"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-by: Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx> Signed-off-by: Jonathan Nieder <jrnieder@xxxxxxxxx> --- Hi, Nguyen Thai Ngoc Duy wrote: > My builtin/.depend/add.o.d says > > add.o: .... cache.h ... > > Shouldn't it be "builtin/add.o: ... cache.h ..."? The following seems to do the trick for me. Thanks again for catching it. Makefile | 5 +++-- 1 files changed, 3 insertions(+), 2 deletions(-) diff --git a/Makefile b/Makefile index ee34eab8..71ad4b26 100644 --- a/Makefile +++ b/Makefile @@ -1250,7 +1250,8 @@ USE_COMPUTED_HEADER_DEPENDENCIES = else ifndef COMPUTE_HEADER_DEPENDENCIES 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) COMPUTE_HEADER_DEPENDENCIES=YesPlease @@ -1912,7 +1913,7 @@ $(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 ifdef CHECK_HEADER_DEPENDENCIES $(error cannot compute header dependencies outside a normal build. \ Please unset CHECK_HEADER_DEPENDENCIES and try again) -- 1.7.8.rc3 -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html