[lldb] [llgs] Fix multi-resume bugs with nonstop mode

[mgorny]

Summary

Improve handling of multiple successive continue packets in non-stop
mode. More specifically:

1. Explicitly send error response (instead of crashing on assertion) if the user attempts to resume the same process twice. Since we do not support thread-level non-stop mode, one needs to always stop the process explicitly before resuming another thread set.

2. Actually stop the process if "vCont;t" is delivered to a running process. Similarly, we only support stopping all the running threads simultaneously and return an error if the action would result in a subset of threads still running.

With this patch, running multiple processes simultaneously is still
unsupported. The patch also employs a hack to avoid enabling stdio
forwarding on "vCont;t" packet. Both of these issues will be addressed
by followup patches.

Sponsored by: The FreeBSD Foundation

[mgorny]

Rebase on top of m_debugged_processes changes.

[labath]

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp

1814–1817

I think this is going to be racy if new threads appear before we are able to stop everything. I mean that in the sense that if the client has listed all (known) threads of the process explicitly, and a new thread appears before we're able to act on it, then (I guess) the expected behavior would be to keep that thread running (but we won't do that).

Do we need to support this kind of stopping right now? Maybe we could only support the pid.-1 syntax for stopping all threads within a process? (which should also make the ResumeActionListStopsAllThreads logic simpler)

2989–2996

Could we factor even more of these functions into a common place? If we e.g. moved this block right before the m_continue_process->Resume, then we could put it, and into a helper function.

[mgorny]

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp

1814–1817

No, I don't think we need to support it. I'll remove it then and simplify the logic.

2989–2996

Makes sense.

[mgorny]

Remove support for t with individual thread numbers and simplify code. Move resuming the process (and checking whether it can be resumed) into a common ResumeProcess() method.

[labath]

flake here: https://lab.llvm.org/buildbot/#/builders/68/builds/35932