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[trace][intel-pt] Implement trace start and trace stop

Authored by wallace on Nov 9 2020, 1:36 PM.

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[trace][intel-pt] Implement trace start and trace stop

This implements the interactive trace start and stop methods.

This diff ended up being much larger than I anticipated because, by doing it, I found that I had implemented in the beginning many things in a non optimal way. In any case, the code is much better now.

There's a lot of boilerplate code due to the gdb-remote protocol, but the main changes are:

  • New tracing packets: jLLDBTraceStop, jLLDBTraceStart, jLLDBTraceGetBinaryData. The gdb-remote packet definitions are quite comprehensive.
  • Implementation of the "process trace start|stop" and "thread trace start|stop" commands.
  • Implementaiton of an API in Trace.h to interact with live traces.
  • Created an IntelPTDecoder for live threads, that use the debugger's stop id as checkpoint for its internal cache.
  • Added a functionality to stop the process in case "process tracing" is enabled and a new thread can't traced.
  • Added tests

I have some ideas to unify the code paths for post mortem and live threads, but I'll do that in another diff.

Differential Revision: https://reviews.llvm.org/D91679

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