Omit needless words and sentences; reorganize and tighten sentence structure; swap sections 2.2 and 2.3 for a more logical flow; and cleanup some of the inconsistency with the margin width. Signed-off-by: matt mooney <mfm@xxxxxxxxxxxxx> --- A couple of notes: I chose to use the environment variable $PWD in the examples for both the commandline and Makefile; however, I was wondering if I should have set PWD in the Makefile and used $(PWD) instead. Also, the $@ variable was removed from the 'make' command within the Makefile. I did not understand the purpose of this for building kernel modules and it would break my test build. Documentation/kbuild/modules.txt | 264 ++++++++++++++++++------------------- 1 files changed, 128 insertions(+), 136 deletions(-) diff --git a/Documentation/kbuild/modules.txt b/Documentation/kbuild/modules.txt index 0767cf6..42d7329 100644 --- a/Documentation/kbuild/modules.txt +++ b/Documentation/kbuild/modules.txt @@ -10,8 +10,8 @@ In this document you will find information about: === 1 Introduction === 2 How to build external modules --- 2.1 Building external modules - --- 2.2 Available targets - --- 2.3 Available options + --- 2.2 Options + --- 2.3 Targets --- 2.4 Preparing the kernel tree for module build --- 2.5 Building separate files for a module === 3. Example commands @@ -34,128 +34,123 @@ In this document you will find information about: === 1. Introduction -kbuild includes functionality for building modules both -within the kernel source tree and outside the kernel source tree. -The latter is usually referred to as external or "out-of-tree" -modules and is used both during development and for modules that -are not planned to be included in the kernel tree. +kbuild is the build system that is used by the Linux kernel. It includes +functionality for building modules both inside and outside of the kernel +source tree. The latter is usually referred to as an external or +"out-of-tree" module. This is commonly used during development, and for a +module that is not planned for inclusion within the kernel tree. -What is covered within this file is mainly information to authors -of modules. The author of an external module should supply -a makefile that hides most of the complexity, so one only has to type -'make' to build the module. A complete example will be presented in -chapter 4, "Creating a kbuild file for an external module". +Covered in this document is information aimed at developers interested in +building modules. The author of an external module should supply a Makefile +that hides most of the complexity, so one only has to type 'make' to build +the module. A complete example will be presented in section 4, "Creating a +kbuild file for an external module". === 2. How to build external modules -kbuild offers functionality to build external modules, with the -prerequisite that there is a pre-built kernel available with full source. -A subset of the targets available when building the kernel is available -when building an external module. +To build external modules you must have a pre-built kernel available with +full source. If you are using a distribution kernel, there will be a package +containing the source for their kernel build. --- 2.1 Building external modules Use the following command to build an external module: - make -C <path-to-kernel> M=`pwd` + make -C <path-to-kernel> M=$PWD For the running kernel use: - make -C /lib/modules/`uname -r`/build M=`pwd` + make -C /lib/modules/`uname -r`/build M=$PWD For the above command to succeed, the kernel must have been built with modules enabled. To install the modules that were just built: - make -C <path-to-kernel> M=`pwd` modules_install + make -C <path-to-kernel> M=$PWD modules_install More complex examples will be shown later, the above should be enough to get you started. ---- 2.2 Available targets +--- 2.2 Options - $KDIR refers to the path to the kernel source top-level directory + $KDIR is the path to the kernel source directory. - make -C $KDIR M=`pwd` - Will build the module(s) located in current directory. - All output files will be located in the same directory - as the module source. - No attempts are made to update the kernel source, and it is - a precondition that a successful make has been executed - for the kernel. + make -C $KDIR + -C is used to specify where to find the kernel source. + 'make' will actually change to the specified directory + when executing and will change back when finished. - make -C $KDIR M=`pwd` modules - The modules target is implied when no target is given. - Same functionality as if no target was specified. - See description above. + make -C $KDIR M=$PWD + M= is used to tell kbuild that an external module is being + built. The option given to M= is the directory where the + external module (kbuild file) is located. - 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. + make -C $KDIR SUBDIRS=$PWD + Same as M=. The SUBDIRS= syntax is kept for backwards + compatibility, but its usage is deprecated. - make -C $KDIR M=`pwd` clean - Remove all generated files for the module - the kernel - source directory is not modified. +--- 2.3 Targets - make -C $KDIR M=`pwd` help - help will list the available target when building external - modules. + When building an external module, only a subset of the 'make' + targets are available. ---- 2.3 Available options: + make -C $KDIR M=$PWD + Build the module(s) located in the current directory; all + output files will also be generated in this directory. No + attempts are made to update the kernel source, and it is a + precondition that a successful 'make' has been executed for + the kernel. - $KDIR refers to the path to the kernel source top-level directory + make -C $KDIR M=$PWD modules + modules is the default target, it has the same functionality + as if no target was specified. See description above. - make -C $KDIR - Used to specify where to find the kernel source. - '$KDIR' represent the directory where the kernel source is. - Make will actually change directory to the specified directory - when executed but change back when finished. - - make -C $KDIR M=`pwd` - M= is used to tell kbuild that an external module is - being built. - The option given to M= is the directory where the external - module (kbuild file) is located. - When an external module is being built only a subset of the - usual targets are available. - - make -C $KDIR SUBDIRS=`pwd` - Same as M=. The SUBDIRS= syntax is kept for backwards - compatibility. + make -C $KDIR M=$PWD modules_install + Install the external module(s). The default location is + /lib/modules/<kernel-version>/extra, but a prefix may be + added with INSTALL_MOD_PATH (discussed in section 6). + + make -C $KDIR M=$PWD clean + Remove all generated files in the module directory only. + + make -C $KDIR M=$PWD help + help will list the available targets when building external + modules. --- 2.4 Preparing the kernel tree for module build To make sure the kernel contains the information required to - build external modules the target 'modules_prepare' must be used. - 'modules_prepare' exists solely as a simple way to prepare - a kernel source tree for building external modules. + build external modules the target modules_prepare must be used. + modules_prepare exists solely as a simple way to prepare a kernel + source tree for building external modules. + Note: modules_prepare will not build Module.symvers even if - CONFIG_MODVERSIONS is set. Therefore a full kernel build + CONFIG_MODVERSIONS is set; 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 are part of a module. - This works equally well for the kernel, a module and even for + + It is possible to build single files that are part of a module. + This works equally well 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` / + + Example (The module foo.ko, consist of bar.o and baz.o): + make -C $KDIR M=$PWD bar.o + make -C $KDIR M=$PWD baz.o + make -C $KDIR M=$PWD foo.ko + make -C $KDIR M=$PWD / === 3. Example commands -This example shows the actual commands to be executed when building -an external module for the currently running kernel. -In the example below, the distribution is supposed to use the -facility to locate output files for a kernel compile in a different -directory than the kernel source - but the examples will also work -when the source and the output files are mixed in the same directory. +This example shows the actual commands to be executed when building an +external module for the currently running kernel. In the example below, +the distribution is supposed to use the facility to locate output files +for a kernel compile in a different directory than the kernel source; +however, the example will also work when the source and the output files +are mixed in the same directory, provided the links exist. # Kernel source /lib/modules/<kernel-version>/source -> /usr/src/linux-<version> @@ -164,39 +159,36 @@ when the source and the output files are mixed in the same directory. /lib/modules/<kernel-version>/build -> /usr/src/linux-<version>-up Change to the directory where the kbuild file is located and execute -the following commands to build the module: +the following command to build the module: + + cd /home/<username>/src/module - cd /home/user/src/module make -C /usr/src/`uname -r`/source \ O=/lib/modules/`uname-r`/build \ - M=`pwd` + M=$PWD Then, to install the module use the following command: make -C /usr/src/`uname -r`/source \ O=/lib/modules/`uname-r`/build \ - M=`pwd` \ + M=$PWD \ modules_install -If you look closely you will see that this is the same command as -listed before - with the directories spelled out. - -The above are rather long commands, and the following chapter -lists a few tricks to make it all easier. +Since the commands above are rather long, the subsequent section lists a +few tricks to make it easier. === 4. Creating a kbuild file for an external module -kbuild is the build system for the kernel, and external modules -must use kbuild to stay compatible with changes in the build system -and to pick up the right flags to gcc etc. +External modules must use kbuild to stay compatible with changes in the +build system and to pick up the right flags to gcc. As you will soon learn, +this can be done by using a separate Kbuild file or by using a conditional +branch within a Makefile. Further documentation describing the syntax used +by kbuild is located in Documentation/kbuild/makefiles.txt. -The kbuild file used as input shall follow the syntax described -in Documentation/kbuild/makefiles.txt. This chapter will introduce a few -more tricks to be used when dealing with external modules. +The examples below demonstrate how to create a Makefile for the module +8123.ko, which is built from the following files: -In the following a Makefile will be created for a module with the -following files: 8123_if.c 8123_if.h 8123_pci.c @@ -204,26 +196,24 @@ following files: --- 4.1 Shared Makefile for module and kernel - An external module always includes a wrapper Makefile supporting - building the module using 'make' with no arguments. - The Makefile provided will most likely include additional - functionality such as test targets etc. and this part shall - be filtered away from kbuild since it may impact kbuild if - name clashes occurs. + An external module always includes a wrapper Makefile that supports + building the module using 'make' with no arguments. The Makefile + provided may include additional functionality, such as test targets, + that will be filtered out from kbuild due to possible name clashes. Example 1: --> filename: Makefile ifneq ($(KERNELRELEASE),) - # kbuild part of makefile + # kbuild part of Makefile obj-m := 8123.o 8123-y := 8123_if.o 8123_pci.o 8123_bin.o else # Normal Makefile + KDIR := /lib/modules/`uname -r`/build - KERNELDIR := /lib/modules/`uname -r`/build all:: - $(MAKE) -C $(KERNELDIR) M=`pwd` $@ + $(MAKE) -C $(KDIR) M=$$PWD # Module specific targets genbin: @@ -231,15 +221,14 @@ following files: endif - In example 1, the check for KERNELRELEASE is used to separate - the two parts of the Makefile. kbuild will only see the two - assignments whereas make will see everything except the two - kbuild assignments. + In example 1, the check for KERNELRELEASE is used to separate the + two parts of the Makefile. kbuild will only see the two assignments + whereas 'make' will see everything except the two kbuild assignments. - In recent versions of the kernel, kbuild will look for a file named - Kbuild and as second option look for a file named Makefile. - Utilising the Kbuild file makes us split up the Makefile in example 1 - into two files as shown in example 2: + In newer versions of the kernel, kbuild will first look for a file + named Kbuild and only if that is not found, will it look for a + Makefile. Utilizing a Kbuild file allows us to split up the Makefile + from example 1 into two files: Example 2: --> filename: Kbuild @@ -247,20 +236,21 @@ following files: 8123-y := 8123_if.o 8123_pci.o 8123_bin.o --> filename: Makefile - KERNELDIR := /lib/modules/`uname -r`/build + KDIR := /lib/modules/`uname -r`/build + all:: - $(MAKE) -C $(KERNELDIR) M=`pwd` $@ + $(MAKE) -C $(KDIR) M=$$PWD # Module specific targets genbin: echo "X" > 8123_bin.o_shipped + The split in example 2 is questionable due to the simplicity of + each file; however, some external modules use Makefiles consisting + of several hundred lines, and here it really pays off to separate + the kbuild part from the rest. - In example 2, we are down to two fairly simple files and for simple - files as used in this example the split is questionable. But some - external modules use Makefiles of several hundred lines and here it - really pays off to separate the kbuild part from the rest. - Example 3 shows a backward compatible version. + The next example shows a backward compatible version. Example 3: --> filename: Kbuild @@ -269,13 +259,14 @@ following files: --> filename: Makefile ifneq ($(KERNELRELEASE),) + # kbuild part of Makefile include Kbuild else # Normal Makefile + KDIR := /lib/modules/`uname -r`/build - KERNELDIR := /lib/modules/`uname -r`/build all:: - $(MAKE) -C $(KERNELDIR) M=`pwd` $@ + $(MAKE) -C $(KDIR) M=$$PWD # Module specific targets genbin: @@ -283,28 +274,29 @@ following files: endif - The trick here is to include the Kbuild file from Makefile, so - if an older version of kbuild picks up the Makefile, the Kbuild - file will be included. + Here the Kbuild file is included from the Makefile. This allows an + older version of kbuild, which only knows of Makefiles, to be used + when the 'make' and kbuild parts are split into separate files. --- 4.2 Binary blobs included in a module - Some external modules needs to include a .o as a blob. kbuild - has support for this, but requires the blob file to be named - <filename>_shipped. In our example the blob is named - 8123_bin.o_shipped and when the kbuild rules kick in the file - 8123_bin.o is created as a simple copy off the 8213_bin.o_shipped file - with the _shipped part stripped of the filename. - This allows the 8123_bin.o filename to be used in the assignment to - the module. + Some external modules need to include an object file as a blob. + kbuild has support for this, but requires the blob file to be + named <filename>_shipped. When the kbuild rules kick in, a copy + of <filename>_shipped is created with _shipped stripped off + giving us <filename>. The shortened filename can be used in the + assignment to the module. + + Throughout this section, 8123_bin.o_shipped has been used to build + the kernel module 8123.ko; it has been included as 8123_bin.o. Example 4: obj-m := 8123.o 8123-y := 8123_if.o 8123_pci.o 8123_bin.o - In example 4, there is no distinction between the ordinary .c/.h files - and the binary file. But kbuild will pick up different rules to create - the .o file. + Although there is no distinction between the ordinary source files + and the binary file, kbuild will pick up different rules to create + the object file. === 5. Include files -- 1.7.2.1 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html