Added some comments.

llvm-svn: 132066
diff --git a/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp b/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp
index 565983d..39b4522 100644
--- a/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp
+++ b/lldb/source/Plugins/Process/Utility/UnwindLLDB.cpp
@@ -164,6 +164,8 @@
                 return false; // Infinite loop where the current cursor is the same as the previous one...
             else if (abi->StackUsesFrames())
             {
+                // We might have a CFA that is not using the frame pointer and
+                // we want to validate that the frame pointer is valid.
                 if (reg_ctx_sp->GetFP() == 0)
                     return false;
             }