diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 8f4b3964445d..7dfe5e8a9209 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2004-09-29  Richard Henderson  <rth@redhat.com>
+
+	* unwind-dw2.c (_Unwind_GetGR): Honor DWARF_ZERO_REG.
+	* doc/tm.texi (DWARF_ZERO_REG): New.
+
+	* config/alpha/alpha.c (alpha_sa_mask, alpha_expand_prologue,
+	alpha_expand_epilogue): Revert 2003-09-30 change to store zero.
+	* config/alpha/alpha.h (DWARF_ZERO_REG): New.
+
 2004-09-29  Ulrich Weigand  <uweigand@de.ibm.com>
 
 	* builtins.c (expand_builtin_strlen): Do not call emit_move_insn
diff --git a/gcc/config/alpha/alpha.c b/gcc/config/alpha/alpha.c
index 114170b8b474..b1de390bc533 100644
--- a/gcc/config/alpha/alpha.c
+++ b/gcc/config/alpha/alpha.c
@@ -5924,11 +5924,6 @@ alpha_sa_mask (unsigned long *imaskP, unsigned long *fmaskP)
 	    break;
 	  imask |= 1UL << regno;
 	}
-
-      /* Glibc likes to use $31 as an unwind stopper for crt0.  To
-	 avoid hackery in unwind-dw2.c, we need to actively store a
-	 zero in the prologue of _Unwind_RaiseException et al.  */
-      imask |= 1UL << 31;
     }
 
   /* If any register spilled, then spill the return address also.  */
@@ -6451,14 +6446,6 @@ alpha_expand_prologue (void)
 	    reg_offset += 8;
 	  }
 
-      /* Store a zero if requested for unwinding.  */
-      if (imask & (1UL << 31))
-	{
-	  emit_frame_store_1 (const0_rtx, sa_reg, sa_bias, reg_offset,
-			      gen_rtx_REG (Pmode, 31));
-	  reg_offset += 8;
-	}
-
       for (i = 0; i < 31; i++)
 	if (fmask & (1UL << i))
 	  {
@@ -6876,9 +6863,6 @@ alpha_expand_epilogue (void)
 	    reg_offset += 8;
 	  }
 
-      if (imask & (1UL << 31))
-	reg_offset += 8;
-
       for (i = 0; i < 31; ++i)
 	if (fmask & (1UL << i))
 	  {
diff --git a/gcc/config/alpha/alpha.h b/gcc/config/alpha/alpha.h
index 35d6f4ac3a1a..fe3cedcb520b 100644
--- a/gcc/config/alpha/alpha.h
+++ b/gcc/config/alpha/alpha.h
@@ -1183,6 +1183,7 @@ do {						\
 #define INCOMING_RETURN_ADDR_RTX  gen_rtx_REG (Pmode, 26)
 #define DWARF_FRAME_RETURN_COLUMN DWARF_FRAME_REGNUM (26)
 #define DWARF_ALT_FRAME_RETURN_COLUMN DWARF_FRAME_REGNUM (64)
+#define DWARF_ZERO_REG 31
 
 /* Describe how we implement __builtin_eh_return.  */
 #define EH_RETURN_DATA_REGNO(N)	((N) < 4 ? (N) + 16 : INVALID_REGNUM)
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index fc033ecc6913..f72713cee675 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -2974,6 +2974,14 @@ general register, but an alternate column needs to be used for
 signal frames.
 @end defmac
 
+@defmac DWARF_ZERO_REG
+A C expression whose value is an integer giving a DWARF 2 register
+number that is considered to always have the value zero.  This should
+only be defined if the target has an architected zero register, and
+someone decided it was a good idea to use that register number to
+terminate the stack backtrace.  New ports should avoid this.
+@end defmac
+
 @defmac INCOMING_FRAME_SP_OFFSET
 A C expression whose value is an integer giving the offset, in bytes,
 from the value of the stack pointer register to the top of the stack
diff --git a/gcc/unwind-dw2.c b/gcc/unwind-dw2.c
index 67b8d1cd0661..baa4481c7471 100644
--- a/gcc/unwind-dw2.c
+++ b/gcc/unwind-dw2.c
@@ -125,6 +125,11 @@ _Unwind_GetGR (struct _Unwind_Context *context, int index)
   int size;
   void *ptr;
 
+#ifdef DWARF_ZERO_REG
+  if (index == DWARF_ZERO_REG)
+    return 0;
+#endif
+
   index = DWARF_REG_TO_UNWIND_COLUMN (index);
   if (index >= (int) sizeof(dwarf_reg_size_table))
     abort ();