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

[Ian Rogers]

On Wed, Oct 16, 2024 at 5:30 AM Athira Rajeev
<atrajeev at linux.vnet.ibm.com> wrote:
>
>
>
> > On 14 Oct 2024, at 10:56 PM, Namhyung Kim <namhyung at kernel.org> wrote:
> >
> > 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
> >
>
> Sure
>
> Thanks Namhyung for pulling in the change
>
> Athira

Thanks for the fixes. As this is test code I don't think performance,
style, etc. matter much. The GCC strncpy warnings are annoying imo,
I'm not sure it makes sense for them to be enabled. I see in the
kernel lots of "sizeof(foo)-1" as a workaround. strlcpy looks like a
better alternative but it gets a checkpatch warning as in the kernel
strscpy is preferred. Perhaps we should create a strscpy shim.

Thanks,
Ian

> >> ---
> >> 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
>
>