perf trace: Avoid garbage when not printing a syscall's arguments

syscall__scnprintf_args may not place anything in the output buffer
(e.g., because the arguments are all zero). If that happened in
trace__fprintf_sys_enter, its fprintf would receive an unitialized
buffer leading to garbage output.

Fix the problem by passing the (possibly zero) bounds of the argument
buffer to the output fprintf.

Fixes: a98392b ("perf trace: Use beautifiers on syscalls:sys_enter_ handlers")
Signed-off-by: Benjamin Peterson <benjamin@engflow.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Howard Chu <howardchu95@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241107232128.108981-2-benjamin@engflow.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: benjaminp

tools/perf/builtin-trace.c

@@ -2702,6 +2702,7 @@ static int trace__fprintf_sys_enter(struct trace *trace, struct evsel *evsel,
 	char msg[1024];
 	void *args, *augmented_args = NULL;
 	int augmented_args_size;
+	size_t printed = 0;
 
 	if (sc == NULL)
 		return -1;
@@ -2717,8 +2718,8 @@ static int trace__fprintf_sys_enter(struct trace *trace, struct evsel *evsel,
 
 	args = perf_evsel__sc_tp_ptr(evsel, args, sample);
 	augmented_args = syscall__augmented_args(sc, sample, &augmented_args_size, trace->raw_augmented_syscalls_args_size);
-	syscall__scnprintf_args(sc, msg, sizeof(msg), args, augmented_args, augmented_args_size, trace, thread);
-	fprintf(trace->output, "%s", msg);
+	printed += syscall__scnprintf_args(sc, msg, sizeof(msg), args, augmented_args, augmented_args_size, trace, thread);
+	fprintf(trace->output, "%.*s", (int)printed, msg);
 	err = 0;
 out_put:
 	thread__put(thread);