[kbuild-devel] Override autoconf.h fixdep intelligence

[John W. <jwi...@it...>]

Hello,

Is there a sensible way of forcing a .c file to be explicitly dependent 
on autoconf.h, thus bypassing the CONFIG_ dependency intelligence built 
into fixdep?

Here's why I want to do this:  In some platform setup code I use a 
structure initialiser macro like this:

#include <autoconf.h>

...
struct device_struct {
  unsigned baseaddr;
  unsigned highaddr;
};

#define INITIALIZER(n) \
{    \
   .baseaddr = CONFIG_FOOBAR_##n##_BASEADDR,  \
   .highaddr = CONFIG_FOOBAR_##n##_HIGHADDR,  \
}


struct device_struct my_devices[]={
INITIALIZER(0),
INITIALIZER(1),
..

}

and so on.

fixdep sees that I am including autoconf.h, and attempts its 
substitution trick.

The problem is, that the "dependent" config variables, in this case 
CONFIG_FOOBAR_0_BASEADDR, CONFIG_FOOBAR_0_HIGHADDR, and so on, are not 
explicitly referenced in my source file.  They only exist after the 
expansion of the initialiser macro, which fixdep never sees.

As a result, if any of these config variables change, my C file is not 
rebuilt.

As I see it I have a few ways of fixing or working around this:

1. Tweak my Makefile to force a dependency on include/linux/autoconf.h 
for this source file. (I don't care if it is rebuilt more often than 
strictly necessary)

2. Do something horrible like reference these CONFIG_FOOBAR_0... 
identifiers in a comment, to trick fixdep into giving me the dependency

3. Make fixdep smart enough to look into the macro expansion and 
parameter substitution (no thanks!)

I've read the kbuild doco in the kernel tree and still couldn't see how 
to achieve (1), which seems by far my simplest approach.

Any comments or suggestions welcomed.

Thanks,

John