Some version of compilers reported unaligned accesses in perf trace when undefined-behavior sanitizer is on. I found that it uses raw data in the sample directly and assuming it's properly aligned. Unlike other sample fields, the raw data is not 8-byte aligned because there's a size field (u32) before the actual data. So I added a static buffer in syscall__augmented_args() and return it instead. This is not ideal but should work well as perf trace is single-threaded. A better approach would be aligning the raw data by adding a 4-byte data before the augmented args but I'm afraid it'd break the backward compatibility. Closes: https://lore.kernel.org/r/Z2STgyD1p456Qqhg@xxxxxxxxxx Cc: Howard Chu <howardchu95@xxxxxxxxx> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx> --- tools/perf/builtin-trace.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c index e70e634fbfaf33f5..3f06411514c5b58a 100644 --- a/tools/perf/builtin-trace.c +++ b/tools/perf/builtin-trace.c @@ -2582,7 +2582,6 @@ static int trace__fprintf_sample(struct trace *trace, struct evsel *evsel, static void *syscall__augmented_args(struct syscall *sc, struct perf_sample *sample, int *augmented_args_size, int raw_augmented_args_size) { - void *augmented_args = NULL; /* * For now with BPF raw_augmented we hook into raw_syscalls:sys_enter * and there we get all 6 syscall args plus the tracepoint common fields @@ -2600,10 +2599,24 @@ static void *syscall__augmented_args(struct syscall *sc, struct perf_sample *sam int args_size = raw_augmented_args_size ?: sc->args_size; *augmented_args_size = sample->raw_size - args_size; - if (*augmented_args_size > 0) - augmented_args = sample->raw_data + args_size; + if (*augmented_args_size > 0) { + static uintptr_t argbuf[1024]; /* assuming single-threaded */ + + if ((size_t)(*augmented_args_size) > sizeof(argbuf)) + return NULL; + + /* + * The perf ring-buffer is 8-byte aligned but sample->raw_data + * is not because it's preceded by u32 size. Later, beautifier + * will use the augmented args with stricter alignments like in + * some struct. To make sure it's aligned, let's copy the args + * into a static buffer as it's single-threaded for now. + */ + memcpy(argbuf, sample->raw_data + args_size, *augmented_args_size); - return augmented_args; + return argbuf; + } + return NULL; } static void syscall__exit(struct syscall *sc) -- 2.47.1.613.gc27f4b7a9f-goog
