[Lldb-commits] [lldb] 66b9283 - [lldb] [debugserver] Shut down the exception thread when clearing (#70979)

[via lldb-commits]

Author: Jason Molenda
Date: 2023-11-01T16:14:36-07:00
New Revision: 66b92830c963158c9f74dd5533265c28d60cc265

URL: https://github.com/llvm/llvm-project/commit/66b92830c963158c9f74dd5533265c28d60cc265
DIFF: https://github.com/llvm/llvm-project/commit/66b92830c963158c9f74dd5533265c28d60cc265.diff

LOG: [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

Added: 
    

Modified: 
    lldb/tools/debugserver/source/MacOSX/MachTask.mm

Removed: 
    


################################################################################
diff  --git a/lldb/tools/debugserver/source/MacOSX/MachTask.mm b/lldb/tools/debugserver/source/MacOSX/MachTask.mm
index 4f5b4039243f662..fd2ac64ac6cf79c 100644
--- a/lldb/tools/debugserver/source/MacOSX/MachTask.mm
+++ b/lldb/tools/debugserver/source/MacOSX/MachTask.mm
@@ -145,6 +145,8 @@
 //----------------------------------------------------------------------
 void MachTask::Clear() {
   // Do any cleanup needed for this task
+  if (m_exception_thread)
+    ShutDownExcecptionThread();
   m_task = TASK_NULL;
   m_exception_thread = 0;
   m_exception_port = MACH_PORT_NULL;