Module yaxpeax_x86::real_mode::register_class[−][src]

Expand description

high-level register classes in an x86 machine, such as “2-byte general purpose”, “xmm”, “x87”, and so on. constants in this module are useful for inspecting the register class of a decoded instruction. as an example:

use yaxpeax_x86::real_mode::{self as amd64};
use yaxpeax_x86::real_mode::{Opcode, Operand, RegisterClass};
use yaxpeax_arch::{Decoder, U8Reader};

let movsx_ax_cl = &[0x0f, 0xbe, 0xc1];
let decoder = amd64::InstDecoder::default();
let instruction = decoder
    .decode(&mut U8Reader::new(movsx_ax_cl))
    .expect("can decode");

assert_eq!(instruction.opcode(), Opcode::MOVSX);

fn show_register_class_info(regclass: RegisterClass) {
    match regclass {
        amd64::register_class::W => {
            println!("  and is a word register");
        }
        amd64::register_class::B => {
            println!("  and is a byte register");
        }
        other => {
            panic!("unexpected and invalid register class {:?}", other);
        }
    }
}

if let Operand::Register(regspec) = instruction.operand(0) {
    println!("first operand is {}", regspec);
    show_register_class_info(regspec.class());
}

if let Operand::Register(regspec) = instruction.operand(1) {
    println!("first operand is {}", regspec);
    show_register_class_info(regspec.class());
}

this is preferable to alternatives like checking register names against a known list: a register class is one byte and “is qword general-purpose” can then be a simple one-byte compare, instead of 16 string compares.

yaxpeax-x86 does not attempt to further distinguish between, for example, register suitability as operands. as an example, cl is only a byte register, with no additional register class to describe its use as an implicit shift operand.