kbuild: Make dependencies at compile time
Making dependencies once up front is not ideal. For one, you don't need them initially, since when you don't have the .o file, you bet you have to build it no matter what the dependencies say - dependencies are about deciding when to *re*build. There's more reasons, like: o you don't even know which files you'll build, so you have to go over all files (even over drivers/{sbus,s390,...} on i386) o generated files don't exist yet, so you cannot pick up dependencies on them o even if dependencies are right initially, they change when you work on your tree or patch it, and nobody will notice unless you run "make dep" explicitly again Anyway, gcc knows hows to emit a correct dependency list, so we just use that. Well, a little bit of hacking is necessary to remove the dependency on autoconf.h and put in individual CONFIG_WHAT_EVER dependencies instead, since otherwise changing one config option would cause everything to be rebuilt. I should add that I didn't come up with this all by myself, most work is actually done in gcc and there were discussions about using -MD on kbuild-devel way back, so I should mention Keith Owens and Michael Elizabeth Chastain, and probably others that I forgot, so I apologize just in case.
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scripts/fixdep.c
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scripts/mkdep.c
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