Update build to run qemu on MacOS

README.md

@@ -13,11 +13,13 @@ kernel heap. See [`docs/`](docs/README.md) for how each piece works.
   versions are rejected, because Zig makes breaking changes between releases
   pre-1.0. A toolchain manager such as [zvm](https://github.com/tristanisham/zvm)
   or `zigup` will pick up `.zig-version` automatically.
-- **QEMU** (`qemu-system-x86_64`) — to run and test the kernel.
+- **QEMU** (`qemu-system-x86_64`) — to run and test the kernel. On macOS,
+  `brew install qemu` also bundles the OVMF firmware below.
 - **OVMF** UEFI firmware — the `edk2-ovmf` package (Arch), `ovmf` (Debian/Ubuntu),
-  or `edk2-ovmf` (Fedora). The build defaults to the Arch paths
+  or `edk2-ovmf` (Fedora); on macOS it ships inside the Homebrew `qemu` formula.
-  (`/usr/share/edk2/x64/OVMF_{CODE,VARS}.4m.fd`); override with `-Dovmf-code=` and
+  Both the build and the test harness probe the known Arch/Debian/Fedora/macOS
-  `-Dovmf-vars=` if your distro installs them elsewhere.
+  layouts and use the first that exists, so no configuration is normally needed.
+  Override with `-Dovmf-code=` / `-Dovmf-vars=` (build) if yours lives elsewhere.
 - **Python 3** — for the QEMU integration test harness.
 
 ## Build

build.zig

@@ -16,6 +16,18 @@ fn ensureZigVersion() void {
     }
 }
 
+/// Return the first path in `candidates` that exists on the build host, else the
+/// first candidate as a fallback so a missing-firmware error still names a
+/// concrete (and, by convention, the primary) path. Used to locate OVMF firmware
+/// across distro/OS layouts without configuration.
+fn firstExisting(io: std.Io, candidates: []const []const u8) []const u8 {
+    for (candidates) |path| {
+        std.Io.Dir.accessAbsolute(io, path, .{}) catch continue;
+        return path;
+    }
+    return candidates[0];
+}
+
 pub fn build(b: *std.Build) void {
     ensureZigVersion();
 
@@ -105,18 +117,33 @@ pub fn build(b: *std.Build) void {
     b.installArtifact(efiexe);
 
     // --- run-efi: boot BOOTX64.efi in QEMU with OVMF firmware ---
-    // OVMF paths follow the Arch (edk2-ovmf) layout; override with -Dovmf-code
+    // Firmware lives in different places per OS/distro, so probe the known
-    // and -Dovmf-vars if your distro installs them elsewhere.
+    // layouts (Arch, Debian/Ubuntu, Fedora, macOS Homebrew) and use the first
+    // that exists. Override with -Dovmf-code / -Dovmf-vars if yours is elsewhere.
     const ovmf_code = b.option(
         []const u8,
         "ovmf-code",
         "Path to the OVMF_CODE firmware image",
-    ) orelse "/usr/share/edk2/x64/OVMF_CODE.4m.fd";
+    ) orelse firstExisting(b.graph.io, &.{
+        "/usr/share/edk2/x64/OVMF_CODE.4m.fd", // Arch
+        "/usr/share/OVMF/OVMF_CODE_4M.fd", // Debian/Ubuntu
+        "/usr/share/OVMF/OVMF_CODE.fd", // older Debian/Ubuntu
+        "/usr/share/edk2-ovmf/x64/OVMF_CODE.fd", // Fedora
+        "/opt/homebrew/share/qemu/edk2-x86_64-code.fd", // macOS Homebrew (Apple Silicon)
+        "/usr/local/share/qemu/edk2-x86_64-code.fd", // macOS Homebrew (Intel)
+    });
     const ovmf_vars = b.option(
         []const u8,
         "ovmf-vars",
         "Path to the OVMF_VARS firmware image (a writable copy is made)",
-    ) orelse "/usr/share/edk2/x64/OVMF_VARS.4m.fd";
+    ) orelse firstExisting(b.graph.io, &.{
+        "/usr/share/edk2/x64/OVMF_VARS.4m.fd", // Arch
+        "/usr/share/OVMF/OVMF_VARS_4M.fd", // Debian/Ubuntu
+        "/usr/share/OVMF/OVMF_VARS.fd", // older Debian/Ubuntu
+        "/usr/share/edk2-ovmf/x64/OVMF_VARS.fd", // Fedora
+        "/opt/homebrew/share/qemu/edk2-i386-vars.fd", // macOS Homebrew (Apple Silicon)
+        "/usr/local/share/qemu/edk2-i386-vars.fd", // macOS Homebrew (Intel)
+    });
 
     // Assemble an EFI System Partition layout: esp/EFI/BOOT/BOOTX64.efi
     const efi_install = b.addInstallArtifact(efiexe, .{

test/qemu_test.py

@@ -35,8 +35,26 @@ ARCHES = {
     "x86_64": {
         "zig_flags": [],  # build.zig currently pins the kernel to x86_64
         "qemu": "qemu-system-x86_64",
-        "ovmf_code": "/usr/share/edk2/x64/OVMF_CODE.4m.fd",
+        # Firmware lives in different places per OS/distro; resolve_firmware()
-        "ovmf_vars": "/usr/share/edk2/x64/OVMF_VARS.4m.fd",
+        # picks the first that exists so the harness runs unconfigured on Arch,
+        # Debian/Ubuntu, Fedora, and macOS (Homebrew). Override by reordering or
+        # dropping an absolute path at the front.
+        "ovmf_code": [
+            "/usr/share/edk2/x64/OVMF_CODE.4m.fd",          # Arch
+            "/usr/share/OVMF/OVMF_CODE_4M.fd",              # Debian/Ubuntu
+            "/usr/share/OVMF/OVMF_CODE.fd",                 # older Debian/Ubuntu
+            "/usr/share/edk2-ovmf/x64/OVMF_CODE.fd",        # Fedora
+            "/opt/homebrew/share/qemu/edk2-x86_64-code.fd", # macOS Homebrew (Apple Silicon)
+            "/usr/local/share/qemu/edk2-x86_64-code.fd",    # macOS Homebrew (Intel)
+        ],
+        "ovmf_vars": [
+            "/usr/share/edk2/x64/OVMF_VARS.4m.fd",          # Arch
+            "/usr/share/OVMF/OVMF_VARS_4M.fd",              # Debian/Ubuntu
+            "/usr/share/OVMF/OVMF_VARS.fd",                 # older Debian/Ubuntu
+            "/usr/share/edk2-ovmf/x64/OVMF_VARS.fd",        # Fedora
+            "/opt/homebrew/share/qemu/edk2-i386-vars.fd",   # macOS Homebrew (Apple Silicon)
+            "/usr/local/share/qemu/edk2-i386-vars.fd",      # macOS Homebrew (Intel)
+        ],
         "efi_app": ("EFI/BOOT/BOOTX64.efi", "BOOTX64.efi"),  # (dest in ESP, name in zig-out/bin)
         "kernel": ("danos", "danos"),
         # Built as a function so we can splice in per-run paths.
@@ -123,6 +141,24 @@ def make_esp(arch):
     return esp
 
 
+def resolve_firmware(arch):
+    """Collapse the ovmf_code/ovmf_vars candidate lists to the first path that
+    exists on this machine. Mutates `arch` in place; idempotent (a resolved
+    string is left untouched). Exits with a clear message if none is found."""
+    for key, label in (("ovmf_code", "OVMF_CODE"), ("ovmf_vars", "OVMF_VARS")):
+        val = arch[key]
+        if isinstance(val, str):
+            continue  # already resolved on a previous call
+        for cand in val:
+            if os.path.exists(cand):
+                arch[key] = cand
+                break
+        else:
+            sys.exit(f"error: no {label} firmware image found; looked in:\n  "
+                     + "\n  ".join(val)
+                     + "\nInstall OVMF (edk2-ovmf / ovmf) or add its path above.")
+
+
 def run_case(arch, case):
     err = build(arch, case["name"])
     if err:
@@ -176,6 +212,7 @@ def main():
     if not shutil.which(arch["qemu"]):
         print(f"error: {arch['qemu']} not found on PATH", file=sys.stderr)
         return 2
+    resolve_firmware(arch)
 
     selected = [c for c in CASES if not args.cases or c["name"] in args.cases]
     os.makedirs(WORK, exist_ok=True)