linux-kernel - Re: [RFC PATCH v1] perf parse-events: Make legacy events lower priority than sysfs/json

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Date:   Fri, 24 Nov 2023 10:49:17 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Hector Martin <marcan@...can.st>,
        Mark Rutland <mark.rutland@....com>,
        Marc Zyngier <maz@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        James Clark <james.clark@....com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1] perf parse-events: Make legacy events lower
 priority than sysfs/json

Em Thu, Nov 23, 2023 at 06:15:09PM -0300, Arnaldo Carvalho de Melo escreveu:
> 
> I'll collect those, but only after addressing these:
> 
> [perfbuilder@...e ~]$ export BUILD_TARBALL=http://192.168.86.5/perf/perf-6.6.0-rc1.tar.xz
> [perfbuilder@...e ~]$ time dm
>    1   100.09 almalinux:8                   : FAIL clang version 15.0.7 (Red Hat 15.0.7-1.module_el8.8.0+3466+dfcbc058)
>     util/parse-events.c:1461:6: error: variable 'alias_rewrote_terms' is used uninitialized whenever '&&' condition is false [-Werror,-Wsometimes-uninitialized]
>             if (!parse_state->fake_pmu && perf_pmu__check_alias(pmu, &parsed_terms,
>                 ^~~~~~~~~~~~~~~~~~~~~~
>     util/parse-events.c:1477:6: note: uninitialized use occurs here
>             if (alias_rewrote_terms &&
>                 ^~~~~~~~~~~~~~~~~~~
>     util/parse-events.c:1461:6: note: remove the '&&' if its condition is always true
>             if (!parse_state->fake_pmu && perf_pmu__check_alias(pmu, &parsed_terms,
>                 ^~~~~~~~~~~~~~~~~~~~~~~~~
>     util/parse-events.c:1401:26: note: initialize the variable 'alias_rewrote_terms' to silence this warning
>             bool alias_rewrote_terms;
>                                     ^
>                                      = false
>     1 error generated.
>     make[3]: *** [/git/perf-6.6.0-rc1/tools/build/Makefile.build:158: util] Error 2

It built well with gcc but clang didn't notice that
perf_pmu__check_alias() unconditionally initializes that variable to
false as one of its first steps.

So I just did what clang suggested.

- Arnaldo