Hello, On Mon, Dec 9, 2024 at 5:42 AM Kuan-Wei Chiu <visitorckw@xxxxxxxxx> wrote: > > The comparison function cmp_profile_data() violates the C standard's > requirements for qsort() comparison functions, which mandate symmetry > and transitivity: > > * Symmetry: If x < y, then y > x. > * Transitivity: If x < y and y < z, then x < z. > > When v1 and v2 are equal, the function incorrectly returns 1, breaking > symmetry and transitivity. This causes undefined behavior, which can > lead to memory corruption in certain versions of glibc [1]. > > Fix the issue by returning 0 when v1 and v2 are equal, ensuring > compliance with the C standard and preventing undefined behavior. > > Link: https://www.qualys.com/2024/01/30/qsort.txt [1] > Fixes: 0f223813edd0 ("perf ftrace: Add 'profile' command") > Fixes: 74ae366c37b7 ("perf ftrace profile: Add -s/--sort option") > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Kuan-Wei Chiu <visitorckw@xxxxxxxxx> Reviewed-by: Namhyung Kim <namhyung@xxxxxxxxxx> Thanks for the fix. Namhyung > --- > tools/perf/builtin-ftrace.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c > index 272d3c70810e..a56cf8b0a7d4 100644 > --- a/tools/perf/builtin-ftrace.c > +++ b/tools/perf/builtin-ftrace.c > @@ -1151,8 +1151,9 @@ static int cmp_profile_data(const void *a, const void *b) > > if (v1 > v2) > return -1; > - else > + if (v1 < v2) > return 1; > + return 0; > } > > static void print_profile_result(struct perf_ftrace *ftrace) > -- > 2.34.1 >
