Re: Trivial fix in value_sub

[Jim Ingham <jingham at apple dot com>]

Okay, so to be consistent, I throw errors in both value_add & 
value_sub.  How about this:

Index: valarith.c
===================================================================
RCS file: /cvs/src/src/gdb/valarith.c,v
retrieving revision 1.14
diff -c -w -p -r1.14 valarith.c
*** valarith.c  2002/03/27 21:35:35     1.14
--- valarith.c  2002/04/04 21:39:58
*************** value_add (struct value *arg1, struct va
*** 48,55 ****
   {
     struct value *valint;
     struct value *valptr;
!   register int len;
     struct type *type1, *type2, *valptrtype;

     COERCE_NUMBER (arg1);
     COERCE_NUMBER (arg2);
--- 48,56 ----
   {
     struct value *valint;
     struct value *valptr;
!   register int sz;
     struct type *type1, *type2, *valptrtype;
+   struct type *valtargettype;

     COERCE_NUMBER (arg1);
     COERCE_NUMBER (arg2);
*************** value_add (struct value *arg1, struct va
*** 77,88 ****
           valint = arg1;
           valptrtype = type2;
         }
!       len = TYPE_LENGTH (check_typedef (TYPE_TARGET_TYPE 
(valptrtype)));
!       if (len == 0)
!       len = 1;                /* For (void *) */
         retval = value_from_pointer (valptrtype,
                                    value_as_address (valptr)
!                                  + (len * value_as_long (valint)));
         VALUE_BFD_SECTION (retval) = VALUE_BFD_SECTION (valptr);
         return retval;
       }
--- 78,109 ----
           valint = arg1;
           valptrtype = type2;
         }
!
!       valtargettype = check_typedef (TYPE_TARGET_TYPE (valptrtype));
!       sz = TYPE_LENGTH (valtargettype);
!       if (sz == 0)
!       {
!         if (TYPE_CODE (type1) == TYPE_CODE_VOID)
!           sz = 1;
!         else
!           {
!             char *name;
!
!             name = TYPE_NAME (valtargettype);
!             if (name == NULL)
!               name = TYPE_TAG_NAME (valtargettype);
!             if (name == NULL)
!               error ("Cannot perform pointer addition on incomplete 
types, "
!                      "try casting to a known type, or void *.");
!             else
!               error ("Cannot perform pointer addition on incomplete 
type \"%s\", "
!                      "try casting to a known type, or void *.", name);
!           }
!       }
!
         retval = value_from_pointer (valptrtype,
                                    value_as_address (valptr)
!                                  + (sz * value_as_long (valint)));
         VALUE_BFD_SECTION (retval) = VALUE_BFD_SECTION (valptr);
         return retval;
       }
*************** value_sub (struct value *arg1, struct va
*** 104,110 ****
         if (TYPE_CODE (type2) == TYPE_CODE_INT)
         {
           /* pointer - integer.  */
!         LONGEST sz = TYPE_LENGTH (check_typedef (TYPE_TARGET_TYPE 
(type1)));
           return value_from_pointer (type1,
                                      (value_as_address (arg1)
                                       - (sz * value_as_long (arg2))));
--- 125,156 ----
         if (TYPE_CODE (type2) == TYPE_CODE_INT)
         {
           /* pointer - integer.  */
!         struct type *type1target = check_typedef (TYPE_TARGET_TYPE 
(type1));
!         LONGEST sz = TYPE_LENGTH (type1target);
!         /* This is the way value_add does it.  Is this right, because
!            it means you have a different result depending on whether 
you
!            have an incomplete type or not... */
!
!         if (sz == 0)
!           {
!             if (TYPE_CODE (type1) == TYPE_CODE_VOID)
!               sz = 1;
!             else
!               {
!                 char *name;
!
!                 name = TYPE_NAME (type1target);
!                 if (name == NULL)
!                   name = TYPE_TAG_NAME (type1target);
!                 if (name == NULL)
!                   error ("Cannot perform pointer subtraction on 
incomplete types, "
!                          "try casting to a known type, or void *.");
!               else
!                 error ("Cannot perform pointer subtraction on 
incomplete type \"%s\", "
!                        "try casting to a known type, or void *.", 
name);
!               }
!           }
!
           return value_from_pointer (type1,
                                      (value_as_address (arg1)
                                       - (sz * value_as_long (arg2))));


Jim

P.S. I have long ago given up being amazed at all the egregiously 
heinous uses to which people will put debuggers...  To quote my revered 
father: "If I were to shake my head and say "Oh, my god" every time I 
see something like this, I would spend so much time with my head & mouth 
in motion people would think I had acquired some form of ecclesiastical 
palsy..."

Jim

On Wednesday, April 3, 2002, at 08:11  PM, Daniel Jacobowitz wrote:

> On Wed, Apr 03, 2002 at 10:54:57PM -0500, Jim Blandy wrote:
>>
>> Jim Ingham <jingham@apple.com> writes:
>>> So... I don't think you should keep the size at 0.  This seems like
>>> gdb is just silently ignoring the " -  x" part of what they typed, and
>>> you should always be explicit about what you have done.  But if you
>>> think an error is more appropriate, I am fine with that...
>>
>> Oh, no, I didn't mean to suggest that zero was the right size to use;
>> I agree with you completely that that would be pretty confusing.
>>
>> Your story is pretty amazing --- I would never have guessed that
>> people actually *use* the sizeof (struct incomplete) == 1 behavior!  I
>> think it is much more common for people to be unaware that the type is
>> incomplete; if this hunch is correct, then the behavior your toolbox
>> folks love will be very confusing.  I think an error for arithmetic on
>> any incomplete type other than (void *) is the right thing.
>
> FWIW, I agree.  If we don't know what the size is, we should say so;
> having the behavior change based on whether a version of the
> implementation (which might have debug symbols) is loaded would be
> baffling.
>
> --
> Daniel Jacobowitz                           Carnegie Mellon University
> MontaVista Software                         Debian GNU/Linux Developer
>
--
Jim Ingham                                   jingham@apple.com
Developer Tools - gdb
Apple Computer