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 <>
Reported-by: : 허종만 <>
Signed-off-by: Jonathan Nieder <>
 Makefile | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 731b6a8..5a2e02d 100644
--- a/Makefile
+++ b/Makefile
@@ -973,7 +973,8 @@ endif
 dep_check = $(shell $(CC) $(ALL_CFLAGS) \
-       -c -MF /dev/null -MMD -MP -x c /dev/null -o /dev/null 2>&1; \
+       -c -MF /dev/null -MQ /dev/null -MMD -MP \
+       -x c /dev/null -o /dev/null 2>&1; \
        echo $$?)
 ifeq ($(dep_check),0)
@@ -1843,7 +1844,7 @@ $(dep_dirs):
 missing_dep_dirs := $(filter-out $(wildcard $(dep_dirs)),$(dep_dirs))
 dep_file = $(dir $@).depend/$(notdir $@).d
-dep_args = -MF $(dep_file) -MMD -MP
+dep_args = -MF $(dep_file) -MQ $@ -MMD -MP
 $(error cannot compute header dependencies outside a normal build. \
 Please unset CHECK_HEADER_DEPENDENCIES and try again)

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