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, 2 insertions, 2 deletions

diff --git a/lldb/source/Symbol/UnwindPlan.cpp b/lldb/source/Symbol/UnwindPlan.cpp
index 0a1ec6076d4..9bccaa8ea8f 100644
--- a/lldb/source/Symbol/UnwindPlan.cpp
+++ b/lldb/source/Symbol/UnwindPlan.cpp
@@ -153,7 +153,7 @@ void
 UnwindPlan::Row::Clear ()
 {
     m_offset = 0;
-    m_cfa_reg_num = 0;
+    m_cfa_reg_num = LLDB_INVALID_REGNUM;
     m_cfa_offset = 0;
     m_register_locations.clear();
 }
@@ -189,7 +189,7 @@ UnwindPlan::Row::Dump (Stream& s, const UnwindPlan* unwind_plan, Thread* thread,
 
 UnwindPlan::Row::Row() :
     m_offset(0),
-    m_cfa_reg_num(0),
+    m_cfa_reg_num(LLDB_INVALID_REGNUM),
     m_cfa_offset(0),
     m_register_locations()
 {