Signals in Assembly Language

Here’s the translation of the Go signals example to Assembly Language, formatted in Markdown suitable for Hugo:

section .data
    awaiting_msg db "awaiting signal", 0
    exiting_msg db "exiting", 0
    newline db 10, 0

section .bss
    signal resb 8

section .text
    global _start

_start:
    ; Print "awaiting signal" message
    mov rax, 1
    mov rdi, 1
    mov rsi, awaiting_msg
    mov rdx, 16
    syscall

    ; Wait for signal
    mov rax, 13     ; sys_rt_sigaction
    xor rdi, rdi    ; SIGINT
    mov rsi, signal_handler
    xor rdx, rdx
    xor r10, r10
    syscall

    ; Infinite loop to keep program running
.loop:
    jmp .loop

signal_handler:
    ; Print newline
    mov rax, 1
    mov rdi, 1
    mov rsi, newline
    mov rdx, 1
    syscall

    ; Print signal number
    mov rax, 1
    mov rdi, 1
    mov rsi, signal
    mov rdx, 8
    syscall

    ; Print "exiting" message
    mov rax, 1
    mov rdi, 1
    mov rsi, exiting_msg
    mov rdx, 7
    syscall

    ; Exit program
    mov rax, 60
    xor rdi, rdi
    syscall

This Assembly Language program demonstrates how to handle signals, specifically SIGINT (Ctrl+C). Here’s an explanation of how it works:

1. We define our data and text sections. The data section contains our messages, and the text section contains our code.

2. In the _start function, we first print the “awaiting signal” message using the syscall instruction for writing to stdout.

3. We then set up a signal handler for SIGINT using the sys_rt_sigaction system call (number 13 on x86_64 Linux). We provide the address of our signal_handler function.

4. The program enters an infinite loop to keep it running until a signal is received.

5. When a SIGINT is received, the signal_handler function is called. It prints a newline, the signal number (which would be 2 for SIGINT), and then the “exiting” message.

6. Finally, the program exits using the exit system call.

To run this program, you would need to assemble and link it. For example, using NASM and ld on a Linux system:

$ nasm -f elf64 signals.asm
$ ld signals.o -o signals
$ ./signals
awaiting signal
^C
2
exiting

Note that Assembly Language doesn’t have direct equivalents for some of the higher-level concepts in the original example, such as goroutines or channels. This implementation provides a more low-level approach to signal handling, directly interacting with the operating system’s signal mechanisms.