Re: c++/8024: G++ 3.2 vtable layout of implicit destructors is not ABI compliant

Re: c++/8024: G++ 3.2 vtable layout of implicit destructors is not ABI compliant

[mmitchel]

Synopsis: G++ 3.2 vtable layout of implicit destructors is not ABI compliant

Responsible-Changed-From-To: unassigned->mmitchel
Responsible-Changed-By: mmitchel
Responsible-Changed-When: Thu Oct 10 14:54:29 2002
Responsible-Changed-Why:
    I'll look into it.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8024

Re: c++/8024: G++ 3.2 vtable layout of implicit destructors is not ABI compliant

[mmitchel]

Synopsis: G++ 3.2 vtable layout of implicit destructors is not ABI compliant

State-Changed-From-To: open->closed
State-Changed-By: mmitchel
State-Changed-When: Thu Nov  7 14:22:14 2002
State-Changed-Why:
    Fixed in GCC 3.3 with -fabi-version=0.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8024

c++/8024: G++ 3.2 vtable layout of implicit destructors is not ABI compliant

[uday.b.ivaturi]

>Number:         8024
>Category:       c++
>Synopsis:       G++ 3.2 vtable layout of implicit destructors is not ABI compliant
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Sep 24 11:16:00 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     uday.b.ivaturi@intel.com
>Release:        GCC 3.2
>Organization:
>Environment:

>Description:

G++ 3.2 vtable layout of implicit destructors is not ABI compliant.

Consider the following test case,

> cat t.cpp
class A {
public:
  int a;
  virtual int fA1() { return 1; } ;
  virtual int fA2() { return 1; } ;
  virtual ~A() { a = fA2(); }
} a;

class C : public virtual A {
public:
  int c;
  virtual int fA1() { return 34; } ;
  virtual int fC1() { return 34; } ;
} c;

Its vtable layout is,

> g++ -c -fdump-class-hierarchy t.cpp
> cat t.cpp.class
Vtable for A
A::_ZTV1A: 6 entries
0     0
4     &_ZTI1A
8     A::fA1()
12    A::fA2()
16    A::~A()
20    A::~A()

Class A
   size=8 align=4
A (0x40083380) 0
    vptr=((&A::_ZTV1A) + 8)

Vtable for C
C::_ZTV1C: 16 entries
0     8
4     0
8     &_ZTI1C
12    C::~C()
16    C::~C()
20    C::fA1()
24    C::fC1()
28    0fffffff8
32    0
36    0fffffff8
40    0fffffff8
44    &_ZTI1C
48    C::_ZTv0_n12_N1C3fA1Ev()
52    A::fA2()
56    C::_ZTv0_n20_N1CD1Ev()
60    C::_ZTv0_n20_N1CD0Ev()

VTT for C
C::_ZTT1C: 2 entries
0     ((&C::_ZTV1C) + 12)
4     ((&C::_ZTV1C) + 48)

Class C
   size=16 align=4
C (0x40083cc0) 0
    vptridx=0 vptr=((&C::_ZTV1C) + 12)
  A (0x40083d00) 8 virtual canonical
      vptridx=4 vbaseoffset=-12 vptr=((&C::_ZTV1C) + 48)

------

Virtual base class has a virtual destructor. From the ABI: "If a class has an implicitly-defined virtual destructor, its entries come after the declared virtual function pointers." But in GCC output, the implicit destructors for class C are first in order compared to member functions.

 
>How-To-Repeat:
 g++ -c -fdump-class-hierarchy t.cpp
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: