Re: [PATCH] perf trace: Fix SIGSEGV when processing augmented args

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

Hi Arnaldo,

Arnaldo Carvalho de Melo wrote:
> Em Tue, Mar 15, 2022 at 02:52:05PM -0300, Arnaldo Carvalho de Melo escreveu:
>> Em Tue, Mar 15, 2022 at 10:57:57PM +0530, Naveen N. Rao escreveu:
>> > Yes, it looks like the current check in 'perf' isn't working. The below
>> > patch also resolves the crash we are seeing:
>>  
>> > diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
>> > index 2f1d20553a0aa3..86b459f4ebdd61 100644
>> > --- a/tools/perf/builtin-trace.c
>> > +++ b/tools/perf/builtin-trace.c
>> > @@ -2326,7 +2326,7 @@ static int trace__sys_enter(struct trace *trace, struct evsel *evsel,
>> >         * 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)
>> > +       if (strcmp(evsel__name(evsel), "raw_syscalls:sys_enter"))
>> >                augmented_args = syscall__augmented_args(sc, sample, &augmented_args_size, trace->raw_augmented_syscalls_args_size);
>> >        ttrace->entry_time = sample->time;
>> >        msg = ttrace->entry_str;
>> 
>> Interesting, that should be equivalent :-\ humm, not really, understood,
>> when processing perf.data files we don't setup
>> trace->syscalls.events.sys_enter...
>> 
>> switching from strcmp() to something cheaper but equivalent should be
>> the fix for now.
> 
> I'll add a trace->use_augmented_args boolean that will do this test
> once, and then use it in this case and will audit to check if this
> should be used in other places.

Does something like the below look reasonable?

I know this isn't quite what you proposed, but it fixes the problem for 
me while avoiding the need for a string comparison. I also think this 
addresses all uses in 'perf trace', though I didn't audit the need for a 
similar fix elsewhere in 'perf'.


Thanks,
Naveen

---
diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index d2de2a4073e7eb..352b88a51dec2d 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -4291,6 +4292,8 @@ static int trace__replay(struct trace *trace)
                goto out;
        }
 
+       trace->syscalls.events.sys_enter = evsel;
+
        evsel = evlist__find_tracepoint_by_name(session->evlist, "raw_syscalls:sys_exit");
        if (evsel == NULL)
                evsel = evlist__find_tracepoint_by_name(session->evlist, "syscalls:sys_exit");
@@ -4301,6 +4304,8 @@ static int trace__replay(struct trace *trace)
                goto out;
        }
 
+       trace->syscalls.events.sys_exit  = evsel;
+
        evlist__for_each_entry(session->evlist, evsel) {
                if (evsel->core.attr.type == PERF_TYPE_SOFTWARE &&
                    (evsel->core.attr.config == PERF_COUNT_SW_PAGE_FAULTS_MAJ ||