Re: Ping! [PATCH]: Tracking and reporting uninitialized variables

[Caroline Tice <ctice@apple.com>]

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Okay, here is the modified patch.  I went back and double
checked  the variable tracking stuff in GCC and discovered
that there is NOT a way to mark individual pieces in a multi-piece
location expression as initialized or not; it's one initialized value  
for
the whole thing.  Therefore I did not add the initialized field to
the dwarf_expr_piece as suggested below.  But I did address
everything else.

I tested it by running it on a small test case I have
(with DW_OP_GNU_uninit ops in it), as well as running the
dejagnu testsuite with no regressions.  Is this modified patch okay
to commit to FSF GDB?

-- Caroline Tice
ctice@apple.com

2007-05-09  Caroline Tice  <ctice@apple.com>

         * c-valprint.c (c_value_print):  If the initialized field of  
the
         value struct is 0, print out "[uninitialized]" before the  
value.
         * dwarf2expr.c (execute_stack_op): Initialize ctx- 
 >initialized field;
         allow DW_OP_GNU_uninit as legal op following a DW_OP_reg op  
or a
         DW_OP_regx op; add case for DW_OP_GNU_uninit and update
         ctx->initialized appropriately. Verify no location op follows
         DW_OP_GNU_uninit.
         * dwarf2expr.h (struct dwarf_expr_context): New field,  
initialized.
         * dwarf2loc.c (dwarf2_evaluate_loc_desc): Add call to
         set_value_initialized.
         * dwarf2read.c (dwarf_stack_op_name): Add case for  
DW_OP_GNU_uninit.
         (decode_locdesc): Add case for DW_OP_GNU_uninit.
         * value.c (struct value):  New field, initialized.
         (allocate_value): Initialize new field.
         (set_value_initialized): New function.
         (value_initialized): New function.
         * value.h (value_initialized): New extern declaration.
         (set_value_initialized): Likewise.
         * include/elf/dwarf2.h: (enum dwarf_location_atom): Add new  
DW_OP,
         DW_OP_GNU_uninit.


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Index: gdb/c-valprint.c
===================================================================
RCS file: /cvs/src/src/gdb/c-valprint.c,v
retrieving revision 1.42
diff -c -3 -p -r1.42 c-valprint.c
*** gdb/c-valprint.c	26 Jan 2007 20:54:16 -0000	1.42
--- gdb/c-valprint.c	9 May 2007 20:53:21 -0000
*************** c_value_print (struct value *val, struct
*** 556,561 ****
--- 556,564 ----
  	}
      }
  
+   if (value_initialized (val) == 0)
+     fprintf_filtered (stream, " [uninitialized] ");
+ 
    if (objectprint && (TYPE_CODE (type) == TYPE_CODE_CLASS))
      {
        /* Attempt to determine real type of object */
Index: gdb/dwarf2expr.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2expr.c,v
retrieving revision 1.20
diff -c -3 -p -r1.20 dwarf2expr.c
*** gdb/dwarf2expr.c	27 Apr 2007 22:34:56 -0000	1.20
--- gdb/dwarf2expr.c	9 May 2007 20:53:21 -0000
*************** execute_stack_op (struct dwarf_expr_cont
*** 284,289 ****
--- 284,290 ----
  		  gdb_byte *op_ptr, gdb_byte *op_end)
  {
    ctx->in_reg = 0;
+   ctx->initialized = 1;  /* Default is initialized.  */
  
    while (op_ptr < op_end)
      {
*************** execute_stack_op (struct dwarf_expr_cont
*** 410,416 ****
  	case DW_OP_reg29:
  	case DW_OP_reg30:
  	case DW_OP_reg31:
! 	  if (op_ptr != op_end && *op_ptr != DW_OP_piece)
  	    error (_("DWARF-2 expression error: DW_OP_reg operations must be "
  		   "used either alone or in conjuction with DW_OP_piece."));
  
--- 411,419 ----
  	case DW_OP_reg29:
  	case DW_OP_reg30:
  	case DW_OP_reg31:
! 	  if (op_ptr != op_end 
! 	      && *op_ptr != DW_OP_piece
! 	      && *op_ptr != DW_OP_GNU_uninit)
  	    error (_("DWARF-2 expression error: DW_OP_reg operations must be "
  		   "used either alone or in conjuction with DW_OP_piece."));
  
*************** execute_stack_op (struct dwarf_expr_cont
*** 731,736 ****
--- 734,748 ----
            }
            goto no_push;
  
+ 	case DW_OP_GNU_uninit:
+ 	  if (op_ptr != op_end
+ 	      && *op_ptr != DW_OP_piece)
+ 	    error (_("DWARF-2 expression error: DW_OP_reg operations must be "
+ 		   "used either alone or in conjuction with DW_OP_piece."));
+ 
+ 	  ctx->initialized = 0;
+ 	  goto no_push;
+ 
  	default:
  	  error (_("Unhandled dwarf expression opcode 0x%x"), op);
  	}
Index: gdb/dwarf2expr.h
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2expr.h,v
retrieving revision 1.9
diff -c -3 -p -r1.9 dwarf2expr.h
*** gdb/dwarf2expr.h	9 Jan 2007 17:58:50 -0000	1.9
--- gdb/dwarf2expr.h	9 May 2007 20:53:21 -0000
*************** struct dwarf_expr_context
*** 76,81 ****
--- 76,84 ----
       will be on the expression stack.  */
    int in_reg;
  
+   /* Initialization status of variable.  */
+   int initialized;
+ 
    /* An array of pieces.  PIECES points to its first element;
       NUM_PIECES is its length.
  
Index: gdb/dwarf2loc.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2loc.c,v
retrieving revision 1.39
diff -c -3 -p -r1.39 dwarf2loc.c
*** gdb/dwarf2loc.c	24 Jan 2007 22:04:48 -0000	1.39
--- gdb/dwarf2loc.c	9 May 2007 20:53:21 -0000
*************** dwarf2_evaluate_loc_desc (struct symbol 
*** 256,261 ****
--- 256,263 ----
        VALUE_ADDRESS (retval) = address;
      }
  
+   set_value_initialized (retval, ctx->initialized);
+ 
    free_dwarf_expr_context (ctx);
  
    return retval;
Index: gdb/dwarf2read.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2read.c,v
retrieving revision 1.218
diff -c -3 -p -r1.218 dwarf2read.c
*** gdb/dwarf2read.c	18 Apr 2007 13:25:04 -0000	1.218
--- gdb/dwarf2read.c	9 May 2007 20:53:21 -0000
*************** dwarf_stack_op_name (unsigned op)
*** 8629,8634 ****
--- 8629,8636 ----
        return "DW_OP_bit_piece";
      case DW_OP_GNU_push_tls_address:
        return "DW_OP_GNU_push_tls_address";
+     case DW_OP_GNU_uninit:
+       return "DW_OP_GNU_uninit";
      /* HP extensions. */ 
      case DW_OP_HP_is_value:
        return "DW_OP_HP_is_value";
*************** decode_locdesc (struct dwarf_block *blk,
*** 9204,9209 ****
--- 9206,9214 ----
  	    dwarf2_complex_location_expr_complaint ();
            break;
  
+ 	case DW_OP_GNU_uninit:
+ 	  break;
+ 
  	default:
  	  complaint (&symfile_complaints, _("unsupported stack op: '%s'"),
  		     dwarf_stack_op_name (op));
Index: gdb/value.c
===================================================================
RCS file: /cvs/src/src/gdb/value.c,v
retrieving revision 1.41
diff -c -3 -p -r1.41 value.c
*** gdb/value.c	13 Apr 2007 14:17:46 -0000	1.41
--- gdb/value.c	9 May 2007 20:53:21 -0000
*************** struct value
*** 157,162 ****
--- 157,165 ----
       actually exist in the program.  */
    char optimized_out;
  
+   /* If value is a variable, is it initialized or not.  */
+   int initialized;
+ 
    /* Actual contents of the value.  For use of this value; setting it
       uses the stuff above.  Not valid if lazy is nonzero.  Target
       byte-order.  We force it to be aligned properly for any possible
*************** allocate_value (struct type *type)
*** 232,237 ****
--- 235,241 ----
    val->embedded_offset = 0;
    val->pointed_to_offset = 0;
    val->modifiable = 1;
+   val->initialized = 1;  /* Default to initialized.  */
    return val;
  }
  
*************** using_struct_return (struct type *value_
*** 1691,1696 ****
--- 1695,1716 ----
  	  != RETURN_VALUE_REGISTER_CONVENTION);
  }
  
+ /* Set the initialized field in a value struct.  */
+ 
+ void
+ set_value_initialized (struct value *val, int status)
+ {
+   val->initialized = status;
+ }
+ 
+ /* Return the initialized field in a value struct.  */
+ 
+ int
+ value_initialized (struct value *val)
+ {
+   return val->initialized;
+ }
+ 
  void
  _initialize_values (void)
  {
Index: gdb/value.h
===================================================================
RCS file: /cvs/src/src/gdb/value.h,v
retrieving revision 1.96
diff -c -3 -p -r1.96 value.h
*** gdb/value.h	9 Jan 2007 17:58:59 -0000	1.96
--- gdb/value.h	9 May 2007 20:53:21 -0000
*************** extern int value_contents_equal (struct 
*** 193,198 ****
--- 193,204 ----
  extern int value_optimized_out (struct value *value);
  extern void set_value_optimized_out (struct value *value, int val);
  
+ /* Set or return field indicating whether a variable is initialized or
+    not, based on DWARF location information supplied by the compiler. 
+    1 = initialized; 0 = uninitialized.  */
+ extern int value_initialized (struct value *);
+ extern void set_value_initialized (struct value *, int);
+ 
  /* While the following fields are per- VALUE .CONTENT .PIECE (i.e., a
     single value might have multiple LVALs), this hacked interface is
     limited to just the first PIECE.  Expect further change.  */
Index: include/elf/dwarf2.h
===================================================================
RCS file: /cvs/src/src/include/elf/dwarf2.h,v
retrieving revision 1.19
diff -c -3 -p -r1.19 dwarf2.h
*** include/elf/dwarf2.h	2 Mar 2006 00:54:27 -0000	1.19
--- include/elf/dwarf2.h	9 May 2007 20:53:22 -0000
*************** enum dwarf_location_atom
*** 540,545 ****
--- 540,546 ----
      DW_OP_bit_piece = 0x9d,
      /* GNU extensions.  */
      DW_OP_GNU_push_tls_address = 0xe0,
+     DW_OP_GNU_uninit     = 0xf0,
      /* HP extensions.  */
      DW_OP_HP_unknown     = 0xe0, /* Ouch, the same as GNU_push_tls_address.  */
      DW_OP_HP_is_value    = 0xe1,

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On May 9, 2007, at 10:36 AM, Caroline Tice wrote:

>
> On May 8, 2007, at 5:33 PM, Jim Blandy wrote:
>
>>
>> Caroline Tice <ctice@apple.com> writes:
>>>> As part of some work I have been doing on improving debugging of
>>>> optimized code, I
>>>> have created a GCC patch that tags variables it believes are
>>>> uninitialized with a new
>>>> Dwarf op (an extension), DW_OP_GNU_uninit.   I have submitted that
>>>> patch to the
>>>> GCC patches list and am waiting for approval to commit it.   I have
>>>> also created the
>>>> following gdb patch to recognize the new op and inform the user  
>>>> when
>>>> a variable
>>>> the user requests to see is uninitialized.
>>>>
>>>> I have tested this patch on some small testcases and I have run the
>>>> gdb dejagnu
>>>> testsuite with no regressions.  I am new to submitting things to
>>>> this list, so if there
>>>> is anything else I ought to have done, please let me know
>>>> (kindly!).
>>
>> Hi, Caroline.  This seems like a nice patch.
>>
>> In a multi-piece location expression, can each piece be individually
>> initialized or uninitialized?  If that's so, then there should  
>> also be
>> an 'initialized' member of 'struct dwarf_expr_piece', which gets set
>> appropriately for each piece in a multi-piece location expression.
>>
>
> Okay, will do.  (Yes, I believe each piece can be individually
> initialized or uninitialized.)
>
>> Either way, the code for DW_OP_GNU_uninit should check that it's the
>> last opcode in the piece or in the entire expression, as the
>> DW_OP_reg* cases do.
>>
>
> Will do.
>
>> I think the 'struct dwarf_expr_context' member should be named
>> simply 'initialized', instead of 'var_status'.  The 'struct value'
>> field should be named 'initialized', and the accessor functions  
>> should
>> be named 'value_initialized' and 'set_value_initialized'.  The  
>> comment
>> in value.h actually needs to be filled in; the description should be
>> thorough enough to allow someone who otherwise knows how GDB works to
>> use those functions, without reading their definitions.
>>
>
> Will do.
>
>> I couldn't see from your patch why 'signed_address_type',
>> 'unsigned_address_type', and 'add_piece' were made visible outside
>> dwarf2expr.c; that should be left out of the patch if it's not  
>> needed.
>>
>
> I went back and checked; making them globally visible was actually
> for a different patch I did.  Sorry; I will remove that from this  
> patch.
>
>> Have you filed a copyright assignment with the FSF?
>
> Jim Ingham answered this one.
>