perf_event_open: Invalid argument

Hello,

I'm trying to run Mitos on an Intel machine, I manage to install both Dyninst
and Mitos but when I run a command with Mitos I got the following output:

```
mitosrun ./examples/matmul
perf_event_open: Invalid argument
Not ready to begin sampling!
6.47073e+07
Segmentation fault
```

Obviously matmul does not segfault without mitos.

I've run mitos under strace to identify the faulty arguments:

```
strace mitosrun ./examples/matmul 2>&1 | grep perf_event
read(6, "8:perf_event:/\n7:blkio:/\n6:net_c"..., 1024) = 138
perf_event_open(0x7f51d322d148, 3613, -1, -1, 0) = -1 EINVAL (Invalid argument)
write(2, "perf_event_open: Invalid argumen"..., 34perf_event_open: Invalid argument
```

But according to the documentation this seems to be right ...
I've also tryed to put the pid argument at `-1` and to add the
`PERF_FLAG_FD_NO_GROUP` without any results ...

Any idea on what can be wrong ?

I'm running `debian jessie` with a linux kernel `3.16.0-4-amd64` on an Intel
xeon E5520 8 cores processor.

Thanks,
David

Start by reproducing `mitosrun ./examples/matmul` on the reported Debian Jessie, Linux 3.16.0-4-amd64, and Intel Xeon E5520 environment. Inspect the `perf_event_open` invocation with `strace`; done means the command no longer returns EINVAL or causes the instrumented matmul process to segfault.

Written by the indexing model from the issue text.