Assembly in Zig

const std = @import("std");

// Although this function looks imperative, note that its job is to
// declaratively construct a build graph that will be executed by an external
// runner.
pub fn build(b: *std.Build) void {
    // Standard target options allows the person running `zig build` to choose
    // what target to build for. Here we do not override the defaults, which
    // means any target is allowed, and the default is native. Other options
    // for restricting supported target set are available.
    const target = b.standardTargetOptions(.{});

    // Standard optimization options allow the person running `zig build` to select
    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
    // set a preferred release mode, allowing the user to decide how to optimize.
    const optimize = b.standardOptimizeOption(.{});

    const exe = b.addExecutable(.{
        .name = "zig-prac",
        // In this case the main source file is merely a path, however, in more
        // complicated build scripts, this could be a generated file.
        .root_source_file = .{ .path = "src/main.zig" },
        .target = target,
        .optimize = optimize,
    });

    /////////////////
    // we need to notice here, as long as this sentence can add assembly language support
    exe.addAssemblyFile("./src/hello.s");
    ////////////////

    // This declares intent for the executable to be installed into the
    // standard location when the user invokes the "install" step (the default
    // step when running `zig build`).
    exe.install();

    // This *creates* a RunStep in the build graph, to be executed when another
    // step is evaluated that depends on it. The next line below will establish
    // such a dependency.
    const run_cmd = exe.run();

    // By making the run step depend on the install step, it will be run from the
    // installation directory rather than directly from within the cache directory.
    // This is not necessary, however, if the application depends on other installed
    // files, this ensures they will be present and in the expected location.
    run_cmd.step.dependOn(b.getInstallStep());

    // This allows the user to pass arguments to the application in the build
    // command itself, like this: `zig build run -- arg1 arg2 etc`
    if (b.args) |args| {
        run_cmd.addArgs(args);
    }

    // This creates a build step. It will be visible in the `zig build --help` menu,
    // and can be selected like this: `zig build run`
    // This will evaluate the `run` step rather than the default, which is "install".
    const run_step = b.step("run", "Run the app");
    run_step.dependOn(&run_cmd.step);

    // Creates a step for unit testing.
    const exe_tests = b.addTest(.{
        .root_source_file = .{ .path = "src/main.zig" },
        .target = target,
        .optimize = optimize,
    });

    // Similar to creating the run step earlier, this exposes a `test` step to
    // the `zig build --help` menu, providing a way for the user to request
    // running the unit tests.
    const test_step = b.step("test", "Run unit tests");
    test_step.dependOn(&exe_tests.step);
}

const std = @import("std");

extern fn hello_world(?[*:0]const u8) void;

const msg: [:0]const u8 = "Hello World!\n";

pub fn main() void {
    hello_world(msg.ptr);
}

.globl hello_world
# global function, expose the hello_world
.type hello_world, @function
# tell compiler, we define a function
.section .text
hello_world:
  mov $4, %eax
  mov $1, %ebx
  mov %edi, %ecx
  # get parameter from register edi, you can learn more on x86-64 abi document
  mov $0xd, %edx
  # the length of string
  int $0x80
  # system call
  ret

const std = @import("std");

extern fn hello_world(usize) void;

const msg = "Hello World!\n";

pub fn main() void {
    hello_world(@ptrToInt(msg));
}

const std = @import("std");

comptime {
    asm (
        \\.globl hello_world
        \\.type hello_world, @function
        \\.section .text
        \\hello_world:
        \\  mov $4, %eax
        \\  mov $1, %ebx
        \\  mov %edi, %ecx
        \\  mov $0xd, %edx
        \\  int $0x80
        \\  ret
    );
}

// extern fn hello_world(?[*:0]const u8) void;
extern fn hello_world(usize) void;

// const msg: [:0]const u8 = "Hello World!\n";
const msg = "Hello World!\n";

pub fn main() void {
    // hello_world(msg.ptr);
    hello_world(@ptrToInt(msg));
}

pub fn syscall1(number: usize, arg1: usize) usize {
    return asm volatile ("syscall"
        : [ret_reference] "={rax}" (-> usize),
        : [number_reference] "{rax}" (number),
          [arg1_reference] "{rdi}" (arg1),
        : "rcx", "r11"
    );
}