[tip:perf/core] perf trace: Do not print raw args list for syscalls with no args

[tip-bot for Arnaldo Carvalho de Melo <tipbot@zytor.com>]

Commit-ID:  4c4d6e519091a3551a0ad2e2e8423d77f3000400
Gitweb:     http://git.kernel.org/tip/4c4d6e519091a3551a0ad2e2e8423d77f3000400
Author:     Arnaldo Carvalho de Melo <acme@redhat.com>
AuthorDate: Thu, 5 May 2016 23:38:05 -0300
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Fri, 6 May 2016 08:44:30 -0300

perf trace: Do not print raw args list for syscalls with no args

The test to check if the arg format had been read from the
syscall:sys_enter_name/format file was looking at the list of non-commom
fields, and if that is empty, it would think it had failed to read it,
because it doesn't exist, for instance, for the clone() syscall.

So instead before dumping the raw syscall args list check
IS_ERR(sc->tp_format), if that is true, then an attempt was made to read
the format file and failed, in which case dump the raw arg list values.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-ls7pmdqb2xy9339vdburwvnk@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/builtin-trace.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 66aa2a0..9d23edc 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -1606,7 +1606,12 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
 						     "%ld", val);
 			}
 		}
-	} else {
+	} else if (IS_ERR(sc->tp_format)) {
+		/*
+		 * If we managed to read the tracepoint /format file, then we
+		 * may end up not having any args, like with gettid(), so only
+		 * print the raw args when we didn't manage to read it.
+		 */
 		int i = 0;
 
 		while (i < 6) {