) + . += 1000; + file3(.text) + } = 0x12345678; + } +In the previous example, the '.text' section from 'file1' is located at +the beginning of the output section 'output'. It is followed by a 1000 +byte gap. Then the '.text' section from 'file2' appears, also with a +1000 byte gap following before the '.text' section from 'file3'. The +notation '= 0x12345678' specifies what data to write in the gaps (*note +Output Section Fill::). + + Note: '.' actually refers to the byte offset from the start of the +current containing object. Normally this is the 'SECTIONS' statement, +whose start address is 0, hence '.' can be used as an absolute address. +If '.' is used inside a section description however, it refers to the +byte offset from the start of that section, not an absolute address. +Thus in a script like this: + + SECTIONS + { + . = 0x100 + .text: { + *(.text) + . = 0x200 + } + . = 0x500 + .data: { + *(.data) + . += 0x600 + } + } + + The '.text' section will be assigned a starting address of 0x100 and +a size of exactly 0x200 bytes, even if there is not enough data in the +'.text' input sections to fill this area. (If there is too much data, +an error will be produced because this would be an attempt to move '.' +backwards). The '.data' section will start at 0x500 and it will have an +extra 0x600 bytes worth of space after the end of the values from the +'.data' input sections and before the end of the '.data' output section +itself. + + Setting symbols to the value of the location counter outside of an +output section statement can result in unexpected values if the linker +needs to place orphan sections. For example, given the following: + + SECTIONS + { + start_of_text = . ; + .text: { *(.text) } + end_of_text = . ; + + start_of_data = . ; + .data: { *(.data) } + end_of_data = . ; + } + + If the linker needs to place some input section, e.g. '.rodata', not +mentioned in the script, it might choose to place that section between +'.text' and '.data'. You might think the linker should place '.rodata' +on the blank line in the above script, but blank lines are of no +particular significance to the linker. As well, the linker doesn't +associate the above symbol names with their sections. Instead, it +assumes that all assignments or other statements belong to the previous +output section, except for the special case of an assignment to '.'. +I.e., the linker will place the orphan '.rodata' section as if the +script was written as follows: + + SECTIONS + { + start_of_text = . ; + .text: { *(.text) } + end_of_text = . ; + + start_of_data = . ; + .rodata: { *(.rodata) } + .data: { *(.data) } + end_of_data = . ; + } + + This may or may not be the script author's intention for the value of +'start_of_data'. One way to influence the orphan section placement is +to assign the location counter to itself, as the linker assumes that an +assignment to '.' is setting the start address of a following output +section and thus should be grouped with that section. So you could +write: + + SECTIONS + { + start_of_text = . ; + .text: { *(.text) } + end_of_text = . ; + + . = . ; + start_of_data = . ; + .data: { *(.data) } + end_of_data = . ; + } + + Now, the orphan '.rodata' section will be placed between +'end_of_text' and 'start_of_data'. + +3.10.5 Operators +---------------- + +The linker recognizes the standard C set of arithmetic operators, with +the standard bindings and precedence levels: + precedence associativity Operators Notes + (highest) + 1 left ! - ~ (1) + 2 left * / % + 3 left + - + 4 left >> << + 5 left == != > < <= >= + 6 left & + 7 left | + 8 left && + 9 left || + 10 right ? : + 11 right &= += -= *= /= (2) + (lowest) + Notes: (1) Prefix operators (2) *Note Assignments::. + +3.10.6 Evaluation +----------------- + +The linker evaluates expressions lazily. It only computes the value of +an expression when absolutely necessary. + + The linker needs some information, such as the value of the start +address of the first section, and the origins and lengths of memory +regions, in order to do any linking at all. These values are computed +as soon as possible when the linker reads in the linker script. + + However, other values (such as symbol values) are not known or needed +until after storage allocation. Such values are evaluated later, when +other information (such as the sizes of output sections) is available +for use in the symbol assignment expression. + + The sizes of sections cannot be known until after allocation, so +assignments dependent upon these are not performed until after +allocation. + + Some expressions, such as those depending upon the location counter +'.', must be evaluated during section allocation. + + If the result of an expression is required, but the value is not +available, then an error results. For example, a script like the +following + SECTIONS + { + .text 9+this_isnt_constant : + { *(.text) } + } +will cause the error message 'non constant expression for initial +address'. + +3.10.7 The Section of an Expression +----------------------------------- + +When the linker evaluates an expression, the result is either absolute +or relative to some section. A relative expression is expressed as a +fixed offset from the base of a section. + + The position of the expression within the linker script determines +whether it is absolute or relative. An expression which appears within +an output section definition is relative to the base of the output +section. An expression which appears elsewhere will be absolute. + + A symbol set to a relative expression will be relocatable if you +request relocatable output using the '-r' option. That means that a +further link operation may change the value of the symbol. The symbol's +section will be the section of the relative expression. + + A symbol set to an absolute expression will retain the same value +through any further link operation. The symbol will be absolute, and +will not have any particular associated section. + + You can use the builtin function 'ABSOLUTE' to force an expression to +be absolute when it would otherwise be relative. For example, to create +an absolute symbol set to the address of the end of the output section +'.data': + SECTIONS + { + .data : { *(.data) _edata = ABSOLUTE(.); } + } +If 'ABSOLUTE' were not used, '_edata' would be relative to the '.data' +section. + +3.10.8 Builtin Functions +------------------------ + +The linker script language includes a number of builtin functions for +use in linker script expressions. + +'ABSOLUTE(EXP)' + Return the absolute (non-relocatable, as opposed to non-negative) + value of the expression EXP. Primarily useful to assign an + absolute value to a symbol within a section definition, where + symbol values are normally section relative. *Note Expression + Section::. + +'ADDR(SECTION)' + Return the absolute address (the VMA) of the named SECTION. Your + script must previously have defined the location of that section. + In the following example, 'symbol_1' and 'symbol_2' are assigned + identical values: + SECTIONS { ... + .output1 : + { + start_of_output_1 = ABSOLUTE(.); + ... + } + .output : + { + symbol_1 = ADDR(.output1); + symbol_2 = start_of_output_1; + } + ... } + +'ALIGN(ALIGN)' +'ALIGN(EXP,ALIGN)' + Return the location counter ('.') or arbitrary expression aligned + to the next ALIGN boundary. The single operand 'ALIGN' doesn't + change the value of the location counter--it just does arithmetic + on it. The two operand 'ALIGN' allows an arbitrary expression to + be aligned upwards ('ALIGN(ALIGN)' is equivalent to 'ALIGN(., + ALIGN)'). + + Here is an example which aligns the output '.data' section to the + next '0x2000' byte boundary after the preceding section and sets a + variable within the section to the next '0x8000' boundary after the + input sections: + SECTIONS { ... + .data ALIGN(0x2000): { + *(.data) + variable = ALIGN(0x8000); + } + ... } + The first use of 'ALIGN' in this example specifies the location of + a section because it is used as the optional ADDRESS attribute of a + section definition (*note Output Section Address::). The second + use of 'ALIGN' is used to defines the value of a symbol. + + The builtin function 'NEXT' is closely related to 'ALIGN'. + +'ALIGNOF(SECTION)' + Return the alignment in bytes of the named SECTION, if that section + has been allocated. If the section has not been allocated when + this is evaluated, the linker will report an error. In the + following example, the alignment of the '.output' section is stored + as the first value in that section. + SECTIONS{ ... + .output { + LONG (ALIGNOF (.output)) + ... + } + ... } + +'BLOCK(EXP)' + This is a synonym for 'ALIGN', for compatibility with older linker + scripts. It is most often seen when setting the address of an + output section. + +'DATA_SEGMENT_ALIGN(MAXPAGESIZE, COMMONPAGESIZE)' + This is equivalent to either + (ALIGN(MAXPAGESIZE) + (. & (MAXPAGESIZE - 1))) + or + (ALIGN(MAXPAGESIZE) + (. & (MAXPAGESIZE - COMMONPAGESIZE))) + depending on whether the latter uses fewer COMMONPAGESIZE sized + pages for the data segment (area between the result of this + expression and 'DATA_SEGMENT_END') than the former or not. If the + latter form is used, it means COMMONPAGESIZE bytes of runtime + memory will be saved at the expense of up to COMMONPAGESIZE wasted + bytes in the on-disk file. + + This expression can only be used directly in 'SECTIONS' commands, + not in any output section descriptions and only once in the linker + script. COMMONPAGESIZE should be less or equal to MAXPAGESIZE and + should be the system page size the object wants to be optimized for + (while still working on system page sizes up to MAXPAGESIZE). + + Example: + . = DATA_SEGMENT_ALIGN(0x10000, 0x2000); + +'DATA_SEGMENT_END(EXP)' + This defines the end of data segment for 'DATA_SEGMENT_ALIGN' + evaluation purposes. + + . = DATA_SEGMENT_END(.); + +'DATA_SEGMENT_RELRO_END(OFFSET, EXP)' + This defines the end of the 'PT_GNU_RELRO' segment when '-z relro' + option is used. Second argument is returned. When '-z relro' + option is not present, 'DATA_SEGMENT_RELRO_END' does nothing, + otherwise 'DATA_SEGMENT_ALIGN' is padded so that EXP + OFFSET is + aligned to the most commonly used page boundary for particular + target. If present in the linker script, it must always come in + between 'DATA_SEGMENT_ALIGN' and 'DATA_SEGMENT_END'. + + . = DATA_SEGMENT_RELRO_END(24, .); + +'DEFINED(SYMBOL)' + Return 1 if SYMBOL is in the linker global symbol table and is + defined before the statement using DEFINED in the script, otherwise + return 0. You can use this function to provide default values for + symbols. For example, the following script fragment shows how to + set a global symbol 'begin' to the first location in the '.text' + section--but if a symbol called 'begin' already existed, its value + is preserved: + + SECTIONS { ... + .text : { + begin = DEFINED(begin) ? begin : . ; + ... + } + ... + } + +'LENGTH(MEMORY)' + Return the length of the memory region named MEMORY. + +'LOADADDR(SECTION)' + Return the absolute LMA of the named SECTION. This is normally the + same as 'ADDR', but it may be different if the 'AT' attribute is + used in the output section definition (*note Output Section LMA::). + +'MAX(EXP1, EXP2)' + Returns the maximum of EXP1 and EXP2. + +'MIN(EXP1, EXP2)' + Returns the minimum of EXP1 and EXP2. + +'NEXT(EXP)' + Return the next unallocated address that is a multiple of EXP. + This function is closely related to 'ALIGN(EXP)'; unless you use + the 'MEMORY' command to define discontinuous memory for the output + file, the two functions are equivalent. + +'ORIGIN(MEMORY)' + Return the origin of the memory region named MEMORY. + +'SEGMENT_START(SEGMENT, DEFAULT)' + Return the base address of the named SEGMENT. If an explicit value + has been given for this segment (with a command-line '-T' option) + that value will be returned; otherwise the value will be DEFAULT. + At present, the '-T' command-line option can only be used to set + the base address for the "text", "data", and "bss" sections, but + you use 'SEGMENT_START' with any segment name. + +'SIZEOF(SECTION)' + Return the size in bytes of the named SECTION, if that section has + been allocated. If the section has not been allocated when this is + evaluated, the linker will report an error. In the following + example, 'symbol_1' and 'symbol_2' are assigned identical values: + SECTIONS{ ... + .output { + .start = . ; + ... + .end = . ; + } + symbol_1 = .end - .start ; + symbol_2 = SIZEOF(.output); + ... } + +'SIZEOF_HEADERS' +'sizeof_headers' + Return the size in bytes of the output file's headers. This is + information which appears at the start of the output file. You can + use this number when setting the start address of the first + section, if you choose, to facilitate paging. + + When producing an ELF output file, if the linker script uses the + 'SIZEOF_HEADERS' builtin function, the linker must compute the + number of program headers before it has determined all the section + addresses and sizes. If the linker later discovers that it needs + additional program headers, it will report an error 'not enough + room for program headers'. To avoid this error, you must avoid + using the 'SIZEOF_HEADERS' function, or you must rework your linker + script to avoid forcing the linker to use additional program + headers, or you must define the program headers yourself using the + 'PHDRS' command (*note PHDRS::). + +3.11 Implicit Linker Scripts +============================ + +If you specify a linker input file which the linker can not recognize as +an object file or an archive file, it will try to read the file as a +linker script. If the file can not be parsed as a linker script, the +linker will report an error. + + An implicit linker script will not replace the default linker script. + + Typically an implicit linker script would contain only symbol +assignments, or the 'INPUT', 'GROUP', or 'VERSION' commands. + + Any input files read because of an implicit linker script will be +read at the position in the command line where the implicit linker +script was read. This can affect archive searching. + +4 Machine Dependent Features +**************************** + +'ld' has additional features on some platforms; the following sections +describe them. Machines where 'ld' has no additional functionality are +not listed. + +4.1 'ld' and the H8/300 +======================= + +For the H8/300, 'ld' can perform these global optimizations when you +specify the '--relax' command-line option. + +_relaxing address modes_ + 'ld' finds all 'jsr' and 'jmp' instructions whose targets are + within eight bits, and turns them into eight-bit program-counter + relative 'bsr' and 'bra' instructions, respectively. + +_synthesizing instructions_ + 'ld' finds all 'mov.b' instructions which use the sixteen-bit + absolute address form, but refer to the top page of memory, and + changes them to use the eight-bit address form. (That is: the + linker turns 'mov.b '@'AA:16' into 'mov.b '@'AA:8' whenever the + address AA is in the top page of memory). + +_bit manipulation instructions_ + 'ld' finds all bit manipulation instructions like 'band, bclr, + biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, + bxor' which use 32 bit and 16 bit absolute address form, but refer + to the top page of memory, and changes them to use the 8 bit + address form. (That is: the linker turns 'bset #xx:3,'@'AA:32' + into 'bset #xx:3,'@'AA:8' whenever the address AA is in the top + page of memory). + +_system control instructions_ + 'ld' finds all 'ldc.w, stc.w' instructions which use the 32 bit + absolute address form, but refer to the top page of memory, and + changes them to use 16 bit address form. (That is: the linker + turns 'ldc.w '@'AA:32,ccr' into 'ldc.w '@'AA:16,ccr' whenever the + address AA is in the top page of memory). + +4.2 'ld' and the Intel 960 Family +================================= + +You can use the '-AARCHITECTURE' command line option to specify one of +the two-letter names identifying members of the 960 family; the option +specifies the desired output target, and warns of any incompatible +instructions in the input files. It also modifies the linker's search +strategy for archive libraries, to support the use of libraries specific +to each particular architecture, by including in the search loop names +suffixed with the string identifying the architecture. + + For example, if your 'ld' command line included '-ACA' as well as +'-ltry', the linker would look (in its built-in search paths, and in any +paths you specify with '-L') for a library with the names + + try + libtry.a + tryca + libtryca.a + +The first two possibilities would be considered in any event; the last +two are due to the use of '-ACA'. + + You can meaningfully use '-A' more than once on a command line, since +the 960 architecture family allows combination of target architectures; +each use will add another pair of name variants to search for when '-l' +specifies a library. + + 'ld' supports the '--relax' option for the i960 family. If you +specify '--relax', 'ld' finds all 'balx' and 'calx' instructions whose +targets are within 24 bits, and turns them into 24-bit program-counter +relative 'bal' and 'cal' instructions, respectively. 'ld' also turns +'cal' instructions into 'bal' instructions when it determines that the +target subroutine is a leaf routine (that is, the target subroutine does +not itself call any subroutines). + +4.3 'ld' and the Motorola 68HC11 and 68HC12 families +==================================================== + +4.3.1 Linker Relaxation +----------------------- + +For the Motorola 68HC11, 'ld' can perform these global optimizations +when you specify the '--relax' command-line option. + +_relaxing address modes_ + 'ld' finds all 'jsr' and 'jmp' instructions whose targets are + within eight bits, and turns them into eight-bit program-counter + relative 'bsr' and 'bra' instructions, respectively. + + 'ld' also looks at all 16-bit extended addressing modes and + transforms them in a direct addressing mode when the address is in + page 0 (between 0 and 0x0ff). + +_relaxing gcc instruction group_ + When 'gcc' is called with '-mrelax', it can emit group of + instructions that the linker can optimize to use a 68HC11 direct + addressing mode. These instructions consists of 'bclr' or 'bset' + instructions. + +4.3.2 Trampoline Generation +--------------------------- + +For 68HC11 and 68HC12, 'ld' can generate trampoline code to call a far +function using a normal 'jsr' instruction. The linker will also change +the relocation to some far function to use the trampoline address +instead of the function address. This is typically the case when a +pointer to a function is taken. The pointer will in fact point to the +function trampoline. + + The '--pic-veneer' switch makes the linker use PIC sequences for +ARM/Thumb interworking veneers, even if the rest of the binary is not +PIC. This avoids problems on uClinux targets where '--emit-relocs' is +used to generate relocatable binaries. + +4.4 'ld' and the ARM family +=========================== + +For the ARM, 'ld' will generate code stubs to allow functions calls +between ARM and Thumb code. These stubs only work with code that has +been compiled and assembled with the '-mthumb-interwork' command line +option. If it is necessary to link with old ARM object files or +libraries, which have not been compiled with the -mthumb-interwork +option then the '--support-old-code' command line switch should be given +to the linker. This will make it generate larger stub functions which +will work with non-interworking aware ARM code. Note, however, the +linker does not support generating stubs for function calls to +non-interworking aware Thumb code. + + The '--thumb-entry' switch is a duplicate of the generic '--entry' +switch, in that it sets the program's starting address. But it also +sets the bottom bit of the address, so that it can be branched to using +a BX instruction, and the program will start executing in Thumb mode +straight away. + + The '--be8' switch instructs 'ld' to generate BE8 format executables. +This option is only valid when linking big-endian objects. The +resulting image will contain big-endian data and little-endian code. + + The 'R_ARM_TARGET1' relocation is typically used for entries in the +'.init_array' section. It is interpreted as either 'R_ARM_REL32' or +'R_ARM_ABS32', depending on the target. The '--target1-rel' and +'--target1-abs' switches override the default. + + The '--target2=type' switch overrides the default definition of the +'R_ARM_TARGET2' relocation. Valid values for 'type', their meanings, +and target defaults are as follows: +'rel' + 'R_ARM_REL32' (arm*-*-elf, arm*-*-eabi) +'abs' + 'R_ARM_ABS32' (arm*-*-symbianelf) +'got-rel' + 'R_ARM_GOT_PREL' (arm*-*-linux, arm*-*-*bsd) + + The 'R_ARM_V4BX' relocation (defined by the ARM AAELF specification) +enables objects compiled for the ARMv4 architecture to be +interworking-safe when linked with other objects compiled for ARMv4t, +but also allows pure ARMv4 binaries to be built from the same ARMv4 +objects. + + In the latter case, the switch '--fix-v4bx' must be passed to the +linker, which causes v4t 'BX rM' instructions to be rewritten as 'MOV +PC,rM', since v4 processors do not have a 'BX' instruction. + + In the former case, the switch should not be used, and 'R_ARM_V4BX' +relocations are ignored. + + The '--use-blx' switch enables the linker to use ARM/Thumb BLX +instructions (available on ARMv5t and above) in various situations. +Currently it is used to perform calls via the PLT from Thumb code using +BLX rather than using BX and a mode-switching stub before each PLT +entry. This should lead to such calls executing slightly faster. + + This option is enabled implicitly for SymbianOS, so there is no need +to specify it if you are using that target. + + The '--vfp11-denorm-fix' switch enables a link-time workaround for a +bug in certain VFP11 coprocessor hardware, which sometimes allows +instructions with denorm operands (which must be handled by support +code) to have those operands overwritten by subsequent instructions +before the support code can read the intended values. + + The bug may be avoided in scalar mode if you allow at least one +intervening instruction between a VFP11 instruction which uses a +register and another instruction which writes to the same register, or +at least two intervening instructions if vector mode is in use. The bug +only affects full-compliance floating-point mode: you do not need this +workaround if you are using "runfast" mode. Please contact ARM for +further details. + + If you know you are using buggy VFP11 hardware, you can enable this +workaround by specifying the linker option '--vfp-denorm-fix=scalar' if +you are using the VFP11 scalar mode only, or '--vfp-denorm-fix=vector' +if you are using vector mode (the latter also works for scalar code). +The default is '--vfp-denorm-fix=none'. + + If the workaround is enabled, instructions are scanned for +potentially-troublesome sequences, and a veneer is created for each such +sequence which may trigger the erratum. The veneer consists of the +first instruction of the sequence and a branch back to the subsequent +instruction. The original instruction is then replaced with a branch to +the veneer. The extra cycles required to call and return from the +veneer are sufficient to avoid the erratum in both the scalar and vector +cases. + + The '--no-enum-size-warning' switch prevents the linker from warning +when linking object files that specify incompatible EABI enumeration +size attributes. For example, with this switch enabled, linking of an +object file using 32-bit enumeration values with another using +enumeration values fitted into the smallest possible space will not be +diagnosed. + +4.5 'ld' and HPPA 32-bit ELF Support +==================================== + +When generating a shared library, 'ld' will by default generate import +stubs suitable for use with a single sub-space application. The +'--multi-subspace' switch causes 'ld' to generate export stubs, and +different (larger) import stubs suitable for use with multiple +sub-spaces. + + Long branch stubs and import/export stubs are placed by 'ld' in stub +sections located between groups of input sections. '--stub-group-size' +specifies the maximum size of a group of input sections handled by one +stub section. Since branch offsets are signed, a stub section may serve +two groups of input sections, one group before the stub section, and one +group after it. However, when using conditional branches that require +stubs, it may be better (for branch prediction) that stub sections only +serve one group of input sections. A negative value for 'N' chooses +this scheme, ensuring that branches to stubs always use a negative +offset. Two special values of 'N' are recognized, '1' and '-1'. These +both instruct 'ld' to automatically size input section groups for the +branch types detected, with the same behaviour regarding stub placement +as other positive or negative values of 'N' respectively. + + Note that '--stub-group-size' does not split input sections. A +single input section larger than the group size specified will of course +create a larger group (of one section). If input sections are too +large, it may not be possible for a branch to reach its stub. + +4.6 'ld' and MMIX +================= + +For MMIX, there is a choice of generating 'ELF' object files or 'mmo' +object files when linking. The simulator 'mmix' understands the 'mmo' +format. The binutils 'objcopy' utility can translate between the two +formats. + + There is one special section, the '.MMIX.reg_contents' section. +Contents in this section is assumed to correspond to that of global +registers, and symbols referring to it are translated to special +symbols, equal to registers. In a final link, the start address of the +'.MMIX.reg_contents' section corresponds to the first allocated global +register multiplied by 8. Register '$255' is not included in this +section; it is always set to the program entry, which is at the symbol +'Main' for 'mmo' files. + + Symbols with the prefix '__.MMIX.start.', for example +'__.MMIX.start..text' and '__.MMIX.start..data' are special; there must +be only one each, even if they are local. The default linker script +uses these to set the default start address of a section. + + Initial and trailing multiples of zero-valued 32-bit words in a +section, are left out from an mmo file. + +4.7 'ld' and MSP430 +=================== + +For the MSP430 it is possible to select the MPU architecture. The flag +'-m [mpu type]' will select an appropriate linker script for selected +MPU type. (To get a list of known MPUs just pass '-m help' option to +the linker). + + The linker will recognize some extra sections which are MSP430 +specific: + +''.vectors'' + Defines a portion of ROM where interrupt vectors located. + +''.bootloader'' + Defines the bootloader portion of the ROM (if applicable). Any + code in this section will be uploaded to the MPU. + +''.infomem'' + Defines an information memory section (if applicable). Any code in + this section will be uploaded to the MPU. + +''.infomemnobits'' + This is the same as the '.infomem' section except that any code in + this section will not be uploaded to the MPU. + +''.noinit'' + Denotes a portion of RAM located above '.bss' section. + + The last two sections are used by gcc. + +4.8 'ld' and PowerPC 32-bit ELF Support +======================================= + +Branches on PowerPC processors are limited to a signed 26-bit +displacement, which may result in 'ld' giving 'relocation truncated to +fit' errors with very large programs. '--relax' enables the generation +of trampolines that can access the entire 32-bit address space. These +trampolines are inserted at section boundaries, so may not themselves be +reachable if an input section exceeds 33M in size. + +'--bss-plt' + Current PowerPC GCC accepts a '-msecure-plt' option that generates + code capable of using a newer PLT and GOT layout that has the + security advantage of no executable section ever needing to be + writable and no writable section ever being executable. PowerPC + 'ld' will generate this layout, including stubs to access the PLT, + if all input files (including startup and static libraries) were + compiled with '-msecure-plt'. '--bss-plt' forces the old BSS PLT + (and GOT layout) which can give slightly better performance. + +'--secure-plt' + 'ld' will use the new PLT and GOT layout if it is linking new + '-fpic' or '-fPIC' code, but does not do so automatically when + linking non-PIC code. This option requests the new PLT and GOT + layout. A warning will be given if some object file requires the + old style BSS PLT. + +'--sdata-got' + The new secure PLT and GOT are placed differently relative to other + sections compared to older BSS PLT and GOT placement. The location + of '.plt' must change because the new secure PLT is an initialized + section while the old PLT is uninitialized. The reason for the + '.got' change is more subtle: The new placement allows '.got' to be + read-only in applications linked with '-z relro -z now'. However, + this placement means that '.sdata' cannot always be used in shared + libraries, because the PowerPC ABI accesses '.sdata' in shared + libraries from the GOT pointer. '--sdata-got' forces the old GOT + placement. PowerPC GCC doesn't use '.sdata' in shared libraries, + so this option is really only useful for other compilers that may + do so. + +'--emit-stub-syms' + This option causes 'ld' to label linker stubs with a local symbol + that encodes the stub type and destination. + +'--no-tls-optimize' + PowerPC 'ld' normally performs some optimization of code sequences + used to access Thread-Local Storage. Use this option to disable + the optimization. + +4.9 'ld' and PowerPC64 64-bit ELF Support +========================================= + +'--stub-group-size' + Long branch stubs, PLT call stubs and TOC adjusting stubs are + placed by 'ld' in stub sections located between groups of input + sections. '--stub-group-size' specifies the maximum size of a + group of input sections handled by one stub section. Since branch + offsets are signed, a stub section may serve two groups of input + sections, one group before the stub section, and one group after + it. However, when using conditional branches that require stubs, + it may be better (for branch prediction) that stub sections only + serve one group of input sections. A negative value for 'N' + chooses this scheme, ensuring that branches to stubs always use a + negative offset. Two special values of 'N' are recognized, '1' and + '-1'. These both instruct 'ld' to automatically size input section + groups for the branch types detected, with the same behaviour + regarding stub placement as other positive or negative values of + 'N' respectively. + + Note that '--stub-group-size' does not split input sections. A + single input section larger than the group size specified will of + course create a larger group (of one section). If input sections + are too large, it may not be possible for a branch to reach its + stub. + +'--emit-stub-syms' + This option causes 'ld' to label linker stubs with a local symbol + that encodes the stub type and destination. + +'--dotsyms, --no-dotsyms' + These two options control how 'ld' interprets version patterns in a + version script. Older PowerPC64 compilers emitted both a function + descriptor symbol with the same name as the function, and a code + entry symbol with the name prefixed by a dot ('.'). To properly + version a function 'foo', the version script thus needs to control + both 'foo' and '.foo'. The option '--dotsyms', on by default, + automatically adds the required dot-prefixed patterns. Use + '--no-dotsyms' to disable this feature. + +'--no-tls-optimize' + PowerPC64 'ld' normally performs some optimization of code + sequences used to access Thread-Local Storage. Use this option to + disable the optimization. + +'--no-opd-optimize' + PowerPC64 'ld' normally removes '.opd' section entries + corresponding to deleted link-once functions, or functions removed + by the action of '--gc-sections' or linker scrip '/DISCARD/'. Use + this option to disable '.opd' optimization. + +'--non-overlapping-opd' + Some PowerPC64 compilers have an option to generate compressed + '.opd' entries spaced 16 bytes apart, overlapping the third word, + the static chain pointer (unused in C) with the first word of the + next entry. This option expands such entries to the full 24 bytes. + +'--no-toc-optimize' + PowerPC64 'ld' normally removes unused '.toc' section entries. + Such entries are detected by examining relocations that reference + the TOC in code sections. A reloc in a deleted code section marks + a TOC word as unneeded, while a reloc in a kept code section marks + a TOC word as needed. Since the TOC may reference itself, TOC + relocs are also examined. TOC words marked as both needed and + unneeded will of course be kept. TOC words without any referencing + reloc are assumed to be part of a multi-word entry, and are kept or + discarded as per the nearest marked preceding word. This works + reliably for compiler generated code, but may be incorrect if + assembly code is used to insert TOC entries. Use this option to + disable the optimization. + +'--no-multi-toc' + By default, PowerPC64 GCC generates code for a TOC model where TOC + entries are accessed with a 16-bit offset from r2. This limits the + total TOC size to 64K. PowerPC64 'ld' extends this limit by + grouping code sections such that each group uses less than 64K for + its TOC entries, then inserts r2 adjusting stubs between + inter-group calls. 'ld' does not split apart input sections, so + cannot help if a single input file has a '.toc' section that + exceeds 64K, most likely from linking multiple files with 'ld -r'. + Use this option to turn off this feature. + +4.10 'ld' and SPU ELF Support +============================= + +'--plugin' + This option marks an executable as a PIC plugin module. + +'--no-overlays' + Normally, 'ld' recognizes calls to functions within overlay + regions, and redirects such calls to an overlay manager via a stub. + 'ld' also provides a built-in overlay manager. This option turns + off all this special overlay handling. + +'--emit-stub-syms' + This option causes 'ld' to label overlay stubs with a local symbol + that encodes the stub type and destination. + +'--extra-overlay-stubs' + This option causes 'ld' to add overlay call stubs on all function + calls out of overlay regions. Normally stubs are not added on + calls to non-overlay regions. + +'--local-store=lo:hi' + 'ld' usually checks that a final executable for SPU fits in the + address range 0 to 256k. This option may be used to change the + range. Disable the check entirely with '--local-store=0:0'. + +'--stack-analysis' + SPU local store space is limited. Over-allocation of stack space + unnecessarily limits space available for code and data, while + under-allocation results in runtime failures. If given this + option, 'ld' will provide an estimate of maximum stack usage. 'ld' + does this by examining symbols in code sections to determine the + extents of functions, and looking at function prologues for stack + adjusting instructions. A call-graph is created by looking for + relocations on branch instructions. The graph is then searched for + the maximum stack usage path. Note that this analysis does not + find calls made via function pointers, and does not handle + recursion and other cycles in the call graph. Stack usage may be + under-estimated if your code makes such calls. Also, stack usage + for dynamic allocation, e.g. alloca, will not be detected. If a + link map is requested, detailed information about each function's + stack usage and calls will be given. + +'--emit-stack-syms' + This option, if given along with '--stack-analysis' will result in + 'ld' emitting stack sizing symbols for each function. These take + the form '__stack_<function_name>' for global functions, and + '__stack_<number>_<function_name>' for static functions. + '<number>' is the section id in hex. The value of such symbols is + the stack requirement for the corresponding function. The symbol + size will be zero, type 'STT_NOTYPE', binding 'STB_LOCAL', and + section 'SHN_ABS'. + +4.11 'ld''s Support for Various TI COFF Versions +================================================ + +The '--format' switch allows selection of one of the various TI COFF +versions. The latest of this writing is 2; versions 0 and 1 are also +supported. The TI COFF versions also vary in header byte-order format; +'ld' will read any version or byte order, but the output header format +depends on the default specified by the specific target. + +4.12 'ld' and WIN32 (cygwin/mingw) +================================== + +This section describes some of the win32 specific 'ld' issues. See +*note Command Line Options: Options. for detailed description of the +command line options mentioned here. + +_import libraries_ + The standard Windows linker creates and uses so-called import + libraries, which contains information for linking to dll's. They + are regular static archives and are handled as any other static + archive. The cygwin and mingw ports of 'ld' have specific support + for creating such libraries provided with the '--out-implib' + command line option. + +_exporting DLL symbols_ + The cygwin/mingw 'ld' has several ways to export symbols for dll's. + + _using auto-export functionality_ + By default 'ld' exports symbols with the auto-export + functionality, which is controlled by the following command + line options: + + * -export-all-symbols [This is the default] + * -exclude-symbols + * -exclude-libs + + If, however, '--export-all-symbols' is not given explicitly on + the command line, then the default auto-export behavior will + be _disabled_ if either of the following are true: + + * A DEF file is used. + * Any symbol in any object file was marked with the + __declspec(dllexport) attribute. + + _using a DEF file_ + Another way of exporting symbols is using a DEF file. A DEF + file is an ASCII file containing definitions of symbols which + should be exported when a dll is created. Usually it is named + '<dll name>.def' and is added as any other object file to the + linker's command line. The file's name must end in '.def' or + '.DEF'. + + gcc -o <output> <objectfiles> <dll name>.def + + Using a DEF file turns off the normal auto-export behavior, + unless the '--export-all-symbols' option is also used. + + Here is an example of a DEF file for a shared library called + 'xyz.dll': + + LIBRARY "xyz.dll" BASE=0x20000000 + + EXPORTS + foo + bar + _bar = bar + another_foo = abc.dll.afoo + var1 DATA + + This example defines a DLL with a non-default base address and + five symbols in the export table. The third exported symbol + '_bar' is an alias for the second. The fourth symbol, + 'another_foo' is resolved by "forwarding" to another module + and treating it as an alias for 'afoo' exported from the DLL + 'abc.dll'. The final symbol 'var1' is declared to be a data + object. + + The optional 'LIBRARY <name>' command indicates the _internal_ + name of the output DLL. If '<name>' does not include a suffix, + the default library suffix, '.DLL' is appended. + + When the .DEF file is used to build an application, rather + than a library, the 'NAME <name>' command should be used + instead of 'LIBRARY'. If '<name>' does not include a suffix, + the default executable suffix, '.EXE' is appended. + + With either 'LIBRARY <name>' or 'NAME <name>' the optional + specification 'BASE = <number>' may be used to specify a + non-default base address for the image. + + If neither 'LIBRARY <name>' nor 'NAME <name>' is specified, or + they specify an empty string, the internal name is the same as + the filename specified on the command line. + + The complete specification of an export symbol is: + + EXPORTS + ( ( ( <name1> [ = <name2> ] ) + | ( <name1> = <module-name> . <external-name>)) + [ @ <integer> ] [NONAME] [DATA] [CONSTANT] [PRIVATE] ) * + + Declares '<name1>' as an exported symbol from the DLL, or + declares '<name1>' as an exported alias for '<name2>'; or + declares '<name1>' as a "forward" alias for the symbol + '<external-name>' in the DLL '<module-name>'. Optionally, the + symbol may be exported by the specified ordinal '<integer>' + alias. + + The optional keywords that follow the declaration indicate: + + 'NONAME': Do not put the symbol name in the DLL's export + table. It will still be exported by its ordinal alias (either + the value specified by the .def specification or, otherwise, + the value assigned by the linker). The symbol name, however, + does remain visible in the import library (if any), unless + 'PRIVATE' is also specified. + + 'DATA': The symbol is a variable or object, rather than a + function. The import lib will export only an indirect + reference to 'foo' as the symbol '_imp__foo' (ie, 'foo' must + be resolved as '*_imp__foo'). + + 'CONSTANT': Like 'DATA', but put the undecorated 'foo' as well + as '_imp__foo' into the import library. Both refer to the + read-only import address table's pointer to the variable, not + to the variable itself. This can be dangerous. If the user + code fails to add the 'dllimport' attribute and also fails to + explicitly add the extra indirection that the use of the + attribute enforces, the application will behave unexpectedly. + + 'PRIVATE': Put the symbol in the DLL's export table, but do + not put it into the static import library used to resolve + imports at link time. The symbol can still be imported using + the 'LoadLibrary/GetProcAddress' API at runtime or by by using + the GNU ld extension of linking directly to the DLL without an + import library. + + See ld/deffilep.y in the binutils sources for the full + specification of other DEF file statements + + While linking a shared dll, 'ld' is able to create a DEF file + with the '--output-def <file>' command line option. + + _Using decorations_ + Another way of marking symbols for export is to modify the + source code itself, so that when building the DLL each symbol + to be exported is declared as: + + __declspec(dllexport) int a_variable + __declspec(dllexport) void a_function(int with_args) + + All such symbols will be exported from the DLL. If, however, + any of the object files in the DLL contain symbols decorated + in this way, then the normal auto-export behavior is disabled, + unless the '--export-all-symbols' option is also used. + + Note that object files that wish to access these symbols must + _not_ decorate them with dllexport. Instead, they should use + dllimport, instead: + + __declspec(dllimport) int a_variable + __declspec(dllimport) void a_function(int with_args) + + This complicates the structure of library header files, + because when included by the library itself the header must + declare the variables and functions as dllexport, but when + included by client code the header must declare them as + dllimport. There are a number of idioms that are typically + used to do this; often client code can omit the __declspec() + declaration completely. See '--enable-auto-import' and + 'automatic data imports' for more information. + +_automatic data imports_ + The standard Windows dll format supports data imports from dlls + only by adding special decorations (dllimport/dllexport), which let + the compiler produce specific assembler instructions to deal with + this issue. This increases the effort necessary to port existing + Un*x code to these platforms, especially for large c++ libraries + and applications. The auto-import feature, which was initially + provided by Paul Sokolovsky, allows one to omit the decorations to + achieve a behavior that conforms to that on POSIX/Un*x platforms. + This feature is enabled with the '--enable-auto-import' + command-line option, although it is enabled by default on + cygwin/mingw. The '--enable-auto-import' option itself now serves + mainly to suppress any warnings that are ordinarily emitted when + linked objects trigger the feature's use. + + auto-import of variables does not always work flawlessly without + additional assistance. Sometimes, you will see this message + + "variable '<var>' can't be auto-imported. Please read the + documentation for ld's '--enable-auto-import' for details." + + The '--enable-auto-import' documentation explains why this error + occurs, and several methods that can be used to overcome this + difficulty. One of these methods is the _runtime pseudo-relocs_ + feature, described below. + + For complex variables imported from DLLs (such as structs or + classes), object files typically contain a base address for the + variable and an offset (_addend_) within the variable-to specify a + particular field or public member, for instance. Unfortunately, + the runtime loader used in win32 environments is incapable of + fixing these references at runtime without the additional + information supplied by dllimport/dllexport decorations. The + standard auto-import feature described above is unable to resolve + these references. + + The '--enable-runtime-pseudo-relocs' switch allows these references + to be resolved without error, while leaving the task of adjusting + the references themselves (with their non-zero addends) to + specialized code provided by the runtime environment. Recent + versions of the cygwin and mingw environments and compilers provide + this runtime support; older versions do not. However, the support + is only necessary on the developer's platform; the compiled result + will run without error on an older system. + + '--enable-runtime-pseudo-relocs' is not the default; it must be + explicitly enabled as needed. + +_direct linking to a dll_ + The cygwin/mingw ports of 'ld' support the direct linking, + including data symbols, to a dll without the usage of any import + libraries. This is much faster and uses much less memory than does + the traditional import library method, especially when linking + large libraries or applications. When 'ld' creates an import lib, + each function or variable exported from the dll is stored in its + own bfd, even though a single bfd could contain many exports. The + overhead involved in storing, loading, and processing so many bfd's + is quite large, and explains the tremendous time, memory, and + storage needed to link against particularly large or complex + libraries when using import libs. + + Linking directly to a dll uses no extra command-line switches other + than '-L' and '-l', because 'ld' already searches for a number of + names to match each library. All that is needed from the + developer's perspective is an understanding of this search, in + order to force ld to select the dll instead of an import library. + + For instance, when ld is called with the argument '-lxxx' it will + attempt to find, in the first directory of its search path, + + libxxx.dll.a + xxx.dll.a + libxxx.a + xxx.lib + cygxxx.dll (*) + libxxx.dll + xxx.dll + + before moving on to the next directory in the search path. + + (*) Actually, this is not 'cygxxx.dll' but in fact is + '<prefix>xxx.dll', where '<prefix>' is set by the 'ld' option + '--dll-search-prefix=<prefix>'. In the case of cygwin, the + standard gcc spec file includes '--dll-search-prefix=cyg', so in + effect we actually search for 'cygxxx.dll'. + + Other win32-based unix environments, such as mingw or pw32, may use + other '<prefix>'es, although at present only cygwin makes use of + this feature. It was originally intended to help avoid name + conflicts among dll's built for the various win32/un*x + environments, so that (for example) two versions of a zlib dll + could coexist on the same machine. + + The generic cygwin/mingw path layout uses a 'bin' directory for + applications and dll's and a 'lib' directory for the import + libraries (using cygwin nomenclature): + + bin/ + cygxxx.dll + lib/ + libxxx.dll.a (in case of dll's) + libxxx.a (in case of static archive) + + Linking directly to a dll without using the import library can be + done two ways: + + 1. Use the dll directly by adding the 'bin' path to the link line + gcc -Wl,-verbose -o a.exe -L../bin/ -lxxx + + However, as the dll's often have version numbers appended to their + names ('cygncurses-5.dll') this will often fail, unless one + specifies '-L../bin -lncurses-5' to include the version. Import + libs are generally not versioned, and do not have this difficulty. + + 2. Create a symbolic link from the dll to a file in the 'lib' + directory according to the above mentioned search pattern. This + should be used to avoid unwanted changes in the tools needed for + making the app/dll. + + ln -s bin/cygxxx.dll lib/[cyg|lib|]xxx.dll[.a] + + Then you can link without any make environment changes. + + gcc -Wl,-verbose -o a.exe -L../lib/ -lxxx + + This technique also avoids the version number problems, because the + following is perfectly legal + + bin/ + cygxxx-5.dll + lib/ + libxxx.dll.a -> ../bin/cygxxx-5.dll + + Linking directly to a dll without using an import lib will work + even when auto-import features are exercised, and even when + '--enable-runtime-pseudo-relocs' is used. + + Given the improvements in speed and memory usage, one might + justifiably wonder why import libraries are used at all. There are + three reasons: + + 1. Until recently, the link-directly-to-dll functionality did + _not_ work with auto-imported data. + + 2. Sometimes it is necessary to include pure static objects within + the import library (which otherwise contains only bfd's for + indirection symbols that point to the exports of a dll). Again, + the import lib for the cygwin kernel makes use of this ability, and + it is not possible to do this without an import lib. + + 3. Symbol aliases can only be resolved using an import lib. This + is critical when linking against OS-supplied dll's (eg, the win32 + API) in which symbols are usually exported as undecorated aliases + of their stdcall-decorated assembly names. + + So, import libs are not going away. But the ability to replace + true import libs with a simple symbolic link to (or a copy of) a + dll, in many cases, is a useful addition to the suite of tools + binutils makes available to the win32 developer. Given the massive + improvements in memory requirements during linking, storage + requirements, and linking speed, we expect that many developers + will soon begin to use this feature whenever possible. + +_symbol aliasing_ + _adding additional names_ + Sometimes, it is useful to export symbols with additional + names. A symbol 'foo' will be exported as 'foo', but it can + also be exported as '_foo' by using special directives in the + DEF file when creating the dll. This will affect also the + optional created import library. Consider the following DEF + file: + + LIBRARY "xyz.dll" BASE=0x61000000 + + EXPORTS + foo + _foo = foo + + The line '_foo = foo' maps the symbol 'foo' to '_foo'. + + Another method for creating a symbol alias is to create it in + the source code using the "weak" attribute: + + void foo () { /* Do something. */; } + void _foo () __attribute__ ((weak, alias ("foo"))); + + See the gcc manual for more information about attributes and + weak symbols. + + _renaming symbols_ + Sometimes it is useful to rename exports. For instance, the + cygwin kernel does this regularly. A symbol '_foo' can be + exported as 'foo' but not as '_foo' by using special + directives in the DEF file. (This will also affect the import + library, if it is created). In the following example: + + LIBRARY "xyz.dll" BASE=0x61000000 + + EXPORTS + _foo = foo + + The line '_foo = foo' maps the exported symbol 'foo' to + '_foo'. + + Note: using a DEF file disables the default auto-export behavior, + unless the '--export-all-symbols' command line option is used. If, + however, you are trying to rename symbols, then you should list + _all_ desired exports in the DEF file, including the symbols that + are not being renamed, and do _not_ use the '--export-all-symbols' + option. If you list only the renamed symbols in the DEF file, and + use '--export-all-symbols' to handle the other symbols, then the + both the new names _and_ the original names for the renamed symbols + will be exported. In effect, you'd be aliasing those symbols, not + renaming them, which is probably not what you wanted. + +_weak externals_ + The Windows object format, PE, specifies a form of weak symbols + called weak externals. When a weak symbol is linked and the symbol + is not defined, the weak symbol becomes an alias for some other + symbol. There are three variants of weak externals: + * Definition is searched for in objects and libraries, + historically called lazy externals. + * Definition is searched for only in other objects, not in + libraries. This form is not presently implemented. + * No search; the symbol is an alias. This form is not presently + implemented. + As a GNU extension, weak symbols that do not specify an alternate + symbol are supported. If the symbol is undefined when linking, the + symbol uses a default value. + +4.13 'ld' and Xtensa Processors +=============================== + +The default 'ld' behavior for Xtensa processors is to interpret +'SECTIONS' commands so that lists of explicitly named sections in a +specification with a wildcard file will be interleaved when necessary to +keep literal pools within the range of PC-relative load offsets. For +example, with the command: + + SECTIONS + { + .text : { + *(.literal .text) + } + } + +'ld' may interleave some of the '.literal' and '.text' sections from +different object files to ensure that the literal pools are within the +range of PC-relative load offsets. A valid interleaving might place the +'.literal' sections from an initial group of files followed by the +'.text' sections of that group of files. Then, the '.literal' sections +from the rest of the files and the '.text' sections from the rest of the +files would follow. + + Relaxation is enabled by default for the Xtensa version of 'ld' and +provides two important link-time optimizations. The first optimization +is to combine identical literal values to reduce code size. A redundant +literal will be removed and all the 'L32R' instructions that use it will +be changed to reference an identical literal, as long as the location of +the replacement literal is within the offset range of all the 'L32R' +instructions. The second optimization is to remove unnecessary overhead +from assembler-generated "longcall" sequences of 'L32R'/'CALLXN' when +the target functions are within range of direct 'CALLN' instructions. + + For each of these cases where an indirect call sequence can be +optimized to a direct call, the linker will change the 'CALLXN' +instruction to a 'CALLN' instruction, remove the 'L32R' instruction, and +remove the literal referenced by the 'L32R' instruction if it is not +used for anything else. Removing the 'L32R' instruction always reduces +code size but can potentially hurt performance by changing the alignment +of subsequent branch targets. By default, the linker will always +preserve alignments, either by switching some instructions between +24-bit encodings and the equivalent density instructions or by inserting +a no-op in place of the 'L32R' instruction that was removed. If code +size is more important than performance, the '--size-opt' option can be +used to prevent the linker from widening density instructions or +inserting no-ops, except in a few cases where no-ops are required for +correctness. + + The following Xtensa-specific command-line options can be used to +control the linker: + +'--no-relax' + Since the Xtensa version of 'ld' enables the '--relax' option by + default, the '--no-relax' option is provided to disable relaxation. + +'--size-opt' + When optimizing indirect calls to direct calls, optimize for code + size more than performance. With this option, the linker will not + insert no-ops or widen density instructions to preserve branch + target alignment. There may still be some cases where no-ops are + required to preserve the correctness of the code. + +5 BFD +***** + +The linker accesses object and archive files using the BFD libraries. +These libraries allow the linker to use the same routines to operate on +object files whatever the object file format. A different object file +format can be supported simply by creating a new BFD back end and adding +it to the library. To conserve runtime memory, however, the linker and +associated tools are usually configured to support only a subset of the +object file formats available. You can use 'objdump -i' (*note objdump: +(binutils.info)objdump.) to list all the formats available for your +configuration. + + As with most implementations, BFD is a compromise between several +conflicting requirements. The major factor influencing BFD design was +efficiency: any time used converting between formats is time which would +not have been spent had BFD not been involved. This is partly offset by +abstraction payback; since BFD simplifies applications and back ends, +more time and care may be spent optimizing algorithms for a greater +speed. + + One minor artifact of the BFD solution which you should bear in mind +is the potential for information loss. There are two places where +useful information can be lost using the BFD mechanism: during +conversion and during output. *Note BFD information loss::. + +5.1 How It Works: An Outline of BFD +=================================== + +When an object file is opened, BFD subroutines automatically determine +the format of the input object file. They then build a descriptor in +memory with pointers to routines that will be used to access elements of +the object file's data structures. + + As different information from the object files is required, BFD reads +from different sections of the file and processes them. For example, a +very common operation for the linker is processing symbol tables. Each +BFD back end provides a routine for converting between the object file's +representation of symbols and an internal canonical format. When the +linker asks for the symbol table of an object file, it calls through a +memory pointer to the routine from the relevant BFD back end which reads +and converts the table into a canonical form. The linker then operates +upon the canonical form. When the link is finished and the linker +writes the output file's symbol table, another BFD back end routine is +called to take the newly created symbol table and convert it into the +chosen output format. + +5.1.1 Information Loss +---------------------- + +_Information can be lost during output._ The output formats supported +by BFD do not provide identical facilities, and information which can be +described in one form has nowhere to go in another format. One example +of this is alignment information in 'b.out'. There is nowhere in an +'a.out' format file to store alignment information on the contained +data, so when a file is linked from 'b.out' and an 'a.out' image is +produced, alignment information will not propagate to the output file. +(The linker will still use the alignment information internally, so the +link is performed correctly). + + Another example is COFF section names. COFF files may contain an +unlimited number of sections, each one with a textual section name. If +the target of the link is a format which does not have many sections +(e.g., 'a.out') or has sections without names (e.g., the Oasys format), +the link cannot be done simply. You can circumvent this problem by +describing the desired input-to-output section mapping with the linker +command language. + + _Information can be lost during canonicalization._ The BFD internal +canonical form of the external formats is not exhaustive; there are +structures in input formats for which there is no direct representation +internally. This means that the BFD back ends cannot maintain all +possible data richness through the transformation between external to +internal and back to external formats. + + This limitation is only a problem when an application reads one +format and writes another. Each BFD back end is responsible for +maintaining as much data as possible, and the internal BFD canonical +form has structures which are opaque to the BFD core, and exported only +to the back ends. When a file is read in one format, the canonical form +is generated for BFD and the application. At the same time, the back +end saves away any information which may otherwise be lost. If the data +is then written back in the same format, the back end routine will be +able to use the canonical form provided by the BFD core as well as the +information it prepared earlier. Since there is a great deal of +commonality between back ends, there is no information lost when linking +or copying big endian COFF to little endian COFF, or 'a.out' to 'b.out'. +When a mixture of formats is linked, the information is only lost from +the files whose format differs from the destination. + +5.1.2 The BFD canonical object-file format +------------------------------------------ + +The greatest potential for loss of information occurs when there is the +least overlap between the information provided by the source format, +that stored by the canonical format, and that needed by the destination +format. A brief description of the canonical form may help you +understand which kinds of data you can count on preserving across +conversions. + +_files_ + Information stored on a per-file basis includes target machine + architecture, particular implementation format type, a demand + pageable bit, and a write protected bit. Information like Unix + magic numbers is not stored here--only the magic numbers' meaning, + so a 'ZMAGIC' file would have both the demand pageable bit and the + write protected text bit set. The byte order of the target is + stored on a per-file basis, so that big- and little-endian object + files may be used with one another. + +_sections_ + Each section in the input file contains the name of the section, + the section's original address in the object file, size and + alignment information, various flags, and pointers into other BFD + data structures. + +_symbols_ + Each symbol contains a pointer to the information for the object + file which originally defined it, its name, its value, and various + flag bits. When a BFD back end reads in a symbol table, it + relocates all symbols to make them relative to the base of the + section where they were defined. Doing this ensures that each + symbol points to its containing section. Each symbol also has a + varying amount of hidden private data for the BFD back end. Since + the symbol points to the original file, the private data format for + that symbol is accessible. 'ld' can operate on a collection of + symbols of wildly different formats without problems. + + Normal global and simple local symbols are maintained on output, so + an output file (no matter its format) will retain symbols pointing + to functions and to global, static, and common variables. Some + symbol information is not worth retaining; in 'a.out', type + information is stored in the symbol table as long symbol names. + This information would be useless to most COFF debuggers; the + linker has command line switches to allow users to throw it away. + + There is one word of type information within the symbol, so if the + format supports symbol type information within symbols (for + example, COFF, IEEE, Oasys) and the type is simple enough to fit + within one word (nearly everything but aggregates), the information + will be preserved. + +_relocation level_ + Each canonical BFD relocation record contains a pointer to the + symbol to relocate to, the offset of the data to relocate, the + section the data is in, and a pointer to a relocation type + descriptor. Relocation is performed by passing messages through + the relocation type descriptor and the symbol pointer. Therefore, + relocations can be performed on output data using a relocation + method that is only available in one of the input formats. For + instance, Oasys provides a byte relocation format. A relocation + record requesting this relocation type would point indirectly to a + routine to perform this, so the relocation may be performed on a + byte being written to a 68k COFF file, even though 68k COFF has no + such relocation type. + +_line numbers_ + Object formats can contain, for debugging purposes, some form of + mapping between symbols, source line numbers, and addresses in the + output file. These addresses have to be relocated along with the + symbol information. Each symbol with an associated list of line + number records points to the first record of the list. The head of + a line number list consists of a pointer to the symbol, which + allows finding out the address of the function whose line number is + being described. The rest of the list is made up of pairs: offsets + into the section and line numbers. Any format which can simply + derive this information can pass it successfully between formats + (COFF, IEEE and Oasys). + +6 Reporting Bugs +**************** + +Your bug reports play an essential role in making 'ld' reliable. + + Reporting a bug may help you by bringing a solution to your problem, +or it may not. But in any case the principal function of a bug report +is to help the entire community by making the next version of 'ld' work +better. Bug reports are your contribution to the maintenance of 'ld'. + + In order for a bug report to serve its purpose, you must include the +information that enables us to fix the bug. + +6.1 Have You Found a Bug? +========================= + +If you are not sure whether you have found a bug, here are some +guidelines: + + * If the linker gets a fatal signal, for any input whatever, that is + a 'ld' bug. Reliable linkers never crash. + + * If 'ld' produces an error message for valid input, that is a bug. + + * If 'ld' does not produce an error message for invalid input, that + may be a bug. In the general case, the linker can not verify that + object files are correct. + + * If you are an experienced user of linkers, your suggestions for + improvement of 'ld' are welcome in any case. + +6.2 How to Report Bugs +====================== + +A number of companies and individuals offer support for GNU products. +If you obtained 'ld' from a support organization, we recommend you +contact that organization first. + + You can find contact information for many support companies and +individuals in the file 'etc/SERVICE' in the GNU Emacs distribution. + + The fundamental principle of reporting bugs usefully is this: *report +all the facts*. If you are not sure whether to state a fact or leave it +out, state it! + + Often people omit facts because they think they know what causes the +problem and assume that some details do not matter. Thus, you might +assume that the name of a symbol you use in an example does not matter. +Well, probably it does not, but one cannot be sure. Perhaps the bug is +a stray memory reference which happens to fetch from the location where +that name is stored in memory; perhaps, if the name were different, the +contents of that location would fool the linker into doing the right +thing despite the bug. Play it safe and give a specific, complete +example. That is the easiest thing for you to do, and the most helpful. + + Keep in mind that the purpose of a bug report is to enable us to fix +the bug if it is new to us. Therefore, always write your bug reports on +the assumption that the bug has not been reported previously. + + Sometimes people give a few sketchy facts and ask, "Does this ring a +bell?" This cannot help us fix a bug, so it is basically useless. We +respond by asking for enough details to enable us to investigate. You +might as well expedite matters by sending them to begin with. + + To enable us to fix the bug, you should include all these things: + + * The version of 'ld'. 'ld' announces it if you start it with the + '--version' argument. + + Without this, we will not know whether there is any point in + looking for the bug in the current version of 'ld'. + + * Any patches you may have applied to the 'ld' source, including any + patches made to the 'BFD' library. + + * The type of machine you are using, and the operating system name + and version number. + + * What compiler (and its version) was used to compile 'ld'--e.g. + "'gcc-2.7'". + + * The command arguments you gave the linker to link your example and + observe the bug. To guarantee you will not omit something + important, list them all. A copy of the Makefile (or the output + from make) is sufficient. + + If we were to try to guess the arguments, we would probably guess + wrong and then we might not encounter the bug. + + * A complete input file, or set of input files, that will reproduce + the bug. It is generally most helpful to send the actual object + files provided that they are reasonably small. Say no more than + 10K. For bigger files you can either make them available by FTP or + HTTP or else state that you are willing to send the object file(s) + to whomever requests them. (Note - your email will be going to a + mailing list, so we do not want to clog it up with large + attachments). But small attachments are best. + + If the source files were assembled using 'gas' or compiled using + 'gcc', then it may be OK to send the source files rather than the + object files. In this case, be sure to say exactly what version of + 'gas' or 'gcc' was used to produce the object files. Also say how + 'gas' or 'gcc' were configured. + + * A description of what behavior you observe that you believe is + incorrect. For example, "It gets a fatal signal." + + Of course, if the bug is that 'ld' gets a fatal signal, then we + will certainly notice it. But if the bug is incorrect output, we + might not notice unless it is glaringly wrong. You might as well + not give us a chance to make a mistake. + + Even if the problem you experience is a fatal signal, you should + still say so explicitly. Suppose something strange is going on, + such as, your copy of 'ld' is out of sync, or you have encountered + a bug in the C library on your system. (This has happened!) Your + copy might crash and ours would not. If you told us to expect a + crash, then when ours fails to crash, we would know that the bug + was not happening for us. If you had not told us to expect a + crash, then we would not be able to draw any conclusion from our + observations. + + * If you wish to suggest changes to the 'ld' source, send us context + diffs, as generated by 'diff' with the '-u', '-c', or '-p' option. + Always send diffs from the old file to the new file. If you even + discuss something in the 'ld' source, refer to it by context, not + by line number. + + The line numbers in our development sources will not match those in + your sources. Your line numbers would convey no useful information + to us. + + Here are some things that are not necessary: + + * A description of the envelope of the bug. + + Often people who encounter a bug spend a lot of time investigating + which changes to the input file will make the bug go away and which + changes will not affect it. + + This is often time consuming and not very useful, because the way + we will find the bug is by running a single example under the + debugger with breakpoints, not by pure deduction from a series of + examples. We recommend that you save your time for something else. + + Of course, if you can find a simpler example to report _instead_ of + the original one, that is a convenience for us. Errors in the + output will be easier to spot, running under the debugger will take + less time, and so on. + + However, simplification is not vital; if you do not want to do + this, report the bug anyway and send us the entire test case you + used. + + * A patch for the bug. + + A patch for the bug does help us if it is a good one. But do not + omit the necessary information, such as the test case, on the + assumption that a patch is all we need. We might see problems with + your patch and decide to fix the problem another way, or we might + not understand it at all. + + Sometimes with a program as complicated as 'ld' it is very hard to + construct an example that will make the program follow a certain + path through the code. If you do not send us the example, we will + not be able to construct one, so we will not be able to verify that + the bug is fixed. + + And if we cannot understand what bug you are trying to fix, or why + your patch should be an improvement, we will not install it. A + test case will help us to understand. + + * A guess about what the bug is or what it depends on. + + Such guesses are usually wrong. Even we cannot guess right about + such things without first using the debugger to find the facts. + +Appendix A MRI Compatible Script Files +************************************** + +To aid users making the transition to GNU 'ld' from the MRI linker, 'ld' +can use MRI compatible linker scripts as an alternative to the more +general-purpose linker scripting language described in *note Scripts::. +MRI compatible linker scripts have a much simpler command set than the +scripting language otherwise used with 'ld'. GNU 'ld' supports the most +commonly used MRI linker commands; these commands are described here. + + In general, MRI scripts aren't of much use with the 'a.out' object +file format, since it only has three sections and MRI scripts lack some +features to make use of them. + + You can specify a file containing an MRI-compatible script using the +'-c' command-line option. + + Each command in an MRI-compatible script occupies its own line; each +command line starts with the keyword that identifies the command (though +blank lines are also allowed for punctuation). If a line of an +MRI-compatible script begins with an unrecognized keyword, 'ld' issues a +warning message, but continues processing the script. + + Lines beginning with '*' are comments. + + You can write these commands using all upper-case letters, or all +lower case; for example, 'chip' is the same as 'CHIP'. The following +list shows only the upper-case form of each command. + +'ABSOLUTE SECNAME' +'ABSOLUTE SECNAME, SECNAME, ... SECNAME' + Normally, 'ld' includes in the output file all sections from all + the input files. However, in an MRI-compatible script, you can use + the 'ABSOLUTE' command to restrict the sections that will be + present in your output program. If the 'ABSOLUTE' command is used + at all in a script, then only the sections named explicitly in + 'ABSOLUTE' commands will appear in the linker output. You can + still use other input sections (whatever you select on the command + line, or using 'LOAD') to resolve addresses in the output file. + +'ALIAS OUT-SECNAME, IN-SECNAME' + Use this command to place the data from input section IN-SECNAME in + a section called OUT-SECNAME in the linker output file. + + IN-SECNAME may be an integer. + +'ALIGN SECNAME = EXPRESSION' + Align the section called SECNAME to EXPRESSION. The EXPRESSION + should be a power of two. + +'BASE EXPRESSION' + Use the value of EXPRESSION as the lowest address (other than + absolute addresses) in the output file. + +'CHIP EXPRESSION' +'CHIP EXPRESSION, EXPRESSION' + This command does nothing; it is accepted only for compatibility. + +'END' + This command does nothing whatever; it's only accepted for + compatibility. + +'FORMAT OUTPUT-FORMAT' + Similar to the 'OUTPUT_FORMAT' command in the more general linker + language, but restricted to one of these output formats: + + 1. S-records, if OUTPUT-FORMAT is 'S' + + 2. IEEE, if OUTPUT-FORMAT is 'IEEE' + + 3. COFF (the 'coff-m68k' variant in BFD), if OUTPUT-FORMAT is + 'COFF' + +'LIST ANYTHING...' + Print (to the standard output file) a link map, as produced by the + 'ld' command-line option '-M'. + + The keyword 'LIST' may be followed by anything on the same line, + with no change in its effect. + +'LOAD FILENAME' +'LOAD FILENAME, FILENAME, ... FILENAME' + Include one or more object file FILENAME in the link; this has the + same effect as specifying FILENAME directly on the 'ld' command + line. + +'NAME OUTPUT-NAME' + OUTPUT-NAME is the name for the program produced by 'ld'; the + MRI-compatible command 'NAME' is equivalent to the command-line + option '-o' or the general script language command 'OUTPUT'. + +'ORDER SECNAME, SECNAME, ... SECNAME' +'ORDER SECNAME SECNAME SECNAME' + Normally, 'ld' orders the sections in its output file in the order + in which they first appear in the input files. In an + MRI-compatible script, you can override this ordering with the + 'ORDER' command. The sections you list with 'ORDER' will appear + first in your output file, in the order specified. + +'PUBLIC NAME=EXPRESSION' +'PUBLIC NAME,EXPRESSION' +'PUBLIC NAME EXPRESSION' + Supply a value (EXPRESSION) for external symbol NAME used in the + linker input files. + +'SECT SECNAME, EXPRESSION' +'SECT SECNAME=EXPRESSION' +'SECT SECNAME EXPRESSION' + You can use any of these three forms of the 'SECT' command to + specify the start address (EXPRESSION) for section SECNAME. If you + have more than one 'SECT' statement for the same SECNAME, only the + _first_ sets the start address. + +Appendix B GNU Free Documentation License +***************************************** + + Version 1.1, March 2000 + + Copyright (C) 2000, 2003 Free Software Foundation, Inc. + 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + 0. PREAMBLE + + The purpose of this License is to make a manual, textbook, or other + written document "free" in the sense of freedom: to assure everyone + the effective freedom to copy and redistribute it, with or without + modifying it, either commercially or noncommercially. Secondarily, + this License preserves for the author and publisher a way to get + credit for their work, while not being considered responsible for + modifications made by others. + + This License is a kind of "copyleft", which means that derivative + works of the document must themselves be free in the same sense. + It complements the GNU General Public License, which is a copyleft + license designed for free software. + + We have designed this License in order to use it for manuals for + free software, because free software needs free documentation: a + free program should come with manuals providing the same freedoms + that the software does. But this License is not limited to + software manuals; it can be used for any textual work, regardless + of subject matter or whether it is published as a printed book. We + recommend this License principally for works whose purpose is + instruction or reference. + + + 1. APPLICABILITY AND DEFINITIONS + + This License applies to any manual or other work that contains a + notice placed by the copyright holder saying it can be distributed + under the terms of this License. The "Document", below, refers to + any such manual or work. Any member of the public is a licensee, + and is addressed as "you." + + A "Modified Version" of the Document means any work containing the + Document or a portion of it, either copied verbatim, or with + modifications and/or translated into another language. + + A "Secondary Section" is a named appendix or a front-matter section + of the Document that deals exclusively with the relationship of the + publishers or authors of the Document to the Document's overall + subject (or to related matters) and contains nothing that could + fall directly within that overall subject. (For example, if the + Document is in part a textbook of mathematics, a Secondary Section + may not explain any mathematics.) The relationship could be a + matter of historical connection with the subject or with related + matters, or of legal, commercial, philosophical, ethical or + political position regarding them. + + The "Invariant Sections" are certain Secondary Sections whose + titles are designated, as being those of Invariant Sections, in the + notice that says that the Document is released under this License. + + The "Cover Texts" are certain short passages of text that are + listed, as Front-Cover Texts or Back-Cover Texts, in the notice + that says that the Document is released under this License. + + A "Transparent" copy of the Document means a machine-readable copy, + represented in a format whose specification is available to the + general public, whose contents can be viewed and edited directly + and straightforwardly with generic text editors or (for images + composed of pixels) generic paint programs or (for drawings) some + widely available drawing editor, and that is suitable for input to + text formatters or for automatic translation to a variety of + formats suitable for input to text formatters. A copy made in an + otherwise Transparent file format whose markup has been designed to + thwart or discourage subsequent modification by readers is not + Transparent. A copy that is not "Transparent" is called "Opaque." + + Examples of suitable formats for Transparent copies include plain + ASCII without markup, Texinfo input format, LaTeX input format, + SGML or XML using a publicly available DTD, and standard-conforming + simple HTML designed for human modification. Opaque formats + include PostScript, PDF, proprietary formats that can be read and + edited only by proprietary word processors, SGML or XML for which + the DTD and/or processing tools are not generally available, and + the machine-generated HTML produced by some word processors for + output purposes only. + + The "Title Page" means, for a printed book, the title page itself, + plus such following pages as are needed to hold, legibly, the + material this License requires to appear in the title page. For + works in formats which do not have any title page as such, "Title + Page" means the text near the most prominent appearance of the + work's title, preceding the beginning of the body of the text. + + 2. VERBATIM COPYING + + You may copy and distribute the Document in any medium, either + commercially or noncommercially, provided that this License, the + copyright notices, and the license notice saying this License + applies to the Document are reproduced in all copies, and that you + add no other conditions whatsoever to those of this License. You + may not use technical measures to obstruct or control the reading + or further copying of the copies you make or distribute. However, + you may accept compensation in exchange for copies. If you + distribute a large enough number of copies you must also follow the + conditions in section 3. + + You may also lend copies, under the same conditions stated above, + and you may publicly display copies. + + 3. COPYING IN QUANTITY + + If you publish printed copies of the Document numbering more than + 100, and the Document's license notice requires Cover Texts, you + must enclose the copies in covers that carry, clearly and legibly, + all these Cover Texts: Front-Cover Texts on the front cover, and + Back-Cover Texts on the back cover. Both covers must also clearly + and legibly identify you as the publisher of these copies. The + front cover must present the full title with all words of the title + equally prominent and visible. You may add other material on the + covers in addition. Copying with changes limited to the covers, as + long as they preserve the title of the Document and satisfy these + conditions, can be treated as verbatim copying in other respects. + + If the required texts for either cover are too voluminous to fit + legibly, you should put the first ones listed (as many as fit + reasonably) on the actual cover, and continue the rest onto + adjacent pages. + + If you publish or distribute Opaque copies of the Document + numbering more than 100, you must either include a machine-readable + Transparent copy along with each Opaque copy, or state in or with + each Opaque copy a publicly-accessible computer-network location + containing a complete Transparent copy of the Document, free of + added material, which the general network-using public has access + to download anonymously at no charge using public-standard network + protocols. If you use the latter option, you must take reasonably + prudent steps, when you begin distribution of Opaque copies in + quantity, to ensure that this Transparent copy will remain thus + accessible at the stated location until at least one year after the + last time you distribute an Opaque copy (directly or through your + agents or retailers) of that edition to the public. + + It is requested, but not required, that you contact the authors of + the Document well before redistributing any large number of copies, + to give them a chance to provide you with an updated version of the + Document. + + 4. MODIFICATIONS + + You may copy and distribute a Modified Version of the Document + under the conditions of sections 2 and 3 above, provided that you + release the Modified Version under precisely this License, with the + Modified Version filling the role of the Document, thus licensing + distribution and modification of the Modified Version to whoever + possesses a copy of it. In addition, you must do these things in + the Modified Version: + + A. Use in the Title Page (and on the covers, if any) a title + distinct from that of the Document, and from those of previous + versions (which should, if there were any, be listed in the History + section of the Document). You may use the same title as a previous + version if the original publisher of that version gives permission. + B. List on the Title Page, as authors, one or more persons or + entities responsible for authorship of the modifications in the + Modified Version, together with at least five of the principal + authors of the Document (all of its principal authors, if it has + less than five). + C. State on the Title page the name of the publisher of the + Modified Version, as the publisher. + D. Preserve all the copyright notices of the Document. + E. Add an appropriate copyright notice for your modifications + adjacent to the other copyright notices. + F. Include, immediately after the copyright notices, a license + notice giving the public permission to use the Modified Version + under the terms of this License, in the form shown in the Addendum + below. + G. Preserve in that license notice the full lists of Invariant + Sections and required Cover Texts given in the Document's license + notice. + H. Include an unaltered copy of this License. + I. Preserve the section entitled "History", and its title, and add + to it an item stating at least the title, year, new authors, and + publisher of the Modified Version as given on the Title Page. If + there is no section entitled "History" in the Document, create one + stating the title, year, authors, and publisher of the Document as + given on its Title Page, then add an item describing the Modified + Version as stated in the previous sentence. + J. Preserve the network location, if any, given in the Document for + public access to a Transparent copy of the Document, and likewise + the network locations given in the Document for previous versions + it was based on. These may be placed in the "History" section. + You may omit a network location for a work that was published at + least four years before the Document itself, or if the original + publisher of the version it refers to gives permission. + K. In any section entitled "Acknowledgements" or "Dedications", + preserve the section's title, and preserve in the section all the + substance and tone of each of the contributor acknowledgements + and/or dedications given therein. + L. Preserve all the Invariant Sections of the Document, unaltered + in their text and in their titles. Section numbers or the + equivalent are not considered part of the section titles. + M. Delete any section entitled "Endorsements." Such a section may + not be included in the Modified Version. + N. Do not retitle any existing section as "Endorsements" or to + conflict in title with any Invariant Section. + + If the Modified Version includes new front-matter sections or + appendices that qualify as Secondary Sections and contain no + material copied from the Document, you may at your option designate + some or all of these sections as invariant. To do this, add their + titles to the list of Invariant Sections in the Modified Version's + license notice. These titles must be distinct from any other + section titles. + + You may add a section entitled "Endorsements", provided it contains + nothing but endorsements of your Modified Version by various + parties-for example, statements of peer review or that the text has + been approved by an organization as the authoritative definition of + a standard. + + You may add a passage of up to five words as a Front-Cover Text, + and a passage of up to 25 words as a Back-Cover Text, to the end of + the list of Cover Texts in the Modified Version. Only one passage + of Front-Cover Text and one of Back-Cover Text may be added by (or + through arrangements made by) any one entity. If the Document + already includes a cover text for the same cover, previously added + by you or by arrangement made by the same entity you are acting on + behalf of, you may not add another; but you may replace the old + one, on explicit permission from the previous publisher that added + the old one. + + The author(s) and publisher(s) of the Document do not by this + License give permission to use their names for publicity for or to + assert or imply endorsement of any Modified Version. + + 5. COMBINING DOCUMENTS + + You may combine the Document with other documents released under + this License, under the terms defined in section 4 above for + modified versions, provided that you include in the combination all + of the Invariant Sections of all of the original documents, + unmodified, and list them all as Invariant Sections of your + combined work in its license notice. + + The combined work need only contain one copy of this License, and + multiple identical Invariant Sections may be replaced with a single + copy. If there are multiple Invariant Sections with the same name + but different contents, make the title of each such section unique + by adding at the end of it, in parentheses, the name of the + original author or publisher of that section if known, or else a + unique number. Make the same adjustment to the section titles in + the list of Invariant Sections in the license notice of the + combined work. + + In the combination, you must combine any sections entitled + "History" in the various original documents, forming one section + entitled "History"; likewise combine any sections entitled + "Acknowledgements", and any sections entitled "Dedications." You + must delete all sections entitled "Endorsements." + + 6. COLLECTIONS OF DOCUMENTS + + You may make a collection consisting of the Document and other + documents released under this License, and replace the individual + copies of this License in the various documents with a single copy + that is included in the collection, provided that you follow the + rules of this License for verbatim copying of each of the documents + in all other respects. + + You may extract a single document from such a collection, and + distribute it individually under this License, provided you insert + a copy of this License into the extracted document, and follow this + License in all other respects regarding verbatim copying of that + document. + + 7. AGGREGATION WITH INDEPENDENT WORKS + + A compilation of the Document or its derivatives with other + separate and independent documents or works, in or on a volume of a + storage or distribution medium, does not as a whole count as a + Modified Version of the Document, provided no compilation copyright + is claimed for the compilation. Such a compilation is called an + "aggregate", and this License does not apply to the other + self-contained works thus compiled with the Document, on account of + their being thus compiled, if they are not themselves derivative + works of the Document. + + If the Cover Text requirement of section 3 is applicable to these + copies of the Document, then if the Document is less than one + quarter of the entire aggregate, the Document's Cover Texts may be + placed on covers that surround only the Document within the + aggregate. Otherwise they must appear on covers around the whole + aggregate. + + 8. TRANSLATION + + Translation is considered a kind of modification, so you may + distribute translations of the Document under the terms of section + 4. Replacing Invariant Sections with translations requires special + permission from their copyright holders, but you may include + translations of some or all Invariant Sections in addition to the + original versions of these Invariant Sections. You may include a + translation of this License provided that you also include the + original English version of this License. In case of a + disagreement between the translation and the original English + version of this License, the original English version will prevail. + + 9. TERMINATION + + You may not copy, modify, sublicense, or distribute the Document + except as expressly provided for under this License. Any other + attempt to copy, modify, sublicense or distribute the Document is + void, and will automatically terminate your rights under this + License. However, parties who have received copies, or rights, + from you under this License will not have their licenses terminated + so long as such parties remain in full compliance. + + 10. FUTURE REVISIONS OF THIS LICENSE + + The Free Software Foundation may publish new, revised versions of + the GNU Free Documentation License from time to time. Such new + versions will be similar in spirit to the present version, but may + differ in detail to address new problems or concerns. See + http://www.gnu.org/copyleft/. + + Each version of the License is given a distinguishing version + number. If the Document specifies that a particular numbered + version of this License "or any later version" applies to it, you + have the option of following the terms and conditions either of + that specified version or of any later version that has been + published (not as a draft) by the Free Software Foundation. If the + Document does not specify a version number of this License, you may + choose any version ever published (not as a draft) by the Free + Software Foundation. + +ADDENDUM: How to use this License for your documents +==================================================== + +To use this License in a document you have written, include a copy of +the License in the document and put the following copyright and license +notices just after the title page: + + Copyright (C) YEAR YOUR NAME. + Permission is granted to copy, distribute and/or modify this document + under the terms of the GNU Free Documentation License, Version 1.1 + or any later version published by the Free Software Foundation; + with the Invariant Sections being LIST THEIR TITLES, with the + Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. + A copy of the license is included in the section entitled "GNU + Free Documentation License." + + If you have no Invariant Sections, write "with no Invariant Sections" +instead of saying which ones are invariant. If you have no Front-Cover +Texts, write "no Front-Cover Texts" instead of "Front-Cover Texts being +LIST"; likewise for Back-Cover Texts. + + If your document contains nontrivial examples of program code, we +recommend releasing these examples in parallel under your choice of free +software license, such as the GNU General Public License, to permit +their use in free software. + +LD Index +******** + +* Menu: + +* ": Symbols. (line 3620) +* -(: Options. (line 756) +* --accept-unknown-input-arch: Options. (line 774) +* --add-needed: Options. (line 796) +* --add-stdcall-alias: Options. (line 1532) +* --allow-multiple-definition: Options. (line 1004) +* --allow-shlib-undefined: Options. (line 1010) +* --architecture=ARCH: Options. (line 227) +* --as-needed: Options. (line 784) +* --auxiliary: Options. (line 328) +* --bank-window: Options. (line 1867) +* --base-file: Options. (line 1537) +* --be8: ARM. (line 4205) +* --bss-plt: PowerPC ELF32. (line 4376) +* --check-sections: Options. (line 877) +* --cref: Options. (line 887) +* --default-imported-symver: Options. (line 1038) +* --default-script=SCRIPT: Options. (line 601) +* --default-symver: Options. (line 1034) +* --defsym SYMBOL=EXP: Options. (line 915) +* --demangle[=STYLE]: Options. (line 928) +* --disable-auto-image-base: Options. (line 1682) +* --disable-auto-import: Options. (line 1810) +* --disable-new-dtags: Options. (line 1479) +* --disable-runtime-pseudo-reloc: Options. (line 1823) +* --disable-stdcall-fixup: Options. (line 1547) +* --discard-all: Options. (line 647) +* --discard-locals: Options. (line 651) +* --dll: Options. (line 1542) +* --dll-search-prefix: Options. (line 1688) +* --dotsyms: PowerPC64 ELF64. (line 4446) +* --dynamic-linker FILE: Options. (line 941) +* --dynamic-list-cpp-new: Options. (line 869) +* --dynamic-list-cpp-typeinfo: Options. (line 873) +* --dynamic-list-data: Options. (line 866) +* --dynamic-list=DYNAMIC-LIST-FILE: Options. (line 853) +* --eh-frame-hdr: Options. (line 1475) +* --emit-relocs: Options. (line 537) +* --emit-stack-syms: SPU ELF. (line 4541) +* --emit-stub-syms: PowerPC ELF32. (line 4407) +* --emit-stub-syms <1>: PowerPC64 ELF64. (line 4442) +* --emit-stub-syms <2>: SPU ELF. (line 4510) +* --enable-auto-image-base: Options. (line 1674) +* --enable-auto-import: Options. (line 1697) +* --enable-extra-pe-debug: Options. (line 1828) +* --enable-new-dtags: Options. (line 1479) +* --enable-runtime-pseudo-reloc: Options. (line 1815) +* --enable-stdcall-fixup: Options. (line 1547) +* --entry=ENTRY: Options. (line 281) +* --error-unresolved-symbols: Options. (line 1428) +* --exclude-libs: Options. (line 291) +* --exclude-symbols: Options. (line 1588) +* --export-all-symbols: Options. (line 1564) +* --export-dynamic: Options. (line 302) +* --extra-overlay-stubs: SPU ELF. (line 4514) +* --fatal-warnings: Options. (line 947) +* --file-alignment: Options. (line 1594) +* --filter: Options. (line 349) +* --fix-v4bx: ARM. (line 4224) +* --force-dynamic: Options. (line 546) +* --force-exe-suffix: Options. (line 950) +* --format=FORMAT: Options. (line 238) +* --format=VERSION: TI COFF. (line 4554) +* --gc-sections: Options. (line 960) +* --gpsize: Options. (line 381) +* --hash-size=NUMBER: Options. (line 1488) +* --hash-style=STYLE: Options. (line 1496) +* --heap: Options. (line 1600) +* --help: Options. (line 977) +* --image-base: Options. (line 1607) +* --just-symbols=FILE: Options. (line 568) +* --kill-at: Options. (line 1616) +* --large-address-aware: Options. (line 1621) +* --library-path=DIR: Options. (line 440) +* --library=NAMESPEC: Options. (line 407) +* --local-store=lo:hi: SPU ELF. (line 4519) +* --major-image-version: Options. (line 1630) +* --major-os-version: Options. (line 1635) +* --major-subsystem-version: Options. (line 1639) +* --minor-image-version: Options. (line 1644) +* --minor-os-version: Options. (line 1649) +* --minor-subsystem-version: Options. (line 1653) +* --mri-script=MRI-CMDFILE: Options. (line 262) +* --multi-subspace: HPPA ELF32. (line 4285) +* --nmagic: Options. (line 506) +* --no-accept-unknown-input-arch: Options. (line 774) +* --no-add-needed: Options. (line 796) +* --no-allow-shlib-undefined: Options. (line 1010) +* --no-as-needed: Options. (line 784) +* --no-check-sections: Options. (line 877) +* --no-define-common: Options. (line 899) +* --no-demangle: Options. (line 928) +* --no-dotsyms: PowerPC64 ELF64. (line 4446) +* --no-enum-size-warning: ARM. (line 4275) +* --no-gc-sections: Options. (line 960) +* --no-keep-memory: Options. (line 989) +* --no-multi-toc: PowerPC64 ELF64. (line 4487) +* --no-omagic: Options. (line 520) +* --no-opd-optimize: PowerPC64 ELF64. (line 4461) +* --no-overlays: SPU ELF. (line 4504) +* --no-print-gc-sections: Options. (line 968) +* --no-relax: Xtensa. (line 5005) +* --no-tls-optimize: PowerPC ELF32. (line 4411) +* --no-tls-optimize <1>: PowerPC64 ELF64. (line 4456) +* --no-toc-optimize: PowerPC64 ELF64. (line 4473) +* --no-trampoline: Options. (line 1861) +* --no-undefined: Options. (line 996) +* --no-undefined-version: Options. (line 1029) +* --no-warn-mismatch: Options. (line 1042) +* --no-warn-search-mismatch: Options. (line 1051) +* --no-whole-archive: Options. (line 1055) +* --noinhibit-exec: Options. (line 1059) +* --non-overlapping-opd: PowerPC64 ELF64. (line 4467) +* --oformat: Options. (line 1070) +* --omagic: Options. (line 511) +* --out-implib: Options. (line 1666) +* --output-def: Options. (line 1658) +* --output=OUTPUT: Options. (line 526) +* --pic-executable: Options. (line 1083) +* --pic-veneer: M68HC11/68HC12. (line 4180) +* --plugin: SPU ELF. (line 4501) +* --print-gc-sections: Options. (line 968) +* --print-map: Options. (line 472) +* --reduce-memory-overheads: Options. (line 1502) +* --relax: Options. (line 1099) +* '--relax' on i960: i960. (line 4138) +* --relax on PowerPC: PowerPC ELF32. (line 4369) +* '--relax' on Xtensa: Xtensa. (line 4977) +* --relocatable: Options. (line 550) +* --script=SCRIPT: Options. (line 592) +* --sdata-got: PowerPC ELF32. (line 4393) +* --section-alignment: Options. (line 1833) +* --section-start SECTIONNAME=ORG: Options. (line 1265) +* --secure-plt: PowerPC ELF32. (line 4386) +* --sort-common: Options. (line 1212) +* --sort-section alignment: Options. (line 1222) +* --sort-section name: Options. (line 1218) +* --split-by-file: Options. (line 1226) +* --split-by-reloc: Options. (line 1231) +* --stack: Options. (line 1839) +* --stack-analysis: SPU ELF. (line 4524) +* --stats: Options. (line 1244) +* --strip-all: Options. (line 579) +* --strip-debug: Options. (line 583) +* --stub-group-size: PowerPC64 ELF64. (line 4419) +* --stub-group-size=N: HPPA ELF32. (line 4291) +* --subsystem: Options. (line 1846) +* --support-old-code: ARM. (line 4188) +* --sysroot: Options. (line 1248) +* --target-help: Options. (line 981) +* --target1-abs: ARM. (line 4209) +* --target1-rel: ARM. (line 4209) +* --target2=TYPE: ARM. (line 4214) +* --thumb-entry=ENTRY: ARM. (line 4199) +* --trace: Options. (line 588) +* --trace-symbol=SYMBOL: Options. (line 657) +* --traditional-format: Options. (line 1253) +* --undefined=SYMBOL: Options. (line 614) +* --unique[=SECTION]: Options. (line 632) +* --unresolved-symbols: Options. (line 1280) +* --use-blx: ARM. (line 4237) +* --verbose: Options. (line 1309) +* --version: Options. (line 641) +* --version-script=VERSION-SCRIPTFILE: Options. (line 1315) +* --vfp11-denorm-fix: ARM. (line 4246) +* --warn-common: Options. (line 1322) +* --warn-constructors: Options. (line 1390) +* --warn-multiple-gp: Options. (line 1395) +* --warn-once: Options. (line 1409) +* --warn-section-align: Options. (line 1413) +* --warn-shared-textrel: Options. (line 1420) +* --warn-unresolved-symbols: Options. (line 1423) +* --whole-archive: Options. (line 1432) +* --wrap: Options. (line 1446) +* -AARCH: Options. (line 226) +* -aKEYWORD: Options. (line 219) +* -assert KEYWORD: Options. (line 806) +* -b FORMAT: Options. (line 238) +* -Bdynamic: Options. (line 809) +* -Bgroup: Options. (line 819) +* -Bshareable: Options. (line 1204) +* -Bstatic: Options. (line 826) +* -Bsymbolic: Options. (line 840) +* -Bsymbolic-functions: Options. (line 847) +* -c MRI-CMDFILE: Options. (line 262) +* -call_shared: Options. (line 809) +* -d: Options. (line 272) +* -dc: Options. (line 272) +* -dn: Options. (line 826) +* -dp: Options. (line 272) +* -dT SCRIPT: Options. (line 601) +* -dy: Options. (line 809) +* -E: Options. (line 302) +* -e ENTRY: Options. (line 281) +* -EB: Options. (line 321) +* -EL: Options. (line 324) +* -f: Options. (line 328) +* -F: Options. (line 349) +* -fini: Options. (line 372) +* -g: Options. (line 378) +* -G: Options. (line 381) +* -hNAME: Options. (line 389) +* -i: Options. (line 398) +* -IFILE: Options. (line 941) +* -init: Options. (line 401) +* -LDIR: Options. (line 440) +* -lNAMESPEC: Options. (line 407) +* -M: Options. (line 472) +* -m EMULATION: Options. (line 462) +* -Map: Options. (line 985) +* -n: Options. (line 506) +* -N: Options. (line 511) +* -non_shared: Options. (line 826) +* -nostdlib: Options. (line 1065) +* -O LEVEL: Options. (line 532) +* -o OUTPUT: Options. (line 526) +* -pie: Options. (line 1083) +* -q: Options. (line 537) +* -qmagic: Options. (line 1093) +* -Qy: Options. (line 1096) +* -r: Options. (line 550) +* -R FILE: Options. (line 568) +* -rpath: Options. (line 1134) +* -rpath-link: Options. (line 1156) +* -s: Options. (line 579) +* -S: Options. (line 583) +* -shared: Options. (line 1204) +* -soname=NAME: Options. (line 389) +* -static: Options. (line 826) +* -t: Options. (line 588) +* -T SCRIPT: Options. (line 592) +* -Tbss ORG: Options. (line 1274) +* -Tdata ORG: Options. (line 1274) +* -Ttext ORG: Options. (line 1274) +* -u SYMBOL: Options. (line 614) +* -Ur: Options. (line 622) +* -v: Options. (line 641) +* -V: Options. (line 641) +* -x: Options. (line 647) +* -X: Options. (line 651) +* -Y PATH: Options. (line 666) +* -y SYMBOL: Options. (line 657) +* -z defs: Options. (line 996) +* -z KEYWORD: Options. (line 670) +* -z muldefs: Options. (line 1004) +* .: Location Counter. (line 3650) +* /DISCARD/: Output Section Discarding. + (line 2932) +* :PHDR: Output Section Phdr. + (line 3065) +* =FILLEXP: Output Section Fill. + (line 3079) +* >REGION: Output Section Region. + (line 3055) +* [COMMON]: Input Section Common. + (line 2744) +* 'ABSOLUTE' (MRI): MRI. (line 5391) +* absolute and relocatable symbols: Expression Section. (line 3828) +* absolute expressions: Expression Section. (line 3828) +* ABSOLUTE(EXP): Builtin Functions. (line 3864) +* ADDR(SECTION): Builtin Functions. (line 3871) +* address, section: Output Section Address. + (line 2522) +* 'ALIAS' (MRI): MRI. (line 5402) +* 'ALIGN' (MRI): MRI. (line 5408) +* align expression: Builtin Functions. (line 3890) +* align location counter: Builtin Functions. (line 3890) +* ALIGN(ALIGN): Builtin Functions. (line 3890) +* ALIGN(EXP,ALIGN): Builtin Functions. (line 3890) +* ALIGN(SECTION_ALIGN): Forced Output Alignment. + (line 3043) +* ALIGNOF(SECTION): Builtin Functions. (line 3915) +* allocating memory: MEMORY. (line 3196) +* architecture: Miscellaneous Commands. + (line 2254) +* architectures: Options. (line 226) +* archive files, from cmd line: Options. (line 407) +* archive search path in linker script: File Commands. (line 2158) +* arithmetic: Expressions. (line 3591) +* arithmetic operators: Operators. (line 3773) +* ARM interworking support: ARM. (line 4188) +* ASSERT: Miscellaneous Commands. + (line 2217) +* assertion in linker script: Miscellaneous Commands. + (line 2217) +* assignment in scripts: Assignments. (line 2262) +* AS_NEEDED(FILES): File Commands. (line 2138) +* AT(LMA): Output Section LMA. (line 2983) +* AT>LMA_REGION: Output Section LMA. (line 2983) +* automatic data imports: WIN32. (line 4723) +* back end: BFD. (line 5019) +* 'BASE' (MRI): MRI. (line 5412) +* BE8: ARM. (line 4205) +* BFD canonical format: Canonical format. (line 5114) +* BFD requirements: BFD. (line 5029) +* big-endian objects: Options. (line 321) +* binary input format: Options. (line 238) +* BLOCK(EXP): Builtin Functions. (line 3928) +* bug criteria: Bug Criteria. (line 5201) +* bug reports: Bug Reporting. (line 5219) +* bugs in 'ld': Reporting Bugs. (line 5188) +* BYTE(EXPRESSION): Output Section Data. + (line 2788) +* C++ constructors, arranging in link: Output Section Keywords. + (line 2857) +* 'CHIP' (MRI): MRI. (line 5416) +* COLLECT_NO_DEMANGLE: Environment. (line 1899) +* combining symbols, warnings on: Options. (line 1322) +* command files: Scripts. (line 1908) +* command line: Options. (line 130) +* common allocation: Options. (line 272) +* common allocation <1>: Options. (line 899) +* common allocation in linker script: Miscellaneous Commands. + (line 2228) +* common allocation in linker script <1>: Miscellaneous Commands. + (line 2233) +* common symbol placement: Input Section Common. + (line 2721) +* compatibility, MRI: Options. (line 262) +* constants in linker scripts: Constants. (line 3604) +* constructors: Options. (line 622) +* CONSTRUCTORS: Output Section Keywords. + (line 2857) +* constructors, arranging in link: Output Section Keywords. + (line 2857) +* crash of linker: Bug Criteria. (line 5204) +* CREATE_OBJECT_SYMBOLS: Output Section Keywords. + (line 2847) +* creating a DEF file: WIN32. (line 4691) +* cross reference table: Options. (line 887) +* cross references: Miscellaneous Commands. + (line 2238) +* current output location: Location Counter. (line 3650) +* data: Output Section Data. + (line 2788) +* DATA_SEGMENT_ALIGN(MAXPAGESIZE, COMMONPAGESIZE): Builtin Functions. + (line 3933) +* DATA_SEGMENT_END(EXP): Builtin Functions. (line 3954) +* DATA_SEGMENT_RELRO_END(OFFSET, EXP): Builtin Functions. (line 3960) +* dbx: Options. (line 1258) +* DEF files, creating: Options. (line 1658) +* default emulation: Environment. (line 1891) +* default input format: Environment. (line 1879) +* DEFINED(SYMBOL): Builtin Functions. (line 3971) +* deleting local symbols: Options. (line 647) +* demangling, default: Environment. (line 1899) +* demangling, from command line: Options. (line 928) +* direct linking to a dll: WIN32. (line 4771) +* discarding sections: Output Section Discarding. + (line 2917) +* discontinuous memory: MEMORY. (line 3196) +* DLLs, creating: Options. (line 1564) +* DLLs, creating <1>: Options. (line 1658) +* DLLs, creating <2>: Options. (line 1666) +* DLLs, linking to: Options. (line 1688) +* dot: Location Counter. (line 3650) +* dot inside sections: Location Counter. (line 3680) +* dot outside sections: Location Counter. (line 3710) +* dynamic linker, from command line: Options. (line 941) +* dynamic symbol table: Options. (line 302) +* ELF program headers: PHDRS. (line 3293) +* emulation: Options. (line 462) +* emulation, default: Environment. (line 1891) +* 'END' (MRI): MRI. (line 5420) +* endianness: Options. (line 321) +* entry point: Entry Point. (line 2076) +* entry point, from command line: Options. (line 281) +* entry point, thumb: ARM. (line 4199) +* ENTRY(SYMBOL): Entry Point. (line 2076) +* error on valid input: Bug Criteria. (line 5207) +* example of linker script: Simple Example. (line 2005) +* exporting DLL symbols: WIN32. (line 4576) +* expression evaluation order: Evaluation. (line 3794) +* expression sections: Expression Section. (line 3828) +* expression, absolute: Builtin Functions. (line 3864) +* expressions: Expressions. (line 3591) +* EXTERN: Miscellaneous Commands. + (line 2221) +* fatal signal: Bug Criteria. (line 5204) +* file name wildcard patterns: Input Section Wildcards. + (line 2616) +* FILEHDR: PHDRS. (line 3348) +* filename symbols: Output Section Keywords. + (line 2847) +* fill pattern, entire section: Output Section Fill. + (line 3079) +* FILL(EXPRESSION): Output Section Data. + (line 2821) +* finalization function: Options. (line 372) +* first input file: File Commands. (line 2166) +* first instruction: Entry Point. (line 2076) +* FIX_V4BX: ARM. (line 4224) +* FORCE_COMMON_ALLOCATION: Miscellaneous Commands. + (line 2228) +* forcing input section alignment: Forced Input Alignment. + (line 3048) +* forcing output section alignment: Forced Output Alignment. + (line 3043) +* forcing the creation of dynamic sections: Options. (line 546) +* 'FORMAT' (MRI): MRI. (line 5424) +* functions in expressions: Builtin Functions. (line 3860) +* garbage collection: Options. (line 960) +* garbage collection <1>: Options. (line 968) +* garbage collection <2>: Input Section Keep. (line 2750) +* generating optimized output: Options. (line 532) +* GNU linker: Overview. (line 100) +* GNUTARGET: Environment. (line 1879) +* GROUP(FILES): File Commands. (line 2131) +* grouping input files: File Commands. (line 2131) +* groups of archives: Options. (line 756) +* H8/300 support: H8/300. (line 4078) +* header size: Builtin Functions. (line 4035) +* heap size: Options. (line 1600) +* help: Options. (line 977) +* holes: Location Counter. (line 3656) +* holes, filling: Output Section Data. + (line 2821) +* HPPA multiple sub-space stubs: HPPA ELF32. (line 4285) +* HPPA stub grouping: HPPA ELF32. (line 4291) +* i960 support: i960. (line 4112) +* image base: Options. (line 1607) +* implicit linker scripts: Implicit Linker Scripts. + (line 4054) +* import libraries: WIN32. (line 4567) +* INCLUDE FILENAME: File Commands. (line 2096) +* including a linker script: File Commands. (line 2096) +* including an entire archive: Options. (line 1432) +* incremental link: Options. (line 398) +* INHIBIT_COMMON_ALLOCATION: Miscellaneous Commands. + (line 2233) +* initialization function: Options. (line 401) +* initialized data in ROM: Output Section LMA. (line 3003) +* input file format in linker script: Format Commands. (line 2204) +* input filename symbols: Output Section Keywords. + (line 2847) +* input files in linker scripts: File Commands. (line 2103) +* input files, displaying: Options. (line 588) +* input format: Options. (line 238) +* input format <1>: Options. (line 238) +* input object files in linker scripts: File Commands. (line 2103) +* input section alignment: Forced Input Alignment. + (line 3048) +* input section basics: Input Section Basics. + (line 2568) +* input section wildcards: Input Section Wildcards. + (line 2616) +* input sections: Input Section. (line 2558) +* INPUT(FILES): File Commands. (line 2103) +* integer notation: Constants. (line 3604) +* integer suffixes: Constants. (line 3610) +* internal object-file format: Canonical format. (line 5114) +* invalid input: Bug Criteria. (line 5209) +* K and M integer suffixes: Constants. (line 3610) +* KEEP: Input Section Keep. (line 2750) +* l =: MEMORY. (line 3256) +* lazy evaluation: Evaluation. (line 3794) +* 'ld' bugs, reporting: Bug Reporting. (line 5219) +* LDEMULATION: Environment. (line 1891) +* len =: MEMORY. (line 3256) +* LENGTH =: MEMORY. (line 3256) +* LENGTH(MEMORY): Builtin Functions. (line 3988) +* library search path in linker script: File Commands. (line 2158) +* link map: Options. (line 472) +* link-time runtime library search path: Options. (line 1156) +* linker crash: Bug Criteria. (line 5204) +* linker script concepts: Basic Script Concepts. + (line 1935) +* linker script example: Simple Example. (line 2005) +* linker script file commands: File Commands. (line 2093) +* linker script format: Script Format. (line 1985) +* linker script input object files: File Commands. (line 2103) +* linker script simple commands: Simple Commands. (line 2071) +* linker scripts: Scripts. (line 1908) +* 'LIST' (MRI): MRI. (line 5435) +* little-endian objects: Options. (line 324) +* 'LOAD' (MRI): MRI. (line 5442) +* load address: Output Section LMA. (line 2983) +* LOADADDR(SECTION): Builtin Functions. (line 3991) +* loading, preventing: Output Section Type. + (line 2969) +* local symbols, deleting: Options. (line 651) +* location counter: Location Counter. (line 3650) +* LONG(EXPRESSION): Output Section Data. + (line 2788) +* M and K integer suffixes: Constants. (line 3610) +* M68HC11 and 68HC12 support: M68HC11/68HC12. (line 4148) +* machine architecture: Miscellaneous Commands. + (line 2254) +* machine dependencies: Machine Dependent. (line 4071) +* mapping input sections to output sections: Input Section. (line 2558) +* MAX: Builtin Functions. (line 3995) +* MEMORY: MEMORY. (line 3196) +* memory region attributes: MEMORY. (line 3222) +* memory regions: MEMORY. (line 3196) +* memory regions and sections: Output Section Region. + (line 3055) +* memory usage: Options. (line 989) +* MIN: Builtin Functions. (line 3998) +* MRI compatibility: MRI. (line 5365) +* MSP430 extra sections: MSP430. (line 4343) +* 'NAME' (MRI): MRI. (line 5448) +* name, section: Output Section Name. + (line 2506) +* names: Symbols. (line 3620) +* naming the output file: Options. (line 526) +* NEXT(EXP): Builtin Functions. (line 4002) +* NMAGIC: Options. (line 506) +* NOCROSSREFS(SECTIONS): Miscellaneous Commands. + (line 2238) +* NOLOAD: Output Section Type. + (line 2969) +* not enough room for program headers: Builtin Functions. (line 4040) +* NO_ENUM_SIZE_WARNING: ARM. (line 4275) +* o =: MEMORY. (line 3251) +* objdump -i: BFD. (line 5019) +* object file management: BFD. (line 5019) +* object files: Options. (line 153) +* object formats available: BFD. (line 5019) +* object size: Options. (line 381) +* OMAGIC: Options. (line 511) +* OMAGIC <1>: Options. (line 520) +* opening object files: BFD outline. (line 5045) +* operators for arithmetic: Operators. (line 3773) +* options: Options. (line 130) +* 'ORDER' (MRI): MRI. (line 5453) +* org =: MEMORY. (line 3251) +* ORIGIN =: MEMORY. (line 3251) +* ORIGIN(MEMORY): Builtin Functions. (line 4008) +* orphan: Orphan Sections. (line 3635) +* output file after errors: Options. (line 1059) +* output file format in linker script: Format Commands. (line 2179) +* output file name in linker script: File Commands. (line 2148) +* output section alignment: Forced Output Alignment. + (line 3043) +* output section attributes: Output Section Attributes. + (line 2939) +* output section data: Output Section Data. + (line 2788) +* OUTPUT(FILENAME): File Commands. (line 2148) +* OUTPUT_ARCH(BFDARCH): Miscellaneous Commands. + (line 2254) +* OUTPUT_FORMAT(BFDNAME): Format Commands. (line 2179) +* OVERLAY: Overlay Description. + (line 3101) +* overlays: Overlay Description. + (line 3101) +* partial link: Options. (line 550) +* PHDRS: PHDRS. (line 3293) +* PHDRS <1>: PHDRS. (line 3348) +* PIC_VENEER: M68HC11/68HC12. (line 4180) +* position independent executables: Options. (line 1085) +* PowerPC ELF32 options: PowerPC ELF32. (line 4376) +* PowerPC GOT: PowerPC ELF32. (line 4393) +* PowerPC long branches: PowerPC ELF32. (line 4369) +* PowerPC PLT: PowerPC ELF32. (line 4376) +* PowerPC stub symbols: PowerPC ELF32. (line 4407) +* PowerPC TLS optimization: PowerPC ELF32. (line 4411) +* PowerPC64 dot symbols: PowerPC64 ELF64. (line 4446) +* PowerPC64 ELF64 options: PowerPC64 ELF64. (line 4419) +* PowerPC64 multi-TOC: PowerPC64 ELF64. (line 4487) +* PowerPC64 OPD optimization: PowerPC64 ELF64. (line 4461) +* PowerPC64 OPD spacing: PowerPC64 ELF64. (line 4467) +* PowerPC64 stub grouping: PowerPC64 ELF64. (line 4419) +* PowerPC64 stub symbols: PowerPC64 ELF64. (line 4442) +* PowerPC64 TLS optimization: PowerPC64 ELF64. (line 4456) +* PowerPC64 TOC optimization: PowerPC64 ELF64. (line 4473) +* precedence in expressions: Operators. (line 3773) +* prevent unnecessary loading: Output Section Type. + (line 2969) +* program headers: PHDRS. (line 3293) +* program headers and sections: Output Section Phdr. + (line 3065) +* program headers, not enough room: Builtin Functions. (line 4040) +* program segments: PHDRS. (line 3293) +* PROVIDE: PROVIDE. (line 2321) +* PROVIDE_HIDDEN: PROVIDE_HIDDEN. (line 2350) +* 'PUBLIC' (MRI): MRI. (line 5461) +* QUAD(EXPRESSION): Output Section Data. + (line 2788) +* quoted symbol names: Symbols. (line 3620) +* read-only text: Options. (line 506) +* read/write from cmd line: Options. (line 511) +* regions of memory: MEMORY. (line 3196) +* relative expressions: Expression Section. (line 3828) +* relaxing addressing modes: Options. (line 1099) +* relaxing on H8/300: H8/300. (line 4081) +* relaxing on i960: i960. (line 4138) +* relaxing on M68HC11: M68HC11/68HC12. (line 4155) +* relaxing on Xtensa: Xtensa. (line 4977) +* relocatable and absolute symbols: Expression Section. (line 3828) +* relocatable output: Options. (line 550) +* removing sections: Output Section Discarding. + (line 2917) +* reporting bugs in 'ld': Reporting Bugs. (line 5188) +* requirements for BFD: BFD. (line 5029) +* retain relocations in final executable: Options. (line 537) +* retaining specified symbols: Options. (line 1120) +* ROM initialized data: Output Section LMA. (line 3003) +* round up expression: Builtin Functions. (line 3890) +* round up location counter: Builtin Functions. (line 3890) +* runtime library name: Options. (line 389) +* runtime library search path: Options. (line 1134) +* runtime pseudo-relocation: WIN32. (line 4749) +* scaled integers: Constants. (line 3610) +* scommon section: Input Section Common. + (line 2735) +* script files: Options. (line 592) +* script files <1>: Options. (line 601) +* scripts: Scripts. (line 1908) +* search directory, from cmd line: Options. (line 440) +* search path in linker script: File Commands. (line 2158) +* SEARCH_DIR(PATH): File Commands. (line 2158) +* 'SECT' (MRI): MRI. (line 5467) +* section address: Output Section Address. + (line 2522) +* section address in expression: Builtin Functions. (line 3871) +* section alignment: Builtin Functions. (line 3915) +* section alignment, warnings on: Options. (line 1413) +* section data: Output Section Data. + (line 2788) +* section fill pattern: Output Section Fill. + (line 3079) +* section load address: Output Section LMA. (line 2983) +* section load address in expression: Builtin Functions. (line 3991) +* section name: Output Section Name. + (line 2506) +* section name wildcard patterns: Input Section Wildcards. + (line 2616) +* section size: Builtin Functions. (line 4019) +* section, assigning to memory region: Output Section Region. + (line 3055) +* section, assigning to program header: Output Section Phdr. + (line 3065) +* SECTIONS: SECTIONS. (line 2443) +* sections, discarding: Output Section Discarding. + (line 2917) +* segment origins, cmd line: Options. (line 1274) +* segments, ELF: PHDRS. (line 3293) +* SEGMENT_START(SEGMENT, DEFAULT): Builtin Functions. (line 4011) +* shared libraries: Options. (line 1206) +* SHORT(EXPRESSION): Output Section Data. + (line 2788) +* SIZEOF(SECTION): Builtin Functions. (line 4019) +* SIZEOF_HEADERS: Builtin Functions. (line 4035) +* small common symbols: Input Section Common. + (line 2735) +* SORT: Input Section Wildcards. + (line 2665) +* SORT_BY_ALIGNMENT: Input Section Wildcards. + (line 2661) +* SORT_BY_NAME: Input Section Wildcards. + (line 2653) +* SPU: SPU ELF. (line 4524) +* SPU <1>: SPU ELF. (line 4541) +* SPU ELF options: SPU ELF. (line 4501) +* SPU extra overlay stubs: SPU ELF. (line 4514) +* SPU local store size: SPU ELF. (line 4519) +* SPU overlay stub symbols: SPU ELF. (line 4510) +* SPU overlays: SPU ELF. (line 4504) +* SPU plugins: SPU ELF. (line 4501) +* SQUAD(EXPRESSION): Output Section Data. + (line 2788) +* stack size: Options. (line 1839) +* standard Unix system: Options. (line 131) +* start of execution: Entry Point. (line 2076) +* STARTUP(FILENAME): File Commands. (line 2166) +* strip all symbols: Options. (line 579) +* strip debugger symbols: Options. (line 583) +* stripping all but some symbols: Options. (line 1120) +* SUBALIGN(SUBSECTION_ALIGN): Forced Input Alignment. + (line 3048) +* suffixes for integers: Constants. (line 3610) +* symbol defaults: Builtin Functions. (line 3971) +* symbol definition, scripts: Assignments. (line 2262) +* symbol names: Symbols. (line 3620) +* symbol tracing: Options. (line 657) +* symbol versions: VERSION. (line 3424) +* symbol-only input: Options. (line 568) +* symbols, from command line: Options. (line 915) +* symbols, relocatable and absolute: Expression Section. (line 3828) +* symbols, retaining selectively: Options. (line 1120) +* synthesizing linker: Options. (line 1099) +* synthesizing on H8/300: H8/300. (line 4086) +* TARGET(BFDNAME): Format Commands. (line 2204) +* TARGET1: ARM. (line 4209) +* TARGET2: ARM. (line 4214) +* thumb entry point: ARM. (line 4199) +* TI COFF versions: TI COFF. (line 4554) +* traditional format: Options. (line 1253) +* trampoline generation on M68HC11: M68HC11/68HC12. (line 4173) +* trampoline generation on M68HC12: M68HC11/68HC12. (line 4173) +* unallocated address, next: Builtin Functions. (line 4002) +* undefined symbol: Options. (line 614) +* undefined symbol in linker script: Miscellaneous Commands. + (line 2221) +* undefined symbols, warnings on: Options. (line 1409) +* uninitialized data placement: Input Section Common. + (line 2721) +* unspecified memory: Output Section Data. + (line 2821) +* usage: Options. (line 977) +* USE_BLX: ARM. (line 4237) +* using a DEF file: WIN32. (line 4596) +* using auto-export functionality: WIN32. (line 4579) +* Using decorations: WIN32. (line 4695) +* variables, defining: Assignments. (line 2262) +* verbose: Options. (line 1309) +* version: Options. (line 641) +* version script: VERSION. (line 3424) +* version script, symbol versions: Options. (line 1315) +* VERSION {script text}: VERSION. (line 3424) +* versions of symbols: VERSION. (line 3424) +* VFP11_DENORM_FIX: ARM. (line 4246) +* warnings, on combining symbols: Options. (line 1322) +* warnings, on section alignment: Options. (line 1413) +* warnings, on undefined symbols: Options. (line 1409) +* weak externals: WIN32. (line 4938) +* what is this?: Overview. (line 100) +* wildcard file name patterns: Input Section Wildcards. + (line 2616) +* Xtensa options: Xtensa. (line 5005) +* Xtensa processors: Xtensa. (line 4956) + |