From: Arnaldo Carvalho de Melo <acme@redhat.com>

Fixing this symptom:

[acme@mica linux-2.6-tip]$ perf record -a -f
  Fatal: Permission error - are you root?

Bus error
[acme@mica linux-2.6-tip]$

I.e. if for some reason no data is collected, in this case a non root user
trying to do systemwide profiling, no data will be collected, and then we end
up trying to mmap a zero sized file and access the file header, b00m.

Reported-by: Ingo Molnar <mingo@elte.hu>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: stable@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/builtin-record.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index f573bbb..3bf1409 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -394,6 +394,9 @@ static int process_buildids(void)
 {
 	u64 size = lseek(output, 0, SEEK_CUR);
 
+	if (size == 0)
+		return 0;
+
 	session->fd = output;
 	return __perf_session__process_events(session, post_processing_offset,
 					      size - post_processing_offset,
-- 
1.5.5.1

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