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authorBrian Norris <computersforpeace@gmail.com>2015-08-27 15:48:22 -0700
committerBrian Norris <computersforpeace@gmail.com>2015-08-28 09:02:41 -0700
commita2f50d4a0a253e9cb6eaaf0e0e1c67dd02b717ac (patch)
treef2c18920dce36f3c2e01c2eed9dcddad0cea7bef /ftl_check.c
parentd583d1da01eb0a3e38f18dfc8eec0dde07be8320 (diff)
autogenerated dependency files are not being utilized properly
TL;DR Acked-by: Mike Frysinger <vapier@gentoo.org> ===== Auto-generated dependency rules are not being written correctly, so changes to dependent files (e.g., headers) do not actually trigger rebuilds. The problem =========== It appears that when a dependency generation flag is passed directly to the preprocessor (with '-Wp,...'), it loses information about the output path. So, it just makes up the output name as $(basename).o, with no path information. This yields .*.c.dep files that look like this: flash_lock.o: flash_lock.c /usr/include/stdc-predef.h flash_unlock.c \ (...) and nanddump.o: nanddump.c /usr/include/stdc-predef.h /usr/include/ctype.h \ (...) include/libmtd.h This is the case for both in-tree *and* out-of-tree builds. Naturally, this is a problem for out-of-tree builds. But it is also a problem for in-tree builds, because we use rules like this for builds: $(BUILDDIR)/%.o: %.c and make doesn't recognize $(BUILDDIR)/%.o as the same as %.o even when $(BUILDDIR) == $(PWD). Example failures ================ ## Rebuilding after touching common header doesn't recompile anything $ make (...) $ touch include/libmtd.h $ make CHK include/version.h ## Same for out-of-tree builds $ BUILDDIR=test make (...) $ touch include/libmtd.h $ BUILDDIR=test make CHK include/version.h I noticed this when seeing that flash_lock would not get rebuilt when modifying flash_unlock.c (where 99% of the source code lies): $ make (...) $ touch flash_unlock.c $ make CHK include/version.h CC flash_unlock.o LD flash_unlock The fix ======= Just pass -MD straight to the compiler, and make sure to specify the output file for the dependency info with -MF. Signed-off-by: Brian Norris <computersforpeace@gmail.com> Cc: Mike Frysinger <vapier@gentoo.org> Cc: David Woodhouse <David.Woodhouse@intel.com> Signed-off-by: Brian Norris <computersforpeace@gmail.com>
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