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 13:15:22 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Ian Rogers <irogers@...gle.com>, 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 12:52 PM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> On Wed, Apr 03, 2024 at 09:01:56AM -0700, Ian Rogers wrote:
> > 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>
>
> Trying with this on top, i.e. what you suggests:
>
> From 70e6fd996ce7f9c9adbb30640ed666025bf6f1e4 Mon Sep 17 00:00:00 2001
> From: Arnaldo Carvalho de Melo <acme@...hat.com>
> Date: Wed, 3 Apr 2024 16:49:54 -0300
> Subject: [PATCH 1/1] WIP
>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>

Acked-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung


> ---
>  tools/perf/util/annotate.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
> index f316e0b65897957a..35235147b111e788 100644
> --- a/tools/perf/util/annotate.c
> +++ b/tools/perf/util/annotate.c
> @@ -838,8 +838,10 @@ static int evsel__get_arch(struct evsel *evsel, struct arch **parch)
>         struct arch *arch;
>         int err;
>
> -       if (!arch_name)
> +       if (!arch_name) {
> +               *parch = NULL;
>                 return errno;
> +       }
>
>         *parch = arch = arch__find(arch_name);
>         if (arch == NULL) {
> @@ -2266,7 +2268,7 @@ 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 = NULL;
> +       struct arch *arch;
>         struct disasm_line *dl;
>         struct annotated_insn_loc loc;
>         struct annotated_op_loc *op_loc;
> --
> 2.44.0
>