[PATCH resend] Makefile: explicitly set target name for autogenerated dependencies

Date: Fri, 18 Nov 2011 17:23:24 -0600

"gcc -MF depfile -MMD -MP -c -o path/to/file.o" produces a makefile snippet named "depfile" describing what files are needed to build the target given by "-o". When ccache versions before v3.0pre0~187 (Fix handling of the -MD and -MDD options, 2009-11-01) run, they execute

	gcc -MF depfile -MMD -MP -E

instead to get the final content for hashing. Notice that the "-c -o" combination is replaced by "-E". The result is a target name without a leading path.

Thus when building git with such versions of ccache with COMPUTE_HEADER_DEPENDENCIES enabled, the generated makefile snippets define dependencies for the wrong target:

	$ make builtin/add.o
	GIT_VERSION = 1.7.8.rc3
	    * new build flags or prefix
	    CC builtin/add.o
	$ head -1 builtin/.depend/add.o.d
	add.o: builtin/add.c cache.h git-compat-util.h compat/bswap.h strbuf.h \

After a change in a header file, object files in a subdirectory are not automatically rebuilt by "make":

	$ touch cache.h
	$ make builtin/add.o
	$

Luckily we can prevent trouble by explicitly supplying the name of the target to ccache and gcc, using the -MQ option. Do so.

Reported-and-tested-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Reported-by: : 허종만 <jongman.heo@samsung.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
 Makefile | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)