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kbuild: document howto build external modules using several directories

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Update modules.txt with info how to build external modules
with files in several directories.
The question popped up on lkml often enough to warrant this,
let's see if people read this stuff - or google hits it.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
This commit is contained in:
Sam Ravnborg 2006-01-06 20:33:41 +01:00
parent 9f155b9802
commit 253dfa6e46
1 changed files with 40 additions and 0 deletions
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40
Documentation/kbuild/modules.txt
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@ -18,6 +18,7 @@ In this document you will find information about:
=== 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
@ -344,6 +345,45 @@ directory and therefore needs to deal with this in their kbuild file.
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