如何将锈蚀代码编译成裸金属32位x86 (i686)代码？我应该使用什么编译目标？

Question

我想编译裸金属32位代码的x86 (又名i686，又名32位模式下的x86_64 )使用货/锈。我需要什么目标？在官方支持的目标列表中，我找不到任何东西，这是很实用的。

Answer 1

不幸的是，Rust编译器没有内置的目标定义Rust夜1.54 (2021年6月)，但是您可以提供一个自定义目标定义：

/x86-unknown-bare_metal.json

{
  "llvm-target": "i686-unknown-none",
  "data-layout": "e-m:e-i32:32-f80:128-n8:16:32-S128-p:32:32",
  "arch": "x86",
  "target-endian": "little",
  "target-pointer-width": "32",
  "target-c-int-width": "32",
  "os": "none",
  "executables": true,
  "linker-flavor": "ld.lld",
  "linker": "rust-lld",
  "panic-strategy": "abort",
  "disable-redzone": true,
  "features": "+soft-float,+sse"
}

此定义将指针宽度设置为32，用于编译代码，这些代码可用于早期x86引导过程(当您已经处于32位保护模式时)。我对“特性”不是百分之百肯定，因为它们可能取决于您想做什么/需要什么。i686指32位模式下的x86_64和数据布局在这里解释。.

此外，还应该添加文件。

/.cargo/config.toml

[unstable]
# cross compile core library for custom target
build-std = ["core", "compiler_builtins"]
build-std-features = ["compiler-builtins-mem"]

[build]
# points to file in project root
target = "x86-unknown-bare_metal.json"

现在，您可以用32位x86代码使用cargo build构建一个裸金属二进制文件。

// disable rust standard library
#![no_std]
// disables Rust runtime init,
#![no_main]

// see https://docs.rust-embedded.org/embedonomicon/smallest-no-std.html
#![feature(lang_items)]

// see https://docs.rust-embedded.org/embedonomicon/smallest-no-std.html
#[lang = "eh_personality"]
extern "C" fn eh_personality() {}

use core::panic::PanicInfo;
use core::sync::atomic;
use core::sync::atomic::Ordering;

#[no_mangle]
/// The name **must be** `_start`, otherwise the compiler throws away all code as unused. 
/// The name can be changed by passing a different entry symbol as linker argument.
fn _start() -> ! {
    loop {}
}

#[inline(never)]
#[panic_handler]
fn panic(_info: &PanicInfo) -> ! {
    loop {
        atomic::compiler_fence(Ordering::SeqCst);
    }
}

为了方便起见，您还应该添加

/rust-toolchain.toml

# With this file, another toolchain to the currently selected one will be used, when you execute `cargo build`.
# https://rust-lang.github.io/rustup/overrides.html

[toolchain]
# equals to rust nightly 1.54 as of the release day 2021-05-10
channel = "nightly-2021-05-10"
components = [ "rust-src", "rust-std", "rustc", "cargo" ]