alpha.c (struct machine_function): New flag for VMS, uses_condition_handler.

	* config/alpha/alpha.c (struct machine_function): New flag for VMS,
	uses_condition_handler.
	(alpha_expand_builtin_establish_vms_condition_handler): New expander.
	(alpha_expand_builtin_revert_vms_condition_handler): New expander.
	(enum alpha_builtin): New ALPHA_BUILTIN_REVERT_VMS_CONDITION_HANDLER
	and ALPHA_BUILTIN_ESTABLISH_VMS_CONDITION_HANDLER values.
	(code_for_builtin): New insn codes for the new alpha_builtins.
	(alpha_init_builtins): Register the new functions as BUILT_IN_MD.
	(alpha_sa_size): Account for uses_condition_handler.
	(alpha_expand_prologue): Likewise.
	(alpha_start_function): Likewise.
	(alpha_expand_epilogue): Likewise.
	* config/alpha/alpha-protos.h: Prototype the new alpha.c builtin
	establish/revert expanders.
	* config/alpha/alpha.h (DWARF_FRAME_REGNUM): Define.
	* config/alpha/alpha.md	(builtin_establish_vms_condition_handler):
	New expander, resorting to the alpha.c associated function.
	(builtin_revert_vms_condition_handler): Likewise.
	* config/alpha/vms-gcc_shell_handler.c: New file. Implements
	__gcc_shell_handler, the static VMS condition handler used as
	an indirection wrapper to the current dynamically established
	handler.
	* config/alpha/vms-unwind.h: Complete rewrite.
	* config/alpha/t-vms (LIB2FUNCS_EXTRA): Add vms-gcc_shell_handler.c
	* config/alpha/vms.h (MD_UNWIND_SUPPORT):
	

Co-Authored-By: Douglas B Rupp <rupp@gnat.com>

From-SVN: r150612

9 files changed, 563 insertions, 62 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 7028cbd..f9f6ac7 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,32 @@
+2009-08-09  Olivier Hainque  <hainque@adacore.com>
+            Douglas B Rupp  <rupp@gnat.com>
+
+	* config/alpha/alpha.c (struct machine_function): New flag for VMS,
+	uses_condition_handler.
+	(alpha_expand_builtin_establish_vms_condition_handler): New expander.
+	(alpha_expand_builtin_revert_vms_condition_handler): New expander.
+	(enum alpha_builtin): New ALPHA_BUILTIN_REVERT_VMS_CONDITION_HANDLER
+	and ALPHA_BUILTIN_ESTABLISH_VMS_CONDITION_HANDLER values.
+	(code_for_builtin): New insn codes for the new alpha_builtins.
+	(alpha_init_builtins): Register the new functions as BUILT_IN_MD.
+	(alpha_sa_size): Account for uses_condition_handler.
+	(alpha_expand_prologue): Likewise.
+	(alpha_start_function): Likewise.
+	(alpha_expand_epilogue): Likewise.
+	* config/alpha/alpha-protos.h: Prototype the new alpha.c builtin
+	establish/revert expanders.
+	* config/alpha/alpha.h (DWARF_FRAME_REGNUM): Define.
+	* config/alpha/alpha.md	(builtin_establish_vms_condition_handler):
+	New expander, resorting to the alpha.c associated function.
+	(builtin_revert_vms_condition_handler): Likewise.
+	* config/alpha/vms-gcc_shell_handler.c: New file. Implements
+	__gcc_shell_handler, the static VMS condition handler used as
+	an indirection wrapper to the current dynamically established
+	handler.
+	* config/alpha/vms-unwind.h: Complete rewrite.
+	* config/alpha/t-vms (LIB2FUNCS_EXTRA): Add vms-gcc_shell_handler.c
+	* config/alpha/vms.h (MD_UNWIND_SUPPORT):
+	
 2009-08-09  Eric Botcazou  <botcazou@adacore.com>
             Douglas B Rupp  <rupp@gnat.com>
 
diff --git a/gcc/config/alpha/alpha-protos.h b/gcc/config/alpha/alpha-protos.h
index 80c1e4f..244ff71 100644
--- a/gcc/config/alpha/alpha-protos.h
+++ b/gcc/config/alpha/alpha-protos.h
@@ -67,6 +67,9 @@ extern rtx alpha_expand_zap_mask (HOST_WIDE_INT);
 extern void alpha_expand_builtin_vector_binop (rtx (*)(rtx, rtx, rtx),
 					       enum machine_mode,
 					       rtx, rtx, rtx);
+extern void alpha_expand_builtin_establish_vms_condition_handler (rtx, rtx);
+extern void alpha_expand_builtin_revert_vms_condition_handler (rtx);
+
 extern rtx alpha_return_addr (int, rtx);
 extern rtx alpha_gp_save_rtx (void);
 extern void print_operand (FILE *, rtx, int);
diff --git a/gcc/config/alpha/alpha.c b/gcc/config/alpha/alpha.c
index 42cb7a9..3857909 100644
--- a/gcc/config/alpha/alpha.c
+++ b/gcc/config/alpha/alpha.c
@@ -4779,6 +4779,9 @@ struct GTY(()) machine_function
 
   /* For TARGET_LD_BUGGY_LDGP.  */
   struct rtx_def *gp_save_rtx;
+
+  /* For VMS condition handlers.  */
+  bool uses_condition_handler;  
 };
 
 /* How to allocate a 'struct machine_function'.  */
@@ -4790,6 +4793,63 @@ alpha_init_machine_status (void)
 		ggc_alloc_cleared (sizeof (struct machine_function)));
 }
 
+/* Support for frame based VMS condition handlers.  */
+
+/* A VMS condition handler may be established for a function with a call to
+   __builtin_establish_vms_condition_handler, and cancelled with a call to
+   __builtin_revert_vms_condition_handler.
+
+   The VMS Condition Handling Facility knows about the existence of a handler
+   from the procedure descriptor .handler field.  As the VMS native compilers,
+   we store the user specified handler's address at a fixed location in the
+   stack frame and point the procedure descriptor at a common wrapper which
+   fetches the real handler's address and issues an indirect call.
+
+   The indirection wrapper is "__gcc_shell_handler", provided by libgcc.
+
+   We force the procedure kind to PT_STACK, and the fixed frame location is
+   fp+8, just before the register save area. We use the handler_data field in
+   the procedure descriptor to state the fp offset at which the installed
+   handler address can be found.  */
+
+#define VMS_COND_HANDLER_FP_OFFSET 8
+
+/* Expand code to store the currently installed user VMS condition handler
+   into TARGET and install HANDLER as the new condition handler.  */
+
+void
+alpha_expand_builtin_establish_vms_condition_handler (rtx target, rtx handler)
+{
+  rtx handler_slot_address
+    = plus_constant (hard_frame_pointer_rtx, VMS_COND_HANDLER_FP_OFFSET);
+
+  rtx handler_slot
+    = gen_rtx_MEM (DImode, handler_slot_address);
+
+  emit_move_insn (target, handler_slot);
+  emit_move_insn (handler_slot, handler);
+
+  /* Notify the start/prologue/epilogue emitters that the condition handler
+     slot is needed.  In addition to reserving the slot space, this will force
+     the procedure kind to PT_STACK so ensure that the hard_frame_pointer_rtx
+     use above is correct.  */
+  cfun->machine->uses_condition_handler = true;
+}
+
+/* Expand code to store the current VMS condition handler into TARGET and
+   nullify it.  */
+
+void
+alpha_expand_builtin_revert_vms_condition_handler (rtx target)
+{
+  /* We implement this by establishing a null condition handler, with the tiny
+     side effect of setting uses_condition_handler.  This is a little bit
+     pessimistic if no actual builtin_establish call is ever issued, which is
+     not a real problem and expected never to happen anyway.  */
+
+  alpha_expand_builtin_establish_vms_condition_handler (target, const0_rtx);
+}
+
 /* Functions to save and restore alpha_return_addr_rtx.  */
 
 /* Start the ball rolling with RETURN_ADDR_RTX.  */
@@ -6380,6 +6440,8 @@ enum alpha_builtin
   ALPHA_BUILTIN_RPCC,
   ALPHA_BUILTIN_THREAD_POINTER,
   ALPHA_BUILTIN_SET_THREAD_POINTER,
+  ALPHA_BUILTIN_ESTABLISH_VMS_CONDITION_HANDLER,
+  ALPHA_BUILTIN_REVERT_VMS_CONDITION_HANDLER,
 
   /* TARGET_MAX */
   ALPHA_BUILTIN_MINUB8,
@@ -6435,6 +6497,8 @@ static enum insn_code const code_for_builtin[ALPHA_BUILTIN_max] = {
   CODE_FOR_builtin_rpcc,
   CODE_FOR_load_tp,
   CODE_FOR_set_tp,
+  CODE_FOR_builtin_establish_vms_condition_handler,
+  CODE_FOR_builtin_revert_vms_condition_handler,
 
   /* TARGET_MAX */
   CODE_FOR_builtin_minub8,
@@ -6580,6 +6644,21 @@ alpha_init_builtins (void)
 			       NULL, NULL);
   TREE_NOTHROW (decl) = 1;
 
+  if (TARGET_ABI_OPEN_VMS)
+    {
+      ftype = build_function_type_list (ptr_type_node, ptr_type_node,
+					NULL_TREE);
+      add_builtin_function ("__builtin_establish_vms_condition_handler", ftype,
+			    ALPHA_BUILTIN_ESTABLISH_VMS_CONDITION_HANDLER,
+			    BUILT_IN_MD, NULL, NULL_TREE);
+
+      ftype = build_function_type_list (ptr_type_node, void_type_node,
+					NULL_TREE);
+      add_builtin_function ("__builtin_revert_vms_condition_handler", ftype,
+			    ALPHA_BUILTIN_REVERT_VMS_CONDITION_HANDLER,
+			     BUILT_IN_MD, NULL, NULL_TREE);
+    }
+
   alpha_v8qi_u = build_vector_type (unsigned_intQI_type_node, 8);
   alpha_v8qi_s = build_vector_type (intQI_type_node, 8);
   alpha_v4hi_u = build_vector_type (unsigned_intHI_type_node, 4);
@@ -7309,7 +7388,10 @@ alpha_sa_size (void)
 	  if (! fixed_regs[i] && call_used_regs[i] && ! df_regs_ever_live_p (i))
 	    vms_save_fp_regno = i;
 
-      if (vms_save_fp_regno == -1 && alpha_procedure_type == PT_REGISTER)
+      /* A VMS condition handler requires a stack procedure in our
+	 implementation. (not required by the calling standard).  */
+      if ((vms_save_fp_regno == -1 && alpha_procedure_type == PT_REGISTER)
+	  || cfun->machine->uses_condition_handler)
 	vms_base_regno = REG_PV, alpha_procedure_type = PT_STACK;
       else if (alpha_procedure_type == PT_NULL)
 	vms_base_regno = REG_PV;
@@ -7318,9 +7400,10 @@ alpha_sa_size (void)
       vms_unwind_regno = (vms_base_regno == REG_PV
 			  ? HARD_FRAME_POINTER_REGNUM : STACK_POINTER_REGNUM);
 
-      /* If this is a stack procedure, allow space for saving FP and RA.  */
+      /* If this is a stack procedure, allow space for saving FP, RA and
+	 a condition handler slot if needed.  */
       if (alpha_procedure_type == PT_STACK)
-	sa_size += 2;
+	sa_size += 2 + cfun->machine->uses_condition_handler;
     }
   else
     {
@@ -7572,7 +7655,7 @@ alpha_expand_prologue (void)
 				 + crtl->args.pretend_args_size));
 
   if (TARGET_ABI_OPEN_VMS)
-    reg_offset = 8;
+    reg_offset = 8 + 8 * cfun->machine->uses_condition_handler;
   else
     reg_offset = ALPHA_ROUND (crtl->outgoing_args_size);
 
@@ -7910,7 +7993,7 @@ alpha_start_function (FILE *file, const char *fnname,
 				 + crtl->args.pretend_args_size));
 
   if (TARGET_ABI_OPEN_VMS)
-    reg_offset = 8;
+    reg_offset = 8 + 8 * cfun->machine->uses_condition_handler;
   else
     reg_offset = ALPHA_ROUND (crtl->outgoing_args_size);
 
@@ -8049,6 +8132,16 @@ alpha_start_function (FILE *file, const char *fnname,
     }
 
 #if TARGET_ABI_OPEN_VMS
+  /* If a user condition handler has been installed at some point, emit
+     the procedure descriptor bits to point the Condition Handling Facility
+     at the indirection wrapper, and state the fp offset at which the user
+     handler may be found.  */
+  if (cfun->machine->uses_condition_handler)
+    {
+      fprintf (file, "\t.handler __gcc_shell_handler\n");
+      fprintf (file, "\t.handler_data %d\n", VMS_COND_HANDLER_FP_OFFSET);
+    }
+
   /* Ifdef'ed cause link_section are only available then.  */
   switch_to_section (readonly_data_section);
   fprintf (file, "\t.align 3\n");
@@ -8120,7 +8213,7 @@ alpha_expand_epilogue (void)
   if (TARGET_ABI_OPEN_VMS)
     {
        if (alpha_procedure_type == PT_STACK)
-          reg_offset = 8;
+          reg_offset = 8 + 8 * cfun->machine->uses_condition_handler;
        else
           reg_offset = 0;
     }
diff --git a/gcc/config/alpha/alpha.h b/gcc/config/alpha/alpha.h
index 5b74fe1..cd8c11e 100644
--- a/gcc/config/alpha/alpha.h
+++ b/gcc/config/alpha/alpha.h
@@ -882,6 +882,12 @@ do {						\
 
 #define RETURN_ADDR_RTX  alpha_return_addr
 
+/* Provide a definition of DWARF_FRAME_REGNUM here so that fallback unwinders
+   can use DWARF_ALT_FRAME_RETURN_COLUMN defined below.  This is just the same
+   as the default definition in dwarf2out.c.  */
+#undef DWARF_FRAME_REGNUM
+#define DWARF_FRAME_REGNUM(REG) DBX_REGISTER_NUMBER (REG)
+
 /* Before the prologue, RA lives in $26.  */
 #define INCOMING_RETURN_ADDR_RTX  gen_rtx_REG (Pmode, 26)
 #define DWARF_FRAME_RETURN_COLUMN DWARF_FRAME_REGNUM (26)
diff --git a/gcc/config/alpha/alpha.md b/gcc/config/alpha/alpha.md
index fe475c2..935cc94 100644
--- a/gcc/config/alpha/alpha.md
+++ b/gcc/config/alpha/alpha.md
@@ -4976,6 +4976,24 @@
     return "call_pal 0x9f";
 }
   [(set_attr "type" "callpal")])
+
+;; Special builtins for establishing and reverting VMS condition handlers.
+
+(define_expand "builtin_establish_vms_condition_handler"
+  [(set (reg:DI 0) (match_operand:DI 0 "register_operand" ""))
+   (use (match_operand:DI 1 "address_operand" ""))]
+  "TARGET_ABI_OPEN_VMS"
+{
+  alpha_expand_builtin_establish_vms_condition_handler (operands[0],
+                                                        operands[1]);
+})
+
+(define_expand "builtin_revert_vms_condition_handler"
+  [(set (reg:DI 0) (match_operand:DI 0 "register_operand" ""))]
+  "TARGET_ABI_OPEN_VMS"
+{
+  alpha_expand_builtin_revert_vms_condition_handler (operands[0]);
+})
 
 ;; Finally, we have the basic data motion insns.  The byte and word insns
 ;; are done via define_expand.  Start with the floating-point insns, since
diff --git a/gcc/config/alpha/t-vms b/gcc/config/alpha/t-vms
index e110512..410e219 100644
--- a/gcc/config/alpha/t-vms
+++ b/gcc/config/alpha/t-vms
@@ -17,6 +17,8 @@
 # along with GCC; see the file COPYING3.  If not see
 # <http://www.gnu.org/licenses/>.
 
+LIB2FUNCS_EXTRA = $(srcdir)/config/alpha/vms-gcc_shell_handler.c
+
 EXTRA_PARTS = vms-dwarf2.o vms-dwarf2eh.o $(VMS_EXTRA_PARTS) \
   crtbegin.o crtbeginS.o crtend.o crtendS.o
 
diff --git a/gcc/config/alpha/vms-gcc_shell_handler.c b/gcc/config/alpha/vms-gcc_shell_handler.c
new file mode 100644
index 0000000..67d0fe7
--- /dev/null
+++ b/gcc/config/alpha/vms-gcc_shell_handler.c
@@ -0,0 +1,124 @@
+/* Static condition handler for Alpha/VMS.
+   Copyright (C) 2005-2009
+   Free Software Foundation, Inc.
+
+   This file is part of GCC.
+
+   GCC is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published
+   by the Free Software Foundation; either version 3, or (at your
+   option) any later version.
+
+   GCC is distributed in the hope that it will be useful, but WITHOUT
+   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+   or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+   License for more details.
+
+   Under Section 7 of GPL version 3, you are granted additional
+   permissions described in the GCC Runtime Library Exception, version
+   3.1, as published by the Free Software Foundation.
+
+   You should have received a copy of the GNU General Public License and
+   a copy of the GCC Runtime Library Exception along with this program;
+   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* This file implements __gcc_shell_handler, the static VMS condition handler
+   used as the indirection wrapper around user level handlers installed with
+   establish_vms_condition_handler GCC builtin.
+
+   [ABI] in comments refers to the "HP OpenVMS calling standard" document
+   dated January 2005.  */
+
+#include <vms/chfdef.h>
+#include <vms/pdscdef.h>
+#include <vms/ssdef.h>
+
+typedef void * ADDR;
+typedef unsigned long long REG;
+
+#define REG_AT(addr) (*(REG *)(addr))
+
+/* Compute pointer to procedure descriptor (Procedure Value) from Frame
+   Pointer FP, according to the rules in [ABI-3.5.1 Current Procedure].  */
+#define PV_FOR(FP) \
+  (((FP) != 0) \
+    ? (((REG_AT (FP) & 0x7) == 0) ? *(PDSCDEF **)(FP) : (PDSCDEF *)(FP)) : 0)
+
+long
+__gcc_shell_handler (struct chf$signal_array *sig_arr,
+		     struct chf$mech_array *mech_arr);
+
+/* Helper for __gcc_shell_handler.  Fetch the pointer to procedure currently
+   registered as the VMS condition handler for the live function with a frame
+   pointer FP.  */
+
+static ADDR
+get_dyn_handler_pointer (REG fp)
+{
+  /* From the frame pointer we find the procedure descriptor, and fetch
+     the handler_data field from there.  This field contains the offset
+     from FP at which the address of the currently installed handler is
+     to be found.  */
+  
+  PDSCDEF * pd = PV_FOR (fp);
+  /* Procedure descriptor pointer for the live subprogram with FP as the frame
+     pointer, and to which _gcc_shell_handler is attached as a condition
+     handler.  */
+
+  REG handler_slot_offset;
+  /* Offset from FP at which the address of the currently established real
+     condition handler is to be found.  This offset is available from the
+     handler_data field of the procedure descriptor.  */
+
+  REG handler_data_offset;
+  /* The handler_data field position in the procedure descriptor, which
+     depends on the kind of procedure at hand.  */
+
+  switch (pd->pdsc$w_flags & 0xf)
+    {
+    case PDSC$K_KIND_FP_STACK:    /* [3.4.2 PD for stack frame procedures]  */
+      handler_data_offset = 40;
+      break;
+	
+    case PDSC$K_KIND_FP_REGISTER: /* [3.4.5 PD for reg frame procedures]  */
+      handler_data_offset = 32;
+      break;
+      
+    default:
+      handler_data_offset = 0;
+      break;
+    }
+
+  /* If we couldn't determine the handler_data field position, give up.  */
+  if (handler_data_offset == 0)
+    return 0;
+
+  /* Otherwise, fetch the fp offset at which the real handler address is to be
+     found, then fetch and return the latter in turn.  */
+     
+  handler_slot_offset = REG_AT ((REG)pd + handler_data_offset);
+
+  return (ADDR) REG_AT (fp + handler_slot_offset);
+}
+
+/* The static VMS condition handler for GCC code.  Fetch the address of the
+   currently established condition handler, then resignal if there is none or
+   call the handler with the VMS condition arguments.  */
+
+long
+__gcc_shell_handler (struct chf$signal_array *sig_arr,
+		     struct chf$mech_array *mech_arr)
+{
+  long ret;
+  long (*user_handler) (struct chf$signal_array *, struct chf$mech_array *);
+
+  user_handler = get_dyn_handler_pointer (mech_arr->chf$q_mch_frame);
+  if (!user_handler)
+    ret = SS$_RESIGNAL;
+  else
+    ret = user_handler (sig_arr, mech_arr);
+
+  return ret;
+}
+   
diff --git a/gcc/config/alpha/vms-unwind.h b/gcc/config/alpha/vms-unwind.h
index 78c77442..09b2f8f 100644
--- a/gcc/config/alpha/vms-unwind.h
+++ b/gcc/config/alpha/vms-unwind.h
@@ -1,71 +1,291 @@
-/* DWARF2 EH unwinding support for Alpha VMS.
-   Copyright (C) 2004, 2007 Free Software Foundation, Inc.
+/* Fallback frame unwinding for Alpha/VMS.
+   Copyright (C) 1996, 1997, 1998, 2000, 2001, 2002, 2003, 2009
+   Free Software Foundation, Inc.
 
-This file is part of GCC.
+   This file is part of GCC.
 
-GCC is free software; you can redistribute it and/or modify
-it under the terms of the GNU General Public License as published by
-the Free Software Foundation; either version 3, or (at your option)
-any later version.
+   GCC is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published
+   by the Free Software Foundation; either version 3, or (at your
+   option) any later version.
 
-GCC is distributed in the hope that it will be useful,
-but WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-GNU General Public License for more details.
+   GCC is distributed in the hope that it will be useful, but WITHOUT
+   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+   or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+   License for more details.
 
-You should have received a copy of the GNU General Public License
-along with GCC; see the file COPYING3.  If not see
-<http://www.gnu.org/licenses/>.  */
+   Under Section 7 of GPL version 3, you are granted additional
+   permissions described in the GCC Runtime Library Exception, version
+   3.1, as published by the Free Software Foundation.
 
-#include <pdscdef.h>
+   You should have received a copy of the GNU General Public License and
+   a copy of the GCC Runtime Library Exception along with this program;
+   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+   <http://www.gnu.org/licenses/>.  */
 
-#define MD_FALLBACK_FRAME_STATE_FOR alpha_fallback_frame_state
+#include <stdlib.h>
+#include <stdio.h>
+#include <vms/pdscdef.h>
+#include <vms/libicb.h>
+#include <vms/chfctxdef.h>
+#include <vms/chfdef.h>
 
-static _Unwind_Reason_Code
-alpha_fallback_frame_state (struct _Unwind_Context *context,
-			    _Unwind_FrameState *fs)
+#define MD_FALLBACK_FRAME_STATE_FOR alpha_vms_fallback_frame_state
+
+typedef void * ADDR;
+typedef unsigned long long REG;
+typedef PDSCDEF * PV;
+
+#define REG_AT(addr) (*(REG *)(addr))
+#define ADDR_AT(addr) (*(ADDR *)(addr))
+
+/* Compute pointer to procedure descriptor (Procedure Value) from Frame
+   Pointer FP, according to the rules in [ABI-3.5.1 Current Procedure].  */
+#define PV_FOR(FP) \
+  (((FP) != 0) \
+    ? (((REG_AT (FP) & 0x7) == 0) ? *(PDSCDEF **)(FP) : (PDSCDEF *)(FP)) : 0)
+
+extern int SYS$GL_CALL_HANDL;
+/* This is actually defined as a "long", but in system code where longs
+   are always 4bytes while GCC longs might be 8bytes.  */
+
+#define UPDATE_FS_FOR_CFA_GR(FS, GRN, LOC, CFA) \
+do { \
+(FS)->regs.reg[GRN].how = REG_SAVED_OFFSET;      \
+(FS)->regs.reg[GRN].loc.offset = (_Unwind_Sword) ((REG) (LOC) - (REG) (CFA)); \
+} while (0);
+
+#define GIVEUP_ON_FAILURE(STATUS) \
+  { if ((((STATUS) & 1) != 1)) return _URC_END_OF_STACK; }
+#define DENOTES_EXC_DISPATCHER(PV) ((PV) == (ADDR) (REG) SYS$GL_CALL_HANDL)
+
+#define RA_COLUMN (DWARF_ALT_FRAME_RETURN_COLUMN)
+
+static int
+alpha_vms_fallback_frame_state (struct _Unwind_Context *context,
+				_Unwind_FrameState *fs)
 {
-  PDSCDEF *pv = *((PDSCDEF **) context->reg [29]);
+  static int eh_debug = -1;
+
+  /* Our goal is to update FS to reflect the state one step up CONTEXT, that
+     is: the CFA, return address and *saved* registers locations associated
+     with the function designated by CONTEXT->ra.  We are called when the
+     libgcc unwinder has not found any dwarf FDE for this address, which
+     typically happens when trying to propagate a language exception through a
+     signal global vector or frame based handler.
+
+     The CONTEXT->reg[] entries reflect the state/location of register saves
+     so designate values live at the CONTEXT->ra point.  Of precious value to
+     us here is the frame pointer (r29), which gets us a procedure value.  */
+
+  PV pv = (context->reg[29] != 0) ? PV_FOR (ADDR_AT (context->reg[29])) : 0;
+
+  int pkind = pv ? pv->pdsc$w_flags & 0xf : 0;
+  /* VMS procedure kind, as indicated by the procedure descriptor.  We only
+     know how to deal with FP_STACK or FP_REGISTER here.  */
+
+  ADDR new_cfa = 0;
+  /* CFA we will establish for the caller, computed in different ways,
+     e.g. depending whether we cross an exception dispatcher frame.  */
+
+  CHFCTX *chfctx = 0;
+  /* Pointer to the VMS CHF context associated with an exception dispatcher
+     frame, if we happen to come across one.  */
+
+  int i,j;
+
+  if (eh_debug == -1)
+    {
+      char * eh_debug_env = getenv ("EH_DEBUG");
+      eh_debug = eh_debug_env ? atoi (eh_debug_env) : 0;
+    }
+
+  if (eh_debug)
+    printf ("MD_FALLBACK running ...\n");
+
+  /* We only know how to deal with stack or reg frame procedures, so give
+     up if we're handed anything else.  */
+  if (pkind != PDSC$K_KIND_FP_STACK && pkind != PDSC$K_KIND_FP_REGISTER)
+    return _URC_END_OF_STACK;
+  
+  if (eh_debug)
+    printf ("FALLBACK: CTX FP = 0x%p, PV = 0x%p, EN = 0x%llx, RA = 0x%p\n",
+	    ADDR_AT (context->reg[29]), pv, pv->pdsc$q_entry, context->ra);
+
+  fs->retaddr_column = RA_COLUMN;
+
+  /* If PV designates a VMS exception vector or condition handler, we need to
+     do as if the caller was the signaling point and estabish the state of the
+     intermediate VMS code (CFA, RA and saved register locations) as if it was
+     a single regular function.  This requires special processing.
+
+     The datastructures available from an condition dispatcher frame (signal
+     context) do not contain the values of most callee-saved registers, so
+     whathever PV designates, we need to account for the registers it saves.
+
+     Besides, we need to express all the locations with respect to a
+     consistent CFA value, so we compute this first.  */
+
+  if (DENOTES_EXC_DISPATCHER (pv))
+    {
+      /* The CFA to establish is the signaling point's stack pointer. We
+	 compute it using the system invocation context unwinding services and
+	 save the CHF context data pointer along the way for later uses.  */
+
+      INVO_CONTEXT_BLK icb;
+      int status, invo_handle;
+
+      if (eh_debug)
+	printf ("FALLBACK: SYS$HANDLER\n");
+
+      icb.libicb$q_ireg [29] = REG_AT (context->reg[29]);
+      icb.libicb$q_ireg [30] = 0;
+      invo_handle = LIB$GET_INVO_HANDLE (&icb);
+
+      status = LIB$GET_INVO_CONTEXT (invo_handle, &icb);
+      GIVEUP_ON_FAILURE (status);
+
+      chfctx = (CHFCTX *) icb.libicb$ph_chfctx_addr;
+
+      status = LIB$GET_PREV_INVO_CONTEXT (&icb);
+      GIVEUP_ON_FAILURE (status);
 
-  if (pv && ((long) pv & 0x7) == 0) /* low bits 0 means address */
-    pv = *(PDSCDEF **) pv;
+      new_cfa = (ADDR) icb.libicb$q_ireg[30];      
+    }
+  else
+    {
+      /* The CFA to establish is the SP value on entry of the procedure
+	 designated by PV, which we compute as the corresponding frame base
+	 register value + frame size.  Note that the frame base may differ
+	 from CONTEXT->cfa, typically if the caller has performed dynamic
+	 stack allocations.  */
+      
+      int  base_reg  = pv->pdsc$w_flags & PDSC$M_BASE_REG_IS_FP ? 29 : 30;
+      ADDR base_addr = ADDR_AT (context->reg[base_reg]);
+      
+      new_cfa = base_addr + pv->pdsc$l_size;
+    }
+
+  /* State to compute the caller's CFA by adding an offset to the current
+     one in CONTEXT.  */
+  fs->regs.cfa_how = CFA_REG_OFFSET;
+  fs->regs.cfa_reg = __builtin_dwarf_sp_column ();
+  fs->regs.cfa_offset = new_cfa - context->cfa;
 
-  if (pv && ((pv->pdsc$w_flags & 0xf) == PDSC$K_KIND_FP_STACK))
+  /* Regular unwind first, accounting for the register saves performed by
+     the procedure designated by PV.  */
+
+  switch (pkind)
     {
-      int i, j;
-
-      fs->regs.cfa_offset = pv->pdsc$l_size;
-      fs->regs.cfa_reg = pv->pdsc$w_flags & PDSC$M_BASE_REG_IS_FP ? 29 : 30;
-      fs->retaddr_column = 26;
-      fs->regs.cfa_how = CFA_REG_OFFSET;
-      fs->regs.reg[27].loc.offset = -pv->pdsc$l_size;
-      fs->regs.reg[27].how = REG_SAVED_OFFSET;
-      fs->regs.reg[26].loc.offset
-	= -(pv->pdsc$l_size - pv->pdsc$w_rsa_offset);
-      fs->regs.reg[26].how = REG_SAVED_OFFSET;
-
-      for (i = 0, j = 0; i < 32; i++)
-	if (1<<i & pv->pdsc$l_ireg_mask)
-	  {
-	    fs->regs.reg[i].loc.offset
-	      = -(pv->pdsc$l_size - pv->pdsc$w_rsa_offset - 8 * ++j);
-	    fs->regs.reg[i].how = REG_SAVED_OFFSET;
-	  }
-
-      return _URC_NO_REASON;
+    case PDSC$K_KIND_FP_STACK:
+      {
+	/* The saved registers are all located in the Register Save Area,
+	   except for the procedure value register (R27) found at the frame
+	   base address.  */
+
+	int  base_reg  = pv->pdsc$w_flags & PDSC$M_BASE_REG_IS_FP ? 29 : 30;
+	ADDR base_addr = ADDR_AT (context->reg[base_reg]);
+	ADDR rsa_addr  = base_addr + pv->pdsc$w_rsa_offset;
+
+	if (eh_debug)
+	  printf ("FALLBACK: STACK frame procedure\n");
+
+	UPDATE_FS_FOR_CFA_GR (fs, 27, base_addr, new_cfa);
+
+	/* The first RSA entry is for the return address register, R26.  */
+
+	UPDATE_FS_FOR_CFA_GR (fs, 26, rsa_addr, new_cfa);
+	UPDATE_FS_FOR_CFA_GR (fs, RA_COLUMN, rsa_addr, new_cfa);
+
+	/* The following entries are for registers marked as saved according
+	   to ireg_mask.  */
+	for (i = 0, j = 0; i < 32; i++)
+	  if ((1 << i) & pv->pdsc$l_ireg_mask)
+	    UPDATE_FS_FOR_CFA_GR (fs, i, rsa_addr + 8 * ++j, new_cfa);
+	
+	/* ??? floating point registers ?  */
+
+	break;
+      }
+
+    case PDSC$K_KIND_FP_REGISTER:
+      {
+	if (eh_debug)
+	  printf ("FALLBACK: REGISTER frame procedure\n");
+
+	fs->regs.reg[RA_COLUMN].how = REG_SAVED_REG;
+	fs->regs.reg[RA_COLUMN].loc.reg = pv->pdsc$b_save_ra;
+	
+	fs->regs.reg[29].how = REG_SAVED_REG;
+	fs->regs.reg[29].loc.reg = pv->pdsc$b_save_fp;
+	
+	break;
+      }
+
+    default:
+      /* Should never reach here.  */
+      return _URC_END_OF_STACK;
     }
-  else if (pv && ((pv->pdsc$w_flags & 0xf) == PDSC$K_KIND_FP_REGISTER))
+
+  /* If PV designates an exception dispatcher, we have to adjust the return
+     address column to get at the signal occurrence point, and account for
+     for what the CHF context contains.  */
+
+  if (DENOTES_EXC_DISPATCHER (pv))
     {
-      fs->regs.cfa_offset = pv->pdsc$l_size;
-      fs->regs.cfa_reg = pv->pdsc$w_flags & PDSC$M_BASE_REG_IS_FP ? 29 : 30;
-      fs->retaddr_column = 26;
-      fs->regs.cfa_how = CFA_REG_OFFSET;
-      fs->regs.reg[26].loc.reg = pv->pdsc$b_save_ra;
-      fs->regs.reg[26].how = REG_SAVED_REG;
-      fs->regs.reg[29].loc.reg = pv->pdsc$b_save_fp;
-      fs->regs.reg[29].how = REG_SAVED_REG;
-
-      return _URC_NO_REASON;
+      /* The PC of the instruction causing the condition is available from the
+	 signal argument vector.  Extra saved register values are available
+	 from the mechargs array.  */
+
+      CHF$SIGNAL_ARRAY *sigargs
+	= (CHF$SIGNAL_ARRAY *) chfctx->chfctx$q_sigarglst;
+
+      CHF$MECH_ARRAY *mechargs
+	= (CHF$MECH_ARRAY *) chfctx->chfctx$q_mcharglst;
+
+      ADDR condpc_addr
+	= &((int *)(&sigargs->chf$l_sig_name)) [sigargs->chf$is_sig_args-2];
+
+      ADDR rei_frame_addr = (void *) mechargs->chf$q_mch_esf_addr;
+
+      /* Adjust the return address location.  */
+
+      UPDATE_FS_FOR_CFA_GR (fs, RA_COLUMN, condpc_addr, new_cfa);
+
+      /* The frame pointer at the condition point is available from the
+	 chf context directly.  */
+
+      UPDATE_FS_FOR_CFA_GR (fs, 29, &chfctx->chfctx$q_expt_fp, new_cfa);
+
+      /* Registers available from the mechargs array.  */
+
+      UPDATE_FS_FOR_CFA_GR (fs, 0, &mechargs->chf$q_mch_savr0, new_cfa);
+      UPDATE_FS_FOR_CFA_GR (fs, 1, &mechargs->chf$q_mch_savr1, new_cfa);
+
+      UPDATE_FS_FOR_CFA_GR (fs, 16, &mechargs->chf$q_mch_savr16, new_cfa);
+      UPDATE_FS_FOR_CFA_GR (fs, 17, &mechargs->chf$q_mch_savr17, new_cfa);
+      UPDATE_FS_FOR_CFA_GR (fs, 18, &mechargs->chf$q_mch_savr18, new_cfa);
+      UPDATE_FS_FOR_CFA_GR (fs, 19, &mechargs->chf$q_mch_savr19, new_cfa);
+      UPDATE_FS_FOR_CFA_GR (fs, 20, &mechargs->chf$q_mch_savr20, new_cfa);
+      UPDATE_FS_FOR_CFA_GR (fs, 21, &mechargs->chf$q_mch_savr21, new_cfa);
+      UPDATE_FS_FOR_CFA_GR (fs, 22, &mechargs->chf$q_mch_savr22, new_cfa);
+      UPDATE_FS_FOR_CFA_GR (fs, 23, &mechargs->chf$q_mch_savr23, new_cfa);
+      UPDATE_FS_FOR_CFA_GR (fs, 24, &mechargs->chf$q_mch_savr24, new_cfa);
+      UPDATE_FS_FOR_CFA_GR (fs, 25, &mechargs->chf$q_mch_savr25, new_cfa);
+      UPDATE_FS_FOR_CFA_GR (fs, 26, &mechargs->chf$q_mch_savr26, new_cfa);
+      UPDATE_FS_FOR_CFA_GR (fs, 27, &mechargs->chf$q_mch_savr27, new_cfa);
+      UPDATE_FS_FOR_CFA_GR (fs, 28, &mechargs->chf$q_mch_savr28, new_cfa);
+      
+      /* Registers R2 to R7 are available from the rei frame pointer.  */
+      
+      for (i = 2; i <= 7; i ++)
+	UPDATE_FS_FOR_CFA_GR (fs, i, rei_frame_addr+(i - 2)*8, new_cfa);
+      
+      /* ??? floating point registers ?  */
     }
-  return _URC_END_OF_STACK;
+
+  return _URC_NO_REASON;
 }
+
+
+
diff --git a/gcc/config/alpha/vms.h b/gcc/config/alpha/vms.h
index ff5e5d2..7b149f1 100644
--- a/gcc/config/alpha/vms.h
+++ b/gcc/config/alpha/vms.h
@@ -287,7 +287,13 @@ do {									\
 #define LINK_EH_SPEC "vms-dwarf2eh.o%s "
 #define LINK_GCC_C_SEQUENCE_SPEC "%G"
 
+#ifdef IN_LIBGCC2
+/* Get the definition for MD_FALLBACK_FRAME_STATE_FOR from a separate
+   file. This avoids having to recompile the world instead of libgcc only
+   when changes to this macro are exercised.  */
+
 #define MD_UNWIND_SUPPORT "config/alpha/vms-unwind.h"
+#endif
 
 /* This is how to output an assembler line
    that says to advance the location counter