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* [Bug c++/53762] New: pointer-casts don't always check null-pointers
@ 2012-06-24 16:09 imzhuli at vip dot qq.com
2012-06-24 16:26 ` [Bug c++/53762] " redi at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: imzhuli at vip dot qq.com @ 2012-06-24 16:09 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53762
Bug #: 53762
Summary: pointer-casts don't always check null-pointers
Classification: Unclassified
Product: gcc
Version: 4.2.1
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c++
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: imzhuli@vip.qq.com
Created attachment 27695
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27695
examples of lacking null-pointer check
under these situations, null-pointers are not converted to null-pointers as the
standard says;
1. with 'this' pointer:
class A
{
public:
int asomething; // important: if there's nothing in class A, the functions
seems right;
};
class B
: public A
{
public:
virtual ~B() {}
void* thisoffset() {
return static_cast<A*>(this);
}
void* offset() {
B * pb = this;
return static_cast<A*>(pb);
}
};
the two 'offset' function returns a 'offset of object of type A in objec of
type B ', and a null-pointer. i think null-point should be right.
2. with reference from DERIVED class to BASE class:
// class A & B defined as the above
A* pa = NULL; B*pb = NULL;
pa = &static_cast<A&>(*pb);
^^^^^^^^^^^^^^^^^^^^^^^^^^ will not perform null-pointer check;
A* pa = NULL; B*pb = NULL;
pa = static_cast<A*>(pb);
^^^^^^^^^^^^^^^^^^^^^^^^^ will perform null-pointer check;
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/53762] pointer-casts don't always check null-pointers
2012-06-24 16:09 [Bug c++/53762] New: pointer-casts don't always check null-pointers imzhuli at vip dot qq.com
@ 2012-06-24 16:26 ` redi at gcc dot gnu.org
2012-06-24 16:31 ` redi at gcc dot gnu.org
2012-06-24 18:09 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: redi at gcc dot gnu.org @ 2012-06-24 16:26 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53762
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|major |normal
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-06-24 16:26:17 UTC ---
Your program dereferences null pointers, that's undefined behaviour.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/53762] pointer-casts don't always check null-pointers
2012-06-24 16:09 [Bug c++/53762] New: pointer-casts don't always check null-pointers imzhuli at vip dot qq.com
2012-06-24 16:26 ` [Bug c++/53762] " redi at gcc dot gnu.org
@ 2012-06-24 16:31 ` redi at gcc dot gnu.org
2012-06-24 18:09 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: redi at gcc dot gnu.org @ 2012-06-24 16:31 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53762
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-06-24 16:30:54 UTC ---
These are allowed:
pa = static_cast<A*>(pb);
pb = static_cast<B*>(pa);
All the other casts are not because they involve dereferencing a null pointer
which is not allowed by [expr.unary.op]/1
Also, GCC 4.2 is not supported or maintained so there's no point reporting
bugs against it, you should check a newer release before reporting bugs.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/53762] pointer-casts don't always check null-pointers
2012-06-24 16:09 [Bug c++/53762] New: pointer-casts don't always check null-pointers imzhuli at vip dot qq.com
2012-06-24 16:26 ` [Bug c++/53762] " redi at gcc dot gnu.org
2012-06-24 16:31 ` redi at gcc dot gnu.org
@ 2012-06-24 18:09 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2012-06-24 18:09 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53762
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-06-24 18:09:39 UTC ---
Invalid as mentioned as:
pa = &static_cast<A&>(*pb);
^^^
Deferences a null pointer at the caret.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2012-06-24 18:09 UTC | newest]
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2012-06-24 16:09 [Bug c++/53762] New: pointer-casts don't always check null-pointers imzhuli at vip dot qq.com
2012-06-24 16:26 ` [Bug c++/53762] " redi at gcc dot gnu.org
2012-06-24 16:31 ` redi at gcc dot gnu.org
2012-06-24 18:09 ` pinskia at gcc dot gnu.org
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