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c++/1611: c++ new-abi generates bad code with virtual derivation



>Number:         1611
>Category:       c++
>Synopsis:       c++ new-abi generates bad code with virtual derivation
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Wed Jan 10 20:16:01 PST 2001
>Closed-Date:
>Last-Modified:
>Originator:     scott snyder
>Release:        2.97 20010110 (experimental)
>Organization:
>Environment:
System: Linux karma 2.2.16-22 #1 Tue Aug 22 16:49:06 EDT 2000 i686 unknown
Architecture: i686

	
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: ../egcs/configure --prefix=/usr/local/egcs --enable-libstdcxx-v3 --enable-threads=posix --enable-cheaders=c_shadow : (reconfigured) 
>Description:

  I'm seeing a crash in my code when i try to use new abi, with a
   somewhat complicated virtual derivation layout.
  It looks like the destructor for a virtual base class is being
  called with the wrong offset into the complete object --- members
  of the virtual base have garbage values.

>How-To-Repeat:

  Here's a test case:

-------------------------------------------------------------------
#include <assert.h>


struct d0_Object
{
  d0_Object () : _indptr (12345) {}
  virtual ~d0_Object () { assert (_indptr == 12345); }
  int _indptr;
};



class M10 : virtual public d0_Object {};
struct M8 : virtual public d0_Object {};
struct M9 : public M8, virtual public M10 {};


int main (int argc, char* argv[])
{
  M9 dum;
  return 0;
}
-------------------------------------------------------------------

This program should run and exit silently without error.
In the d0_Object virtual base, the constructor initializes
the member field _indptr; the destructor then just checks to be
sure that the member has the same value to which it was
set in the constructor.  But when i run it, i see the assertion
firing:

$ g++ -o x x.cc
$ ./x
x: x.cc:7: virtual d0_Object::~d0_Object(): Assertion `_indptr == 12345' failed.
Aborted (core dumped)


I did not see this problem using the old abi.


>Fix:
	
>Release-Note:
>Audit-Trail:
>Unformatted:
   With Ben's patch:
 2001-01-10  Benjamin Kosnik  <bkoz@redhat.com>
 
 	* pt.c (check_explicit_specialization): Disable 2000-12-14 change.
 
 

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