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authorjdp <jdp@FreeBSD.org>1998-03-01 22:58:51 +0000
committerjdp <jdp@FreeBSD.org>1998-03-01 22:58:51 +0000
commit2cbd0590cd191c81b59e94970f4c40c371f9e415 (patch)
treeb7676f996414b979dcbb7de92a3e86b97320d023 /contrib/binutils/bfd/doc/coffcode.texi
downloadFreeBSD-src-2cbd0590cd191c81b59e94970f4c40c371f9e415.zip
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Initial import of GNU binutils version 2.8.1. Believe it or not,
this is heavily stripped down.
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+@section coff backends
+BFD supports a number of different flavours of coff format.
+The major differences between formats are the sizes and
+alignments of fields in structures on disk, and the occasional
+extra field.
+
+Coff in all its varieties is implemented with a few common
+files and a number of implementation specific files. For
+example, The 88k bcs coff format is implemented in the file
+@file{coff-m88k.c}. This file @code{#include}s
+@file{coff/m88k.h} which defines the external structure of the
+coff format for the 88k, and @file{coff/internal.h} which
+defines the internal structure. @file{coff-m88k.c} also
+defines the relocations used by the 88k format
+@xref{Relocations}.
+
+The Intel i960 processor version of coff is implemented in
+@file{coff-i960.c}. This file has the same structure as
+@file{coff-m88k.c}, except that it includes @file{coff/i960.h}
+rather than @file{coff-m88k.h}.
+@*
+@subsection Porting to a new version of coff
+The recommended method is to select from the existing
+implementations the version of coff which is most like the one
+you want to use. For example, we'll say that i386 coff is
+the one you select, and that your coff flavour is called foo.
+Copy @file{i386coff.c} to @file{foocoff.c}, copy
+@file{../include/coff/i386.h} to @file{../include/coff/foo.h},
+and add the lines to @file{targets.c} and @file{Makefile.in}
+so that your new back end is used. Alter the shapes of the
+structures in @file{../include/coff/foo.h} so that they match
+what you need. You will probably also have to add
+@code{#ifdef}s to the code in @file{coff/internal.h} and
+@file{coffcode.h} if your version of coff is too wild.
+
+You can verify that your new BFD backend works quite simply by
+building @file{objdump} from the @file{binutils} directory,
+and making sure that its version of what's going on and your
+host system's idea (assuming it has the pretty standard coff
+dump utility, usually called @code{att-dump} or just
+@code{dump}) are the same. Then clean up your code, and send
+what you've done to Cygnus. Then your stuff will be in the
+next release, and you won't have to keep integrating it.
+@*
+@subsection How the coff backend works
+
+@*
+@subsubsection File layout
+The Coff backend is split into generic routines that are
+applicable to any Coff target and routines that are specific
+to a particular target. The target-specific routines are
+further split into ones which are basically the same for all
+Coff targets except that they use the external symbol format
+or use different values for certain constants.
+
+The generic routines are in @file{coffgen.c}. These routines
+work for any Coff target. They use some hooks into the target
+specific code; the hooks are in a @code{bfd_coff_backend_data}
+structure, one of which exists for each target.
+
+The essentially similar target-specific routines are in
+@file{coffcode.h}. This header file includes executable C code.
+The various Coff targets first include the appropriate Coff
+header file, make any special defines that are needed, and
+then include @file{coffcode.h}.
+
+Some of the Coff targets then also have additional routines in
+the target source file itself.
+
+For example, @file{coff-i960.c} includes
+@file{coff/internal.h} and @file{coff/i960.h}. It then
+defines a few constants, such as @code{I960}, and includes
+@file{coffcode.h}. Since the i960 has complex relocation
+types, @file{coff-i960.c} also includes some code to
+manipulate the i960 relocs. This code is not in
+@file{coffcode.h} because it would not be used by any other
+target.
+@*
+@subsubsection Bit twiddling
+Each flavour of coff supported in BFD has its own header file
+describing the external layout of the structures. There is also
+an internal description of the coff layout, in
+@file{coff/internal.h}. A major function of the
+coff backend is swapping the bytes and twiddling the bits to
+translate the external form of the structures into the normal
+internal form. This is all performed in the
+@code{bfd_swap}_@i{thing}_@i{direction} routines. Some
+elements are different sizes between different versions of
+coff; it is the duty of the coff version specific include file
+to override the definitions of various packing routines in
+@file{coffcode.h}. E.g., the size of line number entry in coff is
+sometimes 16 bits, and sometimes 32 bits. @code{#define}ing
+@code{PUT_LNSZ_LNNO} and @code{GET_LNSZ_LNNO} will select the
+correct one. No doubt, some day someone will find a version of
+coff which has a varying field size not catered to at the
+moment. To port BFD, that person will have to add more @code{#defines}.
+Three of the bit twiddling routines are exported to
+@code{gdb}; @code{coff_swap_aux_in}, @code{coff_swap_sym_in}
+and @code{coff_swap_linno_in}. @code{GDB} reads the symbol
+table on its own, but uses BFD to fix things up. More of the
+bit twiddlers are exported for @code{gas};
+@code{coff_swap_aux_out}, @code{coff_swap_sym_out},
+@code{coff_swap_lineno_out}, @code{coff_swap_reloc_out},
+@code{coff_swap_filehdr_out}, @code{coff_swap_aouthdr_out},
+@code{coff_swap_scnhdr_out}. @code{Gas} currently keeps track
+of all the symbol table and reloc drudgery itself, thereby
+saving the internal BFD overhead, but uses BFD to swap things
+on the way out, making cross ports much safer. Doing so also
+allows BFD (and thus the linker) to use the same header files
+as @code{gas}, which makes one avenue to disaster disappear.
+@*
+@subsubsection Symbol reading
+The simple canonical form for symbols used by BFD is not rich
+enough to keep all the information available in a coff symbol
+table. The back end gets around this problem by keeping the original
+symbol table around, "behind the scenes".
+
+When a symbol table is requested (through a call to
+@code{bfd_canonicalize_symtab}), a request gets through to
+@code{coff_get_normalized_symtab}. This reads the symbol table from
+the coff file and swaps all the structures inside into the
+internal form. It also fixes up all the pointers in the table
+(represented in the file by offsets from the first symbol in
+the table) into physical pointers to elements in the new
+internal table. This involves some work since the meanings of
+fields change depending upon context: a field that is a
+pointer to another structure in the symbol table at one moment
+may be the size in bytes of a structure at the next. Another
+pass is made over the table. All symbols which mark file names
+(@code{C_FILE} symbols) are modified so that the internal
+string points to the value in the auxent (the real filename)
+rather than the normal text associated with the symbol
+(@code{".file"}).
+
+At this time the symbol names are moved around. Coff stores
+all symbols less than nine characters long physically
+within the symbol table; longer strings are kept at the end of
+the file in the string table. This pass moves all strings
+into memory and replaces them with pointers to the strings.
+
+The symbol table is massaged once again, this time to create
+the canonical table used by the BFD application. Each symbol
+is inspected in turn, and a decision made (using the
+@code{sclass} field) about the various flags to set in the
+@code{asymbol}. @xref{Symbols}. The generated canonical table
+shares strings with the hidden internal symbol table.
+
+Any linenumbers are read from the coff file too, and attached
+to the symbols which own the functions the linenumbers belong to.
+@*
+@subsubsection Symbol writing
+Writing a symbol to a coff file which didn't come from a coff
+file will lose any debugging information. The @code{asymbol}
+structure remembers the BFD from which the symbol was taken, and on
+output the back end makes sure that the same destination target as
+source target is present.
+
+When the symbols have come from a coff file then all the
+debugging information is preserved.
+
+Symbol tables are provided for writing to the back end in a
+vector of pointers to pointers. This allows applications like
+the linker to accumulate and output large symbol tables
+without having to do too much byte copying.
+
+This function runs through the provided symbol table and
+patches each symbol marked as a file place holder
+(@code{C_FILE}) to point to the next file place holder in the
+list. It also marks each @code{offset} field in the list with
+the offset from the first symbol of the current symbol.
+
+Another function of this procedure is to turn the canonical
+value form of BFD into the form used by coff. Internally, BFD
+expects symbol values to be offsets from a section base; so a
+symbol physically at 0x120, but in a section starting at
+0x100, would have the value 0x20. Coff expects symbols to
+contain their final value, so symbols have their values
+changed at this point to reflect their sum with their owning
+section. This transformation uses the
+@code{output_section} field of the @code{asymbol}'s
+@code{asection} @xref{Sections}.
+
+@itemize @bullet
+
+@item
+@code{coff_mangle_symbols}
+@end itemize
+This routine runs though the provided symbol table and uses
+the offsets generated by the previous pass and the pointers
+generated when the symbol table was read in to create the
+structured hierachy required by coff. It changes each pointer
+to a symbol into the index into the symbol table of the asymbol.
+
+@itemize @bullet
+
+@item
+@code{coff_write_symbols}
+@end itemize
+This routine runs through the symbol table and patches up the
+symbols from their internal form into the coff way, calls the
+bit twiddlers, and writes out the table to the file.
+@*
+@findex coff_symbol_type
+@subsubsection @code{coff_symbol_type}
+@strong{Description}@*
+The hidden information for an @code{asymbol} is described in a
+@code{combined_entry_type}:
+@*
+.
+@example
+typedef struct coff_ptr_struct
+@{
+
+ /* Remembers the offset from the first symbol in the file for
+ this symbol. Generated by coff_renumber_symbols. */
+unsigned int offset;
+
+ /* Should the value of this symbol be renumbered. Used for
+ XCOFF C_BSTAT symbols. Set by coff_slurp_symbol_table. */
+unsigned int fix_value : 1;
+
+ /* Should the tag field of this symbol be renumbered.
+ Created by coff_pointerize_aux. */
+unsigned int fix_tag : 1;
+
+ /* Should the endidx field of this symbol be renumbered.
+ Created by coff_pointerize_aux. */
+unsigned int fix_end : 1;
+
+ /* Should the x_csect.x_scnlen field be renumbered.
+ Created by coff_pointerize_aux. */
+unsigned int fix_scnlen : 1;
+
+ /* Fix up an XCOFF C_BINCL/C_EINCL symbol. The value is the
+ index into the line number entries. Set by
+ coff_slurp_symbol_table. */
+unsigned int fix_line : 1;
+
+ /* The container for the symbol structure as read and translated
+ from the file. */
+
+union @{
+ union internal_auxent auxent;
+ struct internal_syment syment;
+ @} u;
+@} combined_entry_type;
+
+
+/* Each canonical asymbol really looks like this: */
+
+typedef struct coff_symbol_struct
+@{
+ /* The actual symbol which the rest of BFD works with */
+asymbol symbol;
+
+ /* A pointer to the hidden information for this symbol */
+combined_entry_type *native;
+
+ /* A pointer to the linenumber information for this symbol */
+struct lineno_cache_entry *lineno;
+
+ /* Have the line numbers been relocated yet ? */
+boolean done_lineno;
+@} coff_symbol_type;
+@end example
+@findex bfd_coff_backend_data
+@subsubsection @code{bfd_coff_backend_data}
+Special entry points for gdb to swap in coff symbol table parts:
+@example
+typedef struct
+@{
+ void (*_bfd_coff_swap_aux_in) PARAMS ((
+ bfd *abfd,
+ PTR ext,
+ int type,
+ int class,
+ int indaux,
+ int numaux,
+ PTR in));
+
+ void (*_bfd_coff_swap_sym_in) PARAMS ((
+ bfd *abfd ,
+ PTR ext,
+ PTR in));
+
+ void (*_bfd_coff_swap_lineno_in) PARAMS ((
+ bfd *abfd,
+ PTR ext,
+ PTR in));
+
+@end example
+Special entry points for gas to swap out coff parts:
+@example
+ unsigned int (*_bfd_coff_swap_aux_out) PARAMS ((
+ bfd *abfd,
+ PTR in,
+ int type,
+ int class,
+ int indaux,
+ int numaux,
+ PTR ext));
+
+ unsigned int (*_bfd_coff_swap_sym_out) PARAMS ((
+ bfd *abfd,
+ PTR in,
+ PTR ext));
+
+ unsigned int (*_bfd_coff_swap_lineno_out) PARAMS ((
+ bfd *abfd,
+ PTR in,
+ PTR ext));
+
+ unsigned int (*_bfd_coff_swap_reloc_out) PARAMS ((
+ bfd *abfd,
+ PTR src,
+ PTR dst));
+
+ unsigned int (*_bfd_coff_swap_filehdr_out) PARAMS ((
+ bfd *abfd,
+ PTR in,
+ PTR out));
+
+ unsigned int (*_bfd_coff_swap_aouthdr_out) PARAMS ((
+ bfd *abfd,
+ PTR in,
+ PTR out));
+
+ unsigned int (*_bfd_coff_swap_scnhdr_out) PARAMS ((
+ bfd *abfd,
+ PTR in,
+ PTR out));
+
+@end example
+Special entry points for generic COFF routines to call target
+dependent COFF routines:
+@example
+ unsigned int _bfd_filhsz;
+ unsigned int _bfd_aoutsz;
+ unsigned int _bfd_scnhsz;
+ unsigned int _bfd_symesz;
+ unsigned int _bfd_auxesz;
+ unsigned int _bfd_relsz;
+ unsigned int _bfd_linesz;
+ boolean _bfd_coff_long_filenames;
+ boolean _bfd_coff_long_section_names;
+ unsigned int _bfd_coff_default_section_alignment_power;
+ void (*_bfd_coff_swap_filehdr_in) PARAMS ((
+ bfd *abfd,
+ PTR ext,
+ PTR in));
+ void (*_bfd_coff_swap_aouthdr_in) PARAMS ((
+ bfd *abfd,
+ PTR ext,
+ PTR in));
+ void (*_bfd_coff_swap_scnhdr_in) PARAMS ((
+ bfd *abfd,
+ PTR ext,
+ PTR in));
+ void (*_bfd_coff_swap_reloc_in) PARAMS ((
+ bfd *abfd,
+ PTR ext,
+ PTR in));
+ boolean (*_bfd_coff_bad_format_hook) PARAMS ((
+ bfd *abfd,
+ PTR internal_filehdr));
+ boolean (*_bfd_coff_set_arch_mach_hook) PARAMS ((
+ bfd *abfd,
+ PTR internal_filehdr));
+ PTR (*_bfd_coff_mkobject_hook) PARAMS ((
+ bfd *abfd,
+ PTR internal_filehdr,
+ PTR internal_aouthdr));
+ flagword (*_bfd_styp_to_sec_flags_hook) PARAMS ((
+ bfd *abfd,
+ PTR internal_scnhdr,
+ const char *name));
+ void (*_bfd_set_alignment_hook) PARAMS ((
+ bfd *abfd,
+ asection *sec,
+ PTR internal_scnhdr));
+ boolean (*_bfd_coff_slurp_symbol_table) PARAMS ((
+ bfd *abfd));
+ boolean (*_bfd_coff_symname_in_debug) PARAMS ((
+ bfd *abfd,
+ struct internal_syment *sym));
+ boolean (*_bfd_coff_pointerize_aux_hook) PARAMS ((
+ bfd *abfd,
+ combined_entry_type *table_base,
+ combined_entry_type *symbol,
+ unsigned int indaux,
+ combined_entry_type *aux));
+ boolean (*_bfd_coff_print_aux) PARAMS ((
+ bfd *abfd,
+ FILE *file,
+ combined_entry_type *table_base,
+ combined_entry_type *symbol,
+ combined_entry_type *aux,
+ unsigned int indaux));
+ void (*_bfd_coff_reloc16_extra_cases) PARAMS ((
+ bfd *abfd,
+ struct bfd_link_info *link_info,
+ struct bfd_link_order *link_order,
+ arelent *reloc,
+ bfd_byte *data,
+ unsigned int *src_ptr,
+ unsigned int *dst_ptr));
+ int (*_bfd_coff_reloc16_estimate) PARAMS ((
+ bfd *abfd,
+ asection *input_section,
+ arelent *r,
+ unsigned int shrink,
+ struct bfd_link_info *link_info));
+ boolean (*_bfd_coff_sym_is_global) PARAMS ((
+ bfd *abfd,
+ struct internal_syment *));
+ boolean (*_bfd_coff_compute_section_file_positions) PARAMS ((
+ bfd *abfd));
+ boolean (*_bfd_coff_start_final_link) PARAMS ((
+ bfd *output_bfd,
+ struct bfd_link_info *info));
+ boolean (*_bfd_coff_relocate_section) PARAMS ((
+ bfd *output_bfd,
+ struct bfd_link_info *info,
+ bfd *input_bfd,
+ asection *input_section,
+ bfd_byte *contents,
+ struct internal_reloc *relocs,
+ struct internal_syment *syms,
+ asection **sections));
+ reloc_howto_type *(*_bfd_coff_rtype_to_howto) PARAMS ((
+ bfd *abfd,
+ asection *sec,
+ struct internal_reloc *rel,
+ struct coff_link_hash_entry *h,
+ struct internal_syment *sym,
+ bfd_vma *addendp));
+ boolean (*_bfd_coff_adjust_symndx) PARAMS ((
+ bfd *obfd,
+ struct bfd_link_info *info,
+ bfd *ibfd,
+ asection *sec,
+ struct internal_reloc *reloc,
+ boolean *adjustedp));
+ boolean (*_bfd_coff_link_add_one_symbol) PARAMS ((
+ struct bfd_link_info *info,
+ bfd *abfd,
+ const char *name,
+ flagword flags,
+ asection *section,
+ bfd_vma value,
+ const char *string,
+ boolean copy,
+ boolean collect,
+ struct bfd_link_hash_entry **hashp));
+
+@} bfd_coff_backend_data;
+
+#define coff_backend_info(abfd) ((bfd_coff_backend_data *) (abfd)->xvec->backend_data)
+
+#define bfd_coff_swap_aux_in(a,e,t,c,ind,num,i) \
+ ((coff_backend_info (a)->_bfd_coff_swap_aux_in) (a,e,t,c,ind,num,i))
+
+#define bfd_coff_swap_sym_in(a,e,i) \
+ ((coff_backend_info (a)->_bfd_coff_swap_sym_in) (a,e,i))
+
+#define bfd_coff_swap_lineno_in(a,e,i) \
+ ((coff_backend_info ( a)->_bfd_coff_swap_lineno_in) (a,e,i))
+
+#define bfd_coff_swap_reloc_out(abfd, i, o) \
+ ((coff_backend_info (abfd)->_bfd_coff_swap_reloc_out) (abfd, i, o))
+
+#define bfd_coff_swap_lineno_out(abfd, i, o) \
+ ((coff_backend_info (abfd)->_bfd_coff_swap_lineno_out) (abfd, i, o))
+
+#define bfd_coff_swap_aux_out(a,i,t,c,ind,num,o) \
+ ((coff_backend_info (a)->_bfd_coff_swap_aux_out) (a,i,t,c,ind,num,o))
+
+#define bfd_coff_swap_sym_out(abfd, i,o) \
+ ((coff_backend_info (abfd)->_bfd_coff_swap_sym_out) (abfd, i, o))
+
+#define bfd_coff_swap_scnhdr_out(abfd, i,o) \
+ ((coff_backend_info (abfd)->_bfd_coff_swap_scnhdr_out) (abfd, i, o))
+
+#define bfd_coff_swap_filehdr_out(abfd, i,o) \
+ ((coff_backend_info (abfd)->_bfd_coff_swap_filehdr_out) (abfd, i, o))
+
+#define bfd_coff_swap_aouthdr_out(abfd, i,o) \
+ ((coff_backend_info (abfd)->_bfd_coff_swap_aouthdr_out) (abfd, i, o))
+
+#define bfd_coff_filhsz(abfd) (coff_backend_info (abfd)->_bfd_filhsz)
+#define bfd_coff_aoutsz(abfd) (coff_backend_info (abfd)->_bfd_aoutsz)
+#define bfd_coff_scnhsz(abfd) (coff_backend_info (abfd)->_bfd_scnhsz)
+#define bfd_coff_symesz(abfd) (coff_backend_info (abfd)->_bfd_symesz)
+#define bfd_coff_auxesz(abfd) (coff_backend_info (abfd)->_bfd_auxesz)
+#define bfd_coff_relsz(abfd) (coff_backend_info (abfd)->_bfd_relsz)
+#define bfd_coff_linesz(abfd) (coff_backend_info (abfd)->_bfd_linesz)
+#define bfd_coff_long_filenames(abfd) (coff_backend_info (abfd)->_bfd_coff_long_filenames)
+#define bfd_coff_long_section_names(abfd) \
+ (coff_backend_info (abfd)->_bfd_coff_long_section_names)
+#define bfd_coff_default_section_alignment_power(abfd) \
+ (coff_backend_info (abfd)->_bfd_coff_default_section_alignment_power)
+#define bfd_coff_swap_filehdr_in(abfd, i,o) \
+ ((coff_backend_info (abfd)->_bfd_coff_swap_filehdr_in) (abfd, i, o))
+
+#define bfd_coff_swap_aouthdr_in(abfd, i,o) \
+ ((coff_backend_info (abfd)->_bfd_coff_swap_aouthdr_in) (abfd, i, o))
+
+#define bfd_coff_swap_scnhdr_in(abfd, i,o) \
+ ((coff_backend_info (abfd)->_bfd_coff_swap_scnhdr_in) (abfd, i, o))
+
+#define bfd_coff_swap_reloc_in(abfd, i, o) \
+ ((coff_backend_info (abfd)->_bfd_coff_swap_reloc_in) (abfd, i, o))
+
+#define bfd_coff_bad_format_hook(abfd, filehdr) \
+ ((coff_backend_info (abfd)->_bfd_coff_bad_format_hook) (abfd, filehdr))
+
+#define bfd_coff_set_arch_mach_hook(abfd, filehdr)\
+ ((coff_backend_info (abfd)->_bfd_coff_set_arch_mach_hook) (abfd, filehdr))
+#define bfd_coff_mkobject_hook(abfd, filehdr, aouthdr)\
+ ((coff_backend_info (abfd)->_bfd_coff_mkobject_hook) (abfd, filehdr, aouthdr))
+
+#define bfd_coff_styp_to_sec_flags_hook(abfd, scnhdr, name)\
+ ((coff_backend_info (abfd)->_bfd_styp_to_sec_flags_hook) (abfd, scnhdr, name))
+
+#define bfd_coff_set_alignment_hook(abfd, sec, scnhdr)\
+ ((coff_backend_info (abfd)->_bfd_set_alignment_hook) (abfd, sec, scnhdr))
+
+#define bfd_coff_slurp_symbol_table(abfd)\
+ ((coff_backend_info (abfd)->_bfd_coff_slurp_symbol_table) (abfd))
+
+#define bfd_coff_symname_in_debug(abfd, sym)\
+ ((coff_backend_info (abfd)->_bfd_coff_symname_in_debug) (abfd, sym))
+
+#define bfd_coff_print_aux(abfd, file, base, symbol, aux, indaux)\
+ ((coff_backend_info (abfd)->_bfd_coff_print_aux)\
+ (abfd, file, base, symbol, aux, indaux))
+
+#define bfd_coff_reloc16_extra_cases(abfd, link_info, link_order, reloc, data, src_ptr, dst_ptr)\
+ ((coff_backend_info (abfd)->_bfd_coff_reloc16_extra_cases)\
+ (abfd, link_info, link_order, reloc, data, src_ptr, dst_ptr))
+
+#define bfd_coff_reloc16_estimate(abfd, section, reloc, shrink, link_info)\
+ ((coff_backend_info (abfd)->_bfd_coff_reloc16_estimate)\
+ (abfd, section, reloc, shrink, link_info))
+
+#define bfd_coff_sym_is_global(abfd, sym)\
+ ((coff_backend_info (abfd)->_bfd_coff_sym_is_global)\
+ (abfd, sym))
+
+#define bfd_coff_compute_section_file_positions(abfd)\
+ ((coff_backend_info (abfd)->_bfd_coff_compute_section_file_positions)\
+ (abfd))
+
+#define bfd_coff_start_final_link(obfd, info)\
+ ((coff_backend_info (obfd)->_bfd_coff_start_final_link)\
+ (obfd, info))
+#define bfd_coff_relocate_section(obfd,info,ibfd,o,con,rel,isyms,secs)\
+ ((coff_backend_info (ibfd)->_bfd_coff_relocate_section)\
+ (obfd, info, ibfd, o, con, rel, isyms, secs))
+#define bfd_coff_rtype_to_howto(abfd, sec, rel, h, sym, addendp)\
+ ((coff_backend_info (abfd)->_bfd_coff_rtype_to_howto)\
+ (abfd, sec, rel, h, sym, addendp))
+#define bfd_coff_adjust_symndx(obfd, info, ibfd, sec, rel, adjustedp)\
+ ((coff_backend_info (abfd)->_bfd_coff_adjust_symndx)\
+ (obfd, info, ibfd, sec, rel, adjustedp))
+#define bfd_coff_link_add_one_symbol(info,abfd,name,flags,section,value,string,cp,coll,hashp)\
+ ((coff_backend_info (abfd)->_bfd_coff_link_add_one_symbol)\
+ (info, abfd, name, flags, section, value, string, cp, coll, hashp))
+
+@end example
+@subsubsection Writing relocations
+To write relocations, the back end steps though the
+canonical relocation table and create an
+@code{internal_reloc}. The symbol index to use is removed from
+the @code{offset} field in the symbol table supplied. The
+address comes directly from the sum of the section base
+address and the relocation offset; the type is dug directly
+from the howto field. Then the @code{internal_reloc} is
+swapped into the shape of an @code{external_reloc} and written
+out to disk.
+@*
+@subsubsection Reading linenumbers
+Creating the linenumber table is done by reading in the entire
+coff linenumber table, and creating another table for internal use.
+
+A coff linenumber table is structured so that each function
+is marked as having a line number of 0. Each line within the
+function is an offset from the first line in the function. The
+base of the line number information for the table is stored in
+the symbol associated with the function.
+
+The information is copied from the external to the internal
+table, and each symbol which marks a function is marked by
+pointing its...
+
+How does this work ?
+@*
+@subsubsection Reading relocations
+Coff relocations are easily transformed into the internal BFD form
+(@code{arelent}).
+
+Reading a coff relocation table is done in the following stages:
+
+@itemize @bullet
+
+@item
+Read the entire coff relocation table into memory.
+
+@item
+Process each relocation in turn; first swap it from the
+external to the internal form.
+
+@item
+Turn the symbol referenced in the relocation's symbol index
+into a pointer into the canonical symbol table.
+This table is the same as the one returned by a call to
+@code{bfd_canonicalize_symtab}. The back end will call that
+routine and save the result if a canonicalization hasn't been done.
+
+@item
+The reloc index is turned into a pointer to a howto
+structure, in a back end specific way. For instance, the 386
+and 960 use the @code{r_type} to directly produce an index
+into a howto table vector; the 88k subtracts a number from the
+@code{r_type} field and creates an addend field.
+@end itemize
+@*
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