[Bug c++/22132] New: Wrong code: upcasting a const class pointer to struct the class derives from

[Bug c++/22132] New: Wrong code: upcasting a const class pointer to struct the class derives from

[scott dot tupaj at line6 dot com]

Upcasting a const class pointer for a class that was derived from a struct causes the upcasted pointer to 
incorrectly access members of the derived struct.

Conditions:
1) The derived class object must have a virtual destructor (or possibly any v-table entries)
2) The upcast must be a straight 'C' cast that does not preserve the const.

I've attached a code sample that demonstrates the error, but this is the scenario:

struct foo {
   int a;
   int b;
};

class Foobar : public foo {
public:
    Foobar() { a = 1; b = 2; };
    virtual ~Foobar() {};
};

Foobar obj;
const Foobar* objPtr = &obj;
foo* f = (foo*)objPtr;

contents of f->a and f->b during runtime are not 1 and 2 as expected.
f->a is garbage
f->b is 1 (expected value of f->a)

-- 
           Summary: Wrong code: upcasting a const class pointer to struct
                    the class derives from
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: scott dot tupaj at line6 dot com
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] Wrong code: upcasting a const class pointer to struct the class derives from

[scott dot tupaj at line6 dot com]

------- Additional Comments From scott dot tupaj at line6 dot com  2005-06-21 01:37 -------
Created an attachment (id=9120)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=9120&action=view)
Sample code to illustrate bug


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] Wrong code: upcasting a const class pointer to struct the class derives from

[scott dot tupaj at line6 dot com]

------- Additional Comments From scott dot tupaj at line6 dot com  2005-06-21 01:38 -------
Created an attachment (id=9122)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=9122&action=view)
Compiler Info


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] Wrong code: upcasting a const class pointer to struct the class derives from

[scott dot tupaj at line6 dot com]

------- Additional Comments From scott dot tupaj at line6 dot com  2005-06-21 01:38 -------
Created an attachment (id=9123)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=9123&action=view)
Compiler output


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] Wrong code: upcasting a const class pointer to struct the class derives from

[scott dot tupaj at line6 dot com]

------- Additional Comments From scott dot tupaj at line6 dot com  2005-06-21 01:38 -------
Created an attachment (id=9121)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=9121&action=view)
preprocessed source file


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] Wrong code: upcasting a const class pointer to struct the class derives from

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-06-21 03:05 -------
I think this is invalid, you want:
   OBJ* p1 = const_cast<AnObject*>(objPtr);
but I don't have prove at this point if this invalid.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] Wrong code: upcasting a const class pointer to struct the class derives from

[scott dot tupaj at line6 dot com]

------- Additional Comments From scott dot tupaj at line6 dot com  2005-06-21 17:01 -------
Yes, agreeably this is 'bad' c++ practice in my example.  However, if wrong 
code is produced, I think it would be prudent for at least a compiler warning 
or error be produced if the reason for wrong code is because invalid or 
questionable c++ syntax is being used.  

Every other compiler I've used, including gcc 3.x.x doesn't not corrupt access 
to the members in this scenario like gcc 4.0.0 does.  Other compilers either 
error because of the const violation, or accepts it and produces the proper 
results when accessing the pointer.



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] [4.0/4.1 Regression] Wrong code: upcasting a const class pointer to struct the class derives from (C/old-style cast)

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mmitchel at gcc dot gnu dot
                   |                            |org
           Keywords|                            |wrong-code
            Summary|Wrong code: upcasting a     |[4.0/4.1 Regression] Wrong
                   |const class pointer to      |code: upcasting a const
                   |struct the class derives    |class pointer to struct the
                   |from                        |class derives from (C/old-
                   |                            |style cast)
   Target Milestone|---                         |4.0.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] [4.0/4.1 Regression] Wrong code: upcasting a const class pointer to struct the class derives from (C/old-style cast)

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |22281


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] [4.0/4.1 Regression] Wrong code: upcasting a const class pointer to struct the class derives from (C/old-style cast)

[mmitchel at gcc dot gnu dot org]

------- Additional Comments From mmitchel at gcc dot gnu dot org  2005-07-06 16:29 -------
This is a bug in my static_cast rewrite.  I will fix it for 4.0.2.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |mark at codesourcery dot com
                   |dot org                     |
             Status|UNCONFIRMED                 |ASSIGNED
   Target Milestone|4.0.1                       |4.0.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] [4.0/4.1 Regression] Wrong code: upcasting a const class pointer to struct the class derives from (C/old-style cast)

[mmitchel at gcc dot gnu dot org]

------- Additional Comments From mmitchel at gcc dot gnu dot org  2005-07-15 16:00 -------
*** Bug 22281 has been marked as a duplicate of this bug. ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
Bug 22132 depends on bug 22281, which changed state.

Bug 22281 Summary: [4.0/4.1 Regression] C-Style cast does reinterpret_cast when it should do a static_cast
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22281

           What    |Old Value                   |New Value
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |DUPLICATEBug 22132 depends on bug 22281, which changed state.

Bug 22281 Summary: [4.0/4.1 Regression] C-Style cast does reinterpret_cast when it should do a static_cast
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22281

           What    |Old Value                   |New Value
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |DUPLICATE

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] [4.0/4.1 Regression] Wrong code: upcasting a const class pointer to struct the class derives from (C/old-style cast)

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2005-07-15 16:10 -------
Subject: Bug 22132

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	mmitchel@gcc.gnu.org	2005-07-15 16:10:08

Modified files:
	gcc/testsuite  : ChangeLog 
	gcc/cp         : ChangeLog call.c cp-tree.h typeck.c 
Added files:
	gcc/testsuite/g++.dg/expr: cast4.C 

Log message:
	PR c++/22132
	* call.c (implicit_conversion): Add c_cast_p parameter.
	(standard_conversion): Likewise.  Allow conversions between
	differently-qualified pointer types when performing a C-style
	cast.
	(add_function_candidate): Adjust callee.
	(build_builtin_candidate): Likewise.
	(build_user_type_conversion_1): Likewise.
	(conditional_conversion): Likewise.
	(can_convert_arg): Likewise.
	(can_convert_arg_bad): Likewise.
	(perform_implicit_conversion): Likewise.
	* cp-tree.h (comp_ptr_ttypes_const): Declare.
	* typeck.c (comp_ptr_ttypes_const): Give it external linkage.
	Return bool.
	
	PR c++/22132
	* g++.dg/expr/cast4.C: New test.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.5771&r2=1.5772
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/expr/cast4.C.diff?cvsroot=gcc&r1=NONE&r2=1.1
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/ChangeLog.diff?cvsroot=gcc&r1=1.4819&r2=1.4820
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/call.c.diff?cvsroot=gcc&r1=1.543&r2=1.544
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/cp-tree.h.diff?cvsroot=gcc&r1=1.1153&r2=1.1154
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/typeck.c.diff?cvsroot=gcc&r1=1.642&r2=1.643



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] [4.0/4.1 Regression] Wrong code: upcasting a const class pointer to struct the class derives from (C/old-style cast)

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2005-07-15 18:47 -------
Subject: Bug 22132

CVSROOT:	/cvs/gcc
Module name:	gcc
Branch: 	gcc-4_0-branch
Changes by:	mmitchel@gcc.gnu.org	2005-07-15 18:47:20

Modified files:
	gcc/testsuite  : ChangeLog 
	gcc/cp         : ChangeLog call.c cp-tree.h typeck.c 
Added files:
	gcc/testsuite/g++.dg/expr: cast4.C 

Log message:
	PR c++/22132
	* g++.dg/expr/cast4.C: New test.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-4_0-branch&r1=1.5084.2.278&r2=1.5084.2.279
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/expr/cast4.C.diff?cvsroot=gcc&only_with_tag=gcc-4_0-branch&r1=NONE&r2=1.1.2.1
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-4_0-branch&r1=1.4648.2.66&r2=1.4648.2.67
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/call.c.diff?cvsroot=gcc&only_with_tag=gcc-4_0-branch&r1=1.531.2.4&r2=1.531.2.5
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/cp-tree.h.diff?cvsroot=gcc&only_with_tag=gcc-4_0-branch&r1=1.1106.2.9&r2=1.1106.2.10
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/typeck.c.diff?cvsroot=gcc&only_with_tag=gcc-4_0-branch&r1=1.616.2.12&r2=1.616.2.13



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] [4.0/4.1 Regression] Wrong code: upcasting a const class pointer to struct the class derives from (C/old-style cast)

[mmitchel at gcc dot gnu dot org]

------- Additional Comments From mmitchel at gcc dot gnu dot org  2005-07-15 18:50 -------
Fixed in 4.0.2.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] [4.0/4.1 Regression] Wrong code: upcasting a const class pointer to struct the class derives from (C/old-style cast)

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2005-08-03 02:17 -------
Subject: Bug 22132

CVSROOT:	/cvs/gcc
Module name:	gcc
Branch: 	apple-local-200502-branch
Changes by:	mrs@gcc.gnu.org	2005-08-03 02:17:44

Modified files:
	gcc/cp         : call.c ChangeLog cp-tree.h typeck.c 
Added files:
	gcc/testsuite/g++.dg/expr: cast4.C 

Log message:
	PR c++/22132
	* call.c (implicit_conversion): Add c_cast_p parameter.
	(standard_conversion): Likewise.  Allow conversions between
	differently-qualified pointer types when performing a C-style
	cast.
	(add_function_candidate): Adjust callee.
	(build_builtin_candidate): Likewise.
	(build_user_type_conversion_1): Likewise.
	(conditional_conversion): Likewise.
	(can_convert_arg): Likewise.
	(can_convert_arg_bad): Likewise.
	(perform_implicit_conversion): Likewise.
	* cp-tree.h (comp_ptr_ttypes_const): Declare.
	* typeck.c (comp_ptr_ttypes_const): Give it external linkage.
	Return bool.
	Radar 4076725

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/call.c.diff?cvsroot=gcc&only_with_tag=apple-local-200502-branch&r1=1.530.4.5&r2=1.530.4.6
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/ChangeLog.diff?cvsroot=gcc&only_with_tag=apple-local-200502-branch&r1=1.4631.2.7&r2=1.4631.2.8
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/cp-tree.h.diff?cvsroot=gcc&only_with_tag=apple-local-200502-branch&r1=1.1104.2.8&r2=1.1104.2.9
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/typeck.c.diff?cvsroot=gcc&only_with_tag=apple-local-200502-branch&r1=1.614.2.14&r2=1.614.2.15
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/expr/cast4.C.diff?cvsroot=gcc&only_with_tag=apple-local-200502-branch&r1=NONE&r2=1.1.14.1



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132

[Bug c++/22132] [4.0/4.1 Regression] Wrong code: upcasting a const class pointer to struct the class derives from (C/old-style cast)

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-08-16 11:56 -------
*** Bug 23418 has been marked as a duplicate of this bug. ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |stephan dot bergmann at sun
                   |                            |dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22132