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[PATCH] tools build: Use -Xpreprocessor instead of -Wp and leave pathnames intact

Build.include invokes the pre-processor via GCC in order to generate a
dependency list for the input file. Since these options are passed using
'-Wp,-M...,$(depfile)' it is important that $(depfile) does not contain
any commas, so these are substituted with underscores. This substitution
will break the build if the directory name of the output directory happens
to include a comma, e.g. when using "aiaiai" for bisection testing:

  | cc1: fatal error: x86/tools/objtool/fixdep.o: No such file or directory
  | compilation terminated.
  | cat: /tmp/aiaiai-test-patchset.qroS/before/obj.defconfig_x86/tools/objtool/.fixdep.o.d: No such file or directory
  | make[5]: *** [tools/objtool/fixdep.o] Error 1

We can address this by using -Xpreprocessor instead of -Wp, which allows
us to pass down an unmodified pathname.

Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Dave Martin <Dave.Martin@xxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>

As an aside, the way we currently pass the depfile to -MD appears to be
in direct contradiction with the preprocessor documentation, although it
does work with the cc1 implementation.

 tools/build/Build.include | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/tools/build/Build.include b/tools/build/Build.include
index 418871d02ebf..e1914f8e2328 100644
--- a/tools/build/Build.include
+++ b/tools/build/Build.include
@@ -22,9 +22,7 @@ dot-target = $(dir $@).$(notdir $@)
 basetarget = $(basename $(notdir $@))
-# The temporary file to save gcc -MD generated dependencies must not
-# contain a comma
-depfile = $(subst $(comma),_,$(dot-target).d)
+depfile = $(dot-target).d
 # Check if both arguments has same arguments. Result is empty string if equal.
@@ -89,12 +87,12 @@ if_changed = $(if $(strip $(any-prereq) $(arg-check)),                   \
 # - per target C flags
 # - per object C flags
 # - BUILD_STR macro to allow '-D"$(variable)"' constructs
-c_flags_1 = -Wp,-MD,$(depfile) -Wp,-MT,$@ $(CFLAGS) -D"BUILD_STR(s)=\#s" $(CFLAGS_$(basetarget).o) $(CFLAGS_$(obj))
+c_flags_1 = -Xpreprocessor -MD -Xpreprocessor $(depfile) -Xpreprocessor -MT -Xpreprocessor $@ $(CFLAGS) -D"BUILD_STR(s)=\#s" $(CFLAGS_$(basetarget).o) $(CFLAGS_$(obj))
 c_flags_2 = $(filter-out $(CFLAGS_REMOVE_$(basetarget).o), $(c_flags_1))
 c_flags   = $(filter-out $(CFLAGS_REMOVE_$(obj)), $(c_flags_2))
-cxx_flags = -Wp,-MD,$(depfile) -Wp,-MT,$@ $(CXXFLAGS) -D"BUILD_STR(s)=\#s" $(CXXFLAGS_$(basetarget).o) $(CXXFLAGS_$(obj))
+cxx_flags = -Xpreprocessor -MD -Xpreprocessor $(depfile) -Xpreprocessor -MT -Xpreprocessor $@ $(CXXFLAGS) -D"BUILD_STR(s)=\#s" $(CXXFLAGS_$(basetarget).o) $(CXXFLAGS_$(obj))
 ## HOSTCC C flags
-host_c_flags = -Wp,-MD,$(depfile) -Wp,-MT,$@ $(CHOSTFLAGS) -D"BUILD_STR(s)=\#s" $(CHOSTFLAGS_$(basetarget).o) $(CHOSTFLAGS_$(obj))
+host_c_flags = -Xpreprocessor -MD -Xpreprocessor $(depfile) -Xpreprocessor -MT -Xpreprocessor $@ $(CHOSTFLAGS) -D"BUILD_STR(s)=\#s" $(CHOSTFLAGS_$(basetarget).o) $(CHOSTFLAGS_$(obj))