linux-kernel - Re: [PATCH 1/1] perf annotate: Initialize 'arch' variable not to trip some -Werror=maybe-uninitialized

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Date: Wed, 3 Apr 2024 09:01:56 -0700
From: Ian Rogers <irogers@...gle.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>, 
	Jiri Olsa <jolsa@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] perf annotate: Initialize 'arch' variable not to trip
 some -Werror=maybe-uninitialized

On Wed, Apr 3, 2024 at 8:16 AM Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
>
> In some older distros the build is failing due to
> -Werror=maybe-uninitialized, in this case we know that this isn't the
> case because 'arch' gets initialized by evsel__get_arch(), so just init
> it to NULL to silence those cases.
>
> E.g.:
>
>     32    17.12 opensuse:15.5                 : FAIL gcc version 7.5.0 (SUSE Linux)
>         util/annotate.c: In function 'hist_entry__get_data_type':
>     util/annotate.c:2269:15: error: 'arch' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>       struct arch *arch;
>                    ^~~~
>     cc1: all warnings being treated as errors
>
>       43     7.30 ubuntu:18.04-x-powerpc64el    : FAIL gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)
>     util/annotate.c: In function 'hist_entry__get_data_type':
>     util/annotate.c:2351:36: error: 'arch' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>        if (map__dso(ms->map)->kernel && arch__is(arch, "x86") &&
>                                         ^~~~~~~~~~~~~~~~~~~~~
>     cc1: all warnings being treated as errors
>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: Ian Rogers <irogers@...gle.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>

This looks fine but I couldn't line up the errors with code in the
tree. I was curious why the "maybe-uninitialized" was failing. Perhaps
evsel__get_arch should set the out argument to NULL when an error
occurs. This fix is also good but may potentially need repeating for
other evsel__get_arch cases, so a fix in evsel__get_arch may be
preferable.

Reviewed-by: Ian Rogers <irogers@...gle.com>

Thanks,
Ian

> ---
>  tools/perf/util/annotate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
> index b795f27f26024f35..f316e0b65897957a 100644
> --- a/tools/perf/util/annotate.c
> +++ b/tools/perf/util/annotate.c
> @@ -2266,7 +2266,7 @@ struct annotated_data_type *hist_entry__get_data_type(struct hist_entry *he)
>  {
>         struct map_symbol *ms = &he->ms;
>         struct evsel *evsel = hists_to_evsel(he->hists);
> -       struct arch *arch;
> +       struct arch *arch = NULL;
>         struct disasm_line *dl;
>         struct annotated_insn_loc loc;
>         struct annotated_op_loc *op_loc;
> --
> 2.44.0
>