Re: [PATCH v1] perf trace: Fix possible insufficient allocation of argument formats

[Namhyung Kim <namhyung@kernel.org>]

On Wed, Mar 26, 2025 at 11:30:11AM -0700, Howard Chu wrote:
> Hello Namhyung,
> 
> LGTM. This is better. :)

Great, can you please resend it with my Suggested-by?

Thanks,
Namhyung

> 
> On Wed, Mar 26, 2025 at 11:21 AM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > On Mon, Mar 24, 2025 at 04:52:45PM -0700, Howard Chu wrote:
> > > In my previous fix of runtime error(Link:
> > > https://lore.kernel.org/linux-perf-users/20250122025519.361873-1-howardchu95@gmail.com/),
> > > I made a mistake of decrementing one unconditionally, regardless of
> > > whether an extra 'syscall_nr' or 'nr' field was present in
> > > libtraceevent's tp_format. This may cause perf trace to allocate one
> > > fewer arg_fmt entry than needed for the accurate representation of syscall
> > > arguments.
> > >
> > > This patch corrects the mistake by checking the presence of'syscall_nr' or
> > > 'nr', and adjusting the length of arg_fmt[] accordingly.
> >
> > Thanks for the fix.  I've noticed this too but I feel like we can make
> > syscall__alloc_arg_fmts() a bit simpler.
> >
> > How about this?
> >
> > Thanks,
> > Namhyung
> >
> >
> > ---8<---
> > diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> > index 6ac51925ea4249c2..b9bdab52f5801c3a 100644
> > --- a/tools/perf/builtin-trace.c
> > +++ b/tools/perf/builtin-trace.c
> > @@ -2022,9 +2022,6 @@ static int syscall__alloc_arg_fmts(struct syscall *sc, int nr_args)
> >  {
> >         int idx;
> >
> > -       if (nr_args == RAW_SYSCALL_ARGS_NUM && sc->fmt && sc->fmt->nr_args != 0)
> > -               nr_args = sc->fmt->nr_args;
> > -
> >         sc->arg_fmt = calloc(nr_args, sizeof(*sc->arg_fmt));
> >         if (sc->arg_fmt == NULL)
> >                 return -1;
> > @@ -2034,7 +2031,6 @@ static int syscall__alloc_arg_fmts(struct syscall *sc, int nr_args)
> >                         sc->arg_fmt[idx] = sc->fmt->arg[idx];
> >         }
> >
> > -       sc->nr_args = nr_args;
> >         return 0;
> >  }
> >
> > @@ -2176,14 +2172,9 @@ static int syscall__read_info(struct syscall *sc, struct trace *trace)
> >                 return err;
> >         }
> >
> > -       /*
> > -        * The tracepoint format contains __syscall_nr field, so it's one more
> > -        * than the actual number of syscall arguments.
> > -        */
> > -       if (syscall__alloc_arg_fmts(sc, sc->tp_format->format.nr_fields - 1))
> > -               return -ENOMEM;
> > -
> >         sc->args = sc->tp_format->format.fields;
> > +       sc->nr_args = sc->tp_format->format.nr_fields;
> > +
> >         /*
> >          * We need to check and discard the first variable '__syscall_nr'
> >          * or 'nr' that mean the syscall number. It is needless here.
> > @@ -2194,6 +2185,9 @@ static int syscall__read_info(struct syscall *sc, struct trace *trace)
> >                 --sc->nr_args;
> >         }
> >
> > +       if (syscall__alloc_arg_fmts(sc, sc->nr_args))
> > +               return -ENOMEM;
> > +
> >         sc->is_exit = !strcmp(name, "exit_group") || !strcmp(name, "exit");
> >         sc->is_open = !strcmp(name, "open") || !strcmp(name, "openat");
> >
> > --
> > 2.49.0.395.g12beb8f557-goog
> >