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Diffstat (limited to 'Documentation/kbuild')
| -rw-r--r-- | Documentation/kbuild/modules.txt | 87 |
1 files changed, 80 insertions, 7 deletions
diff --git a/Documentation/kbuild/modules.txt b/Documentation/kbuild/modules.txt index 87d858d..fcccf24 100644 --- a/Documentation/kbuild/modules.txt +++ b/Documentation/kbuild/modules.txt @@ -23,7 +23,10 @@ In this document you will find information about: === 6. Module installation --- 6.1 INSTALL_MOD_PATH --- 6.2 INSTALL_MOD_DIR - === 7. Module versioning + === 7. Module versioning & Module.symvers + --- 7.1 Symbols fron the kernel (vmlinux + modules) + --- 7.2 Symbols and external modules + --- 7.3 Symbols from another external module === 8. Tips & Tricks --- 8.1 Testing for CONFIG_FOO_BAR @@ -89,7 +92,8 @@ when building an external module. make -C $KDIR M=$PWD modules_install Install the external module(s). Installation default is in /lib/modules/<kernel-version>/extra, - but may be prefixed with INSTALL_MOD_PATH - see separate chapter. + but may be prefixed with INSTALL_MOD_PATH - see separate + chapter. make -C $KDIR M=$PWD clean Remove all generated files for the module - the kernel @@ -433,7 +437,7 @@ External modules are installed in the directory: => Install dir: /lib/modules/$(KERNELRELEASE)/gandalf -=== 7. Module versioning +=== 7. Module versioning & Module.symvers Module versioning is enabled by the CONFIG_MODVERSIONS tag. @@ -443,11 +447,80 @@ when a module is loaded/used then the CRC values contained in the kernel are compared with similar values in the module. If they are not equal then the kernel refuses to load the module. -During a kernel build a file named Module.symvers will be generated. This -file includes the symbol version of all symbols within the kernel. If the -Module.symvers file is saved from the last full kernel compile one does not -have to do a full kernel compile to build a module version's compatible module. +Module.symvers contains a list of all exported symbols from a kernel build. +--- 7.1 Symbols fron the kernel (vmlinux + modules) + + During a kernel build a file named Module.symvers will be generated. + Module.symvers contains all exported symbols from the kernel and + compiled modules. For each symbols the corresponding CRC value + is stored too. + + The syntax of the Module.symvers file is: + <CRC> <Symbol> <module> + Sample: + 0x2d036834 scsi_remove_host drivers/scsi/scsi_mod + + For a kernel build without CONFIG_MODVERSIONING enabled the crc + would read: 0x00000000 + + Module.symvers serve two purposes. + 1) It list all exported symbols both from vmlinux and all modules + 2) It list CRC if CONFIG_MODVERSION is enabled + +--- 7.2 Symbols and external modules + + When building an external module the build system needs access to + the symbols from the kernel to check if all external symbols are + defined. This is done in the MODPOST step and to obtain all + symbols modpost reads Module.symvers from the kernel. + If a Module.symvers file is present in the directory where + the external module is being build this file will be read too. + During the MODPOST step a new Module.symvers file will be written + containing all exported symbols that was not defined in the kernel. + +--- 7.3 Symbols from another external module + + Sometimes one external module uses exported symbols from another + external module. Kbuild needs to have full knowledge on all symbols + to avoid spitting out warnings about undefined symbols. + Two solutions exist to let kbuild know all symbols of more than + one external module. + The method with a top-level kbuild file is recommended but may be + impractical in certain situations. + + Use a top-level Kbuild file + If you have two modules: 'foo', 'bar' and 'foo' needs symbols + from 'bar' then one can use a common top-level kbuild file so + both modules are compiled in same build. + + Consider following directory layout: + ./foo/ <= contains the foo module + ./bar/ <= contains the bar module + The top-level Kbuild file would then look like: + + #./Kbuild: (this file may also be named Makefile) + obj-y := foo/ bar/ + + Executing: + make -C $KDIR M=`pwd` + + will then do the expected and compile both modules with full + knowledge on symbols from both modules. + + Use an extra Module.symvers file + When an external module is build a Module.symvers file is + generated containing all exported symbols which are not + defined in the kernel. + To get access to symbols from module 'bar' one can copy the + Module.symvers file from the compilation of the 'bar' module + to the directory where the 'foo' module is build. + During the module build kbuild will read the Module.symvers + file in the directory of the external module and when the + build is finished a new Module.symvers file is created + containing the sum of all symbols defined and not part of the + kernel. + === 8. Tips & Tricks --- 8.1 Testing for CONFIG_FOO_BAR |
