linux-kernel - [PATCH v6.19-rc1 1/1] libperf: Compile using -std=gnu17 to deal with visibility attribute issues

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Message-ID: <aTCpiDG6WOzMv7ji@x1>
Date: Wed, 3 Dec 2025 18:20:08 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Adrian Hunter <adrian.hunter@...el.com>,
	Ian Rogers <irogers@...gle.com>,
	James Clark <james.clark@...aro.org>, Jiri Olsa <jolsa@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org
Subject: [PATCH v6.19-rc1 1/1] libperf: Compile using -std=gnu17 to deal with
 visibility attribute issues

We seem to need a more invasive patch using 'extern' on all LIBPERF_API
prefixed functions to be future proof, so use -std=gnu17 which is the
one in gcc 14, present in the distro generation before ubuntu 25.10 (gcc
15).

But to make progress and avoid this on Ubuntu 25.10/gcc 15, lets to with
the easy workaround:

  evlist.c: In function 'perf_evlist__purge':
  evlist.c:202:17: error: implicit declaration of function 'perf_evsel__delete'; did you mean 'perf_evsel__exit'? [-Wimplicit-function-declaration]
    202 |                 perf_evsel__delete(pos);
        |                 ^~~~~~~~~~~~~~~~~~
        |                 perf_evsel__exit
  evlist.c:202:17: error: nested extern declaration of 'perf_evsel__delete' [-Werror=nested-externs]
  evlist.c: In function 'perf_evlist__open':
  evlist.c:261:23: error: implicit declaration of function 'perf_evsel__open'; did you mean 'perf_evsel__exit'? [-Wimplicit-function-declaration]
    261 |                 err = perf_evsel__open(evsel, evsel->cpus, evsel->threads);
        |                       ^~~~~~~~~~~~~~~~
        |                       perf_evsel__exit
  evlist.c:261:23: error: nested extern declaration of 'perf_evsel__open' [-Werror=nested-externs]

libbpf doesn't experience this because for some other reason it already
has this line:

  override CFLAGS += -std=gnu89

Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Ian Rogers <irogers@...gle.com>
Cc: James Clark <james.clark@...aro.org>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/lib/perf/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/lib/perf/Makefile b/tools/lib/perf/Makefile
index 7fbb50b74c00b3b9..5e12fd97f50c1efb 100644
--- a/tools/lib/perf/Makefile
+++ b/tools/lib/perf/Makefile
@@ -51,6 +51,7 @@ INCLUDES = \
 -I$(srctree)/tools/include/uapi
 
 # Append required CFLAGS
+override CFLAGS += -std=gnu17
 override CFLAGS += -g -Werror -Wall
 override CFLAGS += -fPIC
 override CFLAGS += $(INCLUDES)
-- 
2.52.0