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kbuild: linguistic fixes for Documentation/kbuild/modules.txt
I have done a look-through through Documentation/kbuild/ and my corrections (proposed) are attached. Cc'ed are original author Michael (responsible for comitting changes to these files?), Sam (kbuild maintainer), Adrian (-trivial maintainer). Signed-off-by: Jan Engelhardt <jengelh@gmx.de> Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
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Jan Engelhardt
Sam Ravnborg
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@ -1,7 +1,7 @@
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In this document you will find information about:
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- how to build external modules
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- how to make your module use kbuild infrastructure
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- how to make your module use the kbuild infrastructure
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- how kbuild will install a kernel
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- how to install modules in a non-standard location
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@ -36,13 +36,13 @@ In this document you will find information about:
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kbuild includes functionality for building modules both
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within the kernel source tree and outside the kernel source tree.
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The latter is usually referred to as external modules and is used
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both during development and for modules that are not planned to be
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included in the kernel tree.
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The latter is usually referred to as external or "out-of-tree"
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modules and is used both during development and for modules that
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are not planned to be included in the kernel tree.
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What is covered within this file is mainly information to authors
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of modules. The author of an external modules should supply
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a makefile that hides most of the complexity so one only has to type
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of modules. The author of an external module should supply
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a makefile that hides most of the complexity, so one only has to type
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'make' to build the module. A complete example will be present in
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chapter 4, "Creating a kbuild file for an external module".
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@ -137,7 +137,7 @@ when building an external module.
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module versioning work.
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--- 2.5 Building separate files for a module
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It is possible to build single files which is part of a module.
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It is possible to build single files which are part of a module.
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This works equal for the kernel, a module and even for external
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modules.
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Examples (module foo.ko, consist of bar.o, baz.o):
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@ -151,7 +151,7 @@ when building an external module.
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This example shows the actual commands to be executed when building
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an external module for the currently running kernel.
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In the example below the distribution is supposed to use the
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In the example below, the distribution is supposed to use the
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facility to locate output files for a kernel compile in a different
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directory than the kernel source - but the examples will also work
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when the source and the output files are mixed in the same directory.
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@ -170,7 +170,7 @@ the following commands to build the module:
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O=/lib/modules/`uname-r`/build \
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M=`pwd`
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Then to install the module use the following command:
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Then, to install the module use the following command:
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make -C /usr/src/`uname -r`/source \
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O=/lib/modules/`uname-r`/build \
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@ -230,7 +230,7 @@ following files:
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endif
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In example 1 the check for KERNELRELEASE is used to separate
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In example 1, the check for KERNELRELEASE is used to separate
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the two parts of the Makefile. kbuild will only see the two
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assignments whereas make will see everything except the two
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kbuild assignments.
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@ -255,7 +255,7 @@ following files:
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echo "X" > 8123_bin_shipped
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In example 2 we are down to two fairly simple files and for simple
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In example 2, we are down to two fairly simple files and for simple
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files as used in this example the split is questionable. But some
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external modules use Makefiles of several hundred lines and here it
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really pays off to separate the kbuild part from the rest.
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@ -282,9 +282,9 @@ following files:
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endif
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The trick here is to include the Kbuild file from Makefile so
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if an older version of kbuild picks up the Makefile the Kbuild
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file will be included.
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The trick here is to include the Kbuild file from Makefile, so
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if an older version of kbuild picks up the Makefile, the Kbuild
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file will be included.
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--- 4.2 Binary blobs included in a module
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@ -301,18 +301,19 @@ following files:
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obj-m := 8123.o
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8123-y := 8123_if.o 8123_pci.o 8123_bin.o
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In example 4 there is no distinction between the ordinary .c/.h files
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In example 4, there is no distinction between the ordinary .c/.h files
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and the binary file. But kbuild will pick up different rules to create
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the .o file.
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=== 5. Include files
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Include files are a necessity when a .c file uses something from another .c
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files (not strictly in the sense of .c but if good programming practice is
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used). Any module that consist of more than one .c file will have a .h file
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Include files are a necessity when a .c file uses something from other .c
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files (not strictly in the sense of C, but if good programming practice is
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used). Any module that consists of more than one .c file will have a .h file
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for one of the .c files.
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- If the .h file only describes a module internal interface then the .h file
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- If the .h file only describes a module internal interface, then the .h file
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shall be placed in the same directory as the .c files.
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- If the .h files describe an interface used by other parts of the kernel
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located in different directories, the .h files shall be located in
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@ -323,11 +324,11 @@ under include/ such as include/scsi. Another exception is arch-specific
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.h files which are located under include/asm-$(ARCH)/*.
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External modules have a tendency to locate include files in a separate include/
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directory and therefore needs to deal with this in their kbuild file.
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directory and therefore need to deal with this in their kbuild file.
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--- 5.1 How to include files from the kernel include dir
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When a module needs to include a file from include/linux/ then one
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When a module needs to include a file from include/linux/, then one
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just uses:
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#include <linux/modules.h>
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@ -348,7 +349,7 @@ directory and therefore needs to deal with this in their kbuild file.
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The trick here is to use either EXTRA_CFLAGS (take effect for all .c
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files) or CFLAGS_$F.o (take effect only for a single file).
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In our example if we move 8123_if.h to a subdirectory named include/
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In our example, if we move 8123_if.h to a subdirectory named include/
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the resulting Kbuild file would look like:
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--> filename: Kbuild
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@ -362,9 +363,9 @@ directory and therefore needs to deal with this in their kbuild file.
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--- 5.3 External modules using several directories
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If an external module does not follow the usual kernel style but
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decide to spread files over several directories then kbuild can
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support this too.
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If an external module does not follow the usual kernel style, but
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decides to spread files over several directories, then kbuild can
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handle this too.
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Consider the following example:
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@ -374,7 +375,7 @@ directory and therefore needs to deal with this in their kbuild file.
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| +- hal/include/hardwareif.h
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+- include/complex.h
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To build a single module named complex.ko we then need the following
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To build a single module named complex.ko, we then need the following
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kbuild file:
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Kbuild:
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@ -387,12 +388,12 @@ directory and therefore needs to deal with this in their kbuild file.
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kbuild knows how to handle .o files located in another directory -
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although this is NOT reccommended practice. The syntax is to specify
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although this is NOT recommended practice. The syntax is to specify
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the directory relative to the directory where the Kbuild file is
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located.
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To find the .h files we have to explicitly tell kbuild where to look
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for the .h files. When kbuild executes current directory is always
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To find the .h files, we have to explicitly tell kbuild where to look
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for the .h files. When kbuild executes, the current directory is always
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the root of the kernel tree (argument to -C) and therefore we have to
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tell kbuild how to find the .h files using absolute paths.
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$(src) will specify the absolute path to the directory where the
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@ -412,7 +413,7 @@ External modules are installed in the directory:
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--- 6.1 INSTALL_MOD_PATH
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Above are the default directories, but as always some level of
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Above are the default directories, but as always, some level of
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customization is possible. One can prefix the path using the variable
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INSTALL_MOD_PATH:
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@ -420,17 +421,17 @@ External modules are installed in the directory:
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=> Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel
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INSTALL_MOD_PATH may be set as an ordinary shell variable or as in the
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example above be specified on the command line when calling make.
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example above, can be specified on the command line when calling make.
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INSTALL_MOD_PATH has effect both when installing modules included in
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the kernel as well as when installing external modules.
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--- 6.2 INSTALL_MOD_DIR
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When installing external modules they are default installed in a
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When installing external modules they are by default installed to a
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directory under /lib/modules/$(KERNELRELEASE)/extra, but one may wish
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to locate modules for a specific functionality in a separate
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directory. For this purpose one can use INSTALL_MOD_DIR to specify an
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alternative name than 'extra'.
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directory. For this purpose, one can use INSTALL_MOD_DIR to specify an
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alternative name to 'extra'.
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$ make INSTALL_MOD_DIR=gandalf -C KERNELDIR \
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M=`pwd` modules_install
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@ -444,16 +445,16 @@ Module versioning is enabled by the CONFIG_MODVERSIONS tag.
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Module versioning is used as a simple ABI consistency check. The Module
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versioning creates a CRC value of the full prototype for an exported symbol and
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when a module is loaded/used then the CRC values contained in the kernel are
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compared with similar values in the module. If they are not equal then the
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compared with similar values in the module. If they are not equal, then the
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kernel refuses to load the module.
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Module.symvers contains a list of all exported symbols from a kernel build.
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--- 7.1 Symbols fron the kernel (vmlinux + modules)
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During a kernel build a file named Module.symvers will be generated.
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During a kernel build, a file named Module.symvers will be generated.
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Module.symvers contains all exported symbols from the kernel and
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compiled modules. For each symbols the corresponding CRC value
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compiled modules. For each symbols, the corresponding CRC value
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is stored too.
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The syntax of the Module.symvers file is:
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@ -461,27 +462,27 @@ Module.symvers contains a list of all exported symbols from a kernel build.
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Sample:
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0x2d036834 scsi_remove_host drivers/scsi/scsi_mod
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For a kernel build without CONFIG_MODVERSIONING enabled the crc
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For a kernel build without CONFIG_MODVERSIONING enabled, the crc
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would read: 0x00000000
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Module.symvers serve two purposes.
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1) It list all exported symbols both from vmlinux and all modules
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2) It list CRC if CONFIG_MODVERSION is enabled
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Module.symvers serves two purposes:
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1) It lists all exported symbols both from vmlinux and all modules
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2) It lists the CRC if CONFIG_MODVERSION is enabled
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--- 7.2 Symbols and external modules
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When building an external module the build system needs access to
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When building an external module, the build system needs access to
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the symbols from the kernel to check if all external symbols are
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defined. This is done in the MODPOST step and to obtain all
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symbols modpost reads Module.symvers from the kernel.
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symbols, modpost reads Module.symvers from the kernel.
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If a Module.symvers file is present in the directory where
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the external module is being build this file will be read too.
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During the MODPOST step a new Module.symvers file will be written
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containing all exported symbols that was not defined in the kernel.
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the external module is being built, this file will be read too.
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During the MODPOST step, a new Module.symvers file will be written
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containing all exported symbols that were not defined in the kernel.
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--- 7.3 Symbols from another external module
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Sometimes one external module uses exported symbols from another
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Sometimes, an external module uses exported symbols from another
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external module. Kbuild needs to have full knowledge on all symbols
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to avoid spitting out warnings about undefined symbols.
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Two solutions exist to let kbuild know all symbols of more than
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@ -490,9 +491,9 @@ Module.symvers contains a list of all exported symbols from a kernel build.
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impractical in certain situations.
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Use a top-level Kbuild file
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If you have two modules: 'foo', 'bar' and 'foo' needs symbols
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from 'bar' then one can use a common top-level kbuild file so
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both modules are compiled in same build.
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If you have two modules: 'foo' and 'bar', and 'foo' needs
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symbols from 'bar', then one can use a common top-level kbuild
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file so both modules are compiled in same build.
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Consider following directory layout:
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./foo/ <= contains the foo module
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@ -509,15 +510,15 @@ Module.symvers contains a list of all exported symbols from a kernel build.
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knowledge on symbols from both modules.
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Use an extra Module.symvers file
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When an external module is build a Module.symvers file is
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When an external module is built, a Module.symvers file is
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generated containing all exported symbols which are not
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defined in the kernel.
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To get access to symbols from module 'bar' one can copy the
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To get access to symbols from module 'bar', one can copy the
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Module.symvers file from the compilation of the 'bar' module
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to the directory where the 'foo' module is build.
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During the module build kbuild will read the Module.symvers
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to the directory where the 'foo' module is built.
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During the module build, kbuild will read the Module.symvers
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file in the directory of the external module and when the
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build is finished a new Module.symvers file is created
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build is finished, a new Module.symvers file is created
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containing the sum of all symbols defined and not part of the
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kernel.
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@ -525,7 +526,7 @@ Module.symvers contains a list of all exported symbols from a kernel build.
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--- 8.1 Testing for CONFIG_FOO_BAR
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Modules often needs to check for certain CONFIG_ options to decide if
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Modules often need to check for certain CONFIG_ options to decide if
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a specific feature shall be included in the module. When kbuild is used
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this is done by referencing the CONFIG_ variable directly.
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@ -537,7 +538,7 @@ Module.symvers contains a list of all exported symbols from a kernel build.
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External modules have traditionally used grep to check for specific
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CONFIG_ settings directly in .config. This usage is broken.
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As introduced before external modules shall use kbuild when building
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and therefore can use the same methods as in-kernel modules when testing
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for CONFIG_ definitions.
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As introduced before, external modules shall use kbuild when building
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and therefore can use the same methods as in-kernel modules when
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testing for CONFIG_ definitions.
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