[lldb] [debugserver] Shut down the exception thread when clearing (#70979) #7763
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…vm#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 (cherry picked from commit 66b9283)
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@swift-ci please test |
JDevlieghere
approved these changes
Nov 8, 2023
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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
(cherry picked from commit 66b9283)