Hello, World and build.zig

build.zig

@@ -4,113 +4,60 @@ const std = @import("std");
 // 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
+    const initramfs = addNasmFiles(b, AddNasmFilesOptions{
-    // what target to build for. Here we do not override the defaults, which
+        .filename = "src/initramfs.asm",
-    // means any target is allowed, and the default is native. Other options
+        .outputname = "initramfs.bin",
-    // for restricting supported target set are available.
+        .addAsObjFile = false,
-    const target = b.standardTargetOptions(.{});
+        .flags = &.{"-f bin"},
-
-    // 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(.{});
-
-    // This creates a "module", which represents a collection of source files alongside
-    // some compilation options, such as optimization mode and linked system libraries.
-    // Every executable or library we compile will be based on one or more modules.
-    const lib_mod = b.createModule(.{
-        // `root_source_file` is the Zig "entry point" of the module. If a module
-        // only contains e.g. external object files, you can make this `null`.
-        // 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 = b.path("src/root.zig"),
-        .target = target,
-        .optimize = optimize,
     });
 
-    // We will also create a module for our other entry point, 'main.zig'.
+    const initramfs_install = b.addInstallBinFile(initramfs.obj, "initramfs.img");
-    const exe_mod = b.createModule(.{
+    initramfs_install.step.dependOn(&truncate(b, initramfs).step);
-        // `root_source_file` is the Zig "entry point" of the module. If a module
-        // only contains e.g. external object files, you can make this `null`.
-        // 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 = b.path("src/main.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
 
-    // Modules can depend on one another using the `std.Build.Module.addImport` function.
+    b.getInstallStep().dependOn(&initramfs_install.step);
-    // This is what allows Zig source code to use `@import("foo")` where 'foo' is not a
-    // file path. In this case, we set up `exe_mod` to import `lib_mod`.
-    exe_mod.addImport("zos_lib", lib_mod);
 
-    // Now, we will create a static library based on the module we created above.
+    const run = b.addSystemCommand(&.{ "qemu-system-i386", "-fda" });
-    // This creates a `std.Build.Step.Compile`, which is the build step responsible
+    run.addFileArg(b.path("zig-out/bin/initramfs.img"));
-    // for actually invoking the compiler.
-    const lib = b.addLibrary(.{
-        .linkage = .static,
-        .name = "zos",
-        .root_module = lib_mod,
-    });
 
-    // This declares intent for the library to be installed into the standard
+    const run_step = b.step("run", "run the os in qemu");
-    // location when the user invokes the "install" step (the default step when
+    run_step.dependOn(&run.step);
-    // running `zig build`).
-    b.installArtifact(lib);
-
-    // This creates another `std.Build.Step.Compile`, but this one builds an executable
-    // rather than a static library.
-    const exe = b.addExecutable(.{
-        .name = "zos",
-        .root_module = exe_mod,
-    });
-
-    // 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`).
-    b.installArtifact(exe);
-
-    // This *creates* a Run step 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 = b.addRunArtifact(exe);
-
-    // 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,
+const AddNasmFilesOptions = struct {
-    // and can be selected like this: `zig build run`
+    filename: []const u8,
-    // This will evaluate the `run` step rather than the default, which is "install".
+    outputname: ?[]const u8 = null,
-    const run_step = b.step("run", "Run the app");
+    addAsObjFile: bool = true,
-    run_step.dependOn(&run_cmd.step);
+    flags: []const []const u8 = &.{},
+};
 
-    // Creates a step for unit testing. This only builds the test executable
+const NasmFile = struct {
-    // but does not run it.
+    run: *std.Build.Step.Run,
-    const lib_unit_tests = b.addTest(.{
+    obj: std.Build.LazyPath,
-        .root_module = lib_mod,
+};
-    });
 
-    const run_lib_unit_tests = b.addRunArtifact(lib_unit_tests);
+// adapted from https://codeberg.org/raddari/zig-nasm-lib.git
+fn addNasmFiles(b: *std.Build, options: AddNasmFilesOptions) NasmFile {
+    std.debug.assert(!std.fs.path.isAbsolute(options.filename));
+    const src_file = b.path(options.filename);
+    const output = options.outputname orelse b.fmt("{s}.o", .{std.mem.sliceTo(options.filename, '.')});
 
-    const exe_unit_tests = b.addTest(.{
+    const nasm = b.addSystemCommand(&.{"nasm"});
-        .root_module = exe_mod,
+    nasm.addArgs(options.flags);
-    });
+    nasm.addPrefixedDirectoryArg("-i", b.path("src"));
+    const obj = nasm.addPrefixedOutputFileArg("-o", output);
+    nasm.addFileArg(src_file);
 
-    const run_exe_unit_tests = b.addRunArtifact(exe_unit_tests);
+    return .{
-
+        .run = nasm,
-    // Similar to creating the run step earlier, this exposes a `test` step to
+        .obj = obj,
-    // 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(&run_lib_unit_tests.step);
+fn truncate(b: *std.Build, bin: NasmFile) *std.Build.Step.Run {
-    test_step.dependOn(&run_exe_unit_tests.step);
+    const exec = b.addSystemCommand(&.{"truncate"});
+    exec.addArgs(&.{ "-s", "1440k" });
+    exec.addFileArg(bin.obj);
+    exec.step.dependOn(&bin.run.step);
+
+    return exec;
 }

src/initramfs.asm

@@ -0,0 +1,62 @@
+; vim: ft=nasm
+org 0x7C00
+bits 16
+
+%define ENDL 0x0D, 0x0A
+
+start:
+	jmp main
+
+; 
+; echo:
+; print something to the screen
+;  - ds:si points to string
+;
+echo:
+	; save the registers we want to modify
+	push si
+	push ax
+	push bx
+
+	mov ah, 0xe
+	mov bh, 0
+
+.loop:
+	lodsb			; load byte from ds:si to al
+	or al, al		; check if next char is null
+	jz .done
+
+	int 0x10
+	jmp .loop
+
+.done:
+	pop bx
+	pop ax
+	pop si
+	ret
+
+main:
+
+	; setup data segments
+	; use ax as and intermediary as we can't write to es/ds directly
+	mov ax, 0
+	mov ds, ax
+	mov es, ax
+
+	; setup stack
+	mov ss, ax
+	mov sp, 0x7C00	; stack grows downward from where we are loaded in memory
+
+	; print the hello world
+	mov si, msg_hello
+	call echo
+
+	hlt
+
+.halt:
+	jmp .halt
+
+msg_hello: db 'Hello, world!', ENDL, 0
+
+times 510-($-$$) db 0
+dw 0AA55h

src/main.zig

@@ -1,46 +0,0 @@
-//! By convention, main.zig is where your main function lives in the case that
-//! you are building an executable. If you are making a library, the convention
-//! is to delete this file and start with root.zig instead.
-
-pub fn main() !void {
-    // Prints to stderr (it's a shortcut based on `std.io.getStdErr()`)
-    std.debug.print("All your {s} are belong to us.\n", .{"codebase"});
-
-    // stdout is for the actual output of your application, for example if you
-    // are implementing gzip, then only the compressed bytes should be sent to
-    // stdout, not any debugging messages.
-    const stdout_file = std.io.getStdOut().writer();
-    var bw = std.io.bufferedWriter(stdout_file);
-    const stdout = bw.writer();
-
-    try stdout.print("Run `zig build test` to run the tests.\n", .{});
-
-    try bw.flush(); // Don't forget to flush!
-}
-
-test "simple test" {
-    var list = std.ArrayList(i32).init(std.testing.allocator);
-    defer list.deinit(); // Try commenting this out and see if zig detects the memory leak!
-    try list.append(42);
-    try std.testing.expectEqual(@as(i32, 42), list.pop());
-}
-
-test "use other module" {
-    try std.testing.expectEqual(@as(i32, 150), lib.add(100, 50));
-}
-
-test "fuzz example" {
-    const Context = struct {
-        fn testOne(context: @This(), input: []const u8) anyerror!void {
-            _ = context;
-            // Try passing `--fuzz` to `zig build test` and see if it manages to fail this test case!
-            try std.testing.expect(!std.mem.eql(u8, "canyoufindme", input));
-        }
-    };
-    try std.testing.fuzz(Context{}, Context.testOne, .{});
-}
-
-const std = @import("std");
-
-/// This imports the separate module containing `root.zig`. Take a look in `build.zig` for details.
-const lib = @import("zos_lib");

src/root.zig

@@ -1,13 +0,0 @@
-//! By convention, root.zig is the root source file when making a library. If
-//! you are making an executable, the convention is to delete this file and
-//! start with main.zig instead.
-const std = @import("std");
-const testing = std.testing;
-
-pub export fn add(a: i32, b: i32) i32 {
-    return a + b;
-}
-
-test "basic add functionality" {
-    try testing.expect(add(3, 7) == 10);
-}