Syscalls

This page goes over the concept of syscalls in x86-64 architecture

Recall at the end of

x86-64 Assembly Cheatsheet

The mention of syscalls, but let us do a slightly deeper dive...

What Are Syscalls?

• Syscalls (System Calls) are how programs interact with the operating system (OS).

• They allow programs to request services from the OS, such as:

  • Reading or writing data (e.g., files, console)

  • Allocating memory

  • Exiting a program

  • Communicating with hardware

How Syscalls Work

• Syscalls are invoked by placing specific values into CPU registers and using a special instruction.

• The general steps for performing a syscall in x86_64 Assembly:

  1. rax: Specify the syscall number (which service you want).

  2. Registers: Pass additional arguments:

     • rdi: 1st argument

     • rsi: 2nd argument

     • rdx: 3rd argument

     • r10: 4th argument

     • r8: 5th argument

     • r9: 6th argument

  3. Use the syscall instruction to trigger the system call. Here's a table of syscall numbers for reference https://x64.syscall.sh/