Add two new memory region based checks to the Unwinder:

Check that the pc value for frames up the stack is in a
mapped+executable region of memory.

Check that the stack pointer for frames up the stack is
in a mapped+readable region of memory.

If the unwinder ever makes a mistake walking the stack,
these checks will help to keep it from going too far into
the weeds.

These aren't fixing any bugs that I know of, but they
add extra robustness to a complicated task.

llvm-svn: 146478

Author: jasonmolenda

lldb/source/Plugins/Process/Utility/RegisterContextLLDB.cpp

@@ -236,6 +236,17 @@ RegisterContextLLDB::InitializeNonZerothFrame()
         m_frame_type = eNotAValidFrame;
         return;
     }
+
+    // Test the pc value to see if we know it's in an unmapped/non-executable region of memory.
+    // If so, our unwind has made a mistake somewhere and we should stop.
+    uint32_t permissions;
+    if (m_thread.GetProcess().GetLoadAddressPermissions(pc, permissions)
+        && (permissions & ePermissionsExecutable) == 0)
+    {
+        m_frame_type = eNotAValidFrame;
+        return;
+    }
+
     m_thread.GetProcess().GetTarget().GetSectionLoadList().ResolveLoadAddress (pc, m_current_pc);
 
     // If we don't have a Module for some reason, we're not going to find symbol/function information - just
@@ -287,6 +298,15 @@ RegisterContextLLDB::InitializeNonZerothFrame()
                     m_frame_type = eNotAValidFrame;
                     return;
                 }
+
+                // cfa_regval should point into the stack memory; if we can query memory region permissions,
+                // see if the memory is allocated & readable.
+                if (m_thread.GetProcess().GetLoadAddressPermissions(cfa_regval, permissions)
+                    && (permissions & ePermissionsReadable) == 0)
+                {
+                    m_frame_type = eNotAValidFrame;
+                    return;
+                }
             }
             else
             {