libstdc++/4292: dynamic_cast incorrectly returns 0
kainz@ilm.com
kainz@ilm.com
Mon Sep 10 16:06:00 GMT 2001
>Number: 4292
>Category: libstdc++
>Synopsis: dynamic_cast incorrectly returns 0
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Mon Sep 10 16:06:01 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator: Philip Hubbard / Florian Kainz, Industrial Light + Magic
>Release: unknown-1.0
>Organization:
>Environment:
gcc 3.0.1 on RedHat Linux 7.1 / Pentium
% g++ -v
Reading specs from /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/specs
Configured with: ../gcc-3.0.1/configure --enable-threads --prefix=/usr/local --enable-languages=c,c++
Thread model: posix
gcc version 3.0.1
>Description:
dynamic_cast incorrectly returns 0 in programs that load
dynamic shared objects (DSOs) via dlopen().
Header file <typeinfo> assumes that typeinfo names are merged
across all DSOs in a program if weak symbols are supported.
At least on Linux, this assumption is wrong for DSOs loaded
via dlopen().
>How-To-Repeat:
Reproducing the bug requires multiple source files:
a.C a.h main.C Makefile
The files are listed below.
The example program should print:
castInMain()
1
castInDso()
1
castInMain()
1
castInDso()
1
The program prints this instead:
castInMain()
1
castInDso()
0
castInMain()
0
castInDso()
1
The source files:
::::::::::::::
a.C
::::::::::::::
#include <a.h>
#include <iostream>
extern "C"
{
D *
DInDso ()
{
static D d;
return &d;
}
bool
castInDso (B *b)
{
std::cout << "castInDso()\n";
return 0 != dynamic_cast <D *> (b);
}
}
::::::::::::::
a.h
::::::::::::::
struct B
{
virtual ~B() {}
};
struct D: public B
{
virtual ~D() {}
};
::::::::::::::
main.C
::::::::::::::
#include <a.h>
#include <dlfcn.h>
#include <iostream>
using std::cout;
using std::endl;
extern "C"
{
typedef bool func1 (B *);
typedef D * func2 ();
}
bool
castInMain (B *b)
{
std::cout << "castInMain()\n";
return 0 != dynamic_cast <D *> (b);
}
int
main ()
{
void *liba = dlopen ("./liba.so", RTLD_LAZY);
if (!liba)
{
cout << dlerror () << endl;
return 1;
}
func1 *castInDso = (func1 *) dlsym (liba, "castInDso");
if (!castInDso)
{
cout << dlerror () << endl;
return 1;
}
func2 *DInDso = (func2 *) dlsym (liba, "DInDso");
if (!DInDso)
{
cout << dlerror () << endl;
return 1;
}
{
D d;
cout << castInMain (&d) << endl;
cout << castInDso (&d) << endl;
}
{
D *d = DInDso();
cout << castInMain (d) << endl;
cout << castInDso (d) << endl;
}
}
::::::::::::::
Makefile
::::::::::::::
t = liba.so test
all: $t
clean:
rm -f $t core
liba.so: a.C a.h
g++ -I. -shared -o $@ a.C
test: main.C a.h
g++ -I. -L. main.C -o $@ -ldl
>Fix:
*** gcc-3.0.1/libstdc++-v3/libsupc++/typeinfo Wed Jul 11 12:37:58 2001
--- /net/rnd/gs/home/kainz/pub/gcc-3.0.1/libstdc++-v3/libsupc++/typeinfo
Mon Sep 10 15:23:30 2001
***************
*** 43,54 ****
class __class_type_info;
} // namespace __cxxabiv1
! #if !__GXX_WEAK__
! // If weak symbols are not supported, typeinfo names are not merged.
! #define __GXX_MERGED_TYPEINFO_NAMES 0
#else
! // On platforms that support weak symbols, typeinfo names are merged.
! #define __GXX_MERGED_TYPEINFO_NAMES 1
#endif
namespace std
--- 43,65 ----
class __class_type_info;
} // namespace __cxxabiv1
! #if 0
!
! #if !__GXX_WEAK__
! // If weak symbols are not supported, typeinfo names are not merged.
! #define __GXX_MERGED_TYPEINFO_NAMES 0
! #else
! // On platforms that support weak symbols, typeinfo names are merged.
! #define __GXX_MERGED_TYPEINFO_NAMES 1
! #endif
!
#else
!
! // Even if weak symbols are supported, typeinfo names are not
! // always merged. On Linux, dynamic shared objects opened with
! // dlopen() have their own, non-shared copies of typeinfo names.
! #define __GXX_MERGED_TYPEINFO_NAMES 0
!
#endif
namespace std
>Release-Note:
>Audit-Trail:
>Unformatted:
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