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

[Paul Gilliam <pgilliam at us dot ibm dot com>]

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);