How do I write inline assembly for `"={ecx}"(features)` in stable Rust?

Question

I have the following inline assembly which used to work in Rust, but it seems there has been some changes to the syntax, and it throws error at "={ecx}(features) with the message expected type. How can I rewrite this in new assembly syntax?

use std::arch::asm;

let features: u32;
unsafe {
    asm!("mov eax, 1
          cpuid"
         : "={ecx}"(features)
         :
         : "eax"
         : "intel"
    );
}

let support: u32 = (features >> 25) & 1;

Answer 1

Try this:

use std::arch::asm;

fn main() {
    let features: u32;
    unsafe {
        asm!("mov eax, 1",
             "push rbx",
             "cpuid",
             "pop rbx",
             out("ecx") features,
             out("eax") _,
             out("edx") _,
        );
    }
    println!("features: {:x}", features);
}

Playground

Note that you are not allowed to clobber ebx since it is used internally by LLVM, so you need to save and restore it.