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 16:52:28 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Ian Rogers <irogers@...gle.com>
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 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>
---
 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