perf ftrace: Fix undefined behavior in cmp_profile_data()

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
Fixes: 0f223813edd0 ("perf ftrace: Add 'profile' command")
Fixes: 74ae366c37b7 ("perf ftrace profile: Add -s/--sort option")
Cc: stable@vger.kernel.org
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Reviewed-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: jserv@ccns.ncku.edu.tw
Cc: chuang@cs.nycu.edu.tw
Link: https://lore.kernel.org/r/20241209134226.1939163-1-visitorckw@gmail.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index 272d3c70810e7dc34c78c202b9e005384927955c..a56cf8b0a7d405d2dbec29ef0a5abd3ccf2c2511 100644 (file)
--- 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)