- 1) It lists all exported symbols both from vmlinux and all modules
- 2) It lists the CRC if CONFIG_MODVERSIONS 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 built, this file will be read too.
- During the MODPOST step, a new Module.symvers file will be written
- containing all exported symbols that were not defined in the kernel.
-
---- 7.3 Symbols from another external module
-
- Sometimes, an 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.
- Three 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' and '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)
+ 1) It lists all exported symbols from vmlinux and all modules.
+ 2) It lists the CRC if CONFIG_MODVERSIONS is enabled.
+
+--- 6.2 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. modpost obtains
+ the symbols by reading Module.symvers from the kernel source
+ tree. If a Module.symvers file is present in the directory
+ where the external module is being built, this file will be
+ read too. During the MODPOST step, a new Module.symvers file
+ will be written containing all exported symbols that were not
+ defined in the kernel.
+
+--- 6.3 Symbols From Another External Module
+
+ Sometimes, an external module uses exported symbols from
+ another external module. kbuild needs to have full knowledge of
+ all symbols to avoid spitting out warnings about undefined
+ symbols. Three solutions exist for this situation.
+
+ NOTE: 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.ko and bar.ko, where
+ foo.ko needs symbols from bar.ko, you can use a
+ common top-level kbuild file so both modules are
+ compiled in the same build. Consider the following
+ directory layout:
+
+ ./foo/ <= contains foo.ko
+ ./bar/ <= contains bar.ko
+
+ The top-level kbuild file would then look like:
+
+ #./Kbuild (or ./Makefile):