Message-ID: <a47d5c0807282322k7ebe9bbap63046f65dd8548f0@mail.gmail.com>
Date: Tue, 29 Jul 2008 14:22:12 +0800
From: "Bo Yang" <techrazy DOT yang AT gmail DOT com>
To: cygwin AT cygwin DOT com
Subject: Mingw gcc emit wrong symbols in multiple inheritance case
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Hi Dear Gcc developers,

   When I am trying to build Mozilla with gcc-mingw, I came across
the linkage error of undefined symbols in multiple inheritance case.
And I have made a simple test case to reproduce the problem. But the
test case is still very complex, I think. So, I came down to find the
what are the real problems. And now, I think I have, so I just
describe what I found here:

For a class hierarchy :

class SuperSuperBase {
public:
       SuperSuperBase();
       ~SuperSuperBase();

       virtual void __attribute__((__stdcall__)) funcSSB() = 0;
};

class SuperBase : public SuperSuperBase {
public:
       SuperBase();
       ~SuperBase();

       virtual void __attribute__((__stdcall__)) funcSB() = 0;
};

class Base : public SuperBase {
public:
       Base();
       ~Base();

       virtual void __attribute__((__stdcall__)) funcB() = 0;
};

class ChildA: public Base {
public:
       ChildA();
       ~ChildA();

       virtual void __attribute__((__stdcall__)) funcCA() = 0;
};

class ChildB: public SuperBase {
public:
       ChildB();
       ~ChildB();

       virtual void __attribute__((__stdcall__)) funcCB() = 0;
};

class DLL Child :       public  ChildA,
                public  ChildB {
public:
       Child();
       ~Child();

       virtual void __attribute__((__stdcall__)) funcSSB();
       virtual void __attribute__((__stdcall__)) funcSB();
       virtual void __attribute__((__stdcall__)) funcB();
       virtual void __attribute__((__stdcall__)) funcCB();
       virtual void __attribute__((__stdcall__)) funcCA();
};

I make the Child in a DLL and then I import it from the DLL to build a
test application. But I failed with the undefined symbols of
"funcSSB,funcSB,funcCB".
And the errors occurs when I build with gcc 4.3.0 but not with gcc
3.4.2. So, I use i686-mingw32-nm to dump the object file which
contains the definition of the Child class. And for the three
undefined functions, the two compiler output different symbols,
Gcc 3.4.2:
        U __ZTVN10__cxxabiv117__class_type_infoE
        U __ZTVN10__cxxabiv120__si_class_type_infoE
        U __ZTVN10__cxxabiv121__vmi_class_type_infoE
00000000 T __ZThn4_N5Child6funcCBEv AT 4
00000000 T __ZThn4_N5Child6funcSBEv AT 4
00000000 T __ZThn4_N5Child7funcSSBEv AT 4

Gcc 4.3.0:
        U __ZTVN10__cxxabiv117__class_type_infoE
        U __ZTVN10__cxxabiv120__si_class_type_infoE
        U __ZTVN10__cxxabiv121__vmi_class_type_infoE
00000306 T __ZThn4_N5Child6funcCBEv
        U __ZThn4_N5Child6funcCBEv AT 4
000002d7 T __ZThn4_N5Child6funcSBEv
        U __ZThn4_N5Child6funcSBEv AT 4
000002c8 T __ZThn4_N5Child7funcSSBEv
        U __ZThn4_N5Child7funcSSBEv AT 4

I think the difference here is the key point of the linkage error.
Could anybody help to give some more insight here? Any advice will be
appreciated very much!

Regards!
Bo

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