After we've completed a full backtrace, we'll have one frame which

is "invalid" -- it is past the end of the stack trace.  Add a new
method IsCompletedStackWalk() so we can tell if an invalid stack
frame is from a complete backtrace or if it might be worth re-trying
the last unwind with a different method.

This fixes the unwinder problems Ryan Brown was having with go
programs.  The unwinder can (under the right circumstances) still
destructively replace unwind plans permanently - I'll work on
that in a different patch.  

<rdar://problem/18683658> 

llvm-svn: 221229

3 files changed, 26 insertions, 2 deletions

diff --git a/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp b/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp
index 5071b1aa578..88bb608ea9e 100644
--- a/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp
+++ b/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp
@@ -62,7 +62,8 @@ RegisterContextLLDB::RegisterContextLLDB
     m_sym_ctx_valid (false),
     m_frame_number (frame_number),
     m_registers(),
-    m_parent_unwind (unwind_lldb)
+    m_parent_unwind (unwind_lldb),
+    m_completed_stack_walk (false)
 {
     m_sym_ctx.Clear(false);
     m_sym_ctx_valid = false;
@@ -306,6 +307,7 @@ RegisterContextLLDB::InitializeNonZerothFrame()
     if (pc == 0)
     {
         m_frame_type = eNotAValidFrame;
+        m_completed_stack_walk = true;
         UnwindLogMsg ("this frame has a pc of 0x0");
         return;
     }
@@ -386,6 +388,10 @@ RegisterContextLLDB::InitializeNonZerothFrame()
                 {
                     UnwindLogMsg ("could not find a valid cfa address");
                     m_frame_type = eNotAValidFrame;
+                    if (cfa_regval == 0 || cfa_regval == 1)
+                    {
+                        m_completed_stack_walk = true;
+                    }
                     return;
                 }
 
@@ -582,6 +588,10 @@ RegisterContextLLDB::InitializeNonZerothFrame()
     {
         UnwindLogMsg ("could not find a valid cfa address");
         m_frame_type = eNotAValidFrame;
+        if (cfa_regval == 0 || cfa_regval == 1)
+        {
+            m_completed_stack_walk = true;
+        }
         return;
     }
 
@@ -1031,6 +1041,12 @@ RegisterContextLLDB::IsValid () const
 }
 
 bool
+RegisterContextLLDB::IsCompletedStackWalk () const
+{
+    return m_completed_stack_walk;
+}
+
+bool
 RegisterContextLLDB::IsTrapHandlerFrame () const
 {
     return m_frame_type == eTrapHandlerFrame;
diff --git a/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.h b/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.h
index ff0b77488eb..d272073de55 100644
--- a/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.h
+++ b/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.h
@@ -73,6 +73,9 @@ public:
     IsValid () const;
 
     bool
+    IsCompletedStackWalk () const;
+
+    bool
     IsTrapHandlerFrame () const;
 
     bool
@@ -240,6 +243,10 @@ private:
 
     lldb_private::UnwindLLDB& m_parent_unwind;    // The UnwindLLDB that is creating this RegisterContextLLDB
 
+    bool m_completed_stack_walk;                  // indicates that we completed a full stack walk 
+                                                  // (this frame is likely eNotAValidFrame aka !IsValid())
+                                                  // and we should not continue trying to unwind
+
     //------------------------------------------------------------------
     // For RegisterContextLLDB only
     //------------------------------------------------------------------
diff --git a/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp b/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp
index 37fd4f48955..b61819af0d8 100644
--- a/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp
+++ b/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp
@@ -174,7 +174,8 @@ UnwindLLDB::AddOneMoreFrame (ABI *abi)
     {
         // If the RegisterContextLLDB has a fallback UnwindPlan, it will switch to that and return
         // true.  Subsequent calls to TryFallbackUnwindPlan() will return false.
-        if (m_frames[cur_idx - 1]->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
+        if (reg_ctx_sp->IsCompletedStackWalk() == false
+            && m_frames[cur_idx - 1]->reg_ctx_lldb_sp->TryFallbackUnwindPlan())
         {
             return AddOneMoreFrame (abi);
         }