[Bug c++/12326] New: Thunk not generated for virtual func

["thomas at koeller dot dyndns dot org" <gcc-bugzilla at gcc dot gnu dot org>]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12326

           Summary: Thunk not generated for virtual func
           Product: gcc
           Version: 3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: thomas at koeller dot dyndns dot org
                CC: gcc-bugs at gcc dot gnu dot org,thomas dot koeller at
                    baslerweb dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu

If both -fvtable-gc and -ffunction-sections are given to the compiler and the linker (GNU ld)  
is invoked with --gc-sections, then virtual functions are eliminated in spite of being called,  
and no thunks are generated for these functions either. A set of files to reproduce the  
problem is included at the end of this PR.  
  
When the program is built with the Makefile included, the output from nm shows that  
neither the function Drvd::func2() nor a thunk for it is present in the executable. Its vtable  
slot is zeroed and the program segfaults.  
  
bash-2.05b$ nm -C testprog | grep '.*::func'  
08048298 T Drvd::func1()  
bash-2.05b$ testprog  
Segmentation fault  
bash-2.05b$  
  
If I leave out -fvtable-gc, then the output from nm looks ok and the program runs fine.  
  
bash-2.05b$ nm -C testprog | grep '.*::func'  
08048298 T Drvd::func1()  
0804829e T Drvd::func2()  
080482a4 W non-virtual thunk to Drvd::func2()  
bash-2.05b$ testprog  
bash-2.05b$  
  
These are the files to reproduce the bug (why can't I just attach a tar.bz2 archive?):  
  
Makefile:  
-----------------------------------------------------------------------------------------------------------------------------  
APPNAME		:= testprog  
CXX		:= /opt/gcc/bin/g++  
CXXFLAGS	:= -O0 -ggdb2  -fno-rtti -ffunction-sections -fdata-sections \  
		   -fvtable-gc  
LD		:= $(CXX)  
LDFLAGS		:= -static -O0 -Wl,-Map -Wl,$(APPNAME).map -Wl,--gc-sections  
RM		:= rm  
RMFLAGS		:= -f  
  
.PHONY		: all clean  
  
all		: $(APPNAME)  
  
$(APPNAME)	: testprog.o drvd.o  
	$(LD) $(LDFLAGS) -o $@ $^  
  
testprog.o	: testprog.cxx testprog.hxx  
	$(CXX) $(CXXFLAGS) -c -o $@ $<  
  
drvd.o		: drvd.cxx testprog.hxx  
	$(CXX) $(CXXFLAGS) -c -o $@ $<  
  
clean		:  
	$(RM) $(RMFLAGS) testprog.o drvd.o $(APPNAME) $(APPNAME).map  
-----------------------------------------------------------------------------------------------------------------------------  
  
testprog.hxx:  
-----------------------------------------------------------------------------------------------------------------------------  
#if !defined (TESTPROG_HXX)  
#define TESTPROG_HXX  
  
class Base1  
{  
  public:  
    virtual void func1(void) = 0;  
};  
  
class Base2  
{  
  public:  
    virtual void func2(void) = 0;  
};  
  
class Drvd : public Base1, public Base2  
{  
  public:  
    virtual void func1(void);  
    virtual void func2(void);  
};  
  
#endif // !defined (TESTPROG_HXX)  
-----------------------------------------------------------------------------------------------------------------------------  
  
testprog.cxx:  
-----------------------------------------------------------------------------------------------------------------------------  
#include "testprog.hxx"  
  
Drvd drvd;  
  
int  
main(void)  
{  
  Base1 &base1(drvd);  
  Base2 &base2(drvd);  
  
  base1.func1();  
  base2.func2();  
  return 0;  
};  
-----------------------------------------------------------------------------------------------------------------------------  
  
drvd.cxx:  
-----------------------------------------------------------------------------------------------------------------------------  
#include "testprog.hxx"  
  
void  
Drvd::func1(void)  
{  
}  
  
void  
Drvd::func2(void)  
{  
}  
-----------------------------------------------------------------------------------------------------------------------------