X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=Documentation%2Fkbuild%2Fmodules.txt;fp=Documentation%2Fkbuild%2Fmodules.txt;h=61fc079eb9661a7bd5eff33bc11e05e437734cc9;hb=43bc926fffd92024b46cafaf7350d669ba9ca884;hp=c91caf7eb3036624e88d5e6c37fefb7aaf95f167;hpb=cee37fe97739d85991964371c1f3a745c00dd236;p=linux-2.6.git diff --git a/Documentation/kbuild/modules.txt b/Documentation/kbuild/modules.txt index c91caf7eb..61fc079eb 100644 --- a/Documentation/kbuild/modules.txt +++ b/Documentation/kbuild/modules.txt @@ -13,15 +13,20 @@ In this document you will find information about: --- 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 @@ -38,8 +43,8 @@ included in the kernel tree. 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 @@ -69,7 +74,7 @@ when building an external module. --- 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. @@ -87,11 +92,12 @@ when building an external module. make -C $KDIR M=$PWD modules_install Install the external module(s). Installation default is in /lib/modules//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 @@ -99,7 +105,7 @@ when building an external module. --- 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. @@ -130,6 +136,16 @@ when building an external module. 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 @@ -206,11 +222,11 @@ following files: KERNELDIR := /lib/modules/`uname -r`/build all:: - $(MAKE) -C $KERNELDIR M=`pwd` $@ + $(MAKE) -C $(KERNELDIR) M=`pwd` $@ # Module specific targets genbin: - echo "X" > 8123_bini.o_shipped + echo "X" > 8123_bin.o_shipped endif @@ -341,13 +357,52 @@ directory and therefore needs to deal with this in their kbuild file. EXTRA_CFLAGS := -Iinclude 8123-y := 8123_if.o 8123_pci.o 8123_bin.o - Note that in the assingment there is no space between -I and the path. - This is a kbuild limitation and no space must be present. - + Note that in the assignment there is no space between -I and the path. + This is a kbuild limitation: there must be no space present. + +--- 5.3 External modules using several directories + + If an external module does not follow the usual kernel style but + decide to spread files over several directories then kbuild can + support this too. + + Consider the following example: + + | + +- src/complex_main.c + | +- hal/hardwareif.c + | +- hal/include/hardwareif.h + +- include/complex.h + + To build a single module named complex.ko we then need the following + kbuild file: + + Kbuild: + obj-m := complex.o + complex-y := src/complex_main.o + complex-y += src/hal/hardwareif.o + + EXTRA_CFLAGS := -I$(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/$(KERNELRELEASE)/kernel @@ -365,7 +420,7 @@ External modules are installed in the directory: => Install dir: /frodo/lib/modules/$(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. @@ -382,9 +437,9 @@ External modules are installed in the directory: => 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 @@ -392,11 +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: + + 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