Add Fuchsia Trace Format output to olly

[tomjridge]

FTF is a binary format viewable in Perfetto. FTF is supported by the opam tracing package. This commit is a simple change to add FTF output to olly, following the [trace] code that already outputs Chrome Tracing Format traces.

[kayceesrk]

Thanks. It would be useful to check whether the same traces are produced for json and FTF traces.

If you happen to run a long-running program, could you report the size of the json trace and the FTF trace for the same program?

[tomjridge]

Some more data after running binarytrees5_multicore.ml from sandmark. The test was run with 3 domains and varying arguments for max_depth. fxt is the binary format; json is the text format. The resulting trace sizes are:

|  n | fxt size (bytes) | json size (bytes) | ratio (json/fxt) |
| 15 |            32768 |            143360 |            4.375 |
| 16 |            61440 |            299008 |      4.866666667 |
| 17 |           106496 |            565248 |      5.307692308 |
| 18 |           233472 |           1294336 |      5.543859649 |
| 19 |           430080 |           2498560 |       5.80952381 |
| 20 |          1003520 |           5783552 |      5.763265306 |
| 21 |          1953792 |          11382784 |      5.825995807 |
| 22 |          4542464 |          26243072 |      5.777276826 |

I think we expected better the binary format to have a better ratio than this as n increases. At the moment, the long binary traces seem to be only about 5.8 times smaller than the json equivalent.

[Update: trying n at 24 and 25, the ratio is still about 5.8; json file size is 232MB for n=25]

[kayceesrk]

If I am reading the PR right, this introduces a new command olly trace_ftf. This is not desirable given that the existing command trace and trace_ftf are exactly the same except for the trace format.

A better way to do this would be to introduce an option under the existing trace command called --format which can either be json or fuschia (default).

$ olly trace --format json prog.trace prog.exe    # emits the trace in json format
$ olly trace --format fuschia prog.trace prog.exe # emits the trace in fuschia trace format
$ olly trace prog.trace prof.exe                  # emits the trace in fuschia trace format

[tomjridge]

I've implemented your request - hopefully the command line interface is now a bit more sensible. (I am a cmdliner novice, so let me know if this is still not right.)

[kayceesrk]

Thanks. I’ll get to this tomorrow.

[kayceesrk]

LGTM.