bootloader/build.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(.{});

    // 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 mod = b.addModule("bootloader", .{
        // `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,
    });

    const kernel = b.option([]const u8, "kernel", "Path to kernel executable");
    const output = b.option([]const u8, "output", "Output image name");

    const image = buildBootableImage(b, b.path(kernel orelse "kernel"), target.result.cpu.arch);
    const install = b.addInstallFile(image, output orelse "bootimage.iso");
    b.getInstallStep().dependOn(&install.step);

    // Creates a step for unit testing. This only builds the test executable
    // but does not run it.
    const unit_tests = b.addTest(.{
        .root_module = mod,
    });

    const run_unit_tests = b.addRunArtifact(unit_tests);

    // 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(&run_unit_tests.step);
}

pub fn buildBootableImage(b: *std.Build, kernel: std.Build.LazyPath, arch: std.Target.Cpu.Arch) std.Build.LazyPath {
    // Add Limine to the dependency tree.
    const limine = b.dependency("limine", .{});
    const rootfs = b.addNamedWriteFiles("rootfs");

    const exe = b.addExecutable(.{
        .name = "limine",
        .target = b.resolveTargetQuery(.{}),
        .optimize = .ReleaseSafe,
    });

    exe.addCSourceFile(.{
        .file = limine.path("limine.c"),
        .flags = &.{"-std=c99"},
    });
    exe.linkLibC();

    _ = rootfs.addCopyFile(b.path("limine.conf"), "boot/limine/limine.conf");
    _ = rootfs.addCopyFile(kernel, "boot/kernel");

    const run_cmd = b.addSystemCommand(switch (arch) {
        .aarch64 => block: {
            _ = rootfs.addCopyFile(limine.path("limine-uefi-cd.bin"), "boot/limine/limine-uefi-cd.bin");
            _ = rootfs.addCopyFile(limine.path("BOOTAA64.EFI"), "EFI/BOOT/BOOTAA64.EFI");

            break :block &.{
                "xorriso", "-as", "mkisofs",
                    "-R", "-r", "-J", 
                    "-hfsplus",
                    "-apm-block-size", "2048",
                    "--efi-boot", "boot/limine/limine-uefi-cd.bin",
                    "-efi-boot-part",
                    "--efi-boot-image",
                    "--protective-msdos-label",
            };
        },
        .loongarch64 => block: {
            _ = rootfs.addCopyFile(limine.path("limine-uefi-cd.bin"), "boot/limine/limine-uefi-cd.bin");
            _ = rootfs.addCopyFile(limine.path("BOOTLOONGARCH64.EFI"), "EFI/BOOT/BOOTLOONGARCH64.EFI");

            break :block &.{
                "xorriso", "-as", "mkisofs",
                    "-R", "-r", "-J",
                    "-hfsplus",
                    "-apm-block-size", "2048",
                    "--efi-boot", "boot/limine/limine-uefi-cd.bin",
                    "-efi-boot-part",
                    "--efi-boot-image",
                    "--protective-msdos-label",
            };
        },
        .riscv64 => block: {
            _ = rootfs.addCopyFile(limine.path("limine-uefi-cd.bin"), "boot/limine/limine-uefi-cd.bin");
            _ = rootfs.addCopyFile(limine.path("BOOTRISCV64.EFI"), "EFI/BOOT/BOOTRISCV64.EFI");

            break :block &.{
                "xorriso", "-as", "mkisofs",
                    "-R", "-r", "-J", 
                    "-hfsplus",
                    "-apm-block-size", "2048",
                    "--efi-boot", "boot/limine/limine-uefi-cd.bin",
                    "-efi-boot-part",
                    "--efi-boot-image",
                    "--protective-msdos-label",
            };
        },
        .x86_64 => block: {
            _ = rootfs.addCopyFile(limine.path("limine-bios.sys"), "boot/limine/limine-bios.sys");
            _ = rootfs.addCopyFile(limine.path("limine-bios-cd.bin"), "boot/limine/limine-bios-cd.bin");
            _ = rootfs.addCopyFile(limine.path("limine-uefi-cd.bin"), "boot/limine/limine-uefi-cd.bin");
            _ = rootfs.addCopyFile(limine.path("BOOTX64.EFI"), "EFI/BOOT/BOOTX64.EFI");
            _ = rootfs.addCopyFile(limine.path("BOOTIA32.EFI"), "EFI/BOOT/BOOTIA32.EFI");

            break :block &.{
                "xorriso", "-as", "mkisofs",
                    "-R", "-r", "-J", 
                    "-b", "boot/limine/limine-bios-cd.bin",
                    "-no-emul-boot",
                    "-boot-load-size", "4",
                    "-boot-info-table",
                    "-hfsplus",
                    "-apm-block-size", "2048",
                    "--efi-boot", "boot/limine/limine-uefi-cd.bin",
                    "-efi-boot-part",
                    "--efi-boot-image",
                    "--protective-msdos-label",
            };
        },
        else => unreachable,
    });

    run_cmd.step.dependOn(&rootfs.step);
    run_cmd.addDirectoryArg(rootfs.getDirectory());
    run_cmd.addArg("-o");
    // Retrieve the bootable image from command.
    const raw = run_cmd.addOutputFileArg("raw.iso");

    // Install Limine stage 1 and 2 for legacy BIOS boot.
    // This is only required on x86_64, but we are deploying for all anyway.
    const deploy = b.addRunArtifact(exe);
    deploy.step.dependOn(&run_cmd.step);
    deploy.addArg("bios-install");
    deploy.addFileArg(raw);

    const wf = b.addWriteFiles();
    const image = wf.addCopyFile(raw, "image.iso");
    wf.step.dependOn(&deploy.step);

    return image;
}