Re: [PATCH] Let dwarf2 CFI's execute_stack_op be used outside of CFI

[Jim Blandy <jimb at redhat dot com>]

Actually, Daniel, I'm sorry --- I've re-read the change more
carefully, and I've gotten more confused than I was before.

You've changed the Dwarf 2 location expression evaluator to consult
the current register values --- not the values of the registers with
respect to a specific stack frame.  I can't think of any situations in
which this the correct behavior.  Can you explain more about the
contexts in which this change is useful?  It seems to me that it's
wrong in most of the cases I can think of.  It really needs to take a
frame argument, or at the very least, read registers from the selected
frame (although that's kind of gross and global-variable-ish).


Daniel Berlin <dan@dberlin.org> writes:

> This patch simply adds an external entry point (dwarf2_execute_stack_op), 
> that doesn't require the CFA context. It also adds code so that when the 
> context passed to execute_stack_op is NULL, we use read_register_gen to 
> get registers.
> 
> Along the way, I made an obvious fix to DW_OP_deref_size that i'll commit 
> separately, but included in the changelog/patch because i didn't want to 
> hand edit it out.
> 
> 
> I also added my name to the top of the file, since in reality, it's based 
> on code I sent Jiri.
> 
> --Dan
> 2002-03-25  Daniel Berlin  <dan@dberlin.org>
> 
> 	* dwarf2cfi.c (dwarf2_execute_stack_op): New function, external
> 	entry point to execute_stack_op that doesn't require context.
> 	(execute_stack_op): If context is NULL, don't use get_reg, use
> 	read_register_gen.
>         Also fix bug in DW_OP_deref_size.
> 
> 	* dwarf2cfi.h (dwarf2_execute_stack_op): New prototype.
> Index: dwarf2cfi.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/dwarf2cfi.c,v
> retrieving revision 1.1
> diff -c -3 -p -w -B -b -r1.1 dwarf2cfi.c
> *** dwarf2cfi.c	2001/12/07 12:10:15	1.1
> --- dwarf2cfi.c	2002/03/25 23:50:16
> ***************
> *** 1,7 ****
>   /* Stack unwinding code based on dwarf2 frame info for GDB, the GNU debugger.
> !    Copyright 2001
>      Free Software Foundation, Inc.
>      Contributed by Jiri Smid, SuSE Labs.
>   
>      This file is part of GDB.
>   
> --- 1,8 ----
>   /* Stack unwinding code based on dwarf2 frame info for GDB, the GNU debugger.
> !    Copyright 2001, 2002
>      Free Software Foundation, Inc.
>      Contributed by Jiri Smid, SuSE Labs.
> +    Based on code written by Daniel Berlin (dan@dberlin.org)
>   
>      This file is part of GDB.
>   
> *************** get_reg (char *reg, struct context *cont
> *** 840,845 ****
> --- 841,854 ----
>       }
>   }
>   
> + /* External entry point for executing dwarf2 stack operations. */
> + CORE_ADDR
> + dwarf2_execute_stack_op (struct objfile *objfile, char *op_ptr,
> + 			 char *op_end, CORE_ADDR initial)
> + {
> +   return execute_stack_op (objfile, op_ptr, op_end, NULL, initial);
> + }
> + 
>   /* Decode a DW_OP stack program.  Return the top of stack.  Push INITIAL
>      onto the stack to start.  */
>   static CORE_ADDR
> *************** execute_stack_op (struct objfile *objfil
> *** 963,973 ****
> --- 972,989 ----
>   	case DW_OP_reg29:
>   	case DW_OP_reg30:
>   	case DW_OP_reg31:
> + 	  if (context)
>   	    get_reg ((char *) &result, context, op - DW_OP_reg0);
> + 	  else
> + 	    read_register_gen (op - DW_OP_reg0, (char *)&result);
> + 	  
>   	  break;
>   	case DW_OP_regx:
>   	  reg = read_uleb128 (objfile->obfd, &op_ptr);
> + 	  if (context)
>   	    get_reg ((char *) &result, context, reg);
> + 	  else
> + 	    read_register_gen (reg, (char *)&result);
>   	  break;
>   
>   	case DW_OP_breg0:
> *************** execute_stack_op (struct objfile *objfil
> *** 1003,1015 ****
> --- 1019,1038 ----
>   	case DW_OP_breg30:
>   	case DW_OP_breg31:
>   	  offset = read_sleb128 (objfile->obfd, &op_ptr);
> + 	  if (context)
>   	    get_reg ((char *) &result, context, op - DW_OP_breg0);
> + 	  else
> + 	    read_register_gen (op - DW_OP_breg0, (char *)&result);
> + 	  
>   	  result += offset;
>   	  break;
>   	case DW_OP_bregx:
>   	  reg = read_uleb128 (objfile->obfd, &op_ptr);
>   	  offset = read_sleb128 (objfile->obfd, &op_ptr);
> + 	  if (context)
>   	    get_reg ((char *) &result, context, reg);
> + 	  else
> + 	    read_register_gen (reg, (char *)&result);
>   	  result += offset;
>   	  break;
>   
> *************** execute_stack_op (struct objfile *objfil
> *** 1067,1080 ****
>   	    {
>   	    case DW_OP_deref:
>   	      {
> ! 		char *ptr = (char *) result;
>   		result = read_pointer (objfile->obfd, &ptr);
>   	      }
>   	      break;
>   
>   	    case DW_OP_deref_size:
>   	      {
> ! 		char *ptr = (char *) result;
>   		switch (*op_ptr++)
>   		  {
>   		  case 1:
> --- 1090,1103 ----
>   	    {
>   	    case DW_OP_deref:
>   	      {
> ! 		char *ptr = (char *) &result;
>   		result = read_pointer (objfile->obfd, &ptr);
>   	      }
>   	      break;
>   
>   	    case DW_OP_deref_size:
>   	      {
> ! 		char *ptr = (char *) &result;
>   		switch (*op_ptr++)
>   		  {
>   		  case 1:
> Index: dwarf2cfi.h
> ===================================================================
> RCS file: /cvs/src/src/gdb/dwarf2cfi.h,v
> retrieving revision 1.1
> diff -c -3 -p -w -B -b -r1.1 dwarf2cfi.h
> *** dwarf2cfi.h	2001/12/07 12:10:15	1.1
> --- dwarf2cfi.h	2002/03/25 23:50:16
> *************** void cfi_get_saved_register (char *raw_b
> *** 63,66 ****
> --- 63,72 ----
>   void cfi_virtual_frame_pointer (CORE_ADDR pc, int *frame_regnum,
>   				LONGEST * frame_offset);
>   
> + /*  Execute a set of DWARF2 stack operations, starting with INITIAL
> +     as the address on the stack. */
> + CORE_ADDR dwarf2_execute_stack_op (struct objfile *objfile, 
> + 				   char *op_ptr, char *op_end,
> + 				   CORE_ADDR initial);
> + 
>   #endif
> Index: ChangeLog
> ===================================================================
> RCS file: /cvs/src/src/gdb/ChangeLog,v
> retrieving revision 1.2349
> diff -c -3 -p -w -B -b -r1.2349 ChangeLog
> *** ChangeLog	2002/03/25 19:47:39	1.2349
> --- ChangeLog	2002/03/25 23:50:17
> ***************
> *** 1,3 ****
> --- 1,12 ----
> + 2002-03-25  Daniel Berlin  <dan@dberlin.org>
> + 
> + 	* dwarf2cfi.c (dwarf2_execute_stack_op): New function, external
> + 	entry point to execute_stack_op that doesn't require context.
> + 	(execute_stack_op): If context is NULL, don't use get_reg, use
> + 	read_register_gen.
> + 
> + 	* dwarf2cfi.h (dwarf2_execute_stack_op): New prototype.
> + 
>   2002-03-25  Jeff Law (law@redhat.com)
>   
>   	* linux-proc.c (read_mapping): Scan up to end of line for filename.