A simple example to emit code at runtime on AArch64 (ARM64) in Rust using crate `dynasmrt`.

main.rs

//! A simple example to emit code at runtime on AArch64 (ARM64)
//! in Rust using crate `dynasmrt`.
//!
//! Written by MaxXing, 2023-10-12.

use dynasmrt::{dynasm, DynasmApi, DynasmLabelApi};
use std::io::{self, Write};
use std::{mem, slice};

fn main() {
    // Create assembler.
    let mut ops = dynasmrt::aarch64::Assembler::new().unwrap();
    // Emit data.
    let hello = "Fuck, world!\n";
    let hello_len = hello.len();
    dynasm!(ops
        ; -> hello:
        ; .bytes hello.as_bytes()
        ; .align 4                  // LDR requires 4-byte align.
        ; -> print:
        ; .qword print as _
    );
    // Align for the executable code.
    ops.align(4, 0);
    // Emit code.
    let hello = ops.offset();
    dynasm!(ops
        ; .arch aarch64
        ; adr x0, -> hello          // Message.
        ; mov x1, hello_len as _    // Length.
        ; ldr x2, -> print          // Address of the `print` function.
        ; br x2                     // Call the function (actually tail call).
    );
    // Create executable buffer.
    let buf = ops.finalize().unwrap();
    println!("buffer length = {}", buf.len());
    // Call the emitted function.
    let hello_fn: extern "C" fn() = unsafe { mem::transmute(buf.ptr(hello)) };
    hello_fn();
}

extern "C" fn print(buf: *const u8, len: u64) {
    io::stdout()
        .write_all(unsafe { slice::from_raw_parts(buf, len as usize) })
        .unwrap();
}