Introduce experimental macOS build support

Tested on my M4 MacBook Air, builds fine.

README.md

@@ -77,6 +77,9 @@ Additionally you will need a version of the [aarch64-none-elf](https://developer
 #### Any OS
 To install aarch64-none-elf on any os, download the correct release of `aarch64-none-elf` onto your computer, unpack it, then export the `bin` folder to path.
 
+#### macOS
+There is experimental support for macOS in the scripts/mac-experimental folder. The scripts in there are not guaranteed to work for all macOS users and has only been tested on an M4 Apple Silicon MacBook Air.
+
 #### NixOS
 
 Run the following command

scripts/mac-experimental/README.md

@@ -0,0 +1,47 @@
+# Experimental macOS build scripts
+
+This is the folder for experimental macOS build support on Apple Silicon (we do not plan to support x86_64 macOS).
+
+These scripts are not guaranteed to work and are not actively supported by the maintainer or other contributors. 
+If you do have any issues, please mention @IAmTheNerdNextDoor in GitHub Issues.
+
+### Dependencies
+Regardless of stdlib, you will need:
+- [Rustup](https://rustup.rs) (DO NOT install Rustup from Homebrew as you will incur conflicts. If you have Rustup installed from Homebrew, uninstall it and reinstall from the Rustup site.)
+- [aarch64-none-elf](https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads)
+- [Homebrew](https://brew.sh)
+- QEMU (`brew install qemu`)
+- dosfstools (`brew install dosfstools`)
+
+If building for the GNU library:
+- aarch64-unknown-linux-gnu (`brew tap messense/macos-cross-toolchains && brew install aarch64-unknown-linux-gnu`)
+
+If building for the Musl library:
+- Zig (`brew install zig`)
+
+We use Zig to cross-compile to Linux musl on macOS.
+
+When it comes to Rust, you need the nightly toolchain. To install it, run:
+`rustup default nightly`
+
+### Building
+You can start building the initrd programs using this script:
+`./scripts/mac-experimental/build-deps.sh`
+
+musl programs are built by default.
+
+If you want GNU program builds:
+`stdlib=gnu ./scripts/mac-experimental/build-deps.sh`
+
+After building, you can make the initrd with:
+`./scripts/mac-experimental/create-image.sh`
+
+The initrd should now be at `./moss.img`.
+
+You can then build and run moss with:
+`cargo run --release`
+
+If you get an error about `aarch64-unknown-none-softfloat` during building, you need to install the target:
+`rustup target install aarch64-unknown-none-softfloat`
+
+Have fun!

scripts/mac-experimental/build-deps.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+base="$( cd "$( dirname "${BASH_SOURCE[0]}" )"/../.. && pwd )"
+
+mkdir -p "$base/build/bin"
+rm -f "$base/build/bin"/*
+
+pushd "$base/build" &>/dev/null || exit 1
+
+popd &>/dev/null || exit 1
+
+build=${build:-$(ls $base/scripts/deps)}
+
+for script in "$base/scripts/mac-experimental/deps/"*
+do
+    [ -e "$script" ] || continue # skip if no file exists
+    [ -x "$script" ] || continue # skip if not executable
+
+    filename=$(basename "$script")
+
+    if [[ "$filename" == _* ]]
+    then
+        echo "Skipping: $filename"
+        continue
+    fi
+
+    # skip if not in build list
+    if ! grep -qw "$filename" <<< "$build";
+    then
+        echo "Skipping: $filename"
+        continue
+    fi
+
+    echo "Preparing: $filename"
+
+    # make sure each script is run in the base directory
+    pushd "$base" &>/dev/null || exit 1
+    bash "$script"
+    popd &>/dev/null || exit 1
+done

scripts/mac-experimental/create-image.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+base="$( cd "$( dirname "${BASH_SOURCE[0]}" )"/../.. && pwd )"
+pushd "$base" &>/dev/null || exit 1
+
+img="$base/moss.img"
+mount="$base/build/mount"
+
+mkdir -p "$mount"
+
+dd if=/dev/zero of="$img" bs=1M count=128
+mkfs.vfat -F 32 "$img"
+
+if ! mount | grep -q "$mount"; then
+    hdiutil attach -mountpoint "$mount" "$img"
+fi
+
+mkdir -p "$mount/bin"
+mkdir -p "$mount/dev"
+
+cp "$base/build/bin"/* "$mount/bin"
+
+mounted=$(mount | grep "on $mount " | awk '{print $1}')
+if [ -n "$mounted" ]; then
+    hdiutil detach "$mounted"
+fi
+popd &>/dev/null || exit 1

scripts/mac-experimental/deps/bash

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+bash_repo="${bash_repo:-https://git.savannah.gnu.org/git/bash.git}"
+bash_tag="${bash_tag:-bash-5.3}"
+stdlib="${stdlib:-musl}"
+
+if [ "$stdlib" == "gnu" ]; then
+    COMPILER="aarch64-linux-gnu-gcc"
+else
+    COMPILER="zig cc -target aarch64-linux-musl"
+fi
+
+pushd "build" &>/dev/null || exit 1
+
+if [ ! -d "bash" ]; then
+    git clone --depth 1 --branch "$bash_tag" "$bash_repo" "bash"
+else
+    pushd "bash" &>/dev/null || exit 1
+    git pull
+    popd &>/dev/null || exit 1
+fi
+
+pushd "bash" &>/dev/null || exit 1
+./configure --without-bash-malloc --enable-static-link --host="aarch64-linux-$stdlib" CC="$COMPILER"
+make
+mv bash ../bin/bash
+popd &>/dev/null || exit 1
+
+popd &>/dev/null || exit 1

scripts/mac-experimental/deps/busybox

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# busybox -- I couldn't get this to build.  I ended up restoring to a third-party static binary which isn't ideal but it get's things running.
+pushd "build" &>/dev/null || exit 1
+wget https://github.com/shutingrz/busybox-static-binaries-fat/raw/refs/heads/main/busybox-aarch64-linux-gnu
+chmod +x busybox-aarch64-linux-gnu
+mv busybox-aarch64-linux-gnu bin/busybox
+
+popd &>/dev/null || exit 1
+
+popd &>/dev/null || exit 1