--- 2.2 Available targets
--- 2.3 Available options
--- 2.4 Preparing the kernel tree for module build
+ --- 2.5 Building separate files for a module
=== 3. Example commands
=== 4. Creating a kbuild file for an external module
=== 5. Include files
--- 5.1 How to include files from the kernel include dir
--- 5.2 External modules using an include/ dir
+ --- 5.3 External modules using several directories
=== 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
What is covered within this file is mainly information to authors
of modules. The author of an external modules should supply
a makefile that hides most of the complexity so one only has to type
-'make' to buld the module. A complete example will be present in
-chapter ยค. Creating a kbuild file for an external module".
+'make' to build the module. A complete example will be present in
+chapter 4, "Creating a kbuild file for an external module".
=== 2. How to build external modules
--- 2.2 Available targets
- $KDIR refers to path to kernel source top-level directory
+ $KDIR refers to the path to the kernel source top-level directory
make -C $KDIR M=`pwd`
Will build the module(s) located in current directory.
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 chater.
+ 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
- source directory is not moddified.
+ source directory is not modified.
make -C $KDIR M=`pwd` help
help will list the available target when building external
--- 2.3 Available options:
- $KDIR refer to path to kernel src
+ $KDIR refers to the path to the kernel source top-level directory
make -C $KDIR
Used to specify where to find the kernel source.
Therefore a full kernel build needs to be executed to make
module versioning work.
+--- 2.5 Building separate files for a module
+ It is possible to build single files which is part of a module.
+ This works equal for the kernel, a module and even for external
+ modules.
+ Examples (module foo.ko, consist of bar.o, baz.o):
+ make -C $KDIR M=`pwd` bar.lst
+ make -C $KDIR M=`pwd` bar.o
+ make -C $KDIR M=`pwd` foo.ko
+ make -C $KDIR M=`pwd` /
+
=== 3. Example commands
KERNELDIR := /lib/modules/`uname -r`/build
all::
- $(MAKE) -C $KERNELDIR M=`pwd` $@
+ $(MAKE) -C $(KERNELDIR) M=`pwd` $@
# Module specific targets
genbin:
- echo "X" > 8123_bini.o_shipped
+ echo "X" > 8123_bin.o_shipped
endif
EXTRA_CFLAGS := -Iinclude
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
- Note that in the assingment there is no space between -I and the path.
- This is a kbuild limitation and no space must be present.
-
+ Note that in the assignment there is no space between -I and the path.
+ This is a kbuild limitation: there must be no space present.
+
+--- 5.3 External modules using several directories
+
+ If an external module does not follow the usual kernel style but
+ decide to spread files over several directories then kbuild can
+ support this too.
+
+ Consider the following example:
+
+ |
+ +- src/complex_main.c
+ | +- hal/hardwareif.c
+ | +- hal/include/hardwareif.h
+ +- include/complex.h
+
+ To build a single module named complex.ko we then need the following
+ kbuild file:
+
+ Kbuild:
+ obj-m := complex.o
+ complex-y := src/complex_main.o
+ complex-y += src/hal/hardwareif.o
+
+ EXTRA_CFLAGS := -I$(src)/include
+ EXTRA_CFLAGS += -I$(src)src/hal/include
+
+
+ kbuild knows how to handle .o files located in another directory -
+ although this is NOT reccommended practice. The syntax is to specify
+ the directory relative to the directory where the Kbuild file is
+ located.
+
+ To find the .h files we have to explicitly tell kbuild where to look
+ for the .h files. When kbuild executes current directory is always
+ the root of the kernel tree (argument to -C) and therefore we have to
+ tell kbuild how to find the .h files using absolute paths.
+ $(src) will specify the absolute path to the directory where the
+ Kbuild file are located when being build as an external module.
+ Therefore -I$(src)/ is used to point out the directory of the Kbuild
+ file and any additional path are just appended.
=== 6. Module installation
-Modules which are included in the kernel is installed in the directory:
+Modules which are included in the kernel are installed in the directory:
/lib/modules/$(KERNELRELEASE)/kernel
=> Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel
INSTALL_MOD_PATH may be set as an ordinary shell variable or as in the
- example above be specified on the commandline when calling make.
+ example above be specified on the command line when calling make.
INSTALL_MOD_PATH has effect both when installing modules included in
the kernel as well as when installing external modules.
=> Install dir: /lib/modules/$(KERNELRELEASE)/gandalf
-=== 7. Module versioning
+=== 7. Module versioning & Module.symvers
-Module versioning are enabled by the CONFIG_MODVERSIONS tag.
+Module versioning is enabled by the CONFIG_MODVERSIONS tag.
Module versioning is used as a simple ABI consistency check. The Module
versioning creates a CRC value of the full prototype for an exported symbol and
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
git://git.onelab.eu / linux-2.6.git / blobdiff