2007-01-14  Joel Brobecker  <brobecker@gnat.com>
	    Jan Kratochvil <jan.kratochvil@redhat.com>

	* rs6000-tdep.c (bl_to_blrl_insn_p): New function.
	(skip_prologue): Allow bl->blrl used by a PIC code.


--- gdb/rs6000-tdep.c	9 Jan 2007 17:58:57 -0000	1.260
+++ gdb/rs6000-tdep.c	14 Jan 2007 21:24:51 -0000
@@ -902,6 +902,30 @@ store_param_on_stack_p (unsigned long op
   return 0;
 }
 
+/* Assuming that INSN is a "bl" instruction located at PC, return
+   nonzero if the destination of the branch is a "blrl" instruction.
+   
+   This sequence is sometimes found in certain function prologues.
+   It allows the function to load the LR register with a value that
+   they can use to access PIC data using PC-relative offsets.  */
+
+static int
+bl_to_blrl_insn_p (CORE_ADDR pc, int insn)
+{
+  const int opcode = 18;
+  const CORE_ADDR dest = branch_dest (opcode, insn, pc, -1);
+  int dest_insn;
+
+  if (dest == -1)
+    return 0;  /* Should never happen, but just return zero to be safe.  */
+  
+  dest_insn = read_memory_integer (dest, 4);
+  if ((dest_insn & 0xfc00ffff) == 0x4c000021) /* blrl */
+    return 1;
+
+  return 0;
+}
+
 static CORE_ADDR
 skip_prologue (CORE_ADDR pc, CORE_ADDR lim_pc, struct rs6000_framedata *fdata)
 {
@@ -1133,18 +1157,19 @@ skip_prologue (CORE_ADDR pc, CORE_ADDR l
 				   to save fprs??? */
 
 	  fdata->frameless = 0;
-	  /* Don't skip over the subroutine call if it is not within
-	     the first three instructions of the prologue and either
-	     we have no line table information or the line info tells
-	     us that the subroutine call is not part of the line
-	     associated with the prologue.  */
-	  if ((pc - orig_pc) > 8)
-	    {
-	      struct symtab_and_line prologue_sal = find_pc_line (orig_pc, 0);
-	      struct symtab_and_line this_sal = find_pc_line (pc, 0);
 
-	      if ((prologue_sal.line == 0) || (prologue_sal.line != this_sal.line))
-		break;
+          if (bl_to_blrl_insn_p (pc, op))
+	    {
+	      /* If we did not yet retrieved LR into some GPR
+		 all our chances are lost.  On the other hand already
+		 stored LR is still kept intact in its GPR.  */
+	      if (lr_reg == -1)
+		{
+		  /* Invalidate lr_reg, but don't set it to -1.
+		     That would mean that it had never been set.  */
+		  lr_reg = -2;
+		}
+	      continue;
 	    }
 
 	  op = read_memory_integer (pc + 4, 4);