Re: [PATCH] add 'rs6000_in_function_epilogue_p()' (Revised)

Paul Gilliam
2005-12-05T18:29:13Z

On Friday 02 December 2005 12:32, Kevin Buettner wrote:
> On Fri, 2 Dec 2005 11:20:22 -0800
> Paul Gilliam <pgilliam@us.ibm.com> wrote:
>
> > * rs6000-tdep.c: Add new subroutine, 'rs6000_in_function_epilogue_p()'
> > and put it into the architecture vector.
>
> Your patch is okay to commit after you address Mark's concerns.
>
> Kevin
>
>

Kevin,

I made the changes to address Mark's concerns.

But because of the interest this has drawn, I thought I better ask again before I commited the patch.

It's not perfect and will not work under all conditions.

But it doesn't make things worse and does help out in many if not most coditions.

I just want to place this band-aid on the bug and address all the concerns the 'right' way and CFI, etc. for later.

SO, Can I Commit?

-=# Paul #=-

2005-12-05  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       2 Dec 2005 23:08:10 -0000
@@ -502,6 +502,74 @@ 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;
+  /*  b       = (insn>>11) & 0x01f  */
+  int subcode = (insn>> 1) & 0x3ff;
+  /*  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 function'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;
+  struct frame_info *fr;
+
+  /* Find the search limits.  */
+  if (!find_pc_partial_function (pc, NULL, &func_addr, &func_end))
+    return 0;
+
+  /* Get the current frame.  This may be cheap, since we might have
+     just called it in watchpoint_check, before calling
+     gdbarch_in_function_epilogue_p.  */
+
+  fr = get_current_frame ();
+
+  /* Scan forward untill next 'blr'.  */
+  for (scan_pc = pc; scan_pc < func_end; scan_pc += PPC_INSN_SIZE)
+    {
+      if (!safe_frame_unwind_memory (fr, 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 (!safe_frame_unwind_memory (fr, 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 +3409,8 @@ 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);