[PATCH] add 'rs6000_in_function_epilogue_p()'

[Paul Gilliam <pgilliam@us.ibm.com>]

This patch fixes a problem when watching local variables on PowerPC.

Here is a reference from the gdb mailing list:
http://sourceware.org/ml/gdb/2005-11/msg00602.html

I know the patch uses a depreciated function and I am open to ideas.
Here is a reference from the gdb mailing list about ideas to avoid using the depreciated function:
http://sourceware.org/ml/gdb/2005-11/msg00623.html

I wanted to submit this patch as a starting point, but if it is acceptable, I'll commit it.

2005-11-30  Paul Gilliam  <pgilliam@us.ibm.com>

	* rs6000-tdep.c: Add new subroutine, 'rs6000_in_function_epilogue_p()'
	and put it into the architecture vector.

Index: rs6000-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/rs6000-tdep.c,v
retrieving revision 1.248
diff -a -u -p -r1.248 rs6000-tdep.c
--- rs6000-tdep.c	1 Nov 2005 19:32:36 -0000	1.248
+++ rs6000-tdep.c	30 Nov 2005 18:59:27 -0000
@@ -502,6 +502,63 @@ rs6000_skip_prologue (CORE_ADDR pc)
   return pc;
 }
 
+static int
+insn_changes_sp(unsigned long insn)
+{
+  int opcode  = (insn>>26) & 0x03f;
+  int sd      = (insn>>21) & 0x01f;
+  int a       = (insn>>16) & 0x01f;
+  int b       = (insn>>11) & 0x01f;
+  int subcode = (insn>> 1) & 0x3ff;
+  int rc      =  insn      & 0x001;
+
+  if (opcode == 31 && subcode == 444 && a == 1)
+    return 1;  /* mr R1,Rn */
+  if (opcode == 14 && sd == 1)
+    return 1;  /* addi R1,Rn,simm */
+  if (opcode == 58 && sd == 1)
+    return 1;  /* ld R1,ds(Rn) */
+
+  return 0;
+}
+
+/* Return true if we are in the functin's epilogue, i.e. after the
+   instruction that destroyed the function's stack frame.  */
+static int
+rs6000_in_function_epilogue_p (struct gdbarch *gdbarch, CORE_ADDR pc)
+{
+  bfd_byte insn_buf[PPC_INSN_SIZE];
+  CORE_ADDR scan_pc, func_addr, func_end;
+  unsigned long insn;
+
+  /* Find the search limits.  */
+  if (!find_pc_partial_function (pc, NULL, &func_addr, &func_end))
+    return 0;
+
+  /* Scan forward untill next 'blr'.  */
+  for (scan_pc = pc; scan_pc < func_end; scan_pc += PPC_INSN_SIZE)
+    {
+      if (deprecated_read_memory_nobpt (scan_pc, insn_buf, PPC_INSN_SIZE))
+        return 0;
+      insn = extract_signed_integer (insn_buf, PPC_INSN_SIZE);
+      if (insn == 0x4e800020) break;
+      if (insn_changes_sp(insn))
+        return 0;
+    }
+
+  /* Scan backward untill adjustment to stack pointer (R1).  */
+  for (scan_pc=pc-PPC_INSN_SIZE; scan_pc>=func_addr; scan_pc-=PPC_INSN_SIZE)
+    {
+      if (deprecated_read_memory_nobpt (scan_pc, insn_buf, PPC_INSN_SIZE))
+        return 0;
+      insn = extract_signed_integer (insn_buf, PPC_INSN_SIZE);
+      if (insn_changes_sp(insn))
+        return 1;
+    }
+
+  return 0;
+}
+
 
 /* Fill in fi->saved_regs */
 
@@ -3342,6 +3399,8 @@ rs6000_gdbarch_init (struct gdbarch_info
   set_gdbarch_deprecated_extract_struct_value_address (gdbarch, rs6000_extract_struct_value_address);
 
   set_gdbarch_skip_prologue (gdbarch, rs6000_skip_prologue);
+  set_gdbarch_in_function_epilogue_p (gdbarch, rs6000_in_function_epilogue_p);
+
   set_gdbarch_inner_than (gdbarch, core_addr_lessthan);
   set_gdbarch_breakpoint_from_pc (gdbarch, rs6000_breakpoint_from_pc);