lld-link.exe fails to find DATA imports without __declspec(dllimport)

[stasoid]

clang/lld-link version: 19.1.0.

This issue was encountered while porting Ladybird to Windows. Ladybird discord discussions: one two.

If data item (global or class static variable) is imported, lld-link refuses to link it unless __declspec(dllimport) is specified. Functions (global and member functions) don't have this problem. See also: WINDOWS_EXPORT_ALL_SYMBOLS in CMake.

I don't know if it is a bug or a feature, I could not find a similar issue. Does lld-link intentionally behave like Visual Studio link.exe here? It would be great if it behaved like on Linux instead. This is just confusing.

Simplified reproduction:

mylib.h:

struct A
{
    static int static_member; // error
    void member_function(); // OK
};

extern int global; // error
void global_function(); // OK

mylib.cpp:

#include "mylib.h"

int global;

int A::static_member;

void global_function()
{
}

void A::member_function()
{
}

myprog.cpp:

#include "mylib.h"

int main()
{
   global = 1;
   global_function();

   A::static_member = 1;
   A().member_function();
}

build.bat:

:: create dll.o
clang -c mylib.cpp

:: create exports.def
echo mylib.o > objs
cmake -E __create_def exports.def objs

:: create mylib.dll and mylib.lib
lld-link mylib.o /dll libcmt.lib /DEF:exports.def

:: create myprog.o
clang -c myprog.cpp

:: create myprog.exe
lld-link myprog.o mylib.lib libcmt.lib

The last command fails with these errors:

lld-link: error: undefined symbol: int global
>>> referenced by myprog.o:(main)

lld-link: error: undefined symbol: public: static int A::static_member
>>> referenced by myprog.o:(main)

The def/lib/dll export all 4 symbols:

> cat exports.def
EXPORTS
        ?global@@3HA     DATA
        ?static_member@A@@2HA    DATA
        ?global_function@@YAXXZ
        ?member_function@A@@QEAAXXZ

> dumpbin /exports mylib.lib
(some output skipped)

                  ?global@@3HA (int global)
                  ?global_function@@YAXXZ (void __cdecl global_function(void))
                  ?member_function@A@@QEAAXXZ (public: void __cdecl A::member_function(void))
                  ?static_member@A@@2HA (public: static int A::static_member)

> dumpbin /exports mylib.dll
(some output skipped)

          1    0 0001AAC8 ?global@@3HA
          2    1 00001000 ?global_function@@YAXXZ
          3    2 00001010 ?member_function@A@@QEAAXXZ
          4    3 0001AACC ?static_member@A@@2HA