On Wed, Oct 16, 2024 at 11:23 AM Athira Rajeev <[email protected]> wrote: > > > > > On 16 Oct 2024, at 8:36 PM, Ian Rogers <[email protected]> wrote: > > > > On Wed, Oct 16, 2024 at 5:30 AM Athira Rajeev > > <[email protected]> wrote: > >> > >> > >> > >>> On 14 Oct 2024, at 10:56 PM, Namhyung Kim <[email protected]> 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 <[email protected]> > >>> > >>> 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. > > > > IIUC, strscpy is defined in kernel source and is currently not used in tools > side. > > Ian, > Your point here is that we can create an interface in tools side so that we > can later safely use strscpy in cases like this ?
Yeah. Tbh the string code is a bit chaotic in the code base. There's some stuff using char*s, some asprintf, there's strbuf then there all the kernel ways of doing things. I lose track of why strscpy is superior to strlcpy, but strlcpy will get you a checkpath warning. The standard kernel solution to the GCC strncpy warning I've seen, changing "strncpy(a, b, sizeof(a))" to "strncpy(a, b, sizeof(a) - 1)", looks dodgy and possibly worse to me. The point of the warning I think relates to strncpy not necessarily \0 terminating the string and you need to reserve at least 1 character for this, while strlcpy guarantees the \0 termination. Doing "sizeof(..) - 1" likely confuses the checker making it give up, but now you have less space to copy a potential \0 as well as not getting a \0. Thanks, Ian > Thanks > Athira > > > 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 > >
