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

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

[Arnaldo Carvalho de Melo]

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@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.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

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

[Namhyung Kim]

On Wed, Dec 03, 2025 at 06:20:08PM -0300, Arnaldo Carvalho de Melo wrote:
> 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).

Something like this?

Thanks,
Namhyung


diff --git a/tools/lib/perf/include/perf/core.h b/tools/lib/perf/include/perf/core.h
index a3f6d68edad76240..06cc132d88cf3436 100644
--- a/tools/lib/perf/include/perf/core.h
+++ b/tools/lib/perf/include/perf/core.h
@@ -5,7 +5,7 @@
 #include <stdarg.h>
 
 #ifndef LIBPERF_API
-#define LIBPERF_API __attribute__((visibility("default")))
+#define LIBPERF_API extern __attribute__((visibility("default")))
 #endif
 
 enum libperf_print_level {

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

[Arnaldo Melo]

On December 4, 2025 5:41:51 AM GMT-03:00, Namhyung Kim <namhyung@kernel.org> wrote:
>On Wed, Dec 03, 2025 at 06:20:08PM -0300, Arnaldo Carvalho de Melo wrote:
>> 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).
>
>Something like this?

Yeah, I probably got carried away with libbpf's accidental way of "dealing" with it.

Will test build it, or have you already?

- Arnaldo

>
>Thanks,
>Namhyung
>
>
>diff --git a/tools/lib/perf/include/perf/core.h b/tools/lib/perf/include/perf/core.h
>index a3f6d68edad76240..06cc132d88cf3436 100644
>--- a/tools/lib/perf/include/perf/core.h
>+++ b/tools/lib/perf/include/perf/core.h
>@@ -5,7 +5,7 @@
> #include <stdarg.h>
> 
> #ifndef LIBPERF_API
>-#define LIBPERF_API __attribute__((visibility("default")))
>+#define LIBPERF_API extern __attribute__((visibility("default")))
> #endif
> 
> enum libperf_print_level {

- Arnaldo