perf probe: Fix mis-estimation for shortening filename

Fix mis-estimation size for making a short filename.
Since the buffer size is 32 bytes and there are '@' prefix and
'\0' termination, maximum shorten filename length should be
30. This means, before searching '/', it should be 31 bytes.

LKML-Reference: <20100414223935.14630.11954.stgit@localhost6.localdomain6>
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/probe-event.c

@@ -806,12 +806,12 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
 			goto error;
 	}
 	if (pp->file) {
-		len = strlen(pp->file) - 32;
+		len = strlen(pp->file) - 31;
 		if (len < 0)
 			len = 0;
 		tmp = strchr(pp->file + len, '/');
 		if (!tmp)
-			tmp = pp->file + len - 1;
+			tmp = pp->file + len;
 		ret = e_snprintf(file, 32, "@%s", tmp + 1);
 		if (ret <= 0)
 			goto error;