linux-kernel - Re: [PATCH v1 4/6] perf build: Disable fewer flex warnings

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Date:   Fri, 28 Jul 2023 15:10:04 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     James Clark <james.clark@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Eduard Zingerman <eddyz87@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Gaosheng Cui <cuigaosheng1@...wei.com>,
        Rob Herring <robh@...nel.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v1 4/6] perf build: Disable fewer flex warnings

Em Fri, Jul 28, 2023 at 08:26:54AM -0700, Ian Rogers escreveu:
> On Fri, Jul 28, 2023 at 7:02 AM Arnaldo Carvalho de Melo
> <acme@...nel.org> wrote:
> >
> > Em Fri, Jul 28, 2023 at 10:59:38AM -0300, Arnaldo Carvalho de Melo escreveu:
> > > Em Fri, Jul 28, 2023 at 09:50:59AM +0100, James Clark escreveu:
> > > >
> > > >
> > > > On 28/07/2023 07:49, Ian Rogers wrote:
> > > > > If flex is version 2.6.4, reduce the number of flex C warnings
> > > > > disabled. Earlier flex versions have all C warnings disabled.
> > > >
> > > > Hi Ian,
> > > >
> > > > I get a build error with either this one or the bison warning change:
> > > >
> > > >   $ make LLVM=1 -C tools/perf NO_BPF_SKEL=1 DEBUG=1
> > > >
> > > >   util/pmu-bison.c:855:9: error: variable 'perf_pmu_nerrs' set but not
> > > > used [-Werror,-Wunused-but-set-variable]
> > > >     int yynerrs = 0;
> > > >
> > > > I tried a clean build which normally fixes these kind of bison errors.
> > > > Let me know if you need any version info.
> > >
> > > Trying to build it with the command line above I get:
> > >
> > >   CC      util/expr.o
> > >   CC      util/parse-events.o
> > >   CC      util/parse-events-flex.o
> > > util/parse-events-flex.c:7503:13: error: misleading indentation; statement is not part of the previous 'if' [-Werror,-Wmisleading-indentation]
> > >             if ( ! yyg->yy_state_buf )
> > >             ^
> > > util/parse-events-flex.c:7501:9: note: previous statement is here
> > >         if ( ! yyg->yy_state_buf )
> > >         ^
> >
> > I added this to the patch to get it moving:
> >
> > make: Leaving directory '/var/home/acme/git/perf-tools-next/tools/perf'
> > ⬢[acme@...lbox perf-tools-next]$ git diff
> > diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> > index 32239c4b0393c319..afa93eff495811cf 100644
> > --- a/tools/perf/util/Build
> > +++ b/tools/perf/util/Build
> > @@ -281,7 +281,7 @@ $(OUTPUT)util/bpf-filter-bison.c $(OUTPUT)util/bpf-filter-bison.h: util/bpf-filt
> >
> >  FLEX_GE_264 := $(shell expr $(shell $(FLEX) --version | sed -e  's/flex \([0-9]\+\).\([0-9]\+\).\([0-9]\+\)/\1\2\3/g') \>\= 264)
> >  ifeq ($(FLEX_GE_264),1)
> > -  flex_flags := -Wno-redundant-decls -Wno-switch-default -Wno-unused-function
> > +  flex_flags := -Wno-redundant-decls -Wno-switch-default -Wno-unused-function -Wno-misleading-indentation
> >  else
> >    flex_flags := -w
> >  endif
> > ⬢[acme@...lbox perf-tools-next]$
> >
> >
> > > 1 error generated.
> > > make[4]: *** [/var/home/acme/git/perf-tools-next/tools/build/Makefile.build:97: util/parse-events-flex.o] Error 1
> > > make[4]: *** Waiting for unfinished jobs....
> > >   LD      util/scripting-engines/perf-in.o
> > > make[3]: *** [/var/home/acme/git/perf-tools-next/tools/build/Makefile.build:140: util] Error 2
> > > make[2]: *** [Makefile.perf:682: perf-in.o] Error 2
> > > make[2]: *** Waiting for unfinished jobs....
> > >   CC      pmu-events/pmu-events.o
> > >   LD      pmu-events/pmu-events-in.o
> > > make[1]: *** [Makefile.perf:242: sub-make] Error 2
> > > make: *** [Makefile:70: all] Error 2
> > >
> > > ⬢[acme@...lbox perf-tools-next]$ clang --version
> > > clang version 14.0.5 (Fedora 14.0.5-2.fc36)
> > > Target: x86_64-redhat-linux-gnu
> > > Thread model: posix
> > > InstalledDir: /usr/bin
> > > ⬢[acme@...lbox perf-tools-next]$
> 
> Thanks James/Arnaldo, I was trying to be aggressive in having more
> flags, but it seems too aggressive. We should probably bring back the
> logic to make this flag only added if it is supported:
>   CC_HASNT_MISLEADING_INDENTATION := $(shell echo "int main(void) {
> return 0 }" | $(CC) -Werror -Wno-misleading-indentation -o /dev/null
> -xc - 2>&1 | grep -q -- -Wno-misleading-indentation ; echo $$?)
>   ifeq ($(CC_HASNT_MISLEADING_INDENTATION), 1)
>     flex_flags += -Wno-misleading-indentation
>   endif
> Arnaldo, is the misleading indentation in the bison generated code or
> something copy-pasted from the parse-events.l ? If the latter we may
> be able to fix the .l file to keep the warning.

I haven't checked, lemme do it now.

- Arnaldo