Add a new capability to RegisterContextLLDB: To recognize when the

Full UnwindPlan is trying to do an impossible unwind; in that case
invalidate the Full UnwindPlan and replace it with the architecture
default unwind plan.

This is a scenario that happens occasionally with arm unwinds in
particular; the instruction analysis based full unwindplan can
mis-parse the functions and the stack walk stops prematurely.  Now
we can do a simpleminded frame-chain walk to find the caller frame
and continue the unwind.  It's not ideal but given the complicated
nature of analyzing the arm functions, and the lack of eh_frame
information on iOS, it is a distinct improvement and fixes some
long-standing problems with the unwinder on that platform.  

This is fixing <rdar://problem/12091421>.  I may re-use this
invalidate feature in the future if I can identify other cases where
the full unwindplan's unwind information is clearly incorrect.

This checkin also includes some cleanup for the volatile register
definition in the arm ABI plugin for <rdar://problem/10652166> 
although work remains to be done for that bug.

llvm-svn: 166757

1 files changed, 9 insertions, 0 deletions

diff --git a/lldb/source/Symbol/FuncUnwinders.cpp b/lldb/source/Symbol/FuncUnwinders.cpp
index 616bd614bad..07b2144e528 100644
--- a/lldb/source/Symbol/FuncUnwinders.cpp
+++ b/lldb/source/Symbol/FuncUnwinders.cpp
@@ -236,3 +236,12 @@ FuncUnwinders::GetFunctionStartAddress () const
     return m_range.GetBaseAddress();
 }
 
+void
+FuncUnwinders::InvalidateNonCallSiteUnwindPlan (lldb_private::Thread& thread)
+{
+    UnwindPlanSP arch_default = GetUnwindPlanArchitectureDefault (thread);
+    if (arch_default && m_tried_unwind_at_call_site)
+    {
+        m_unwind_plan_call_site_sp = arch_default;
+    }
+}