Commit 4f3a9491 authored by Andrew Morton's avatar Andrew Morton Committed by Linus Torvalds

[PATCH] kbuild documentation fix

From: Ryan Boder <icanoop@bitwiser.org>

Explains how to compile external modules in
Documentation/kbuild/modules.txt.
parent c9700b7e
...@@ -17,12 +17,52 @@ out-of-the-box support for installation on remote machines. ...@@ -17,12 +17,52 @@ out-of-the-box support for installation on remote machines.
Compiling modules outside the official kernel Compiling modules outside the official kernel
--------------------------------------------- ---------------------------------------------
Often modules are developed outside the official kernel.
To keep up with changes in the build system the most portable way Often modules are developed outside the official kernel. To keep up
to compile a module outside the kernel is to use the following command-line: with changes in the build system the most portable way to compile a
module outside the kernel is to use the kernel build system,
kbuild. Use the following command-line:
make -C path/to/kernel/src SUBDIRS=$PWD modules make -C path/to/kernel/src SUBDIRS=$PWD modules
This requires that a makefile exits made in accordance to This requires that a makefile exits made in accordance to
Documentation/kbuild/makefiles.txt. Documentation/kbuild/makefiles.txt. Read that file for more details on
the build system.
The following is a short summary of how to write your Makefile to get
you up and running fast. Assuming your module will be called
yourmodule.ko, your code should be in yourmodule.c and your Makefile
should include
obj-m := yourmodule.o
If the code for your module is in multiple files that need to be
linked, you need to tell the build system which files to compile. In
the case of multiple files, none of these files can be named
yourmodule.c because doing so would cause a problem with the linking
step. Assuming your code exists in file1.c, file2.c, and file3.c and
you want to build yourmodule.ko from them, your Makefile should
include
obj-m := yourmodule.o
yourmodule-objs := file1.o file2.o file3.o
Now for a final example to put it all together. Assuming the
KERNEL_SOURCE environment variable is set to the directory where you
compiled the kernel, a simple Makefile that builds yourmodule.ko as
described above would look like
# Tells the build system to build yourmodule.ko.
obj-m := yourmodule.o
# Tells the build system to build these object files and link them as
# yourmodule.o, before building yourmodule.ko. This line can be left
# out if all the code for your module is in one file, yourmodule.c. If
# you are using multiple files, none of these files can be named
# yourmodule.c.
yourmodule-objs := file1.o file2.o file3.o
# Invokes the kernel build system to come back to the current
# directory and build yourmodule.ko.
default:
make -C ${KERNEL_SOURCE} SUBDIRS=`pwd` modules
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