martialboniou · August 13, 2025 18:08 · Aug 13, 2025
diff --git a/zig-macos-assembly.md b/zig-macos-assembly.md
@@ -0,0 +1,72 @@
+# Assembly
+
+In the [Zig Language Reference](https://ziglang.org/documentation/master), the
+[Assembly](https://ziglang.org/documentation/master/#Assembly) section includes some demos targetting the
+`x86_64` architecture for Linux. Here's the same code adapted for `aarch64` (AKA `arm64`) for macOS (Apple
+Silicon M1 minimum):
+
+## Inline Assembly
+
+Here's the file `inline_assembly.zig`:
+
+```zig
+pub fn main() noreturn {
+    const msg = "hello world\n";
+    _ = syscall3(SYS_write, STDOUT_FILENO, @intFromPtr(msg), msg.len);
+    _ = syscall1(SYS_exit, 0);
+    unreachable;
+}
+
+pub const SYS_write = 4; // write = #4 on macOS
+pub const SYS_exit = 1;
+
+pub const STDOUT_FILENO = 1;
+
+pub fn syscall1(number: usize, arg1: usize) usize {
+    return asm volatile ("svc #0x80"
+        : [ret] "={x0}" (-> usize),
+        : [number] "{x16}" (number),
+          [arg1] "{x0}" (arg1),
+        : .{ .x0 = true, .x5 = true });
+}
+
+pub fn syscall3(number: usize, arg1: usize, arg2: usize, arg3: usize) usize {
+    return asm volatile ("svc #0x80"
+        : [ret] "={x0}" (-> usize),
+        : [number] "{x16}" (number),
+          [arg1] "{x0}" (arg1),
+          [arg2] "{x1}" (arg2),
+          [arg3] "{x2}" (arg3),
+        : .{ .x0 = true, .x5 = true });
+}
+```
+
+```shell
+zig build-exe inline_assembly.zig -target aarch64-macos
+```
+
+## Global Assembly
+
+Here's the file `test_global_assembly.zig`:
+
+```zig
+// don't forget to prepend an underscore to the function name
+comptime {
+    asm (
+        \\.global _my_func
+        \\_my_func:
+        \\  add x0, x0, x1
+        \\  ret
+    );
+}
+
+extern fn my_func(a: i32, b: i32) i32;
+
+test "global assembly" {
+    try @import("std").testing.expect(my_func(12, 34) == 46);
+}
+```
+
+```shell
+zig test test_global_assembly.zig -target aarch64-macos -fllvm
+```
No results found