Kbuild trick

[Sam Ravnborg <sam@ravnborg.org>]

Hi Timur.
Some tricks/hints.

For both kernel 2.4 and 2.6 you can split up your makefile like this:
makefile <= all the external modules specific part
Makefile <= the kbuild specific part

Recent 2.6 kernels looks for a fine named Kbuild before Makefile
so you can use the file Kbuild for a 2.6 compatible kbuild file, and
Makefile for a 2.4 compatible kbuild file.

 
> # Only if the Config.mk file exists will the next line include it.
> # (Inside Ammasso, the needed information is derived differently.)
> ifneq (${wildcard ${SOFTWARE}/../Config.mk},)
>     include ${SOFTWARE}/../Config.mk
> endif
-include does the same

 
> # Determine the kernel version.  We only really care about 2.4 vs 2.6, so 
> this
> # simple code will work with version.h files that have multiple 
> UTS_RELEASEs.

In the kbuild part of the file you can check for KERNELRELEASE.
And a lot of what is below ought to be in the kbuild part of the file.

 
> # If O= is specified on the make command line, then you must have write
> # access to KERNEL_SOURCE, otherwise the build will fail.  So we only pass
> # O= if it is specified in Config.mk.
O= does not require write access to KERNEL_SOURCE. Thats one one the
main concpets. KERNEL_SOURCE may be owned by whoever.

 
> # Define DO_MUNMAP_API_CHANGE if this kernel uses the version of do_unmap()
> # that has four parameters instead of just three.
> 
> ifneq (${shell grep -c -m 1 do_munmap.*acct 
> ${KERNEL_SOURCE}/include/linux/mm.h}, 0)
>     EXTRA_CFLAGS += -DDO_MUNMAP_API_CHANGE
> endif

A macro can simplify this:

feature = $(if $(shell grep -m 1 $(1) $(srctree)/include/$(2)), $(3))

Usage:
EXTRA_CFLAGS += $(call feature, do_munmap.*acct, linux/mm.h, -DDO_MUNMAP_API_CHANGE)
EXTRA_CFLAGS += $(call feature, remap_page_range.*vm_area_struct, \
                  linux/mm.h, -DREMAP_API_CHANGE)

etc..

> 
>     ifneq (${wildcard /proc/ksyms},)
>         SYMFILE = /proc/ksyms
>     else
>         ifneq (${wildcard /proc/kallsyms},)
>             SYMFILE = /proc/kallsyms
>         endif
>     endif
This looks wrong. Either you shall check kernel source or running
kernel.
But mixing it like this is to call for troubles.


 
> # Source files
> 
> CFILES = \
>         devnet.c \
>         ccilnet.c \
>         devccil.c \
>         devccil_adapter.c \
>         devccil_rnic.c \
>         devccil_mem.c \
>         devccil_vq.c \
>         devccil_eh.c \
>         devccil_cq.c \
>         devccil_mq.c \
>         devccil_pd.c \
>         devccil_srq.c \
>         devccil_qp.c \
>         devccil_mm.c \
>         devccil_ep.c \
>         devccil_wrappers.c \
>         devccil_ae.c \
>         devccil_logging.c
> 
> COMMON_CFILES   = \
> 		cc_cq_common.c \
>                 cc_mq_common.c \
>                 cc_qp_common.c
> 
In kbuild files the usual pattern is to specify the .o files not the
source files. So for anyone familiar with kbuild files this looks wrong.
And be explicit. No reason to hide directories behind the addprefix
macro below. This is not an obscufating contest.
> # Fix the paths for the common .c files
> CFILES += $(addprefix ../../common/, ${COMMON_CFILES})

> # Generate an assembly listing for each file
> 
> EXTRA_CFLAGS += -Wa,-aldh=$*.lst
If needed you can use: make cc_mp_common.lst to let kbuild generate
them. Dunno if it works for external modules btw.

> 
> 
> # Linker parameters
> 
> obj-m := ccil.o
> 
> ccil-objs := ${CFILES:.c=.o}
> 
> syscall:
> 	@echo ${SYSCALL_METHOD}

As you have noticed in another mail - this does not work.
An untested approch would be to use:
.PHONY: syscall
$(obj)/ccil.o: syscall

	Sam
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