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Re: [PATCH/RFC] Fix LD test FAIL: weak symbols on Cygwin
On Thu, 19 Mar 2009 23:58:15 +0000, Dave Korn
<dave.korn.cygwin@googlemail.com> wrote:
> Danny, Aaron, Kai:
>
> Do you guys have any references, code samples or testcases that will
show
> me
> the typical MSVC usage of weak externals so that I can understand the
> interop
> requirements a bit better? Googling msdn hasn't told me anything
> informative.
>
> cheers,
> DaveK
I also tried to google a bit because usually I am quite good at it and
unfortunately I have found only
one interesting reference here :
http://support.microsoft.com/default.aspx?scid=kb;en-us;q148652
In the cause section :
The CRT libraries use weak external linkage for the new, delete, and
DllMain functions. The MFC libraries also contain new, delete, and DllMain
functions. These functions require the MFC libraries to be linked before
the CRT library is linked.
So I have disassembled libcmt.lib\new.obj and and found this :
UNDEF:00000230 ;
===========================================================================
UNDEF:00000230
UNDEF:00000230 ; Segment type: Externs
UNDEF:00000230 ; UNDEF
UNDEF:00000230 ; public: __thiscall std::exception::exception(char const *
const &, int)
UNDEF:00000230 extrn ??0exception@std@@QAE@ABQBDH@Z:near
UNDEF:00000230 ; CODE XREF:
std::bad_alloc::bad_alloc(void)+Cp
UNDEF:00000234 ; const type_info::`vftable'
UNDEF:00000234 extrn ??_7type_info@@6B@:near
UNDEF:00000234 ; DATA XREF:
.data:std::bad_alloc `RTTI Type Descriptor'o
UNDEF:00000234 ;
.data:std::exception `RTTI Type Descriptor'o
UNDEF:00000238 ; public: virtual void * __thiscall std::bad_alloc::`scalar
deleting destructor'(unsigned int)
UNDEF:00000238 extrn ??_Gbad_alloc@std@@UAEPAXI@Z_0:near
UNDEF:0000023C ; public: virtual void * __thiscall std::bad_alloc::`vector
deleting destructor'(unsigned int)
UNDEF:0000023C extrn ??_Ebad_alloc@std@@UAEPAXI@Z:near ;
weak
UNDEF:0000023C ; DATA XREF:
.rdata:const std::bad_alloc::`vftable'o
UNDEF:00000240 ; public: virtual char const * __thiscall
std::exception::what(void)const
UNDEF:00000240 extrn ?what@exception@std@@UBEPBDXZ:near
UNDEF:00000240 ; DATA XREF:
.rdata:00000038o
UNDEF:00000244 ; public: virtual __thiscall
std::exception::~exception(void)
UNDEF:00000244 extrn ??1exception@std@@UAE@XZ:near
UNDEF:00000244 ; CODE XREF:
std::bad_alloc::~bad_alloc(void)+6j
UNDEF:00000244 ;
std::bad_alloc::`scalar deleting destructor'(uint)+Ep ...
UNDEF:00000248 ; void __cdecl operator delete(void *)
UNDEF:00000248 extrn ??3@YAXPAX@Z:near ; CODE XREF:
std::bad_alloc::`scalar deleting destructor'(uint)+1Ap
UNDEF:0000024C ; public: __thiscall std::exception::exception(class
exception::exception const &)
UNDEF:0000024C extrn ??0exception@std@@QAE@ABV01@@Z:near
UNDEF:0000024C ; CODE XREF:
std::bad_alloc::bad_alloc(bad_alloc::bad_alloc const &)+Bp
UNDEF:0000024C ; DATA XREF:
.xdata$x:00000210o
UNDEF:00000250 ; int __cdecl atexit(void (__cdecl *)())
UNDEF:00000250 extrn _atexit:near ; CODE XREF:
.text:0000018Fp
UNDEF:00000254 ; void *__cdecl malloc(size_t Size)
UNDEF:00000254 extrn _malloc:near ; CODE XREF:
.text:00000162p
UNDEF:00000258 extrn __callnewh:near ; CODE XREF:
.text:00000155p
UNDEF:0000025C ; __stdcall _CxxThrowException(x, x)
UNDEF:0000025C extrn __CxxThrowException@8:near ; CODE
XREF: .text:000001A7p
UNDEF:0000025C
UNDEF:0000025C
UNDEF:0000025C end
This UNDEF stuff sems to be what pecoff specs is talking about :
"Weak externals are represented by a symbol table record with EXTERNAL
storage class, UNDEF section number, and a value of zero. The weak-external
symbol record is followed by an auxiliary record with the following
format."
I don't think it helps you but this is the only information I found.