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PT Parse

Intel PT is now integrated with perf and exposed as a PMU for usage. As an example, on supported CPUs, intel_pt event can be enabled for recording hardware trace (userspace) while ls executes:

perf record -e intel_pt//u ls

The hardware trace is written in a auxilliary perf buffer the size of which is configurable. The buffer is copied to disk and becomes part of the perf.data file. The ptparse tool allows the raw hardware trace data to be extracted from that file.

The ptparse tool is a totally untested and hastily written piece of software, meant just to learn internals of Perf and its data file format.


$ perf record -e intel_pt//u ls
$ ./ptparse [path to perf.data file] [extracted file.pt]

Without any arguments, ptparse expects a perf.data file containing AUX buff data and generates an extracted.pt file.

You can decode the .pt file using fastdecode written by Andi Kleen. You can also do perf report -D to dump raw data from the perf.data file and check raw bytes.

Extra Fun

We basically learnt about the perf.data file from opening it directly in a hex editor such as bless as well as using perf report -D on the perf.data file. We analysed how Perf builds the file and how events are written. The userspace perf conterpart is what one might call -- quite tight in terms of accesibility from usersapce. Using GDB is highly recommended to uncover the Perf magic :D In our trials, we mmap the file and iterate over the events till we get all PERF_RECORD_AUXTRACE events which are per-CPU. Then, based on each aux->cpu, just dump the auxtrace_event->size number of bytes after removing the event header and save it to a file. As more PERF_RECORD_AUXTRACE events are encountered, we just find aux->cpu and append the binary data to the corresponding file. This may be a highly volatile way but the courageous among you can use this as a template and try to actually go over all events till you find events of your interest. If you have some suggestions or a better way, let us know. :)

Suchakra Sharma suchakrapani.sharma@polymtl.ca Francis Giraldeau francis.giraldeau@gmail.com