From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pa0-x22a.google.com ([2607:f8b0:400e:c03::22a]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1ZV5yd-0004Ur-S8 for linux-mtd@lists.infradead.org; Thu, 27 Aug 2015 22:49:00 +0000 Received: by pacdd16 with SMTP id dd16so39808949pac.2 for ; Thu, 27 Aug 2015 15:48:37 -0700 (PDT) From: Brian Norris To: Cc: Brian Norris , Mike Frysinger , David Woodhouse Subject: [PATCH mtd-utils] autogenerated dependency files are not being utilized properly Date: Thu, 27 Aug 2015 15:48:22 -0700 Message-Id: <1440715702-66843-1-git-send-email-computersforpeace@gmail.com> List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , TL;DR ===== 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 Cc: Mike Frysinger Cc: David Woodhouse --- common.mk | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/common.mk b/common.mk index ba87377a00b6..7c09ab0a46d0 100644 --- a/common.mk +++ b/common.mk @@ -80,7 +80,7 @@ ifneq ($(BUILDDIR),$(CURDIR)) $(Q)mkdir -p $(dir $@) endif $(call BECHO,CC) - $(Q)$(CC) $(CPPFLAGS) $(CFLAGS) -c -o $@ $< -g -Wp,-MD,$(BUILDDIR)/.$(