Re: Automatic macro dependencies

[Sam Ravnborg]

On Tue, Aug 05, 2008 at 01:58:17PM -0400, Harvey Chapman wrote:
> Hello all,
> 
> I'd like to be able to define a list of macros like (DEBUG_XX, DEBUG_YY) 
> and have make detect that a source file needs to be recompiled because 
> of a change in that list. These macros are always used with an "#ifdef" 
> or  an "#if defined()" style pre-processing directive.
> 
> I would appreciate any pointers to solutions.
http://www.kernel.org :-)

In the kernel we use a lot of CONFIG_ named variables and
changing one of these cause the relevant files to be rebuilt.

The steps are basically:
1) Create a hirachy of files representing the possible CONFIG_
variables. For any CONFIG_ variable changed touch the file and
for new ones create the file and delete file for nonexisting ones.

2) When building a .c file parse the .c file (and included files)
and add a dependency to the file representing the CONFIG_ variable.
(See fixdep.c for the scanning)

3) Use the dependency file to update value of $? that is again
used to do an eventual rebuild fo a .c file.


See scripts/Kbuild.include and Makefile.build for details as well as
fixdep.c source.
But expect to use a few days before you get the details.

        Sam