[PATCH v4 2/2] perf trace: Check and discard not only 'nr' but also '__syscall_nr'

[Taeung Song]

Format fields of a syscall have the first variable
'__syscall_nr' or 'nr' that mean the syscall number.
But it isn't relevant here so drop it.

'nr' among fields of syscall was renamed '__syscall_nr'.
So add exception handling to drop '__syscall_nr' and
modify the comment for this excpetion handling.

Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Taeung Song <treeze.taeung@xxxxxxxxx>
---
 tools/perf/builtin-trace.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 20916dd..a252f3a 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -1724,8 +1724,12 @@ static int trace__read_syscall_info(struct trace *trace, int id)
 
 	sc->args = sc->tp_format->format.fields;
 	sc->nr_args = sc->tp_format->format.nr_fields;
-	/* drop nr field - not relevant here; does not exist on older kernels */
-	if (sc->args && strcmp(sc->args->name, "nr") == 0) {
+	/*
+	 * 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"))) {
 		sc->args = sc->args->next;
 		--sc->nr_args;
 	}
-- 
2.5.0