diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1dbae20..201af51 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,29 @@
 2015-07-02  Kevin Buettner  <kevinb@redhat.com>
 
+	* rx-tdep.c (RX_USP_REGNUM, RX_BPC_REGNUM): New constants.
+	(enum rx_frame_type): New.
+	(struct rx_prologue): Add new field `frame_type'.
+	(rx_analyze_prologue): Add `frame_type' parameter. Cache this
+	parameter in the prologue struct.  Add code for recording
+	locations of PC and PSW for fast interrupt and exception frames.
+	(rx_skip_prologue): Adjust call to rx_analyze_prologue.
+	(rx_analyze_frame_prologue): Add `frame_type' parameter.
+	(rx_frame_type): New function.
+	(rx_frame_base): Fetch frame type and pass it to rx_analyze_prologue.
+	(rx_frame_this_id): Rename parameter `this_prologue_cache' to
+	`this_cache'.
+	(rx_frame_prev_register): Rename parameter `this_prologue_cache' to
+	`this_cache'.  Add cases for RX_FRAME_TYPE_EXCEPTION and 
+	RX_FRAME_TYPE_FAST_INTERRUPT.
+	(normal_frame_p, exception_frame_p, rx_frame_sniffer_common)
+	(rx_frame_sniffer, rx_exception_sniffer): New functions.
+	(rx_frame_unwind): Use rx_frame_sniffer instead of
+	default_frame_sniffer.
+	(rx_frame_unwind): New unwinder.
+	(rx_gdbarch_init): Register new unwinder.
+
+2015-07-02  Kevin Buettner  <kevinb@redhat.com>
+
 	* rx-tdep.c (RX_BPSW_REGNUM, RX_FPSW_REGNUM): New constants.
 	(struct gdbarch_tdep): Add fields rx_psw_type and rx_fpsw_type.
 	(rx_register_type): Add cases for RX_PSW_REGNUM, RX_BPSW_REGNUM,
diff --git a/gdb/rx-tdep.c b/gdb/rx-tdep.c
index 15c4cde..8442c76 100644
--- a/gdb/rx-tdep.c
+++ b/gdb/rx-tdep.c
@@ -45,14 +45,23 @@ enum
   RX_R4_REGNUM = 4,
   RX_FP_REGNUM = 6,
   RX_R15_REGNUM = 15,
+  RX_USP_REGNUM = 16,
   RX_PSW_REGNUM = 18,
   RX_PC_REGNUM = 19,
   RX_BPSW_REGNUM = 21,
+  RX_BPC_REGNUM = 22,
   RX_FPSW_REGNUM = 24,
   RX_ACC_REGNUM = 25,
   RX_NUM_REGS = 26
 };
 
+/* RX frame types.  */
+enum rx_frame_type {
+  RX_FRAME_TYPE_NORMAL,
+  RX_FRAME_TYPE_EXCEPTION,
+  RX_FRAME_TYPE_FAST_INTERRUPT
+};
+
 /* Architecture specific data.  */
 struct gdbarch_tdep
 {
@@ -69,6 +78,10 @@ struct gdbarch_tdep
 /* This structure holds the results of a prologue analysis.  */
 struct rx_prologue
 {
+  /* Frame type, either a normal frame or one of two types of exception
+     frames.  */
+  enum rx_frame_type frame_type;
+
   /* The offset from the frame base to the stack pointer --- always
      zero or negative.
 
@@ -203,9 +216,11 @@ rx_get_opcode_byte (void *handle)
 
 /* Analyze a prologue starting at START_PC, going no further than
    LIMIT_PC.  Fill in RESULT as appropriate.  */
+
 static void
-rx_analyze_prologue (CORE_ADDR start_pc,
-		     CORE_ADDR limit_pc, struct rx_prologue *result)
+rx_analyze_prologue (CORE_ADDR start_pc, CORE_ADDR limit_pc,
+                     enum rx_frame_type frame_type,
+		     struct rx_prologue *result)
 {
   CORE_ADDR pc, next_pc;
   int rn;
@@ -216,6 +231,8 @@ rx_analyze_prologue (CORE_ADDR start_pc,
 
   memset (result, 0, sizeof (*result));
 
+  result->frame_type = frame_type;
+
   for (rn = 0; rn < RX_NUM_REGS; rn++)
     {
       reg[rn] = pv_register (rn, 0);
@@ -225,9 +242,30 @@ rx_analyze_prologue (CORE_ADDR start_pc,
   stack = make_pv_area (RX_SP_REGNUM, gdbarch_addr_bit (target_gdbarch ()));
   back_to = make_cleanup_free_pv_area (stack);
 
-  /* The call instruction has saved the return address on the stack.  */
-  reg[RX_SP_REGNUM] = pv_add_constant (reg[RX_SP_REGNUM], -4);
-  pv_area_store (stack, reg[RX_SP_REGNUM], 4, reg[RX_PC_REGNUM]);
+  if (frame_type == RX_FRAME_TYPE_FAST_INTERRUPT)
+    {
+      /* This code won't do anything useful at present, but this is
+         what happens for fast interrupts.  */
+      reg[RX_BPSW_REGNUM] = reg[RX_PSW_REGNUM];
+      reg[RX_BPC_REGNUM] = reg[RX_PC_REGNUM];
+    }
+  else
+    {
+      /* When an exception occurs, the PSW is saved to the interrupt stack
+         first.  */
+      if (frame_type == RX_FRAME_TYPE_EXCEPTION)
+	{
+	  reg[RX_SP_REGNUM] = pv_add_constant (reg[RX_SP_REGNUM], -4);
+	  pv_area_store (stack, reg[RX_SP_REGNUM], 4, reg[RX_PSW_REGNUM]);
+	}
+
+      /* The call instruction (or an exception/interrupt) has saved the return
+          address on the stack.  */
+      reg[RX_SP_REGNUM] = pv_add_constant (reg[RX_SP_REGNUM], -4);
+      pv_area_store (stack, reg[RX_SP_REGNUM], 4, reg[RX_PC_REGNUM]);
+
+    }
+
 
   pc = start_pc;
   while (pc < limit_pc)
@@ -376,7 +414,9 @@ rx_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc)
   if (!find_pc_partial_function (pc, &name, &func_addr, &func_end))
     return pc;
 
-  rx_analyze_prologue (pc, func_end, &p);
+  /* The frame type doesn't matter here, since we only care about
+     where the prologue ends.  We'll use RX_FRAME_TYPE_NORMAL.  */
+  rx_analyze_prologue (pc, func_end, RX_FRAME_TYPE_NORMAL, &p);
   return p.prologue_end;
 }
 
@@ -384,8 +424,10 @@ rx_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc)
    associated function if there is not cache entry as specified by
    THIS_PROLOGUE_CACHE.  Save the decoded prologue in the cache and
    return that struct as the value of this function.  */
+
 static struct rx_prologue *
 rx_analyze_frame_prologue (struct frame_info *this_frame,
+			   enum rx_frame_type frame_type,
 			   void **this_prologue_cache)
 {
   if (!*this_prologue_cache)
@@ -402,19 +444,76 @@ rx_analyze_frame_prologue (struct frame_info *this_frame,
       if (!func_start)
 	stop_addr = func_start;
 
-      rx_analyze_prologue (func_start, stop_addr, *this_prologue_cache);
+      rx_analyze_prologue (func_start, stop_addr, frame_type,
+                           *this_prologue_cache);
     }
 
   return *this_prologue_cache;
 }
 
+/* Determine type of frame by scanning the function for a return
+   instruction.  */
+
+static enum rx_frame_type
+rx_frame_type (struct frame_info *this_frame, void **this_cache)
+{
+  const char *name;
+  CORE_ADDR pc, start_pc, lim_pc;
+  int bytes_read;
+  struct rx_get_opcode_byte_handle opcode_handle;
+  RX_Opcode_Decoded opc;
+
+  gdb_assert (this_cache != NULL);
+
+  /* If we have a cached value, return it.  */
+
+  if (*this_cache != NULL)
+    {
+      struct rx_prologue *p = *this_cache;
+
+      return p->frame_type;
+    }
+
+  /* No cached value; scan the function.  The frame type is cached in
+     rx_analyze_prologue / rx_analyze_frame_prologue.  */
+  
+  pc = get_frame_pc (this_frame);
+  
+  /* Attempt to find the last address in the function.  If it cannot
+     be determined, set the limit to be a short ways past the frame's
+     pc.  */
+  if (!find_pc_partial_function (pc, &name, &start_pc, &lim_pc))
+    lim_pc = pc + 20;
+
+  while (pc < lim_pc)
+    {
+      opcode_handle.pc = pc;
+      bytes_read = rx_decode_opcode (pc, &opc, rx_get_opcode_byte,
+				     &opcode_handle);
+
+      if (bytes_read <= 0 || opc.id == RXO_rts)
+	return RX_FRAME_TYPE_NORMAL;
+      else if (opc.id == RXO_rtfi)
+	return RX_FRAME_TYPE_FAST_INTERRUPT;
+      else if (opc.id == RXO_rte)
+        return RX_FRAME_TYPE_EXCEPTION;
+
+      pc += bytes_read;
+    }
+
+  return RX_FRAME_TYPE_NORMAL;
+}
+
+
 /* Given the next frame and a prologue cache, return this frame's
    base.  */
+
 static CORE_ADDR
-rx_frame_base (struct frame_info *this_frame, void **this_prologue_cache)
+rx_frame_base (struct frame_info *this_frame, void **this_cache)
 {
+  enum rx_frame_type frame_type = rx_frame_type (this_frame, this_cache);
   struct rx_prologue *p
-    = rx_analyze_frame_prologue (this_frame, this_prologue_cache);
+    = rx_analyze_frame_prologue (this_frame, frame_type, this_cache);
 
   /* In functions that use alloca, the distance between the stack
      pointer and the frame base varies dynamically, so we can't use
@@ -435,46 +534,166 @@ rx_frame_base (struct frame_info *this_frame, void **this_prologue_cache)
 }
 
 /* Implement the "frame_this_id" method for unwinding frames.  */
+
 static void
-rx_frame_this_id (struct frame_info *this_frame,
-		  void **this_prologue_cache, struct frame_id *this_id)
+rx_frame_this_id (struct frame_info *this_frame, void **this_cache,
+                  struct frame_id *this_id)
 {
-  *this_id = frame_id_build (rx_frame_base (this_frame, this_prologue_cache),
+  *this_id = frame_id_build (rx_frame_base (this_frame, this_cache),
 			     get_frame_func (this_frame));
 }
 
 /* Implement the "frame_prev_register" method for unwinding frames.  */
+
 static struct value *
-rx_frame_prev_register (struct frame_info *this_frame,
-			void **this_prologue_cache, int regnum)
+rx_frame_prev_register (struct frame_info *this_frame, void **this_cache,
+                        int regnum)
 {
+  enum rx_frame_type frame_type = rx_frame_type (this_frame, this_cache);
   struct rx_prologue *p
-    = rx_analyze_frame_prologue (this_frame, this_prologue_cache);
-  CORE_ADDR frame_base = rx_frame_base (this_frame, this_prologue_cache);
-  int reg_size = register_size (get_frame_arch (this_frame), regnum);
+    = rx_analyze_frame_prologue (this_frame, frame_type, this_cache);
+  CORE_ADDR frame_base = rx_frame_base (this_frame, this_cache);
 
   if (regnum == RX_SP_REGNUM)
-    return frame_unwind_got_constant (this_frame, regnum, frame_base);
+    {
+      if (frame_type == RX_FRAME_TYPE_EXCEPTION)
+        {
+	  struct value *psw_val;
+	  CORE_ADDR psw;
+
+	  psw_val = rx_frame_prev_register (this_frame, this_cache,
+	                                    RX_PSW_REGNUM);
+	  psw = extract_unsigned_integer (value_contents_all (psw_val), 4, 
+					  gdbarch_byte_order (
+					    get_frame_arch (this_frame)));
+
+	  if ((psw & 0x20000 /* U bit */) != 0)
+	    return rx_frame_prev_register (this_frame, this_cache,
+	                                   RX_USP_REGNUM);
+
+          /* Fall through for the case where U bit is zero.  */
+	}
+
+      return frame_unwind_got_constant (this_frame, regnum, frame_base);
+    }
+
+  if (frame_type == RX_FRAME_TYPE_FAST_INTERRUPT)
+    {
+      if (regnum == RX_PC_REGNUM)
+        return rx_frame_prev_register (this_frame, this_cache,
+	                               RX_BPC_REGNUM);
+      if (regnum == RX_PSW_REGNUM)
+        return rx_frame_prev_register (this_frame, this_cache,
+	                               RX_BPSW_REGNUM);
+    }
 
   /* If prologue analysis says we saved this register somewhere,
      return a description of the stack slot holding it.  */
-  else if (p->reg_offset[regnum] != 1)
+  if (p->reg_offset[regnum] != 1)
     return frame_unwind_got_memory (this_frame, regnum,
 				    frame_base + p->reg_offset[regnum]);
 
   /* Otherwise, presume we haven't changed the value of this
      register, and get it from the next frame.  */
+  return frame_unwind_got_register (this_frame, regnum, regnum);
+}
+
+/* Return TRUE if the frame indicated by FRAME_TYPE is a normal frame.  */
+
+static int
+normal_frame_p (enum rx_frame_type frame_type)
+{
+  return (frame_type == RX_FRAME_TYPE_NORMAL);
+}
+
+/* Return TRUE if the frame indicated by FRAME_TYPE is an exception
+   frame.  */
+
+static int
+exception_frame_p (enum rx_frame_type frame_type)
+{
+  return (frame_type == RX_FRAME_TYPE_EXCEPTION
+          || frame_type == RX_FRAME_TYPE_FAST_INTERRUPT);
+}
+
+/* Common code used by both normal and exception frame sniffers.  */
+
+static int
+rx_frame_sniffer_common (const struct frame_unwind *self,
+                         struct frame_info *this_frame,
+			 void **this_cache,
+			 int (*sniff_p)(enum rx_frame_type) )
+{
+  gdb_assert (this_cache != NULL);
+
+  if (*this_cache == NULL)
+    {
+      enum rx_frame_type frame_type = rx_frame_type (this_frame, this_cache);
+
+      if (sniff_p (frame_type))
+        {
+	  /* The call below will fill in the cache, including the frame
+	     type.  */
+	  (void) rx_analyze_frame_prologue (this_frame, frame_type, this_cache);
+
+	  return 1;
+        }
+      else
+        return 0;
+    }
   else
-    return frame_unwind_got_register (this_frame, regnum, regnum);
+    {
+      struct rx_prologue *p = *this_cache;
+
+      return sniff_p (p->frame_type);
+    }
+}
+
+/* Frame sniffer for normal (non-exception) frames.  */
+
+static int
+rx_frame_sniffer (const struct frame_unwind *self,
+                  struct frame_info *this_frame,
+		  void **this_cache)
+{
+  return rx_frame_sniffer_common (self, this_frame, this_cache,
+                                  normal_frame_p);
+}
+
+/* Frame sniffer for exception frames.  */
+
+static int
+rx_exception_sniffer (const struct frame_unwind *self,
+                             struct frame_info *this_frame,
+			     void **this_cache)
+{
+  return rx_frame_sniffer_common (self, this_frame, this_cache,
+                                  exception_frame_p);
 }
 
+/* Data structure for normal code using instruction-based prologue
+   analyzer.  */
+
 static const struct frame_unwind rx_frame_unwind = {
   NORMAL_FRAME,
   default_frame_unwind_stop_reason,
   rx_frame_this_id,
   rx_frame_prev_register,
   NULL,
-  default_frame_sniffer
+  rx_frame_sniffer
+};
+
+/* Data structure for exception code using instruction-based prologue
+   analyzer.  */
+
+static const struct frame_unwind rx_exception_unwind = {
+  /* SIGTRAMP_FRAME could be used here, but backtraces are less informative.  */
+  NORMAL_FRAME,
+  default_frame_unwind_stop_reason,
+  rx_frame_this_id,
+  rx_frame_prev_register,
+  NULL,
+  rx_exception_sniffer
 };
 
 /* Implement the "unwind_pc" gdbarch method.  */
@@ -913,6 +1132,7 @@ rx_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   set_gdbarch_dwarf2_reg_to_regnum (gdbarch, rx_dwarf_reg_to_regnum);
 
   /* Frame unwinding.  */
+  frame_unwind_append_unwinder (gdbarch, &rx_exception_unwind);
   dwarf2_append_unwinders (gdbarch);
   frame_unwind_append_unwinder (gdbarch, &rx_frame_unwind);
 
