Question

NOTE: I’m using a BSD based system so if I remember correctly this means args for called subroutines/functions are pushed onto the stack not placed in registers

I’ve been trying out assembly and I wanted to try my simple kernel-exit program:

.globl _start

_start:
    movl $0x20, %eax
    pushl %eax
    movl $0x1, %eax
    subl $0x4, %esp
    int $0x80

in 64 bit assembly.

I remember reading that a large difference is the registers are now renamed r prefixed instead of the 32 bit standard of an e prefix.

But what is the new postfix for 64 bit opcodes, if l already means long for 32 bits?

Out of curiosity why is it an r prefix for the new registers?

Also if there are any good resources where further information could be found. Or tutorials, tutorials are always fun.

Answer 1

The postfix is q for qword, and r supposedly stands for register. Here’s an introduction in AT&T syntax.