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From:   Ian Rogers <irogers@google.com>
Date:   Fri, 28 Jul 2023 08:26:54 -0700
Message-ID: <CAP-5=fX2LOdd_34ysAYYB5zq5tr7dMje35Nw6hrLXTPLsOHoaw@mail.gmail.com>
Subject: Re: [PATCH v1 4/6] perf build: Disable fewer flex warnings
To:     Arnaldo Carvalho de Melo <acme@kernel.org>
Cc:     James Clark <james.clark@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Eduard Zingerman <eddyz87@gmail.com>,
        Andrii Nakryiko <andrii@kernel.org>,
        Gaosheng Cui <cuigaosheng1@huawei.com>,
        Rob Herring <robh@kernel.org>,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        bpf@vger.kernel.org, llvm@lists.linux.dev
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On Fri, Jul 28, 2023 at 7:02=E2=80=AFAM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> Em Fri, Jul 28, 2023 at 10:59:38AM -0300, Arnaldo Carvalho de Melo escrev=
eu:
> > 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=3D1 -C tools/perf NO_BPF_SKEL=3D1 DEBUG=3D1
> > >
> > >   util/pmu-bison.c:855:9: error: variable 'perf_pmu_nerrs' set but no=
t
> > > used [-Werror,-Wunused-but-set-variable]
> > >     int yynerrs =3D 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; statem=
ent 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'
> =E2=AC=A2[acme@toolbox 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-fi=
lter-bison.h: util/bpf-filt
>
>  FLEX_GE_264 :=3D $(shell expr $(shell $(FLEX) --version | sed -e  's/fle=
x \([0-9]\+\).\([0-9]\+\).\([0-9]\+\)/\1\2\3/g') \>\=3D 264)
>  ifeq ($(FLEX_GE_264),1)
> -  flex_flags :=3D -Wno-redundant-decls -Wno-switch-default -Wno-unused-f=
unction
> +  flex_flags :=3D -Wno-redundant-decls -Wno-switch-default -Wno-unused-f=
unction -Wno-misleading-indentation
>  else
>    flex_flags :=3D -w
>  endif
> =E2=AC=A2[acme@toolbox perf-tools-next]$
>
>
> > 1 error generated.
> > make[4]: *** [/var/home/acme/git/perf-tools-next/tools/build/Makefile.b=
uild: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.b=
uild: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
> >
> > =E2=AC=A2[acme@toolbox 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
> > =E2=AC=A2[acme@toolbox 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 :=3D $(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 +=3D -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.

Thanks,
Ian

> --
>
> - Arnaldo