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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 24 Jul 2023 14:01:46 -0700
Message-ID: <CAKwvOdkkfkoOE7G__gJ1cQq5i2o4bauk7pqudb3vd2R7sneoYg@mail.gmail.com>
Subject: Re: [PATCH v1 2/4] perf parse-events: Avoid use uninitialized warning
To:     Ian Rogers <irogers@google.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        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>,
        Tom Rix <trix@redhat.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Yang Jihong <yangjihong1@huawei.com>,
        Ravi Bangoria <ravi.bangoria@amd.com>,
        Carsten Haitzler <carsten.haitzler@arm.com>,
        Zhengjun Xing <zhengjun.xing@linux.intel.com>,
        James Clark <james.clark@arm.com>,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        bpf@vger.kernel.org, llvm@lists.linux.dev, maskray@google.com
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On Mon, Jul 24, 2023 at 1:13=E2=80=AFPM Ian Rogers <irogers@google.com> wro=
te:
>
> With GCC LTO a potential use uninitialized is spotted:
> ```
> In function =E2=80=98parse_events_config_bpf=E2=80=99,
>     inlined from =E2=80=98parse_events_load_bpf=E2=80=99 at util/parse-ev=
ents.c:874:8:
> util/parse-events.c:792:37: error: =E2=80=98error_pos=E2=80=99 may be use=
d uninitialized [-Werror=3Dmaybe-uninitialized]
>   792 |                                 idx =3D term->err_term + error_po=
s;
>       |                                     ^
> util/parse-events.c: In function =E2=80=98parse_events_load_bpf=E2=80=99:
> util/parse-events.c:765:13: note: =E2=80=98error_pos=E2=80=99 was declare=
d here
>   765 |         int error_pos;
>       |             ^
> ```
> So initialize at declaration.

This common pattern in C is error prone (conditional assignment in the
callee; callers maybe forget to initialize, then unconditionally use
the value). Clang's static analyzer can spot these, but isn't run for
tools/ AFAIK.

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

>
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/perf/util/parse-events.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-event=
s.c
> index acde097e327c..da29061ecf49 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -762,7 +762,7 @@ parse_events_config_bpf(struct parse_events_state *pa=
rse_state,
>                         struct list_head *head_config)
>  {
>         struct parse_events_term *term;
> -       int error_pos;
> +       int error_pos =3D 0;
>
>         if (!head_config || list_empty(head_config))
>                 return 0;
> --
> 2.41.0.487.g6d72f3e995-goog
>


--=20
Thanks,
~Nick Desaulniers