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Re: RTTI working for G++
- To: "Daniel Berlin+mail.gdb" <dan at cgsoftware dot com>
- Subject: Re: RTTI working for G++
- From: Jimmy Guo <guo at cup dot hp dot com>
- Date: Thu, 16 Mar 2000 16:50:47 -0800 (PST)
- Cc: gdb at sourceware dot cygnus dot com
>> ... However, one of the fixes was that when print
>> object is on, and one wants to print member / methods of the derived
>> type, you can now do so.
>
>See, i didn't consider that a bug, i considered it a lacking
>feature. It just wasn't doing the lookup it would need to do, and i've
>been too busy to fix it.
If 'print foo' says it's a pointer to something, and 'print foo->a' says
'There is no member or method named a.', it's very confusing to the
user. When print object is on, this could happen. I'd be more willing
to say it's a bug, since the error message contradicts with what print
says and just misleads user ('which one should I believe from this
debugger?').
The fix is in eval.c (evaluate_subexp_standard): it needs to know if
objectprint is set, and if so, return the pointer to the rtti type when
dealing with STUCTOP_PTR (if target type code is TYPE_CODE_CLASS).
>> Besides, there're some fixes to handle pointer
>> to a derived type and explicit casting of a pointer to a base to a
>> derived type.
>
>This i ran up against. I also handled reference types (By pretending
>they were pointers).
Actually the example you gave at the end of this email looks like
something I fixed, in the casting code. I'm not familiar with
value_rtti_type and don't quite understand what you were dealing with --
full, etc. are all reset to initial values upon entry into
value_rtti_type ().
>Did you notice that it's not really fun to use value_nid (damn
>flyspell keeps "correcting" the IND to nid, as if "nid" was really a word
>either.) in value_rtti_type? value_nid will call the RTTI routine
>during it's lazy evaluation, which gets you into a recursive nightmare
>if you aren't careful.
I wasn't adventuring into that area since I'm looking at the higher
layer of the proper handling of casting, printing, and expression
evaluation.
>I'd be glad to incorporate your fixes into my patch, and i'd
>appreciate it if you'd look at mine.
>I'll post it to gdb-patches in a few days.
Mine is enclosed in this email.
>I'm a little confused about the semantics of using_enc/full/top in value_rtti_type.
>
>It seems if i set full to 0, on multiple inheritance, it gets the name
>right, but the offset wrong, so you have the right name, and the wrong
>values.
>If i set full to 1, it gets the name wrong ("suspicious *", which
>means it couldn't look it up right), but the values right.
See if my changes to c-valprint.c and valops.c solved your problem. I
think at least part of the problem is that the pointer value was _not_
adjusted when you change the type of the thing to a rtti type, which is
fixed in these two files. c-valprint.c deals with printing the pointer
value itself; valops.c deals with printing a member of the pointer value.
Patch follows (the change to typeprint.c probably conflicts with your
version, and I like the output you provided).
- Jimmy Guo, guo@cup.hp.com
Thu Mar 16 15:49:56 2000 Jimmy guo <guo@cup.hp.com>
* c-valprint.c (c_value_print): adjust pointer value when
objectprint is set and pointer type is changed to point to the
rtti type.
* eval.c (evaluate_subexp_standard): for OP_VAR_VALUE, always
return full value object; for STRUCTOP_PTR, use pointer to
rtti type to get member / method if objectprint is set and
target type of pointer is class.
* typeprint.c (whatis_exp): if objectprint is set and exp is of
pointer / reference type to a class object, look up and print
the pointer / reference to rtti type.
* valops.c (value_cast): when casting a pointer / reference type
of a class object to pointer / refer to its rtti type, adjust
the new pointer value accordingly.
Index: c-valprint.c
/usr/local/bin/diff -c -w -L c-valprint.c c-valprint.c@@/main/cygnus/7 c-valprint.c
*** c-valprint.c
--- c-valprint.c Thu Mar 16 10:21:16 2000
***************
*** 497,502 ****
--- 497,505 ----
/* create a reference type referencing the real type */
type = lookup_reference_type (real_type);
}
+ /* JYG: Need to adjust pointer value. */
+ val->aligner.contents[0] -= top;
+
/* Note: When we look up RTTI entries, we don't get any
information on const or volatile attributes */
}
Index: eval.c
/usr/local/bin/diff -c -w -L eval.c eval.c@@/main/cygnus/9 eval.c
*** eval.c
--- eval.c Thu Mar 16 15:41:34 2000
***************
*** 37,42 ****
--- 37,45 ----
/* This is defined in valops.c */
extern int overload_resolution;
+ /* JYG: lookup rtti type of STRUCTOP_PTR when this is set to continue
+ on with successful lookup for member/method of the rtti type. */
+ extern int objectprint;
/* Prototypes for local functions. */
***************
*** 428,459 ****
(*pos) += 3;
if (noside == EVAL_SKIP)
goto nosideret;
- if (noside == EVAL_AVOID_SIDE_EFFECTS)
- {
- struct symbol *sym = exp->elts[pc + 2].symbol;
- enum lval_type lv;
-
- switch (SYMBOL_CLASS (sym))
- {
- case LOC_CONST:
- case LOC_LABEL:
- case LOC_CONST_BYTES:
- lv = not_lval;
- break;
! case LOC_REGISTER:
! case LOC_REGPARM:
! lv = lval_register;
! break;
- default:
- lv = lval_memory;
- break;
- }
-
- return value_zero (SYMBOL_TYPE (sym), lv);
- }
- else
return value_of_variable (exp->elts[pc + 2].symbol,
exp->elts[pc + 1].block);
--- 431,446 ----
(*pos) += 3;
if (noside == EVAL_SKIP)
goto nosideret;
! /* JYG: We used to just return value_zero of the symbol type
! if we're asked to avoid side effects. Otherwise we return
! value_of_variable (...). However I'm not sure if
! value_of_variable () has any side effect.
! We need a full value object returned here for whatis_exp ()
! to call evaluate_type () and then pass the full value to
! value_rtti_target_type () if we are dealing with a pointer
! or reference to a base class and print object is on. */
return value_of_variable (exp->elts[pc + 2].symbol,
exp->elts[pc + 1].block);
***************
*** 1051,1056 ****
--- 1038,1068 ----
arg1 = evaluate_subexp (NULL_TYPE, exp, pos, noside);
if (noside == EVAL_SKIP)
goto nosideret;
+
+ /* JYG: if print object is on we need to replace the base type
+ with rtti type in order to continue on with successful
+ lookup of member / method only available in the rtti type. */
+ {
+ struct type *type = VALUE_TYPE (arg1);
+ struct type *real_type;
+ int full, top, using_enc;
+
+ if (objectprint &&
+ (TYPE_CODE (TYPE_TARGET_TYPE (type)) == TYPE_CODE_CLASS))
+ {
+ real_type = value_rtti_target_type (arg1, &full, &top, &using_enc);
+ if (real_type)
+ {
+ if (TYPE_CODE (type) == TYPE_CODE_PTR)
+ real_type = lookup_pointer_type (real_type);
+ else
+ real_type = lookup_reference_type (real_type);
+
+ arg1 = value_cast (real_type, arg1);
+ }
+ }
+ }
+
if (noside == EVAL_AVOID_SIDE_EFFECTS)
return value_zero (lookup_struct_elt_type (VALUE_TYPE (arg1),
&exp->elts[pc + 2].string,
Index: typeprint.c
/usr/local/bin/diff -c -w -L typeprint.c typeprint.c@@/main/cygnus/6 typeprint.c
*** typeprint.c
--- typeprint.c Thu Mar 16 09:59:00 2000
***************
*** 82,87 ****
--- 82,88 ----
register value_ptr val;
register struct cleanup *old_chain = NULL;
struct type *real_type = NULL;
+ struct type *type;
int full = 0;
int top = -1;
int using_enc = 0;
***************
*** 96,112 ****
else
val = access_value_history (0);
real_type = value_rtti_type (val, &full, &top, &using_enc);
printf_filtered ("type = ");
! if (real_type && objectprint)
! printf_filtered ("/* real type = %s%s */\n",
! TYPE_NAME (real_type),
! full ? "" : " (incomplete object)");
! /* FIXME: maybe better to use type_print (real_type, "", gdb_stdout, -1); */
! type_print (VALUE_TYPE (val), "", gdb_stdout, show);
printf_filtered ("\n");
if (exp)
--- 97,136 ----
else
val = access_value_history (0);
+ type = VALUE_TYPE (val);
+
+ if (objectprint)
+ {
+ if (((TYPE_CODE (type) == TYPE_CODE_PTR) ||
+ (TYPE_CODE (type) == TYPE_CODE_REF))
+ &&
+ (TYPE_CODE (TYPE_TARGET_TYPE (type)) == TYPE_CODE_CLASS))
+ {
+ real_type = value_rtti_target_type (val, &full, &top, &using_enc);
+ if (real_type)
+ {
+ if (TYPE_CODE (type) == TYPE_CODE_PTR)
+ real_type = lookup_pointer_type (real_type);
+ else
+ real_type = lookup_reference_type (real_type);
+ }
+ }
+ else if (TYPE_CODE (type) == TYPE_CODE_CLASS)
real_type = value_rtti_type (val, &full, &top, &using_enc);
+ }
printf_filtered ("type = ");
! if (real_type)
! {
! printf_filtered ("/* real type = ");
! type_print (real_type, "", gdb_stdout, -1);
! if (! full)
! printf_filtered (" (incomplete object)");
! printf_filtered (" */\n");
! }
! type_print (type, "", gdb_stdout, show);
printf_filtered ("\n");
if (exp)
Index: valops.c
/usr/local/bin/diff -c -w -L valops.c valops.c@@/main/cygnus/15 valops.c
*** valops.c
--- valops.c Thu Mar 16 10:01:30 2000
***************
*** 326,331 ****
--- 326,337 ----
value_ptr v2 = value_ind (arg2);
VALUE_ADDRESS (v2) -= VALUE_ADDRESS (v)
+ VALUE_OFFSET (v);
+
+ /* JYG: adjust the new pointer value and
+ embedded offset. */
+ v2->aligner.contents[0] -= VALUE_EMBEDDED_OFFSET (v);
+ VALUE_EMBEDDED_OFFSET (v2) = 0;
+
v2 = value_addr (v2);
VALUE_TYPE (v2) = type;
return v2;