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

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Date:   Wed, 16 Mar 2022 17:36:57 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     cclaudio@...ux.ibm.com, Jiri Olsa <jolsa@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH] perf trace: Fix SIGSEGV when processing augmented args

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.

- Arnaldo