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SubjectRe: [PATCH v2] perf trace: Fix SIGSEGV when processing syscall args
Hello,

On Thu, Jul 7, 2022 at 2:09 AM Naveen N. Rao
<naveen.n.rao@linux.vnet.ibm.com> wrote:
>
> On powerpc, 'perf trace' is crashing with a SIGSEGV when trying to
> process a perf.data file created with 'perf trace record -p':
>
> #0 0x00000001225b8988 in syscall_arg__scnprintf_augmented_string <snip> at builtin-trace.c:1492
> #1 syscall_arg__scnprintf_filename <snip> at builtin-trace.c:1492
> #2 syscall_arg__scnprintf_filename <snip> at builtin-trace.c:1486
> #3 0x00000001225bdd9c in syscall_arg_fmt__scnprintf_val <snip> at builtin-trace.c:1973
> #4 syscall__scnprintf_args <snip> at builtin-trace.c:2041
> #5 0x00000001225bff04 in trace__sys_enter <snip> at builtin-trace.c:2319
>
> That points to the below code in tools/perf/builtin-trace.c:
> /*
> * If this is raw_syscalls.sys_enter, then it always comes with the 6 possible
> * arguments, even if the syscall being handled, say "openat", uses only 4 arguments
> * this breaks syscall__augmented_args() check for augmented args, as we calculate
> * syscall->args_size using each syscalls:sys_enter_NAME tracefs format file,
> * so when handling, say the openat syscall, we end up getting 6 args for the
> * raw_syscalls:sys_enter event, when we expected just 4, we end up mistakenly
> * thinking that the extra 2 u64 args are the augmented filename, so just check
> * here and avoid using augmented syscalls when the evsel is the raw_syscalls one.
> */
> if (evsel != trace->syscalls.events.sys_enter)
> augmented_args = syscall__augmented_args(sc, sample, &augmented_args_size, trace->raw_augmented_syscalls_args_size);
>
> As the comment points out, we should not be trying to augment the args
> for raw_syscalls. However, when processing a perf.data file, we are not
> initializing those properly. Fix the same.
>
> Reported-by: Claudio Carvalho <cclaudio@linux.ibm.com>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
> tools/perf/builtin-trace.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index 897fc504918b91..f075cf37a65ef8 100644
> --- a/tools/perf/builtin-trace.c
> +++ b/tools/perf/builtin-trace.c
> @@ -4280,6 +4280,7 @@ static int trace__replay(struct trace *trace)
> goto out;
>
> evsel = evlist__find_tracepoint_by_name(session->evlist, "raw_syscalls:sys_enter");
> + trace->syscalls.events.sys_enter = evsel;
> /* older kernels have syscalls tp versus raw_syscalls */

Isn't it better to set it after the NULL check below?

> if (evsel == NULL)
> evsel = evlist__find_tracepoint_by_name(session->evlist, "syscalls:sys_enter");
> @@ -4292,6 +4293,7 @@ static int trace__replay(struct trace *trace)
> }
>
> evsel = evlist__find_tracepoint_by_name(session->evlist, "raw_syscalls:sys_exit");
> + trace->syscalls.events.sys_exit = evsel;

Ditto.

Thanks,
Namhyung


> if (evsel == NULL)
> evsel = evlist__find_tracepoint_by_name(session->evlist, "syscalls:sys_exit");
> if (evsel &&
>
> base-commit: 52f28b7bac75da9b8508f17438c9a8d83ab48e5d
> --
> 2.36.1
>

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