Re: [PATCH v2] perf trace: Fix possible insufficient allocation of argument formats

[Namhyung Kim]

Hello,

On Wed, Mar 26, 2025 at 01:05:40PM -0700, Howard Chu wrote:
> Changes in v2:
> * Simplify the code (written by Namhyung)

Please move this below "---" after S-o-b tags so that it can be ignored
when applying.

> 
> 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.
> 
> Signed-off-by: Howard Chu <howardchu95@xxxxxxxxx>
> Suggested-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Also please add the Fixes tag.

Thanks,
Namhyung

> ---
>  tools/perf/builtin-trace.c | 16 +++++-----------
>  1 file changed, 5 insertions(+), 11 deletions(-)
> 
> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index a102748bd0c9..439e152186da 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");
>  
> -- 
> 2.45.2
>