Use NASM with CMake

CMake provides flexibility to integrate various build tools. One option is NASM (Netwide Assembler), a widely-used assembler for the x86 and x86-64 computer architectures. Combining CMake with NASM allows assembly routines to be seamlessly included in C or C++ projects, which can be particularly useful for performance-critical functions. This tutorial shows how to use NASM with CMake.

Let's say we have a simple example which calls an assembly function from C++ which adds two integers and returns the result. The main.cpp file declares the external function and prints the sum to the terminal:

main.cpp

#include <iostream>

extern "C" int add(int a, int b);

int main() {
    std::cout << add(2, 3) << std::endl;

    return 0;
}

The add function is implemented in assembly using the calling convention specific to each platform. For Linux, the assembly code looks like this:

add_linux.asm

global add
section .text

add:
    mov eax, edi
    add eax, esi
    ret

For Windows, the assembly code uses a slightly different calling convention:

add_windows.asm

global add
section .text

add:
    mov eax, ecx
    add eax, edx
    ret

Finally, the CMakeLists.txt ties everything together:

CMakeLists.txt

cmake_minimum_required(VERSION 4.0)
project(myapp CXX ASM_NASM)

set(CMAKE_CXX_STANDARD 17)

if (WIN32)
    set(PROJECT_SOURCES_ASM add_windows.asm)
else ()
    set(PROJECT_SOURCES_ASM add_linux.asm)
endif ()

add_executable(${PROJECT_NAME} main.cpp ${PROJECT_SOURCES_ASM})

Here, NASM is enabled by specifying ASM_NASM in the project command. The if statement selects the correct assembly file depending on the platform, and add_executable combines both C++ and assembly sources into a single executable.

With this setup, CMake handles NASM compilation automatically. The result is a fully functional program where C++ and assembly coexist.