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

[Howard Chu]

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>
---
 tools/perf/builtin-trace.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index a102748bd0c9..ad6dad8e2453 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -2139,6 +2139,7 @@ static int syscall__read_info(struct syscall *sc, struct trace *trace)
 	char tp_name[128];
 	const char *name;
 	int err;
+	bool extra_nr = false;
 
 	if (sc->nonexistent)
 		return -EEXIST;
@@ -2176,20 +2177,22 @@ static int syscall__read_info(struct syscall *sc, struct trace *trace)
 		return err;
 	}
 
+	sc->args = sc->tp_format->format.fields;
+	if (!strcmp(sc->args->name, "__syscall_nr") || !strcmp(sc->args->name, "nr"))
+		extra_nr = true;
 	/*
 	 * 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))
+	if (syscall__alloc_arg_fmts(sc, sc->tp_format->format.nr_fields - (extra_nr ? 1 : 0)))
 		return -ENOMEM;
 
-	sc->args = sc->tp_format->format.fields;
 	/*
 	 * We need to check and discard the first variable '__syscall_nr'
 	 * or 'nr' that mean the syscall number. It is needless here.
 	 * So drop '__syscall_nr' or 'nr' field but does not exist on older kernels.
 	 */
-	if (sc->args && (!strcmp(sc->args->name, "__syscall_nr") || !strcmp(sc->args->name, "nr"))) {
+	if (sc->args && extra_nr) {
 		sc->args = sc->args->next;
 		--sc->nr_args;
 	}
-- 
2.45.2