[RFC] dwarf2_compose_register_pieces for the e500

[Kevin Buettner <kevinb at redhat dot com>]

As promised in

    http://sources.redhat.com/ml/gdb-patches/2003-05/msg00425.html,

here's the what a ``dwarf2_compose_register_pieces'' method looks
like for the e500.

I don't plan on committing this patch unless the other generic portion
referenced above is approved.

	* rs6000-tdep.c (e500_dwarf2_reg_to_regnum): Provide mapping
	for DWARF vector register numbers 1200 thru 1231.
	(e500_dwarf2_compose_register_pieces): New function.
	(rs6000_gdbarch_init): Initialize the
	``dwarf2_compose_register_pieces'' method for the e500.

Index: rs6000-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/rs6000-tdep.c,v
retrieving revision 1.134
diff -u -p -r1.134 rs6000-tdep.c
--- rs6000-tdep.c	17 May 2003 05:59:58 -0000	1.134
+++ rs6000-tdep.c	22 May 2003 16:39:17 -0000
@@ -1970,10 +1970,89 @@ e500_dwarf2_reg_to_regnum (int num)
   int regnum;
   if (0 <= num && num <= 31)
     return num + gdbarch_tdep (current_gdbarch)->ppc_gp0_regnum;
+  else if (1200 <= num && num <= 1231)
+    {
+      /* Note: 1200 thru 1231 are supposed to refer to only the high part
+         of the 64-bit r0 thru r31.  However, this shouldn't matter in
+	 practice because the only way we (should) see one of these is for
+	 e500_dwarf2_compose_register_pieces() to return this value.  */
+      return num - 1200 + gdbarch_tdep (current_gdbarch)->ppc_ev0_regnum;
+    }
   else 
     return num;
 }
 
+/* Determine the register number, if any, that may be used to represent
+   all of pieces of an object.
+   
+   COUNT is the number of pieces.  PIECE_INFO is an vector of
+   CORE_ADDRs which are arranged as follows:
+
+      dwarf reg for piece 1
+      size of piece 1
+      .
+      .
+      .
+      dwarf reg for piece COUNT
+      size of piece COUNT
+      
+  Note that there are 2*COUNT elements in PIECE_INFO.
+
+  The (dwarf) register number that may be used to represent all the pieces is
+  returned.  If there is no such register, then -1 is returned.   */
+   
+long
+e500_dwarf2_compose_register_pieces (struct gdbarch *gdbarch, int count,
+                                     CORE_ADDR *piece_info)
+{
+  if (count == 2)
+    {
+      int hi_idx;
+      int lo_idx;
+
+      /* Make sure that each piece is 4 bytes.  */
+      if (piece_info[1] != 4 || piece_info[3] != 4)
+	return -1;
+
+      /* The endianess affects the order of the pieces.  */
+      if (TARGET_BYTE_ORDER == BFD_ENDIAN_BIG)
+	{
+	  hi_idx = 0;
+	  lo_idx = 2;
+	}
+      else
+	{
+	  lo_idx = 0;
+	  hi_idx = 2;
+	}
+
+      /* Pattern match the pieces that we can handle.  */
+      if (0 <= piece_info[lo_idx] && piece_info[lo_idx] <= 31
+          && piece_info[lo_idx] + 1200 == piece_info[hi_idx])
+	{
+	  /* Return the register number of the high order vector register.
+	     This will be interpreted by e500_dwarf2_reg_to_regnum to be
+	     the entire 64-bit vector register.  */
+	  return piece_info[hi_idx];
+	}
+      else if (0 <= piece_info[lo_idx] && piece_info[lo_idx] <= 31
+	       && piece_info[hi_idx] + 1 == piece_info[lo_idx])
+	{
+	  /* This is the normal way in which a long long type is put into
+	     a pair of 32-bit registers.  Again, return the register number
+	     for the register containing the most significant bits.  */
+	  return piece_info[hi_idx];
+	}
+      else
+	{
+	  /* We don't understand anything else.  */
+	  return -1;
+	}
+    }
+  else
+    return -1;
+}
+
 /* Convert a dbx stab register number (from `r' declaration) to a gdb
    REGNUM.  */
 static int
@@ -2829,6 +2908,7 @@ rs6000_gdbarch_init (struct gdbarch_info
         set_gdbarch_sp_regnum (gdbarch, tdep->ppc_gp0_regnum + 1);
         set_gdbarch_deprecated_fp_regnum (gdbarch, tdep->ppc_gp0_regnum + 1);
         set_gdbarch_dwarf2_reg_to_regnum (gdbarch, e500_dwarf2_reg_to_regnum);
+	set_gdbarch_dwarf2_compose_register_pieces (gdbarch, e500_dwarf2_compose_register_pieces);
         set_gdbarch_pseudo_register_read (gdbarch, e500_pseudo_register_read);
         set_gdbarch_pseudo_register_write (gdbarch, e500_pseudo_register_write);
         set_gdbarch_extract_return_value (gdbarch, e500_extract_return_value);