You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
419 lines
14 KiB
419 lines
14 KiB
|
|
In this document you will find information about:
|
|
- how to build external modules
|
|
- how to make your module use kbuild infrastructure
|
|
- how kbuild will install a kernel
|
|
- how to install modules in a non-standard location
|
|
|
|
=== Table of Contents
|
|
|
|
=== 1 Introduction
|
|
=== 2 How to build external modules
|
|
--- 2.1 Building external modules
|
|
--- 2.2 Available targets
|
|
--- 2.3 Available options
|
|
--- 2.4 Preparing the kernel tree for module build
|
|
=== 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
|
|
=== 6. Module installation
|
|
--- 6.1 INSTALL_MOD_PATH
|
|
--- 6.2 INSTALL_MOD_DIR
|
|
=== 7. Module versioning
|
|
=== 8. Tips & Tricks
|
|
--- 8.1 Testing for CONFIG_FOO_BAR
|
|
|
|
|
|
|
|
=== 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 modules and is used
|
|
both during development and for modules that are not planned to be
|
|
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 ¤. 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.
|
|
|
|
--- 2.1 Building external modules
|
|
|
|
Use the following command to build an external module:
|
|
|
|
make -C <path-to-kernel> M=`pwd`
|
|
|
|
For the running kernel use:
|
|
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
|
|
|
|
More complex examples later, the above should get you going.
|
|
|
|
--- 2.2 Available targets
|
|
|
|
$KDIR refers to path to kernel source top-level 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 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 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.
|
|
|
|
make -C $KDIR M=$PWD clean
|
|
Remove all generated files for the module - the kernel
|
|
source directory is not moddified.
|
|
|
|
make -C $KDIR M=`pwd` help
|
|
help will list the available target when building external
|
|
modules.
|
|
|
|
--- 2.3 Available options:
|
|
|
|
$KDIR refer to path to kernel src
|
|
|
|
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.
|
|
|
|
--- 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.
|
|
'module_prepare' solely exists as a simple way to prepare
|
|
a kernel for building external modules.
|
|
Note: modules_prepare will not build Module.symvers even if
|
|
CONFIG_MODULEVERSIONING is set.
|
|
Therefore a full kernel build needs to be executed to make
|
|
module versioning work.
|
|
|
|
|
|
=== 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.
|
|
|
|
# Kernel source
|
|
/lib/modules/<kernel-version>/source -> /usr/src/linux-<version>
|
|
|
|
# Output from kernel compile
|
|
/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:
|
|
|
|
cd /home/user/src/module
|
|
make -C /usr/src/`uname -r`/source \
|
|
O=/lib/modules/`uname-r`/build \
|
|
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` \
|
|
modules_install
|
|
|
|
If one looks closely you will see that this is the same commands 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.
|
|
|
|
|
|
=== 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.
|
|
|
|
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.
|
|
|
|
In the following a Makefile will be created for a module with the
|
|
following files:
|
|
8123_if.c
|
|
8123_if.h
|
|
8123_pci.c
|
|
8123_bin.o_shipped <= Binary blob
|
|
|
|
--- 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.
|
|
|
|
Example 1:
|
|
--> filename: Makefile
|
|
ifneq ($(KERNELRELEASE),)
|
|
# kbuild part of makefile
|
|
obj-m := 8123.o
|
|
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
|
|
|
|
else
|
|
# Normal Makefile
|
|
|
|
KERNELDIR := /lib/modules/`uname -r`/build
|
|
all::
|
|
$(MAKE) -C $KERNELDIR M=`pwd` $@
|
|
|
|
# Module specific targets
|
|
genbin:
|
|
echo "X" > 8123_bini.o_shipped
|
|
|
|
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 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:
|
|
|
|
Example 2:
|
|
--> filename: Kbuild
|
|
obj-m := 8123.o
|
|
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
|
|
|
|
--> filename: Makefile
|
|
KERNELDIR := /lib/modules/`uname -r`/build
|
|
all::
|
|
$(MAKE) -C $KERNELDIR M=`pwd` $@
|
|
|
|
# Module specific targets
|
|
genbin:
|
|
echo "X" > 8123_bin_shipped
|
|
|
|
|
|
In example 2 we are down to two fairly simple files and for simple
|
|
files as used in this example the split is questionable. But some
|
|
external modules use Makefiles of several hundred lines and here it
|
|
really pays off to separate the kbuild part from the rest.
|
|
Example 3 shows a backward compatible version.
|
|
|
|
Example 3:
|
|
--> filename: Kbuild
|
|
obj-m := 8123.o
|
|
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
|
|
|
|
--> filename: Makefile
|
|
ifneq ($(KERNELRELEASE),)
|
|
include Kbuild
|
|
else
|
|
# Normal Makefile
|
|
|
|
KERNELDIR := /lib/modules/`uname -r`/build
|
|
all::
|
|
$(MAKE) -C $KERNELDIR M=`pwd` $@
|
|
|
|
# Module specific targets
|
|
genbin:
|
|
echo "X" > 8123_bin_shipped
|
|
|
|
endif
|
|
|
|
The trick here is to include the Kbuild file from Makefile so
|
|
if an older version of kbuild picks up the Makefile the Kbuild
|
|
file will be included.
|
|
|
|
--- 4.2 Binary blobs included in a module
|
|
|
|
Some external modules needs to include a .o as a blob. kbuild
|
|
has support for this, but requires the blob file to be named
|
|
<filename>_shipped. In our example the blob is named
|
|
8123_bin.o_shipped and when the kbuild rules kick in the file
|
|
8123_bin.o is created as a simple copy off the 8213_bin.o_shipped file
|
|
with the _shipped part stripped of the filename.
|
|
This allows the 8123_bin.o filename to be used in the assignment to
|
|
the module.
|
|
|
|
Example 4:
|
|
obj-m := 8123.o
|
|
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
|
|
|
|
In example 4 there is no distinction between the ordinary .c/.h files
|
|
and the binary file. But kbuild will pick up different rules to create
|
|
the .o file.
|
|
|
|
|
|
=== 5. Include files
|
|
|
|
Include files are a necessity when a .c file uses something from another .c
|
|
files (not strictly in the sense of .c but if good programming practice is
|
|
used). Any module that consist of more than one .c file will have a .h file
|
|
for one of the .c files.
|
|
- If the .h file only describes a module internal interface then the .h file
|
|
shall be placed in the same directory as the .c files.
|
|
- If the .h files describe an interface used by other parts of the kernel
|
|
located in different directories, the .h files shall be located in
|
|
include/linux/ or other include/ directories as appropriate.
|
|
|
|
One exception for this rule is larger subsystems that have their own directory
|
|
under include/ such as include/scsi. Another exception is arch-specific
|
|
.h files which are located under include/asm-$(ARCH)/*.
|
|
|
|
External modules have a tendency to locate include files in a separate include/
|
|
directory and therefore needs to deal with this in their kbuild file.
|
|
|
|
--- 5.1 How to include files from the kernel include dir
|
|
|
|
When a module needs to include a file from include/linux/ then one
|
|
just uses:
|
|
|
|
#include <linux/modules.h>
|
|
|
|
kbuild will make sure to add options to gcc so the relevant
|
|
directories are searched.
|
|
Likewise for .h files placed in the same directory as the .c file.
|
|
|
|
#include "8123_if.h"
|
|
|
|
will do the job.
|
|
|
|
--- 5.2 External modules using an include/ dir
|
|
|
|
External modules often locate their .h files in a separate include/
|
|
directory although this is not usual kernel style. When an external
|
|
module uses an include/ dir then kbuild needs to be told so.
|
|
The trick here is to use either EXTRA_CFLAGS (take effect for all .c
|
|
files) or CFLAGS_$F.o (take effect only for a single file).
|
|
|
|
In our example if we move 8123_if.h to a subdirectory named include/
|
|
the resulting Kbuild file would look like:
|
|
|
|
--> filename: Kbuild
|
|
obj-m := 8123.o
|
|
|
|
EXTRA_CFLAGS := -Iinclude
|
|
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
|
|
|
|
Note that in the assingment there is no space between -I and the path.
|
|
This is a kbuild limitation and no space must be present.
|
|
|
|
|
|
=== 6. Module installation
|
|
|
|
Modules which are included in the kernel is installed in the directory:
|
|
|
|
/lib/modules/$(KERNELRELEASE)/kernel
|
|
|
|
External modules are installed in the directory:
|
|
|
|
/lib/modules/$(KERNELRELEASE)/extra
|
|
|
|
--- 6.1 INSTALL_MOD_PATH
|
|
|
|
Above are the default directories, but as always some level of
|
|
customization is possible. One can prefix the path using the variable
|
|
INSTALL_MOD_PATH:
|
|
|
|
$ make INSTALL_MOD_PATH=/frodo modules_install
|
|
=> Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel
|
|
|
|
INSTALL_MOD_PATH may be set as an ordinary shell variable or as in the
|
|
example above be specified on the commandline when calling make.
|
|
INSTALL_MOD_PATH has effect both when installing modules included in
|
|
the kernel as well as when installing external modules.
|
|
|
|
--- 6.2 INSTALL_MOD_DIR
|
|
|
|
When installing external modules they are default installed in a
|
|
directory under /lib/modules/$(KERNELRELEASE)/extra, but one may wish
|
|
to locate modules for a specific functionality in a separate
|
|
directory. For this purpose one can use INSTALL_MOD_DIR to specify an
|
|
alternative name than 'extra'.
|
|
|
|
$ make INSTALL_MOD_DIR=gandalf -C KERNELDIR \
|
|
M=`pwd` modules_install
|
|
=> Install dir: /lib/modules/$(KERNELRELEASE)/gandalf
|
|
|
|
|
|
=== 7. Module versioning
|
|
|
|
Module versioning are enabled by the CONFIG_MODVERSIONS tag.
|
|
|
|
Module versioning is used as a simple ABI consistency check. The Module
|
|
versioning creates a CRC value of the full prototype for an exported symbol and
|
|
when a module is loaded/used then the CRC values contained in the kernel are
|
|
compared with similar values in the module. If they are not equal then the
|
|
kernel refuses to load the module.
|
|
|
|
During a kernel build a file named Module.symvers will be generated. This
|
|
file includes the symbol version of all symbols within the kernel. If the
|
|
Module.symvers file is saved from the last full kernel compile one does not
|
|
have to do a full kernel compile to build a module version's compatible module.
|
|
|
|
=== 8. Tips & Tricks
|
|
|
|
--- 8.1 Testing for CONFIG_FOO_BAR
|
|
|
|
Modules often needs to check for certain CONFIG_ options to decide if
|
|
a specific feature shall be included in the module. When kbuild is used
|
|
this is done by referencing the CONFIG_ variable directly.
|
|
|
|
#fs/ext2/Makefile
|
|
obj-$(CONFIG_EXT2_FS) += ext2.o
|
|
|
|
ext2-y := balloc.o bitmap.o dir.o
|
|
ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o
|
|
|
|
External modules have traditionally used grep to check for specific
|
|
CONFIG_ settings directly in .config. This usage is broken.
|
|
As introduced before external modules shall use kbuild when building
|
|
and therefore can use the same methods as in-kernel modules when testing
|
|
for CONFIG_ definitions.
|
|
|
|
|