Re: Build perf with clang, failure with libperf

[Nathan Chancellor <nathan@kernel.org>]

On Thu, Apr 07, 2022 at 12:27:14PM +0200, Sedat Dilek wrote:
> On Mon, Apr 4, 2022 at 11:53 PM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > Hi Arnaldo,
> >
> > On Mon, Apr 04, 2022 at 05:43:11PM -0300, Arnaldo Carvalho de Melo wrote:
> > > Hi,
> > >
> > >       Trying to apply Sedat's patch something changed in my system,
> > > and that patch wasn't enough, so I had to first apply this one:
> > >
> > > commit 173b552663419f40bcd3cf9df4f68285cac72727
> > > Author: Arnaldo Carvalho de Melo <acme@redhat.com>
> > > Date:   Mon Apr 4 17:28:48 2022 -0300
> > >
> > >     tools build: Use $(shell ) instead of `` to get embedded libperl's ccopts
> > >
> > >     Just like its done for ldopts and for both in tools/perf/Makefile.config.
> > >
> > >     Using `` to initialize PERL_EMBED_CCOPTS somehow precludes using:
> > >
> > >       $(filter-out SOMETHING_TO_FILTER,$(PERL_EMBED_CCOPTS))
> > >
> > >     And we need to do it to allow for building with versions of clang where
> > >     some gcc options selected by distros are not available.
> > >
> > >     Cc: Adrian Hunter <adrian.hunter@intel.com>
> > >     Cc: Fangrui Song <maskray@google.com>
> > >     Cc: Florian Fainelli <f.fainelli@gmail.com>
> > >     Cc: Ian Rogers <irogers@google.com>
> > >     Cc: Jiri Olsa <jolsa@kernel.org>
> > >     Cc: John Keeping <john@metanate.com>
> > >     Cc: Leo Yan <leo.yan@linaro.org>
> > >     Cc: Michael Petlan <mpetlan@redhat.com>
> > >     Cc: Namhyung Kim <namhyung@kernel.org>
> > >     Cc: Nathan Chancellor <nathan@kernel.org>
> > >     Cc: Nick Desaulniers <ndesaulniers@google.com>
> > >     Cc: Sedat Dilek <sedat.dilek@gmail.com>
> > >     Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> > >
> > > diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
> > > index 1480910c792e2cb3..90774b60d31b2b8e 100644
> > > --- a/tools/build/feature/Makefile
> > > +++ b/tools/build/feature/Makefile
> > > @@ -217,7 +217,7 @@ strip-libs = $(filter-out -l%,$(1))
> > >  PERL_EMBED_LDOPTS = $(shell perl -MExtUtils::Embed -e ldopts 2>/dev/null)
> > >  PERL_EMBED_LDFLAGS = $(call strip-libs,$(PERL_EMBED_LDOPTS))
> > >  PERL_EMBED_LIBADD = $(call grep-libs,$(PERL_EMBED_LDOPTS))
> > > -PERL_EMBED_CCOPTS = `perl -MExtUtils::Embed -e ccopts 2>/dev/null`
> > > +PERL_EMBED_CCOPTS = $(shell perl -MExtUtils::Embed -e ccopts 2>/dev/null)
> > >  FLAGS_PERL_EMBED=$(PERL_EMBED_CCOPTS) $(PERL_EMBED_LDOPTS)
> > >
> > >  $(OUTPUT)test-libperl.bin:
> > >
> > > ----------------------------------------------------- 8< -------------------
> > >
> > > After this I go on filtering out some of the gcc options that clang
> > > doesn't grok:
> > >
> > > diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
> > > index 90774b60d31b2b8e..bbc5e263e02385ed 100644
> > > --- a/tools/build/feature/Makefile
> > > +++ b/tools/build/feature/Makefile
> > > @@ -215,9 +215,12 @@ grep-libs  = $(filter -l%,$(1))
> > >  strip-libs = $(filter-out -l%,$(1))
> > >
> > >  PERL_EMBED_LDOPTS = $(shell perl -MExtUtils::Embed -e ldopts 2>/dev/null)
> > > +PERL_EMBED_LDOPTS := $(filter-out -specs=%,$(PERL_EMBED_LDOPTS))
> > >  PERL_EMBED_LDFLAGS = $(call strip-libs,$(PERL_EMBED_LDOPTS))
> > >  PERL_EMBED_LIBADD = $(call grep-libs,$(PERL_EMBED_LDOPTS))
> > >  PERL_EMBED_CCOPTS = $(shell perl -MExtUtils::Embed -e ccopts 2>/dev/null)
> > > +PERL_EMBED_CCOPTS := $(filter-out -ffat-lto-objects, $(PERL_EMBED_CCOPTS))
> > > +PERL_EMBED_CCOPTS := $(filter-out -specs=%,$(PERL_EMBED_CCOPTS))
> > >  FLAGS_PERL_EMBED=$(PERL_EMBED_CCOPTS) $(PERL_EMBED_LDOPTS)
> > >
> > >  $(OUTPUT)test-libperl.bin:
> > >
> > > ----------------------------------------------------- 8< -------------------
> > >
> > > And then get to the problems at the end of this message, which seem
> > > similar to the problem described here:
> > >
> > > From  Nathan Chancellor <>
> > > Subject       [PATCH] mwifiex: Remove unnecessary braces from HostCmd_SET_SEQ_NO_BSS_INFO
> > >
> > > https://lkml.org/lkml/2020/9/1/135
> > >
> > > So perhaps in this case its better to disable that
> > > -Werror,-Wcompound-token-split-by-macro when building with clang?
> >
> > Yes, I think that is probably the best solution. As far as I can tell,
> > at least in this file and context, the warning appears harmless, as the
> > "create a GNU C statement expression from two different macros" is very
> > much intentional, based on the presence of PERL_USE_GCC_BRACE_GROUPS.
> > The warning is fixed in upstream Perl by just avoiding creating GNU C
> > statement expressions using STMT_START and STMT_END:
> >
> > https://github.com/Perl/perl5/issues/18780
> > https://github.com/Perl/perl5/pull/18984
> >
> > If I am reading the source code correctly, an alternative to disabling
> > the warning would be specifying -DPERL_GCC_BRACE_GROUPS_FORBIDDEN but it
> > seems like that might end up impacting more than just this site,
> > according to the issue discussion above.
> >
> 
> Thanks for the pointer Nathan.
> 
> As said I hit the problem with Debian's perl v5.34.
> 
> Checking perl5 Git reveals:
> 
> "skip using gcc brace groups for STMT_START/END"
> https://github.com/Perl/perl5/commit/7169efc77525df70484a824bff4ceebd1fafc760

GitHub says this is in 5.35.2, so it would make sense that 5.34 still
shows the issue.

> "Partially Revert "skip using gcc brace groups for STMT_START/END""
> https://github.com/Perl/perl5/commit/e08ee3cb66f362c4901846a46014cfdfcd60326c
> 
> Perl v5.34.x seems not to have these changes:
> https://github.com/Perl/perl5/compare/v5.34.0...v5.34.1
> 
> Unsure if there exists a real fix for perl5.

Perhaps those two changes could be cherry-picked into Debian's 5.34. I
have no idea if that is possible though.

Cheers,
Nathan