[PATCH] Fix _Unwind_Backtrace for libc++abi built with libgcc.

[Logan Chien]

Address the review comments.


http://reviews.llvm.org/D7031

Files:
  include/unwind.h
  src/cxa_personality.cpp

Index: include/unwind.h
===================================================================
--- include/unwind.h
+++ include/unwind.h
@@ -63,6 +63,8 @@
 static const _Unwind_State _US_VIRTUAL_UNWIND_FRAME   = 0;
 static const _Unwind_State _US_UNWIND_FRAME_STARTING  = 1;
 static const _Unwind_State _US_UNWIND_FRAME_RESUME    = 2;
+/* Undocumented flag for force unwinding. */
+static const _Unwind_State _US_FORCE_UNWIND           = 8;
 
 typedef uint32_t _Unwind_EHT_Header;
 
Index: src/cxa_personality.cpp
===================================================================
--- src/cxa_personality.cpp
+++ src/cxa_personality.cpp
@@ -1101,9 +1101,16 @@
     _Unwind_SetGR(context, REG_UCB, reinterpret_cast<uint32_t>(unwind_exception));
 #endif
 
+    // Check the undocumented force unwinding behavior
+    bool is_force_unwinding = state & _US_FORCE_UNWIND;
+    state &= ~_US_FORCE_UNWIND;
+
     scan_results results;
     switch (state) {
     case _US_VIRTUAL_UNWIND_FRAME:
+        if (is_force_unwinding)
+            return continue_unwind(unwind_exception, context);
+
         // Phase 1 search:  All we're looking for in phase 1 is a handler that halts unwinding
         scan_eh_tab(results, _UA_SEARCH_PHASE, native_exception, unwind_exception, context);
         if (results.reason == _URC_HANDLER_FOUND)
@@ -1119,6 +1126,11 @@
         return results.reason;
 
     case _US_UNWIND_FRAME_STARTING:
+        // TODO: Support force unwinding in the phase 2 search.
+        // NOTE: In order to call the cleanup functions, _Unwind_ForcedUnwind()
+        // will call this personality function with (_US_FORCE_UNWIND |
+        // _US_UNWIND_FRAME_STARTING).
+
         // Phase 2 search
         if (unwind_exception->barrier_cache.sp == _Unwind_GetGR(context, REG_SP))
         {

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