[Bug c++/16924] New: dllexport attribute now causes some symbols _not_ to be exported

[dannysmith at users dot sourceforge dot net]

Recent changes to dllexport handling in C++ frontend has broken
the use of dllexport attribute with multiple inheritance.

Now (gcc version 3.5.0 20040806 (experimental)) the dllexport attribute
causes some symbols *not* to be exported.

Here is a testcase:

// dll-mi.C 
#ifdef BUILDING_DLL
#define  DLL_IMPEXP __attribute__ ((dllexport))
#else
#define  DLL_IMPEXP
#endif

class DLL_IMPEXP MBase
{
public:
  virtual int vf() const = 0;
  virtual ~MBase();
};

class DLL_IMPEXP D1 : virtual public MBase
{
public:
  int vf() const;
};

MBase::~MBase(){}

int D1::vf() const { return 1; }



D:\develop\BUGS -shared -DBUILDING_DLL -o test.dll dll-mi.C 
D:\TEMP/ccueaaaa.o(.rdata$_ZTV2D1+0x18):dll-mi.C: undefined reference to 
`D1::~D1()'
D:\TEMP/ccueaaaa.o(.rdata$_ZTV2D1+0x1c):dll-mi.C: undefined reference to 
`D1::~D1()'

And looking at the assembler, the compiler puts those dtors into the
vtable for D1

.globl __ZTV2D1
	.section	.rdata$_ZTV2D1,"dr"
	.linkonce same_size
	.align 32
__ZTV2D1:
	.long	0
	.long	0
	.long	0
	.long	0
	.long	__ZTI2D1
	.long	__ZNK2D12vfEv
	.long	__ZN2D1D1Ev
	.long	__ZN2D1D0Ev
	.text


but doesn't actually emit the code for the two dtor's.

However if I build an object _without_ the dllexport, the dtor's
_ZN2D1D1Ev and _ZN2D1D0Ev (as well as thunks to these dtors) are
emitted. Here is the diff of two compiles without and with the dllexport
attribute enabled. The file dll-mi-no-export.s was built without the export
attribute, the other with:

> diff -up dll-mi-no-export.s dll-mi-export.s

D:\develop\BUGS>diff -up dll-mi-no-export.s dll-mi-export.s 
--- dll-mi-no-export.s	Mon Aug 09 08:30:35 2004
+++ dll-mi-export.s	Mon Aug 09 08:30:41 2004
@@ -165,124 +165,15 @@ LCFI13:
 	leave
 	ret
 LFE6:
-	.section	.text$_ZTv0_n16_N2D1D1Ev,"x"
-	.linkonce discard
-	.align 2
-.globl __ZTv0_n16_N2D1D1Ev
-	.def	__ZTv0_n16_N2D1D1Ev;	.scl	2;	.type	32;	.endef
-__ZTv0_n16_N2D1D1Ev:
-	movl	4(%esp), %eax
-	movl	(%eax), %ecx
-	addl	-16(%ecx), %eax
-	movl	%eax, 4(%esp)
-	jmp	__ZN2D1D1Ev
-	.section	.text$_ZN2D1D1Ev,"x"
-	.linkonce discard
-	.align 2
-.globl __ZN2D1D1Ev
-	.def	__ZN2D1D1Ev;	.scl	2;	.type	32;	.endef
-__ZN2D1D1Ev:
-LFB9:
-	pushl	%ebp
-LCFI14:
-	movl	%esp, %ebp
-LCFI15:
-	subl	$8, %esp
-LCFI16:
-	movl	$__ZTV2D1+20, %eax
-	movl	8(%ebp), %edx
-	movl	%eax, (%edx)
-	movl	8(%ebp), %eax
-	movl	%eax, -4(%ebp)
-	movl	$0, %eax
-	movl	-4(%ebp), %edx
-	addl	%eax, %edx
-	movl	$__ZTV2D1+20, %eax
-	movl	%eax, (%edx)
-	movl	$2, %eax
-	shrl	%eax
-	andl	$1, %eax
-	testb	%al, %al
-	je	L15
-	movl	8(%ebp), %edx
-	movl	%edx, -4(%ebp)
-	subl	$12, %esp
-	pushl	-4(%ebp)
-LCFI17:
-	call	__ZN5MBaseD2Ev
-	addl	$16, %esp
-L15:
-	movl	$0, %eax
-	testb	%al, %al
-	je	L14
-	subl	$12, %esp
-	pushl	8(%ebp)
-	call	__ZdlPv
-	addl	$16, %esp
-L14:
-	leave
-	ret
-LFE9:
-	.section	.text$_ZTv0_n16_N2D1D0Ev,"x"
-	.linkonce discard
-	.align 2
-.globl __ZTv0_n16_N2D1D0Ev
-	.def	__ZTv0_n16_N2D1D0Ev;	.scl	2;	.type	32;	.endef
-__ZTv0_n16_N2D1D0Ev:
-	movl	4(%esp), %eax
-	movl	(%eax), %ecx
-	addl	-16(%ecx), %eax
-	movl	%eax, 4(%esp)
-	jmp	__ZN2D1D0Ev
-	.section	.text$_ZN2D1D0Ev,"x"
-	.linkonce discard
-	.align 2
-.globl __ZN2D1D0Ev
-	.def	__ZN2D1D0Ev;	.scl	2;	.type	32;	.endef
-__ZN2D1D0Ev:
-LFB10:
-	pushl	%ebp
-LCFI18:
-	movl	%esp, %ebp
-LCFI19:
-	subl	$8, %esp
-LCFI20:
-	movl	$__ZTV2D1+20, %eax
-	movl	8(%ebp), %edx
-	movl	%eax, (%edx)
-	movl	8(%ebp), %eax
-	movl	%eax, -4(%ebp)
-	movl	$0, %eax
-	movl	-4(%ebp), %edx
-	addl	%eax, %edx
-	movl	$__ZTV2D1+20, %eax
-	movl	%eax, (%edx)
-	movl	$3, %eax
-	shrl	%eax
-	andl	$1, %eax
-	testb	%al, %al
-	je	L20
-	movl	8(%ebp), %edx
-	movl	%edx, -4(%ebp)
-	subl	$12, %esp
-	pushl	-4(%ebp)
-LCFI21:
-	call	__ZN5MBaseD2Ev
-	addl	$16, %esp
-L20:
-	movl	$1, %eax
-	testb	%al, %al
-	je	L19
-	subl	$12, %esp
-	pushl	8(%ebp)
-	call	__ZdlPv
-	addl	$16, %esp
-L19:
-	leave
-	ret
-LFE10:
-	.def	__ZTv0_n16_N2D1D0Ev;	.scl	3;	.type	32;	.endef
-	.def	__ZTv0_n16_N2D1D1Ev;	.scl	3;	.type	32;	.endef
-	.def	__ZTv0_n12_NK2D12vfEv;	.scl	3;	.type	32;	.endef
 	.def	___cxa_pure_virtual;	.scl	3;	.type	32;	.endef
 	.def	__ZdlPv;	.scl	3;	.type	32;	.endef
+	.section .drectve
+
+	.ascii " -export:_ZNK2D12vfEv"
+	.ascii " -export:_ZTv0_n12_NK2D12vfEv"
+	.ascii " -export:_ZN5MBaseD0Ev"
+	.ascii " -export:_ZN5MBaseD1Ev"
+	.ascii " -export:_ZN5MBaseD2Ev"
+	.ascii " -export:_ZTV2D1,data"
+	.ascii " -export:_ZTT2D1,data"
+	.ascii " -export:_ZTV5MBase,data"

-- 
           Summary: dllexport attribute now causes some symbols _not_ to be
                    exported
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dannysmith at users dot sourceforge dot net
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-mingw32
  GCC host triplet: i686-pc-mingw32
GCC target triplet: i686-pc-mingw32


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16924