[all-commits] [llvm/llvm-project] 66b928: [lldb] [debugserver] Shut down the exception threa...

[Jason Molenda via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 66b92830c963158c9f74dd5533265c28d60cc265
      https://github.com/llvm/llvm-project/commit/66b92830c963158c9f74dd5533265c28d60cc265
  Author: Jason Molenda <jmolenda at apple.com>
  Date:   2023-11-01 (Wed, 01 Nov 2023)

  Changed paths:
    M lldb/tools/debugserver/source/MacOSX/MachTask.mm

  Log Message:
  -----------
  [lldb] [debugserver] Shut down the exception thread when clearing (#70979)

MachProcess has a MachTask as an ivar. In the MachProcess dtor, we call
MachTask::Clear() to clear its state, before running the dtor of all our
ivars, including the MachTask one.

When we attach on darwin, MachProcess calls
MachTask::StartExceptionThread which does the task_for_pid and then
starts a thread to listen for mach messages. Then MachProcess calls
ptrace(PT_ATTACHEXC). If that ptrace() fails, MachProcess will call
MachTask::Clear. But the exception thread is now up & running and is not
stopped; its ivars will be reset by the Clear() method, and its object
will be freed after the dtor runs.

Actually eliciting a crash in this scenario is very timing sensitive; I
hand-modified debugserver to fail to PT_ATTACHEXC trying to simulate it
on my desktop and was unable. But looking at the source, and an
occasional crash report we've received, it's clear that this is
possible.

rdar://117521198