Don't enforce ABI stack alignment rules on the sigtramp frame --

its stack frame is a constructed, fake thing that may not conform
correctly to these rules.  This fixes a problem where lldb couldn't
backtrace past an asynchronous signal handler (_sigtramp) frame on
a stack on Mac OS X.
<rdar://problem/15035673> 

llvm-svn: 198450

3 files changed, 19 insertions, 4 deletions

diff --git a/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp b/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp
index b258f7fede4..f5f499fd01a 100644
--- a/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp
+++ b/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp
@@ -949,6 +949,12 @@ RegisterContextLLDB::IsValid () const
     return m_frame_type != eNotAValidFrame;
 }
 
+bool
+RegisterContextLLDB::IsSigtrampFrame () const
+{
+    return m_frame_type == eSigtrampFrame;
+}
+
 // A skip frame is a bogus frame on the stack -- but one where we're likely to find a real frame farther
 // up the stack if we keep looking.  It's always the second frame in an unwind (i.e. the first frame after
 // frame zero) where unwinding can be the trickiest.  Ideally we'll mark up this frame in some way so the
diff --git a/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.h b/lldb/source/Plugins/Process/Utility/RegisterContextLLDB.h
index dc6d8c61fa4..368cd656edb 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
+    IsSigtrampFrame () const;
+
+    bool
     GetCFA (lldb::addr_t& cfa);
 
     bool
diff --git a/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp b/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp
index 203d4c1f658..ddded5ac224 100644
--- a/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp
+++ b/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp
@@ -171,12 +171,18 @@ UnwindLLDB::AddOneMoreFrame (ABI *abi)
     }
     if (abi && !abi->CallFrameAddressIsValid(cursor_sp->cfa))
     {
-        if (log)
+        // On Mac OS X, the _sigtramp asynchronous signal trampoline frame may not have
+        // its (constructed) CFA aligned correctly -- don't do the abi alignment check for
+        // these.
+        if (reg_ctx_sp->IsSigtrampFrame() == false)
         {
-            log->Printf("%*sFrame %d did not get a valid CFA for this frame, stopping stack walk",
-                        cur_idx < 100 ? cur_idx : 100, "", cur_idx);
+            if (log)
+            {
+                log->Printf("%*sFrame %d did not get a valid CFA for this frame, stopping stack walk",
+                            cur_idx < 100 ? cur_idx : 100, "", cur_idx);
+            }
+            goto unwind_done;
         }
-        goto unwind_done;
     }
     if (!reg_ctx_sp->ReadPC (cursor_sp->start_pc))
     {