[commit] add 'rs6000_in_function_epilogue_p()' (Revised)

[Paul Gilliam]

On Tuesday 17 January 2006 11:28, you wrote:
> > From: Paul Gilliam <pgilliam@us.ibm.com>
> > Date: Mon, 16 Jan 2006 19:15:54 -0800
> > 
> > Mark,
> > 
> > I have made the modifications you asked for.
> > 
> > I would have committed the patch, but I wanted to give you a chance
> > to see if my new variable name was ok: fr became curfrm.
> > 
> > It's still a little criptic, but I was trying to avoid making the
> > condition of an 'if' statement be on two lines.
> 
> Ah, that's a good reason not too make variables and function names
> overly long.  Personally I'd just named the varible "frame" (that
> actually would make the function future safe, since it really should
> work for any frame, and take a frame argument instead of a pc, but
> that's not your fault.)
> 
> > OK to commit?
> 
> I'll leave it up to you to change curfrm into frame as suggested
> above.  So, yes.  Thanks!



-------------- next part --------------
2006-01-16  Paul Gilliam  <pgilliam@us.ibm.com>

        * ppc-tdep.h (PPC_MAX_EPILOGUE_INSTRUCTIONS): New define.
        * rs6000-tdep.c (insn_changes_sp_or_jumps)
        (rs6000_in_function_epilogue_p): New functions.
        (rs6000_gdbarch_init): Set in_function_epilogue_p.

Index: ppc-tdep.h
===================================================================
RCS file: /cvs/src/src/gdb/ppc-tdep.h,v
retrieving revision 1.48
diff -a -u -r1.48 ppc-tdep.h
--- ppc-tdep.h	28 Oct 2005 18:23:32 -0000	1.48
+++ ppc-tdep.h	17 Jan 2006 02:14:16 -0000
@@ -384,4 +384,7 @@
 /* Instruction size.  */
 #define PPC_INSN_SIZE 4
 
+/* Estimate for the maximum number of instrctions in a function epilogue.  */
+#define PPC_MAX_EPILOGUE_INSTRUCTIONS  52
+
 #endif /* ppc-tdep.h */
Index: rs6000-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/rs6000-tdep.c,v
retrieving revision 1.248
diff -a -u -r1.248 rs6000-tdep.c
--- rs6000-tdep.c	1 Nov 2005 19:32:36 -0000	1.248
+++ rs6000-tdep.c	17 Jan 2006 02:14:21 -0000
@@ -502,6 +502,108 @@
   return pc;
 }
 
+static int
+insn_changes_sp_or_jumps (unsigned long insn)
+{
+  int opcode = (insn >> 26) & 0x03f;
+  int sd = (insn >> 21) & 0x01f;
+  int a = (insn >> 16) & 0x01f;
+  int subcode = (insn >> 1) & 0x3ff;
+
+  /* Changes the stack pointer.  */
+
+  /* NOTE: There are many ways to change the value of a given register.
+           The ways below are those used when the register is R1, the SP,
+           in a funtion's epilogue.  */
+
+  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) */
+
+  /* Transfers control.  */
+
+  if (opcode == 18)
+    return 1;  /* b */
+  if (opcode == 16)
+    return 1;  /* bc */
+  if (opcode == 19 && subcode == 16)
+    return 1;  /* bclr */
+  if (opcode == 19 && subcode == 528)
+    return 1;  /* bcctr */
+
+  return 0;
+}
+
+/* Return true if we are in the function's epilogue, i.e. after the
+   instruction that destroyed the function's stack frame.
+
+   1) scan forward from the point of execution:
+       a) If you find an instruction that modifies the stack pointer
+          or transfers control (except a return), execution is not in
+          an epilogue, return.
+       b) Stop scanning if you find a return instruction or reach the
+          end of the function or reach the hard limit for the size of
+          an epilogue.
+   2) scan backward from the point of execution:
+        a) If you find an instruction that modifies the stack pointer,
+            execution *is* in an epilogue, return.
+        b) Stop scanning if you reach an instruction that transfers
+           control or the beginning of the function or reach the hard
+           limit for the size of an epilogue.  */
+
+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_start, func_end, epilogue_start, epilogue_end;
+  unsigned long insn;
+  struct frame_info *curfrm;
+
+  /* Find the search limits based on function boundaries and hard limit.  */
+
+  if (!find_pc_partial_function (pc, NULL, &func_start, &func_end))
+    return 0;
+
+  epilogue_start = pc - PPC_MAX_EPILOGUE_INSTRUCTIONS * PPC_INSN_SIZE;
+  if (epilogue_start < func_start) epilogue_start = func_start;
+
+  epilogue_end = pc + PPC_MAX_EPILOGUE_INSTRUCTIONS * PPC_INSN_SIZE;
+  if (epilogue_end > func_end) epilogue_end = func_end;
+
+  curfrm = get_current_frame ();
+
+  /* Scan forward until next 'blr'.  */
+
+  for (scan_pc = pc; scan_pc < epilogue_end; scan_pc += PPC_INSN_SIZE)
+    {
+      if (!safe_frame_unwind_memory (curfrm, 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_or_jumps (insn))
+        return 0;
+    }
+
+  /* Scan backward until adjustment to stack pointer (R1).  */
+
+  for (scan_pc = pc - PPC_INSN_SIZE;
+       scan_pc >= epilogue_start;
+       scan_pc -= PPC_INSN_SIZE)
+    {
+      if (!safe_frame_unwind_memory (curfrm, scan_pc, insn_buf, PPC_INSN_SIZE))
+        return 0;
+      insn = extract_signed_integer (insn_buf, PPC_INSN_SIZE);
+      if (insn_changes_sp_or_jumps (insn))
+        return 1;
+    }
+
+  return 0;
+}
+
 
 /* Fill in fi->saved_regs */
 
@@ -3342,6 +3444,8 @@
   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);