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

[Namhyung Kim <namhyung@kernel.org>]

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