# arceos-helloworld

A standalone Hello World application running on [ArceOS](https://github.com/arceos-org/arceos) unikernel, with all dependencies sourced from [crates.io](https://crates.io). Supports multiple architectures via `cargo xtask`.

## Supported Architectures

| Architecture | Rust Target | QEMU Machine | Platform |
|---|---|---|---|
| riscv64 | `riscv64gc-unknown-none-elf` | `qemu-system-riscv64 -machine virt` | riscv64-qemu-virt |
| aarch64 | `aarch64-unknown-none-softfloat` | `qemu-system-aarch64 -machine virt` | aarch64-qemu-virt |
| x86_64 | `x86_64-unknown-none` | `qemu-system-x86_64 -machine q35` | x86-pc |
| loongarch64 | `loongarch64-unknown-none` | `qemu-system-loongarch64 -machine virt` | loongarch64-qemu-virt |

## Prerequisites

- **Rust nightly toolchain** (edition 2024)

  ```bash
  rustup install nightly
  rustup default nightly
  ```

- **Bare-metal targets** (install the ones you need)

  ```bash
  rustup target add riscv64gc-unknown-none-elf
  rustup target add aarch64-unknown-none-softfloat
  rustup target add x86_64-unknown-none
  rustup target add loongarch64-unknown-none
  ```

- **QEMU** (install the emulators for your target architectures)

  ```bash
  # Ubuntu/Debian
  sudo apt install qemu-system-riscv64 qemu-system-aarch64 \
                   qemu-system-x86 qemu-system-loongarch64  # OR qemu-systrem-misc

  # macOS (Homebrew)
  brew install qemu
  ```

- **rust-objcopy** (from `cargo-binutils`, required for non-x86_64 targets)

  ```bash
  cargo install cargo-binutils
  rustup component add llvm-tools
  ```

## Quick Start

```bash
# install cargo-clone sub-command
cargo install cargo-clone 
# get source code of arceos-helloworld crate from crates.io
cargo clone arceos-helloworld
# into crate dir
cd arceos-helloworld
# Build and run on RISC-V 64 QEMU (default)
cargo xtask run

# Build and run on other architectures
cargo xtask run --arch aarch64
cargo xtask run --arch x86_64
cargo xtask run --arch loongarch64

# Build only (no QEMU)
cargo xtask build --arch riscv64
cargo xtask build --arch aarch64
```

Expected output (riscv64 example):

```
       d8888                            .d88888b.   .d8888b.
      d88888                           d88P" "Y88b d88P  Y88b
     ...
d88P     888 888      "Y8888P  "Y8888   "Y88888P"   "Y8888P"

arch = riscv64
platform = riscv64-qemu-virt
...
smp = 1

Hello, world!
```

QEMU will automatically exit after printing the message.

## Project Structure

```
app-helloworld/
├── .cargo/
│   └── config.toml       # cargo xtask alias & AX_CONFIG_PATH
├── xtask/
│   ├── Cargo.toml        # xtask build tool (clap CLI)
│   └── src/
│       └── main.rs       # build/run subcommand implementation
├── configs/
│   ├── riscv64.toml      # Platform config for RISC-V 64 QEMU virt
│   ├── aarch64.toml      # Platform config for AArch64 QEMU virt
│   ├── x86_64.toml       # Platform config for x86-64 PC
│   └── loongarch64.toml  # Platform config for LoongArch64 QEMU virt
├── src/
│   └── main.rs           # Application entry point
├── build.rs              # Linker script path setup (auto-detects arch)
├── Cargo.toml            # Dependencies (axstd from crates.io)
└── README.md
```

## How It Works

The `cargo xtask` pattern uses a host-native helper crate (`xtask/`) to orchestrate
cross-compilation and QEMU execution:

1. **`cargo xtask build --arch <ARCH>`**
   - Copies `configs/<ARCH>.toml` to `.axconfig.toml` (platform configuration)
   - Runs `cargo build --release --target <TARGET>`
   - `build.rs` auto-detects the architecture and locates the correct linker script

2. **`cargo xtask run --arch <ARCH>`**
   - Performs the build step above
   - Converts ELF to raw binary via `rust-objcopy` (except x86_64 which uses ELF directly)
   - Launches the appropriate QEMU emulator with architecture-specific flags

## Key Components

| Component | Role |
|---|---|
| `axstd` | ArceOS standard library (replaces Rust's `std` in `no_std` environment) |
| `axhal` | Hardware abstraction layer, generates the linker script at build time |
| `axplat-*` | Platform-specific support crates (one per target board/VM) |
| `axruntime` | Kernel initialization and runtime setup |
| `build.rs` | Locates the linker script generated by `axhal` and passes it to the linker |
| `configs/*.toml` | Pre-generated platform configuration for each architecture |

## ArceOS Tutorial Crates

This crate is part of a series of tutorial crates for learning OS development with [ArceOS](https://github.com/arceos-org/arceos). The crates are organized by functionality and complexity progression:

| # | Crate Name | Description |
|:---:|---|---|
| 1 | **arceos-helloworld** (this crate) | Minimal ArceOS unikernel application that prints Hello World, demonstrating the basic boot flow |
| 2 | [arceos-collections](https://crates.io/crates/arceos-collections) | Dynamic memory allocation on a unikernel, demonstrating the use of String, Vec, and other collection types |
| 3 | [arceos-readpflash](https://crates.io/crates/arceos-readpflash) | MMIO device access via page table remapping, reading data from QEMU's PFlash device |
| 4 | [arceos-readblk](https://crates.io/crates/arceos-readblk) | VirtIO block device driver discovery and disk I/O, demonstrating device probing and block read operations |
| 5 | [arceos-childtask](https://crates.io/crates/arceos-childtask) | Multi-tasking basics: spawning a child task (thread) that accesses a PFlash MMIO device |
| 6 | [arceos-msgqueue](https://crates.io/crates/arceos-msgqueue) | Cooperative multi-task scheduling with a producer-consumer message queue, demonstrating inter-task communication |
| 7 | [arceos-fairsched](https://crates.io/crates/arceos-fairsched) | Preemptive CFS scheduling with timer-interrupt-driven task switching, demonstrating automatic task preemption |
| 8 | [arceos-loadapp](https://crates.io/crates/arceos-loadapp) | FAT filesystem initialization and file I/O, demonstrating the full I/O stack from VirtIO block device to filesystem |
| 9 | [arceos-userprivilege](https://crates.io/crates/arceos-userprivilege) | User-privilege mode switching: loading a user-space program, switching to unprivileged mode, and handling syscalls |
| 10 | [arceos-lazymapping](https://crates.io/crates/arceos-lazymapping) | Lazy page mapping (demand paging): user-space program triggers page faults, and the kernel maps physical pages on demand |
| 11 | [arceos-runlinuxapp](https://crates.io/crates/arceos-runlinuxapp) | Loading and running real Linux ELF applications (musl libc) on ArceOS, with ELF parsing and Linux syscall handling |
| 12 | [arceos-guestmode](https://crates.io/crates/arceos-guestmode) | Minimal hypervisor: creating a guest address space, entering guest mode, and handling a single VM exit (shutdown) |
| 13 | [arceos-guestaspace](https://crates.io/crates/arceos-guestaspace) | Hypervisor address space management: loop-based VM exit handling with nested page fault (NPF) on-demand mapping |
| 14 | [arceos-guestvdev](https://crates.io/crates/arceos-guestvdev) | Hypervisor virtual device support: timer virtualization, console I/O forwarding, and NPF passthrough; guest runs preemptive multi-tasking |
| 15 | [arceos-guestmonolithickernel](https://crates.io/crates/arceos-guestmonolithickernel) | Full hypervisor + guest monolithic kernel: the guest kernel supports user-space process management, syscall handling, and preemptive scheduling |

**Progression Logic:**

- **#1–#8 (Unikernel Stage)**: Starting from the simplest output, these crates progressively introduce memory allocation, device access (MMIO / VirtIO), multi-task scheduling (both cooperative and preemptive), and filesystem support, building up the core capabilities of a unikernel.
- **#8–#10 (Monolithic Kernel Stage)**: Building on the unikernel foundation, these crates add user/kernel privilege separation, page fault handling, and ELF loading, progressively evolving toward a monolithic kernel.
- **#11–#14 (Hypervisor Stage)**: Starting from minimal VM lifecycle management, these crates progressively add address space management, virtual devices, timer injection, and ultimately run a full monolithic kernel inside a virtual machine.

## License

GPL-3.0-or-later OR Apache-2.0 OR MulanPSL-2.0
