using winapi in mingw assembler - winapi

Question

I'm tring to compile the following assembly code into shared library (dll)
.extern _GetProcAddress
.global _main
_main:
CALL _GetProcAddress
using the following commend:
i686-w64-mingw32-gcc -shared -o file.dll file.S
but I'm getting the following link error:
`_GetProcAddress' referenced in section `.text' of /tmp/ccamwU4N.o: defined in discarded section `.text' of /usr/lib/gcc/i686-w64-mingw32/4.6/../../../../i686-w64-mingw32/lib/../lib/libkernel32.a(dxprbs00553.o)
how can I fix this error and call winapi functions?

Answer 1

This code:
// file: winapi0.s
.extern ___main
.extern _GetStdHandle#4
.extern _WriteConsoleA#20
.data
_text:
.ascii "Hello World!\12\0"
.section .text.startup,"x"
.p2align 2,,3
.globl _main
_main:
leal 4(%esp), %ecx
andl $-16, %esp
pushl -4(%ecx)
pushl %ebp
movl %esp, %ebp
pushl %ecx
subl $52, %esp
call ___main
movl $-11, (%esp)
call _GetStdHandle#4
pushl %edx
movl $0, 16(%esp)
leal -12(%ebp), %edx
movl %edx, 12(%esp)
movl $14, 8(%esp)
movl $_text, 4(%esp)
movl %eax, (%esp)
call _WriteConsoleA#20
subl $20, %esp
xorl %eax, %eax
movl -4(%ebp), %ecx
leave
leal -4(%ecx), %esp
ret
Compiles for me just fine with:
gcc -Wall -O2 winapi0.s -o winapi0.exe
And it works by printing this:
Hello World!
It's a slightly cleaned up version of this C code translated by gcc into assembly with the -S switch:
// file: winapi.c
#include <windows.h>
#include <tchar.h>
TCHAR text[] = _T("Hello World!\n");
int main(void)
{
DWORD err;
WriteConsole(GetStdHandle(STD_OUTPUT_HANDLE),
text,
sizeof(text) / sizeof(text[0]),
&err,
NULL);
return 0;
}
I got originally this:
.file "winapi.c"
.def ___main; .scl 2; .type 32; .endef
.section .text.startup,"x"
.p2align 2,,3
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
LFB14:
.cfi_startproc
leal 4(%esp), %ecx
.cfi_def_cfa 1, 0
andl $-16, %esp
pushl -4(%ecx)
pushl %ebp
movl %esp, %ebp
.cfi_escape 0x10,0x5,0x2,0x75,0
pushl %ecx
.cfi_escape 0xf,0x3,0x75,0x7c,0x6
subl $52, %esp
call ___main
movl $-11, (%esp)
call _GetStdHandle#4
pushl %edx
movl $0, 16(%esp)
leal -12(%ebp), %edx
movl %edx, 12(%esp)
movl $14, 8(%esp)
movl $_text, 4(%esp)
movl %eax, (%esp)
call _WriteConsoleA#20
subl $20, %esp
xorl %eax, %eax
movl -4(%ebp), %ecx
.cfi_def_cfa 1, 0
leave
leal -4(%ecx), %esp
.cfi_def_cfa 4, 4
ret
.cfi_endproc
LFE14:
.globl _text
.data
_text:
.ascii "Hello World!\12\0"
.def _GetStdHandle#4; .scl 2; .type 32; .endef
.def _WriteConsoleA#20; .scl 2; .type 32; .endef
Can't you do the same for the 64-bit case?

Answer 2

Link with the import library for the Windows DLL that contains the function you want to call.
I believe that symbol is contained in kernel32.dll. You'll need to make an import library and then link with it.