Kurumi Atelier Day5

Table of Contents

初始化 Rust 工程目录

cargo init --name kurumi

Rust 默认生成 .rlib 文件，这是 Rust 库的格式，而我们需要静态库

# Cargo.toml
crate-type = ["staticlib"]

为 cross-compile 做准备，安装 xargo 并创建 x86_64-kurumi.json 文件

{
    "arch": "x86_64",
    "cpu": "x86-64",
    "llvm-target": "x86_64-unknown-none-gnu",
    "data-layout": "e-m:e-i64:64-f80:128-n8:16:32:64-S128",
    "linker-flavor": "gcc",
    "no-compiler-rt": true,
    "os": "kurumi",
    "target-endian": "little",
    "target-pointer-width": "64",
    "target-c-int-width": "32",
    "features": "-mmx,-fxsr,-sse,-sse2,+soft-float",
    "disable-redzone": true,
    "eliminate-frame-pointer": false
}

用 Rust 编写 kernel 时不能使用 std，因为其依赖操作系统。不过我们需要 libcore，这是必要的

xargo build --release --target x86_64-kurumi.json 编译时会抛出下面的错误

error: language item required, but not found: `panic_fmt`

error: language item required, but not found: `eh_personality`

error: aborting due to 2 previous errors

error: Could not compile `kurumi`.

因为 panic_fmt 和 eh_personality 需要我们自己实现，可以参考文档

// src/lib.rs

#![feature(lang_items)]
#![no_std]

#[lang = "eh_personality"]
#[no_mangle]
extern fn eh_personality() {
}

#[lang = "panic_fmt"]
#[no_mangle]
extern fn rust_begin_panic() -> ! {
    loop {}
}

编写 main 函数

#[no_mangle]
pub extern fn kmain() -> ! {

    // clear screen
    let mut buffer = [0x1fu8; 80*50];
    for i in 0..(80*25) {
        buffer[i*2] = 0x00u8;
    }
    let buffer_ptr = (0xb8000) as *mut _;
    unsafe { *buffer_ptr = buffer};

    // print guest string
    let prompt = b"Welcome to Japari Park"; // length 22

    let mut prompt_buf = [0x1fu8; 44];
    for (i, char_byte) in prompt.into_iter().enumerate() {
        prompt_buf[i*2] = *char_byte;
    }
    let buffer_ptr = (0xb8000) as *mut _;
    unsafe { *buffer_ptr = prompt_buf };

    loop {}
}

在汇编代码中进行跳转

long_mode_start:
    ...

    ; call the kernel main
    extern kmain
    jmp kmain

连接时需要将 rust 部分也放进去，更新一下 Makefile

target ?= $(arch)-kurumi
rust_os := target/$(target)/release/libkurumi.a

$(kernel): kernel $(rust_os) $(assembly_object_files) $(linker_script)
        @ld -n -T $(linker_script) -o $(kernel) $(assembly_object_files) $(rust_os)

kernel:
        @RUST_TARGET_PATH="$(shell pwd)" xargo build --release --target $(target)

会发现如下报错

undefined reference to 'memcpy'

这是因为 memcpy 是 libc 中的函数，通常 libc crate 会和 Rust 程序通过标准库进行连接，但是我们现在不使用标准库，而且 libc 是系统底层 libc 的封装。所以我们现在要手动添加这个 rlibc create

编写 Rust 代码时，需要小心 Rust 将字面量自动整型推断为 i32 的情况

Reference
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Set Up Rust | Writing an OS in Rust

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