Description of problem:
perf code dumps when displaying the performance difference amongst two perf.data files.


Version-Release number of selected component (if applicable):

Linux version 3.3.5-2.fc16.x86_64 
perf version 3.3.7-1.fc16.x86_64


How reproducible:
Always.

Steps to Reproduce:
1. compile simple C/C++ program to executable a.out,
2. Build perf.data files:
       perf record ./a.out; perf record ./a.out
3. perf diff perf.data perf.data.old
  
Actual results:

[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.015 MB perf.data (~650 samples) ]
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.015 MB perf.data (~650 samples) ]
Segmentation fault (core dumped)

# echo $?
139

Expected results:
Should display display the performance difference amongst two perf.data files, without the core dump.

Additional info:

Above test also fails on Fedora 17.

Linux version 3.3.4-5.fc17.x86_64
perf version 3.3.7-1.fc17.x86_64