[PATCH] perf annotate: Fix Clang build by adding block in switch case

[PATCH] perf annotate: Fix Clang build by adding block in switch case

[James Clark]

Clang and GCC disagree with what constitutes a "declaration after
statement". GCC allows declarations in switch cases without an extra
block, as long as it's immediately after the label. Clang does not.
Unfortunately this is the case even in the latest versions of both
compilers. The only option that makes them behave in the same way is
-Wpedantic, which can't be enabled in Perf because of the number of
warnings it generates.

Add a block to fix the Clang build, which is the only thing we can do.

Fixes the build error:

  ui/browsers/annotate.c:999:4: error: expected expression
  struct annotation_line *al = NULL;

  ui/browsers/annotate.c:1008:4: error: use of undeclared identifier 'al'
  al = annotated_source__get_line(notes->src, offset);

  ui/browsers/annotate.c:1009:24: error: use of undeclared identifier 'al'
  browser->curr_hot = al ? &al->rb_node : NULL;

  ui/browsers/annotate.c:1009:30: error: use of undeclared identifier 'al'
  browser->curr_hot = al ? &al->rb_node : NULL;

  ui/browsers/annotate.c:1000:8: error: mixing declarations and code is incompatible with standards before C99 [-Werror,-Wdeclaration-after-statement]
  s64 offset = annotate_browser__curr_hot_offset(browser);

Fixes: ad83f3b7155d ("perf c2c annotate: Start from the contention line")
Signed-off-by: James Clark <james.clark@linaro.org>
---
 tools/perf/ui/browsers/annotate.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/ui/browsers/annotate.c b/tools/perf/ui/browsers/annotate.c
index 3a81912279ad..36aca8d6d003 100644
--- a/tools/perf/ui/browsers/annotate.c
+++ b/tools/perf/ui/browsers/annotate.c
@@ -995,7 +995,7 @@ static int annotate_browser__run(struct annotate_browser *browser,
 		case 'H':
 			nd = browser->curr_hot;
 			break;
-		case 's':
+		case 's': {
 			struct annotation_line *al = NULL;
 			s64 offset = annotate_browser__curr_hot_offset(browser);
 
@@ -1012,6 +1012,7 @@ static int annotate_browser__run(struct annotate_browser *browser,
 			annotate__scnprintf_title(hists, title, sizeof(title));
 			annotate_browser__show(browser, title, help);
 			continue;
+		}
 		case 'o':
 			annotate_opts.use_offset = !annotate_opts.use_offset;
 			annotation__update_column_widths(notes);
-- 
2.34.1

Re: [PATCH] perf annotate: Fix Clang build by adding block in switch case

[Ian Rogers]

On Wed, Oct 22, 2025 at 4:03 AM James Clark <james.clark@linaro.org> wrote:
>
> Clang and GCC disagree with what constitutes a "declaration after
> statement". GCC allows declarations in switch cases without an extra
> block, as long as it's immediately after the label. Clang does not.
> Unfortunately this is the case even in the latest versions of both
> compilers. The only option that makes them behave in the same way is
> -Wpedantic, which can't be enabled in Perf because of the number of
> warnings it generates.
>
> Add a block to fix the Clang build, which is the only thing we can do.
>
> Fixes the build error:
>
>   ui/browsers/annotate.c:999:4: error: expected expression
>   struct annotation_line *al = NULL;
>
>   ui/browsers/annotate.c:1008:4: error: use of undeclared identifier 'al'
>   al = annotated_source__get_line(notes->src, offset);
>
>   ui/browsers/annotate.c:1009:24: error: use of undeclared identifier 'al'
>   browser->curr_hot = al ? &al->rb_node : NULL;
>
>   ui/browsers/annotate.c:1009:30: error: use of undeclared identifier 'al'
>   browser->curr_hot = al ? &al->rb_node : NULL;
>
>   ui/browsers/annotate.c:1000:8: error: mixing declarations and code is incompatible with standards before C99 [-Werror,-Wdeclaration-after-statement]
>   s64 offset = annotate_browser__curr_hot_offset(browser);
>
> Fixes: ad83f3b7155d ("perf c2c annotate: Start from the contention line")
> Signed-off-by: James Clark <james.clark@linaro.org>

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

Thanks,
Ian

> ---
>  tools/perf/ui/browsers/annotate.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/ui/browsers/annotate.c b/tools/perf/ui/browsers/annotate.c
> index 3a81912279ad..36aca8d6d003 100644
> --- a/tools/perf/ui/browsers/annotate.c
> +++ b/tools/perf/ui/browsers/annotate.c
> @@ -995,7 +995,7 @@ static int annotate_browser__run(struct annotate_browser *browser,
>                 case 'H':
>                         nd = browser->curr_hot;
>                         break;
> -               case 's':
> +               case 's': {
>                         struct annotation_line *al = NULL;
>                         s64 offset = annotate_browser__curr_hot_offset(browser);
>
> @@ -1012,6 +1012,7 @@ static int annotate_browser__run(struct annotate_browser *browser,
>                         annotate__scnprintf_title(hists, title, sizeof(title));
>                         annotate_browser__show(browser, title, help);
>                         continue;
> +               }
>                 case 'o':
>                         annotate_opts.use_offset = !annotate_opts.use_offset;
>                         annotation__update_column_widths(notes);
> --
> 2.34.1
>

Re: [PATCH] perf annotate: Fix Clang build by adding block in switch case

[Namhyung Kim]

On Wed, 22 Oct 2025 12:02:40 +0100, James Clark wrote:
> Clang and GCC disagree with what constitutes a "declaration after
> statement". GCC allows declarations in switch cases without an extra
> block, as long as it's immediately after the label. Clang does not.
> Unfortunately this is the case even in the latest versions of both
> compilers. The only option that makes them behave in the same way is
> -Wpedantic, which can't be enabled in Perf because of the number of
> warnings it generates.
> 
> [...]
Applied to perf-tools-next, thanks!

Best regards,
Namhyung