[PATCH] tools/perf/tests: Fix compilation error with strncpy in tests/tool_pmu

[Namhyung Kim]

Hello Athira,

On Sun, Oct 13, 2024 at 11:07:42PM +0530, Athira Rajeev wrote:
> perf fails to compile on systems with GCC version11
> as below:
> 
> In file included from /usr/include/string.h:519,
>                  from /home/athir/perf-tools-next/tools/include/linux/bitmap.h:5,
>                  from /home/athir/perf-tools-next/tools/perf/util/pmu.h:5,
>                  from /home/athir/perf-tools-next/tools/perf/util/evsel.h:14,
>                  from /home/athir/perf-tools-next/tools/perf/util/evlist.h:14,
>                  from tests/tool_pmu.c:3:
> In function ‘strncpy’,
>     inlined from ‘do_test’ at tests/tool_pmu.c:25:3:
> /usr/include/bits/string_fortified.h:95:10: error: ‘__builtin_strncpy’ specified bound 128 equals destination size [-Werror=stringop-truncation]
>    95 |   return __builtin___strncpy_chk (__dest, __src, __len,
>       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    96 |                                   __glibc_objsize (__dest));
>       |                                   ~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> The compile error is from strncpy refernce in do_test:
> 	strncpy(str, tool_pmu__event_to_str(ev), sizeof(str));
> 
> This behaviour is not observed with GCC version 8, but observed
> with GCC version 11 . This is message from gcc for detecting
> truncation while using strncpu. Use snprintf instead of strncpy
> here to be safe.
> 
> Signed-off-by: Athira Rajeev <atrajeev at linux.vnet.ibm.com>

I found this issue now and thanks for the quick fix.  I will push to
perf-tools-next soon.

Thanks,
Namhyung

> ---
>  tools/perf/tests/tool_pmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/tests/tool_pmu.c b/tools/perf/tests/tool_pmu.c
> index 94d0dd8fd3cb..297cc8c55579 100644
> --- a/tools/perf/tests/tool_pmu.c
> +++ b/tools/perf/tests/tool_pmu.c
> @@ -22,7 +22,7 @@ static int do_test(enum tool_pmu_event ev, bool with_pmu)
>  	if (with_pmu)
>  		snprintf(str, sizeof(str), "tool/%s/", tool_pmu__event_to_str(ev));
>  	else
> -		strncpy(str, tool_pmu__event_to_str(ev), sizeof(str));
> +		snprintf(str, sizeof(str), "%s", tool_pmu__event_to_str(ev));
>  
>  	parse_events_error__init(&err);
>  	ret = parse_events(evlist, str, &err);
> -- 
> 2.43.5
>