c++/143: Re: dynamic_cast bugs

["Martin v. Loewis" <martin at loewis dot home dot cs dot tu-berlin dot de>]

>Number:         143
>Category:       c++
>Synopsis:       dynamic_cast bugs
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          analyzed
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Sun Mar 26 12:06:01 PST 2000
>Closed-Date:
>Last-Modified:
>Originator:     Carlo Wood <carlo@runaway.xs4all.nl>
>Release:        2.95.2
>Organization:
>Environment:
>Description:
 Date: Mon, 15 Nov 1999 14:33:01 +0100
 Original-Message-ID: <19991115143301.A1648@xs4all.nl>

 The following code snippet:

 ---
 #include <iostream>

 class V { };

 class A : public virtual V { };

 class B : public ostream, public A { public: virtual void foo(void) { } };

 class C : public istream, public virtual V { };

 class D : public B, public C { };

 class E : public B, public virtual V { };

 int main(void)
 {
   D d;
   E e;

   ostream* osd = &d;
   ostream* ose = &e;

   if (dynamic_cast<V*>(osd))
     cout << "D contains V" << endl;
   else
     cout << "D doesn't contain V?!" << endl;

   if (dynamic_cast<V*>(ose))
     cout << "E contains V" << endl;
   else
     cout << "E doesn't contain V?!" << endl;

   return 0;
 }
 ---

 Produces with gcc-2.95.1 (release):

 ~/c++/tests>g++ -save-temps -v -Wall -ansi -pedantic dc.cc
 Reading specs from /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/specs
 gcc version 2.95.1 19990816/Linux (release)
  /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/cpp -lang-c++ -v -D__GNUC__=2 -D__GNU
 G__=2 -D__GNUC_MINOR__=95 -D__cplusplus -trigraphs -D__STRICT_ANSI__ -D__ELF__ -
 D__unix__ -D__i386__ -D__linux__ -D__unix -D__linux -Asystem(posix) -D__EXCEPTIO
 NS -Wall -pedantic -Acpu(i386) -Amachine(i386) -D__i386 -D__i386__ -D__i686 -D__
 i686__ -D__pentiumpro -D__pentiumpro__ dc.cc dc.ii
 GNU CPP version 2.95.1 19990816/Linux (release) (i386 Linux/ELF)
 #include "..." search starts here:
 #include <...> search starts here:
  /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/../../../../include/g++-3
  /usr/local/include
  /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/include
  /usr/include
 End of search list.
 The following default directories have been omitted from the search path:
  /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/../../../../i686-redhat-linux/include
 End of omitted list.
  /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/cc1plus dc.ii -quiet -dumpbase dc.cc 
 -Wall -pedantic -ansi -version -o dc.s
 GNU C++ version 2.95.1 19990816/Linux (release) (i686-redhat-linux) compiled by 
 GNU C version 2.95.1 19990816/Linux (release).
  as -V -Qy -o dc.o dc.s
 GNU assembler version 2.9.5 (i686-pc-linux-gnu) using BFD version 2.9.5.0.14
  /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/collect2 -m elf_i386 -dynamic-linker 
 /lib/ld-linux.so.2 /usr/lib/crt1.o /usr/lib/crti.o /usr/lib/gcc-lib/i686-redhat-
 linux/2.95.1/crtbegin.o -L/usr/lib/gcc-lib/i686-redhat-linux/2.95.1 -L/usr/i686-
 redhat-linux/lib dc.o -lstdc++ -lm -lgcc -lc -lgcc /usr/lib/gcc-lib/i686-redhat-
 linux/2.95.1/crtend.o /usr/lib/crtn.o

 ~/c++/tests>grep dynamic dc.s
	 call __dynamic_cast
	 call __dynamic_cast

 ~/c++/tests>a.out
 D contains V
 E doesn't contain V?!

 This is, I believe, a bug.  VC++ (on windows) results in:

 D contains V
 E contains V

 which I think is correct.


 A later cvs version results in:

 ~/c++/tests>g++-cvs -save-temps -v -Wall -ansi -pedantic dc.cc
 Reading specs from /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/specs
 gcc version 2.96 19991102 (experimental)
  /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/cpp -lang-c++ -v -D__GNUC__=2 -D__GNUG__=2 -D__GNUC_MINOR__=96 -D__cplusplus -trigraphs -D__STRICT_ANSI__ -D__ELF__ -D__unix__ -D__i386__ -D__linux__ -D__unix -D__linux -Asystem(posix) -D__EXCEPTIONS -Wall -pedantic -Acpu(i386) -Amachine(i386) -D__i386 -D__i386__ -D__tune_pentiumpro__ dc.cc dc.ii
 GNU CPP version 2.96 19991102 (experimental) (i386 Linux/ELF)
 #include "..." search starts here:
 #include <...> search starts here:
  /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/../../../../include/g++-3
  /usr/local/egcs/include
  /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/../../../../i686-pc-linux-gnu/include
  /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/include
  /usr/include
 End of search list.
 The following default directories have been omitted from the search path:
 End of omitted list.
  /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/cc1plus dc.ii -quiet -dumpbase dc.cc -Wall -pedantic -ansi -version -o dc.s
 GNU C++ version 2.96 19991102 (experimental) (i686-pc-linux-gnu) compiled by GNU C version 2.95.1 19990816/Linux (release).
  as -V -Qy -o dc.o dc.s
 GNU assembler version 2.9.5 (i686-pc-linux-gnu) using BFD version 2.9.5.0.14
  /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/collect2 -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 /usr/lib/crt1.o /usr/lib/crti.o /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/crtbegin.o -L/usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96 -L/usr/local/egcs/lib dc.o -lstdc++ -lm -lgcc -lc -lgcc /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/crtend.o /usr/lib/crtn.o

 ~/c++/tests>a.out
 a.out: error in loading shared libraries: a.out: undefined symbol: __dynamic_cast_2

 ~/c++/tests>grep dynamic dc.s
	 call    __dynamic_cast_2
	 call    __dynamic_cast_2


 Regards,
 Carlo Wood

 [MvL: retested with 2.96 20000326]

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