external assembly file in visual studio

Question

I searched and found I can not use __asm in x64 in visual studio. Instead I have to use an external assembly file.

How can I add external assembly file to my win32 console project?

How can compile them?

Can you explain step by step.

Solution

How to build a mixed-source x64-project with a x64 assembly file in Visual Studio:

1) Start Visual Studio (Community) 2015 and choose FILE - New - Project.

2) In the next window choose Win 32 Console Application.

3) You get a confirmation. Click on Next >.

4) In the next window you can accept the default settings. Click on Finish.

5) Make sure, that the project is highlighted in the Solution Explorer and and choose PROJECT - Build Customizations... from the menu.

6) In the next window tick masm(.targets,.props) and click on OK.

7) Choose Build - Configuration Manager...

8) Change the Active solution platform to x64

9) Create callee.asm: PROJECT - Add New Item.

10) In the next window choose C++File(.cpp) and - IMPORTANT! - give it a name with an .asm extension. Click on Add.

10) Now check if the .asm file has the right properties. In the Solution Explorer right-click on the file and choose Properties.

11) In the Property Page you should see at least:

Excluded From Build    (empty) or No
Item Type              Microsoft Macro Assembler

Under Command Line ensure that ml64.exe is chosen as the assembler.

Click on OK.

12) Now you can fill the files with content.

ConsoleApplication1.cpp:

#include <iostream>
using namespace std;

extern "C" void hello_from_asm();

int main()
{
    cout << "Hello from CPP" << endl;
    hello_from_asm();
    return 0;
}

callee.asm:

PUBLIC hello_from_asm
EXTERN puts:PROC

.data

    hello1 db "Hello from ASM.",0

.code

hello_from_asm PROC
    push rbp
    mov rbp, rsp
    sub rsp, 32                 ; Shadow Space
    and spl, -16                ; Align stack at 16

    lea rcx, hello1
    call puts

    leave                       ; Restore stack (rsp) & frame pointer (rbp)
    ret
hello_from_asm ENDP

END

13) Build the .exe

and run it with CTRL-F5.

The application will be opened in a new window.

Comments

[Peter Cordes]

Related: Assembly programming - WinAsm vs Visual Studio 2017 for pure asm projects. (I've added this and the other link to the x86 tag wiki)

[tenghiz]

Works fine on VS 2015. However, VS 2017 shows message: A1000, cannot open file: x.asm.

[mirabilos]

Some gotchas: Build Customisation only shows up in the Project menu when the project itself (second entry) is selected in the Solution Explorer window, not any of the source files or so. You might also run into SAFESEH errors; try to not disable it in the linker but _en_able it in the MASM properties instead.