AT&T to inline asm in Visual Studio 2017 - visual-studio

Question

I'm trying to convert assembly written in AT&T syntax from a DevC++ project to inline assembly in Visual Studio.
This is the AT&T I'm trying to convert:
void Painter::drawRectangle(int surface, int x, int y, int width, int height, int red, int green, int blue) {
asm("mov %0, %%eax":: "r" (0x004EAA90));
asm("call *%eax");
asm("mov %eax, %ecx");
asm("mov (%ecx), %eax");
asm("push %0":: "m" (blue));
asm("push %0":: "m" (green));
asm("push %0":: "m" (red));
asm("push %0":: "m" (height));
asm("push %0":: "m" (width));
asm("push %0":: "m" (y));
asm("push %0":: "m" (x));
asm("push %0":: "m" (surface));
asm("call *0x14(%eax)");
}
what i've done so far:
void _drawrectangle(int surface, int x, int y, int width, int height, int red, int green, int blue)
{
__asm
{
mov eax, 0x004eaa90
call dword ptr [eax]
mov ecx, eax
mov eax, [ecx]
push blue
push green
push red
push height
push width
push y
push x
push surface
call dword ptr [eax + 0x14]
}
}
I'm writing this in my DLL, which I've already injected into the game. The game crashes on opening. And I've already hooked another drawing function in C++, which worked.
Hopefully you can help me/guide me in the right direction. Thank you.

Answer 1

Here's how you could write your function in C++ without the use of inline assembly:
#ifndef _MSC_VER
/* For GCC and clang */
#undef __thiscall
#define __thiscall __attribute__((thiscall))
#endif
struct some_interface {
virtual void _unknown_0() = 0;
virtual void _unknown_4() = 0;
virtual void _unknown_8() = 0;
virtual void _unknown_C() = 0;
virtual void _unknown_10() = 0;
virtual void __thiscall drawRectangle(int surface, int x, int y,
int width, int height,
int red, int green, int blue) = 0;
};
const auto get_interface = (some_interface *(*)()) 0x4EAA90;
void
drawRectangle(int surface, int x, int y, int width, int height,
int red, int green, int blue) {
get_interface()->drawRectangle(surface, x, y, width, height,
red, green, blue);
}
The code you're trying to translate first calls a function that returns a pointer to some class object with at least 6 virtual methods defined. It then calls the 6th virtual method of that object. The some_interface struct minimally recreates that class so the 6th virtual method can be called. The get_interface constant is a function pointer that points to the function located at 0x4EAA90 and in C++ function pointers can be used just like a function.
The above code generates the following assembly in GCC 8.2:
drawRectangle(int, int, int, int, int, int, int, int):
subl $12, %esp
movl $5155472, %eax
call *%eax
movl (%eax), %edx
movl %eax, %ecx
pushl 44(%esp)
pushl 44(%esp)
pushl 44(%esp)
pushl 44(%esp)
pushl 44(%esp)
pushl 44(%esp)
pushl 44(%esp)
pushl 44(%esp)
call *20(%edx)
addl $12, %esp
ret
and the following assembly with Visual C++ 2017:
void drawRectangle(int,int,int,int,int,int,int,int) PROC ; drawRectangle, COMDAT
mov eax, 5155472 ; 004eaa90H
call eax
push DWORD PTR _blue$[esp-4]
mov ecx, eax
push DWORD PTR _green$[esp]
mov edx, DWORD PTR [eax]
push DWORD PTR _red$[esp+4]
push DWORD PTR _height$[esp+8]
push DWORD PTR _width$[esp+12]
push DWORD PTR _y$[esp+16]
push DWORD PTR _x$[esp+20]
push DWORD PTR _surface$[esp+24]
call DWORD PTR [edx+20]
ret 0
void drawRectangle(int,int,int,int,int,int,int,int) ENDP ; drawRectangle