如何将x86 GCC风格的C内联汇编转换为Rust内联汇编? [英] How do I translate x86 GCC-style C inline assembly to Rust inline assembly?

问题描述

我在C中具有以下内联汇编:

I have the following inline assembly in C:

unsigned long long result;
asm volatile(".byte 15;.byte 49;shlq $32,%%rdx;orq %%rdx,%%rax"
    : "=a" (result) ::  "%rdx");
return result;

我试图用Rust重写它:

I tried to rewrite it in Rust:

let result: u64;
unsafe {
    asm!(".byte 15\n\t
          .byte 49\n\t
          shlq 32, rdx\n\t
          orq  rdx, rax"
         : "=a"(result)
         :
         : "rdx"
         : "volatile"
         );
}
result

它不能识别=a约束，它给我shlq和orq指令中rdx和rax的无效操作数错误.在Rust中重写上述C内联汇编的正确方法是什么?

It doesn't recognize the =a constraint an it gives me an invalid operand error for rdx and rax at shlq and orq instructions. What is the proper way to rewrite the above C inline assembly in Rust?

推荐答案

Rust建立在LLVM之上，因此可以从LLVM或Clang的工作中收集到很多这样的底层细节.

Rust is built on top of LLVM, so a lot of low-level detail like this can be gleaned from what LLVM or Clang do.

1. 如果要指定特定的寄存器，请使用寄存器名称作为约束:"={rax}"(result).根据 GCC文档，a约束是一个"寄存器.

1. If you want to specify a specific register, you use the register name as the constraint: "={rax}"(result). Based on the GCC documentation, the a constraint is the "a" register.

文学作品必须以$$

寄存器必须以%

let result: u64;
unsafe {
    asm!(".byte 15
          .byte 49
          shlq $$32, %rdx
          orq  %rdx, %rax"
         : "={rax}"(result)
         :
         : "rdx"
         : "volatile"
    );
}
result

如果我正确理解了有关rdtsc的讨论，您也可以这样做:

If I'm understanding the discussion about rdtsc correctly, you can also do:

let upper: u64;
let lower: u64;
unsafe {
    asm!("rdtsc"
         : "={rax}"(lower), 
           "={rdx}"(upper)
         :
         :
         : "volatile"
    );
}
upper << 32 | lower

我建议在可行的情况下尽快取消内联汇编的 .

I advise getting out of inline assembly as soon as it's practical.

每个功能的组装:

playground::thing1:
    #APP
    .byte   15
    .byte   49
    shlq    $32, %rdx
    orq %rdx, %rax
    #NO_APP
    retq

playground::thing2:
    #APP
    rdtsc
    #NO_APP
    shlq    $32, %rdx
    orq %rdx, %rax
    retq

出于完整性考虑，以下是使用LLVM内部函数的相同代码.这需要 different 不稳定属性:

For completeness, here is the same code using the LLVM intrinsic. This requires a different unstable attribute:

#![feature(link_llvm_intrinsics)]

extern "C" {
    #[link_name = "llvm.x86.rdtsc"]
    fn rdtsc() -> u64;
}

fn main() {
    println!("{}", unsafe { rdtsc() })
}

来源:

• asm .
• LLVM内联程序集引用.
• 我的图书馆 jetscii 和

• The unstable book chapter on asm.
• The LLVM inline assembly reference.
• My libraries jetscii and cupid.

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