NPL: Fix one more bug in the single step workaround

In the case we are stepping over the thread creation instruction, we
will end up calling Thread::SingleStep back-to-back twice (because of
the intermediate PTRACE_EVENT_CLONE stop). This will cause the cpu mask
to be set inappropriately (because the old SingleStepCheck object will
be destroyed after we create the new one), and the single-step will
fail.

Before the refactor the code was still incorrect in this case, but in a
different way (the thread was left with the incorrect mask after the
stepping was complete), so this was not easy to spot.

This fixes TestCreateDuringInstructionStep on the affected devices.

llvm-svn: 295440

1 files changed, 7 insertions, 1 deletions

diff --git a/lldb/source/Plugins/Process/Linux/NativeThreadLinux.cpp b/lldb/source/Plugins/Process/Linux/NativeThreadLinux.cpp
index c2e1214..a50ea7e3 100644
--- a/lldb/source/Plugins/Process/Linux/NativeThreadLinux.cpp
+++ b/lldb/source/Plugins/Process/Linux/NativeThreadLinux.cpp
@@ -225,7 +225,13 @@ Error NativeThreadLinux::SingleStep(uint32_t signo) {
   MaybeLogStateChange(new_state);
   m_state = new_state;
   m_stop_info.reason = StopReason::eStopReasonNone;
-  m_step_workaround = SingleStepWorkaround::Get(m_tid);
+
+  if(!m_step_workaround) {
+    // If we already hava a workaround inplace, don't reset it. Otherwise, the
+    // destructor of the existing instance will run after the new instance has
+    // fetched the cpu mask, and the thread will end up with the wrong mask.
+    m_step_workaround = SingleStepWorkaround::Get(m_tid);
+  }
 
   intptr_t data = 0;
   if (signo != LLDB_INVALID_SIGNAL_NUMBER)