perf tools: Avoid unaligned pointer operations

The sample data is 64-bit aligned basically but raw data starts with
32-bit length field and data follows.  In perf_event__synthesize_sample
it treats the sample data as a 64-bit array.  And it needs some trick
to update the raw data properly.

But it seems some compilers are not happy with this and the program dies
siliently.  I found the sample parsing test failed without any messages
on affected systems.

Let's update the code to use a 32-bit pointer directly and make sure the
result is 64-bit aligned again.  No functional changes intended.

Reviewed-by: Ian Rogers <irogers@google.com>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241128010325.946897-1-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index a58444c4aed1f1eaf9f3d27dc28e3113942920ac..6923b0d5efede4a737202b37075172f51b5e4a68 100644 (file)
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -1686,12 +1686,16 @@ int perf_event__synthesize_sample(union perf_event *event, u64 type, u64 read_fo
        }
 
        if (type & PERF_SAMPLE_RAW) {
-               u.val32[0] = sample->raw_size;
-               *array = u.val64;
-               array = (void *)array + sizeof(u32);
+               u32 *array32 = (void *)array;
+
+               *array32 = sample->raw_size;
+               array32++;
+
+               memcpy(array32, sample->raw_data, sample->raw_size);
+               array = (void *)(array32 + (sample->raw_size / sizeof(u32)));
 
-               memcpy(array, sample->raw_data, sample->raw_size);
-               array = (void *)array + sample->raw_size;
+               /* make sure the array is 64-bit aligned */
+               BUG_ON(((long)array) % sizeof(u64));
        }
 
        if (type & PERF_SAMPLE_BRANCH_STACK) {