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

[Ian Rogers]

On Fri, Jul 28, 2023 at 7:02 AM Arnaldo Carvalho de Melo
<acme@xxxxxxxxxx> 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@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-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 ($(FLEX_GE_264),1)
> -  flex_flags := -Wno-redundant-decls -Wno-switch-default -Wno-unused-function
> +  flex_flags := -Wno-redundant-decls -Wno-switch-default -Wno-unused-function -Wno-misleading-indentation
>  else
>    flex_flags := -w
>  endif
> ⬢[acme@toolbox perf-tools-next]$
>
>
> > 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@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
> > ⬢[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 := $(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.

Thanks,
Ian

> --
>
> - Arnaldo