Messages in this thread | | | Date | Fri, 13 Apr 2018 15:59:42 +0100 | From | Dave Martin <> | Subject | Re: [PATCH] tools build: Use -Xpreprocessor instead of -Wp and leave pathnames intact |
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On Fri, Apr 13, 2018 at 02:53:10PM +0100, Will Deacon wrote: > 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@kernel.org> > Cc: Dave Martin <Dave.Martin@arm.com> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com> > Cc: Ingo Molnar <mingo@kernel.org> > Signed-off-by: Will Deacon <will.deacon@arm.com> > --- > > 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.
Hmmm, I try cc1 --help, and it gives
...
-I <dir> -M -MD -MF <file> -MG -MM
...
so it looks like even cc1 shouldn't really be parsing a depfile name argument after -MD.
The only way to get -MD <file> parsed in the undocumented way seems to be with gcc -Wp,-MD,... or direct invocation of cc1. The cpp frontend, and the gcc frontend itself seem to follow the documentation and don't parse <file> as the depfile name here:
[...]
> diff --git a/tools/build/Build.include b/tools/build/Build.include
We should probably address this everywhere when we've figured out what to do.
> 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))
Any idea why we use -Wp here other than as a bug compatibility hack? The gcc/clang support the depfile options directly. It's possible that gcc didn't support them, or didn't support -MF, sometime in the distant past. This use in the kernel makefiles predates git.
I'm wondering whether we should actually switch to using -M -MF, or -MD -MF (strictly without -Wp or -Xpreprocessor) rather than relying on a combination of undocumented interactions between -Wp and cc1, and cc1 violating its own documentation.
Cheers ---Dave
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