💻 C ASM Template

This is a template for a C project that uses an assembly file for the startup code.

📂 Folder structure

The folder structure is as follows:

.
├── arch
│   ├── aarch64
│   │   └── startup.asm     <- Assembly file for aarch64
│   └── x86_64
│       └── startup.asm     <- Assembly file for x86_64
├── config.mk               <- Configuration file
├── include
│   └── add.h               <- Example header file
├── Makefile                <- Makefile
├── README.md
└── src
    ├── add.c               <- Example C file
    └── main.c              <- Main C file

❓ How it works

When the program is started the assembly file is executed first. Lets use the X86_64 assembly file as an example. The assembly file contains the following code:

.section .text

.globl main

.extern program

main:
    call program         ; Call the C program
    movl %eax, %ebx      ; Move the return value of the C program to ebx
    movl $60, %eax       ; Set the exit syscall number
    movl %ebx, %ebx      ; Move the return value of the C program to ebx
    syscall              ; Call the exit syscall

Then the C file is compiled and linked with the assembly file. The C file contains the following code:

#include <stdio.h>

int program() {
    printf("Hello World!\n");
    return 0;
}

When the C program returns the assembly file will call the exit syscall with the return value of the program function.

🔨 How to build

🖥️ x86_64

You need to set the ARCH variable in config.mk to x86_64 and run make.

ARCH = x86_64

AS = as
CC = gcc

Note

If you are running on aarch64 you need to set the as and cc variables to the cross compiler.

make

🖥️ aarch64

You need to set the ARCH variable in config.mk to aarch64 and run make.

ARCH = aarch64

AS = as
CC = gcc

Note

If you are running on aarch64 you need to set the as and cc variables to the cross compiler.

make

🏃‍♂️ How to run

To run the program you need to execute the following command:

./main

🧽 How to clean

To clean the project you need to execute the following command:

make clean

📝 License

This project is licensed under the GPL-3.0 License - see the LICENCE file for details