diff --git a/include/lldb/Symbol/UnwindPlan.h b/include/lldb/Symbol/UnwindPlan.h
index 40814da..06c76ca 100644
--- a/include/lldb/Symbol/UnwindPlan.h
+++ b/include/lldb/Symbol/UnwindPlan.h
@@ -360,6 +360,25 @@
 
     bool SetRegisterLocationToSame(uint32_t reg_num, bool must_replace);
 
+    // When this UnspecifiedRegistersAreUndefined mode is
+    // set, any register that is not specified by this Row will
+    // be described as Undefined.
+    // This will prevent the unwinder from iterating down the
+    // stack looking for a spill location, or a live register value
+    // at frame 0.
+    // It would be used for an UnwindPlan row where we can't track
+    // spilled registers -- for instance a jitted stack frame where
+    // we have no unwind information or start address -- and registers
+    // MAY have been spilled and overwritten, so providing the
+    // spilled/live value from a newer frame may show an incorrect value.
+    void SetUnspecifiedRegistersAreUndefined(bool unspec_is_undef) {
+      m_unspecified_registers_are_undefined = unspec_is_undef;
+    }
+
+    bool GetUnspecifiedRegistersAreUndefined() {
+      return m_unspecified_registers_are_undefined;
+    }
+
     void Clear();
 
     void Dump(Stream &s, const UnwindPlan *unwind_plan, Thread *thread,
@@ -372,6 +391,7 @@
     FAValue m_cfa_value;
     FAValue m_afa_value;
     collection m_register_locations;
+    bool m_unspecified_registers_are_undefined;
   }; // class Row
 
   typedef std::shared_ptr<Row> RowSP;
diff --git a/source/Plugins/ABI/AArch64/ABIMacOSX_arm64.cpp b/source/Plugins/ABI/AArch64/ABIMacOSX_arm64.cpp
index ea0c09a..861310e 100644
--- a/source/Plugins/ABI/AArch64/ABIMacOSX_arm64.cpp
+++ b/source/Plugins/ABI/AArch64/ABIMacOSX_arm64.cpp
@@ -384,6 +384,7 @@
 
   row->GetCFAValue().SetIsRegisterPlusOffset(fp_reg_num, 2 * ptr_size);
   row->SetOffset(0);
+  row->SetUnspecifiedRegistersAreUndefined(true);
 
   row->SetRegisterLocationToAtCFAPlusOffset(fp_reg_num, ptr_size * -2, true);
   row->SetRegisterLocationToAtCFAPlusOffset(pc_reg_num, ptr_size * -1, true);
diff --git a/source/Plugins/ABI/AArch64/ABISysV_arm64.cpp b/source/Plugins/ABI/AArch64/ABISysV_arm64.cpp
index 5918e2c..0f74c1f 100644
--- a/source/Plugins/ABI/AArch64/ABISysV_arm64.cpp
+++ b/source/Plugins/ABI/AArch64/ABISysV_arm64.cpp
@@ -356,6 +356,7 @@
 
   row->GetCFAValue().SetIsRegisterPlusOffset(fp_reg_num, 2 * ptr_size);
   row->SetOffset(0);
+  row->SetUnspecifiedRegistersAreUndefined(true);
 
   row->SetRegisterLocationToAtCFAPlusOffset(fp_reg_num, ptr_size * -2, true);
   row->SetRegisterLocationToAtCFAPlusOffset(pc_reg_num, ptr_size * -1, true);
diff --git a/source/Plugins/ABI/ARM/ABIMacOSX_arm.cpp b/source/Plugins/ABI/ARM/ABIMacOSX_arm.cpp
index 06c4590..e429f3e 100644
--- a/source/Plugins/ABI/ARM/ABIMacOSX_arm.cpp
+++ b/source/Plugins/ABI/ARM/ABIMacOSX_arm.cpp
@@ -1824,6 +1824,7 @@
 
   row->GetCFAValue().SetIsRegisterPlusOffset(fp_reg_num, 2 * ptr_size);
   row->SetOffset(0);
+  row->SetUnspecifiedRegistersAreUndefined(true);
 
   row->SetRegisterLocationToAtCFAPlusOffset(fp_reg_num, ptr_size * -2, true);
   row->SetRegisterLocationToAtCFAPlusOffset(pc_reg_num, ptr_size * -1, true);
diff --git a/source/Plugins/ABI/ARM/ABISysV_arm.cpp b/source/Plugins/ABI/ARM/ABISysV_arm.cpp
index 26b3152..8a9be3f 100644
--- a/source/Plugins/ABI/ARM/ABISysV_arm.cpp
+++ b/source/Plugins/ABI/ARM/ABISysV_arm.cpp
@@ -1940,6 +1940,7 @@
 
   row->GetCFAValue().SetIsRegisterPlusOffset(fp_reg_num, 2 * ptr_size);
   row->SetOffset(0);
+  row->SetUnspecifiedRegistersAreUndefined(true);
 
   row->SetRegisterLocationToAtCFAPlusOffset(fp_reg_num, ptr_size * -2, true);
   row->SetRegisterLocationToAtCFAPlusOffset(pc_reg_num, ptr_size * -1, true);
diff --git a/source/Plugins/ABI/Hexagon/ABISysV_hexagon.cpp b/source/Plugins/ABI/Hexagon/ABISysV_hexagon.cpp
index 47aaefd..6794f7d 100644
--- a/source/Plugins/ABI/Hexagon/ABISysV_hexagon.cpp
+++ b/source/Plugins/ABI/Hexagon/ABISysV_hexagon.cpp
@@ -1225,6 +1225,7 @@
 
   UnwindPlan::RowSP row(new UnwindPlan::Row);
 
+  row->SetUnspecifiedRegistersAreUndefined(true);
   row->GetCFAValue().SetIsRegisterPlusOffset(LLDB_REGNUM_GENERIC_FP, 8);
 
   row->SetRegisterLocationToAtCFAPlusOffset(fp_reg_num, -8, true);
diff --git a/source/Plugins/ABI/Mips/ABISysV_mips.cpp b/source/Plugins/ABI/Mips/ABISysV_mips.cpp
index d66e092..538ec06 100644
--- a/source/Plugins/ABI/Mips/ABISysV_mips.cpp
+++ b/source/Plugins/ABI/Mips/ABISysV_mips.cpp
@@ -985,6 +985,7 @@
 
   UnwindPlan::RowSP row(new UnwindPlan::Row);
 
+  row->SetUnspecifiedRegistersAreUndefined(true);
   row->GetCFAValue().SetIsRegisterPlusOffset(dwarf_r29, 0);
 
   row->SetRegisterLocationToRegister(dwarf_pc, dwarf_r31, true);
diff --git a/source/Plugins/ABI/Mips/ABISysV_mips64.cpp b/source/Plugins/ABI/Mips/ABISysV_mips64.cpp
index 5e72af0..7220508 100644
--- a/source/Plugins/ABI/Mips/ABISysV_mips64.cpp
+++ b/source/Plugins/ABI/Mips/ABISysV_mips64.cpp
@@ -1156,6 +1156,7 @@
 
   UnwindPlan::RowSP row(new UnwindPlan::Row);
 
+  row->SetUnspecifiedRegistersAreUndefined(true);
   row->GetCFAValue().SetIsRegisterPlusOffset(dwarf_r29, 0);
 
   row->SetRegisterLocationToRegister(dwarf_pc, dwarf_r31, true);
diff --git a/source/Plugins/ABI/PowerPC/ABISysV_ppc.cpp b/source/Plugins/ABI/PowerPC/ABISysV_ppc.cpp
index d560564..cfecf35 100644
--- a/source/Plugins/ABI/PowerPC/ABISysV_ppc.cpp
+++ b/source/Plugins/ABI/PowerPC/ABISysV_ppc.cpp
@@ -900,6 +900,7 @@
   UnwindPlan::RowSP row(new UnwindPlan::Row);
 
   const int32_t ptr_size = 4;
+  row->SetUnspecifiedRegistersAreUndefined(true);
   row->GetCFAValue().SetIsRegisterDereferenced(sp_reg_num);
 
   row->SetRegisterLocationToAtCFAPlusOffset(pc_reg_num, ptr_size * 1, true);
diff --git a/source/Plugins/ABI/PowerPC/ABISysV_ppc64.cpp b/source/Plugins/ABI/PowerPC/ABISysV_ppc64.cpp
index 6031431..7cc9482 100644
--- a/source/Plugins/ABI/PowerPC/ABISysV_ppc64.cpp
+++ b/source/Plugins/ABI/PowerPC/ABISysV_ppc64.cpp
@@ -1003,6 +1003,7 @@
 
   UnwindPlan::RowSP row(new UnwindPlan::Row);
   const int32_t ptr_size = 8;
+  row->SetUnspecifiedRegistersAreUndefined(true);
   row->GetCFAValue().SetIsRegisterDereferenced(sp_reg_num);
 
   row->SetRegisterLocationToAtCFAPlusOffset(pc_reg_num, ptr_size * 2, true);
diff --git a/source/Plugins/ABI/X86/ABIMacOSX_i386.cpp b/source/Plugins/ABI/X86/ABIMacOSX_i386.cpp
index 89112de..461e4af 100644
--- a/source/Plugins/ABI/X86/ABIMacOSX_i386.cpp
+++ b/source/Plugins/ABI/X86/ABIMacOSX_i386.cpp
@@ -389,6 +389,7 @@
 
   row->GetCFAValue().SetIsRegisterPlusOffset(fp_reg_num, 2 * ptr_size);
   row->SetOffset(0);
+  row->SetUnspecifiedRegistersAreUndefined(true);
 
   row->SetRegisterLocationToAtCFAPlusOffset(fp_reg_num, ptr_size * -2, true);
   row->SetRegisterLocationToAtCFAPlusOffset(pc_reg_num, ptr_size * -1, true);
diff --git a/source/Plugins/ABI/X86/ABISysV_i386.cpp b/source/Plugins/ABI/X86/ABISysV_i386.cpp
index 38d7364..7d2f0a6 100644
--- a/source/Plugins/ABI/X86/ABISysV_i386.cpp
+++ b/source/Plugins/ABI/X86/ABISysV_i386.cpp
@@ -652,6 +652,7 @@
 
   row->GetCFAValue().SetIsRegisterPlusOffset(fp_reg_num, 2 * ptr_size);
   row->SetOffset(0);
+  row->SetUnspecifiedRegistersAreUndefined(true);
 
   row->SetRegisterLocationToAtCFAPlusOffset(fp_reg_num, ptr_size * -2, true);
   row->SetRegisterLocationToAtCFAPlusOffset(pc_reg_num, ptr_size * -1, true);
diff --git a/source/Plugins/ABI/X86/ABISysV_x86_64.cpp b/source/Plugins/ABI/X86/ABISysV_x86_64.cpp
index 8d56147..196b45b 100644
--- a/source/Plugins/ABI/X86/ABISysV_x86_64.cpp
+++ b/source/Plugins/ABI/X86/ABISysV_x86_64.cpp
@@ -887,6 +887,7 @@
   const int32_t ptr_size = 8;
   row->GetCFAValue().SetIsRegisterPlusOffset(dwarf_rbp, 2 * ptr_size);
   row->SetOffset(0);
+  row->SetUnspecifiedRegistersAreUndefined(true);
 
   row->SetRegisterLocationToAtCFAPlusOffset(fp_reg_num, ptr_size * -2, true);
   row->SetRegisterLocationToAtCFAPlusOffset(pc_reg_num, ptr_size * -1, true);
diff --git a/source/Plugins/ABI/X86/ABIWindows_x86_64.cpp b/source/Plugins/ABI/X86/ABIWindows_x86_64.cpp
index da24145..6c473c6 100644
--- a/source/Plugins/ABI/X86/ABIWindows_x86_64.cpp
+++ b/source/Plugins/ABI/X86/ABIWindows_x86_64.cpp
@@ -767,6 +767,7 @@
   const int32_t ptr_size = 8;
   row->GetCFAValue().SetIsRegisterPlusOffset(dwarf_rbp, 2 * ptr_size);
   row->SetOffset(0);
+  row->SetUnspecifiedRegistersAreUndefined(true);
 
   row->SetRegisterLocationToAtCFAPlusOffset(fp_reg_num, ptr_size * -2, true);
   row->SetRegisterLocationToAtCFAPlusOffset(pc_reg_num, ptr_size * -1, true);
diff --git a/source/Symbol/UnwindPlan.cpp b/source/Symbol/UnwindPlan.cpp
index d24cabe..d74c78f 100644
--- a/source/Symbol/UnwindPlan.cpp
+++ b/source/Symbol/UnwindPlan.cpp
@@ -217,6 +217,7 @@
   m_cfa_value.SetUnspecified();
   m_afa_value.SetUnspecified();
   m_offset = 0;
+  m_unspecified_registers_are_undefined = false;
   m_register_locations.clear();
 }
 
@@ -242,11 +243,11 @@
     idx->second.Dump(s, unwind_plan, this, thread, verbose);
     s.PutChar(' ');
   }
-  s.EOL();
 }
 
 UnwindPlan::Row::Row()
-    : m_offset(0), m_cfa_value(), m_afa_value(), m_register_locations() {}
+    : m_offset(0), m_cfa_value(), m_afa_value(), m_register_locations(),
+      m_unspecified_registers_are_undefined(false) {}
 
 bool UnwindPlan::Row::GetRegisterInfo(
     uint32_t reg_num,
@@ -256,6 +257,10 @@
     register_location = pos->second;
     return true;
   }
+  if (m_unspecified_registers_are_undefined) {
+    register_location.SetUndefined();
+    return true;
+  }
   return false;
 }
 
@@ -348,10 +353,11 @@
 }
 
 bool UnwindPlan::Row::operator==(const UnwindPlan::Row &rhs) const {
-  return m_offset == rhs.m_offset &&
-      m_cfa_value == rhs.m_cfa_value &&
-      m_afa_value == rhs.m_afa_value &&
-      m_register_locations == rhs.m_register_locations;
+  return m_offset == rhs.m_offset && m_cfa_value == rhs.m_cfa_value &&
+         m_afa_value == rhs.m_afa_value &&
+         m_unspecified_registers_are_undefined ==
+             rhs.m_unspecified_registers_are_undefined &&
+         m_register_locations == rhs.m_register_locations;
 }
 
 void UnwindPlan::AppendRow(const UnwindPlan::RowSP &row_sp) {
@@ -552,6 +558,7 @@
   for (pos = begin; pos != end; ++pos) {
     s.Printf("row[%u]: ", (uint32_t)std::distance(begin, pos));
     (*pos)->Dump(s, this, thread, base_addr);
+    s.Printf("\n");
   }
 }
 
diff --git a/source/Target/RegisterContextUnwind.cpp b/source/Target/RegisterContextUnwind.cpp
index 991a3c8..a677121 100644
--- a/source/Target/RegisterContextUnwind.cpp
+++ b/source/Target/RegisterContextUnwind.cpp
@@ -542,6 +542,8 @@
       StreamString active_row_strm;
       active_row->Dump(active_row_strm, m_fast_unwind_plan_sp.get(), &m_thread,
                        m_start_pc.GetLoadAddress(exe_ctx.GetTargetPtr()));
+      UnwindLogMsg("Using fast unwind plan '%s'",
+                   m_fast_unwind_plan_sp->GetSourceName().AsCString());
       UnwindLogMsg("active row: %s", active_row_strm.GetData());
     }
   } else {
@@ -556,6 +558,8 @@
         active_row->Dump(active_row_strm, m_full_unwind_plan_sp.get(),
                          &m_thread,
                          m_start_pc.GetLoadAddress(exe_ctx.GetTargetPtr()));
+        UnwindLogMsg("Using full unwind plan '%s'",
+                     m_full_unwind_plan_sp->GetSourceName().AsCString());
         UnwindLogMsg("active row: %s", active_row_strm.GetData());
       }
     }
@@ -662,13 +666,6 @@
       *m_thread.CalculateTarget(), m_thread);
   if (unwind_plan_sp) {
     if (unwind_plan_sp->PlanValidAtAddress(m_current_pc)) {
-      Log *log(GetLogIfAllCategoriesSet(LIBLLDB_LOG_UNWIND));
-      if (log && log->GetVerbose()) {
-        if (m_fast_unwind_plan_sp)
-          UnwindLogMsgVerbose("frame, and has a fast UnwindPlan");
-        else
-          UnwindLogMsgVerbose("frame");
-      }
       m_frame_type = eNormalFrame;
       return unwind_plan_sp;
     } else {
@@ -1147,6 +1144,7 @@
 RegisterContextUnwind::SavedLocationForRegister(
     uint32_t lldb_regnum, lldb_private::UnwindLLDB::RegisterLocation &regloc) {
   RegisterNumber regnum(m_thread, eRegisterKindLLDB, lldb_regnum);
+  Log *log(GetLogIfAllCategoriesSet(LIBLLDB_LOG_UNWIND));
 
   // Have we already found this register location?
   if (!m_registers.empty()) {
@@ -1179,8 +1177,17 @@
                    (int)unwindplan_registerkind);
       return UnwindLLDB::RegisterSearchResult::eRegisterNotFound;
     }
+    // The architecture default unwind plan marks unknown registers as
+    // Undefined so that we don't forward them up the stack when a
+    // jitted stack frame may have overwritten them.  But when the
+    // arch default unwind plan is used as the Fast Unwind Plan, we
+    // need to recognize this & switch over to the Full Unwind Plan
+    // to see what unwind rule that (more knoweldgeable, probably)
+    // UnwindPlan has.  If the full UnwindPlan says the register 
+    // location is Undefined, then it really is.
     if (active_row->GetRegisterInfo(regnum.GetAsKind(unwindplan_registerkind),
-                                    unwindplan_regloc)) {
+                                    unwindplan_regloc) &&
+        !unwindplan_regloc.IsUndefined()) {
       UnwindLogMsg(
           "supplying caller's saved %s (%d)'s location using FastUnwindPlan",
           regnum.GetName(), regnum.GetAsKind(eRegisterKindLLDB));
@@ -1191,8 +1198,11 @@
   if (!have_unwindplan_regloc) {
     // m_full_unwind_plan_sp being NULL means that we haven't tried to find a
     // full UnwindPlan yet
-    if (!m_full_unwind_plan_sp)
+    bool got_new_full_unwindplan = false;
+    if (!m_full_unwind_plan_sp) {
       m_full_unwind_plan_sp = GetFullUnwindPlanForFrame();
+      got_new_full_unwindplan = true;
+    }
 
     if (m_full_unwind_plan_sp) {
       RegisterNumber pc_regnum(m_thread, eRegisterKindGeneric,
@@ -1202,6 +1212,16 @@
           m_full_unwind_plan_sp->GetRowForFunctionOffset(m_current_offset);
       unwindplan_registerkind = m_full_unwind_plan_sp->GetRegisterKind();
 
+      if (got_new_full_unwindplan && active_row.get() && log) {
+        StreamString active_row_strm;
+        ExecutionContext exe_ctx(m_thread.shared_from_this());
+        active_row->Dump(active_row_strm, m_full_unwind_plan_sp.get(),
+                         &m_thread,
+                         m_start_pc.GetLoadAddress(exe_ctx.GetTargetPtr()));
+        UnwindLogMsg("Using full unwind plan '%s'",
+                     m_full_unwind_plan_sp->GetSourceName().AsCString());
+        UnwindLogMsg("active row: %s", active_row_strm.GetData());
+      }
       RegisterNumber return_address_reg;
 
       // If we're fetching the saved pc and this UnwindPlan defines a