perf report: More robust error handling

Don't let funny events confuse us, stick to what we know and
try to find sensible data again.

If we find an unknown event, check we're still u64 aligned, and
increment by one u64. This ensures we're bound to happen upon a
valid event soon.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Documentation/perf_counter/builtin-report.c

@@ -645,6 +645,7 @@ static int __cmd_report(void)
 	char *buf;
 	event_t *event;
 	int ret, rc = EXIT_FAILURE;
+	uint32_t size;
 	unsigned long total = 0, total_mmap = 0, total_comm = 0, total_unknown = 0;
 
 	input = open(input_name, O_RDONLY);
@@ -680,6 +681,10 @@ static int __cmd_report(void)
 more:
 	event = (event_t *)(buf + head);
 
+	size = event->header.size;
+	if (!size)
+		size = 8;
+
 	if (head + event->header.size >= page_size * mmap_window) {
 		unsigned long shift = page_size * (head / page_size);
 		int ret;
@@ -692,12 +697,9 @@ static int __cmd_report(void)
 		goto remap;
 	}
 
-
-	if (!event->header.size) {
-		fprintf(stderr, "zero-sized event at file offset %ld\n", offset + head);
-		fprintf(stderr, "skipping %ld bytes of events.\n", stat.st_size - offset - head);
-		goto done;
-	}
+	size = event->header.size;
+	if (!size)
+		goto broken_event;
 
 	if (event->header.misc & PERF_EVENT_MISC_OVERFLOW) {
 		char level;
@@ -787,15 +789,26 @@ static int __cmd_report(void)
 		break;
 	}
 	default: {
+broken_event:
 		fprintf(stderr, "%p [%p]: skipping unknown header type: %d\n",
 			(void *)(offset + head),
 			(void *)(long)(event->header.size),
 			event->header.type);
 		total_unknown++;
+
+		/*
+		 * assume we lost track of the stream, check alignment, and
+		 * increment a single u64 in the hope to catch on again 'soon'.
+		 */
+
+		if (unlikely(head & 7))
+			head &= ~7ULL;
+
+		size = 8;
 	}
 	}
 
-	head += event->header.size;
+	head += size;
 
 	if (offset + head < stat.st_size)
 		goto more;