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

[Howard Chu]

Hello Namhyung,

LGTM. This is better. :)

Thanks,
Howard

On Wed, Mar 26, 2025 at 11:21 AM Namhyung Kim <namhyung@xxxxxxxxxx> 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@xxxxxxxxx/),
> > 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
>