Use xctrace on macOS

[mitsuhiko]

Right now flamegraph uses dtrace on macOS but this runs into some limitations:

• Inline frames are not properly handled (Incorrect or partial flamegraph output on MacOS #113)
• Running dtrace requires root rights
• dtrace is generally considered deprecated functionality on macOS and will likely disappear longer term

One potential solution is to switch to xctrace and then implement a reader for the .trace / .run files. speedscope appears to have partial support for these files but I haven't been able to make it work at all yet. There is an issue from a while ago that it's not working (jlfwong/speedscope#196) but the code there might still be useful.

[djc]

Sounds interesting! In the current model the reader for xctrace output would live in the inferno crate, so that's probably the best place to start.

[mitsuhiko]

There is an instruments to pprof tool from Google: https://github.com/google/instrumentsToPprof

Looks like this does the wrong thing. It can only deal with the text output which is not very useful.

[kraktus]

Created an issue in the inferno repo (see above). For reference I also tried with the sample profiler which is shipped with MacOS and already supported by inferno but it seems to run into the same issues [inline frames missing].

In the mean time I can advice to use https://github.com/cmyr/cargo-instruments, which while not providing flame graph allow easy integration with Instruments