Compile subdir-objects multiple times

Question

Automake 1.14 is causing us a few issues. At first, automake errored with the complaint:

warning: source file 'X' is in a subdirectory but option 'subdir-objects' is disabled

So I enabled subdir-objects, but now it isn't recompiling some files. For example, lets say

src/a/foo.c is compiled in SUBDIR a but in src/b, I would like to compile it again with different preprocessor flags, however since ../a/foo.o already exists, make doesn't rebuild it. This is because subdir-objects changes am_b_OBJECTS to look for ../a/foo.o instead of foo.o. Is there a way I can get around the original complaint and instruct make to build the file a second time with the appropriate preprocessor flags? This all worked on previous versions of automake.

I would settle for executing rm ../a/foo.o before compiling src/b but I don't know how to edit the Makefile.am to make that happen.

Answer 1

This happens if you're using subdir-objects under the same tree from different Makefile.am files. As automake can't see you're using the same source file with different parameters it'll assume it was rebuilt correctly.

The proper solution to this is to not use separate Makefile.am files and instead rephrase the build system as non-recursive automake and so in that case it would then build foo.c as foo-a.o and foo-b.o.