x86 Assembly pushl/popl don't work with “Error: suffix or operands invalid”

Question

I\'m a newbie to assembly programming, working through Programming Ground Up on an Ubuntu x86_64 desktop with GNU assembler v2.20.1.

I\'ve been able to assemble/link

Answer 1

In 64-bit mode you cannot push and pop 32-bit values; you need pushq and popq.

Also, you will not get a proper exit this way. On 32-bit x86, you would need to set %eax to 1 to select the exit() system call, and set %ebx to the exit code you actually wish. On 64-bit x86 (that's what you are using), conventions are different: the system call number for exit() is 60, not 1; the first system call parameter goes in %rdi, not %rbx; the system-call invocation opcode is not int $0x80 but the special, x86-64-only opcode syscall.

Which leads to:

.section .data
.section .text
.globl _start
_start:
    pushq   $60
    popq    %rax
    pushq   $1
    popq    %rdi
    syscall

(each push/pop sequence can be replaced with a simple mov (like mov $60, %eax) of course; I suppose that you are trying to explicitly test push and pop, optimize for code-size, or avoid 0 bytes in the machine code (for an exploit payload))

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Related:

• What are the calling conventions for UNIX & Linux system calls on i386 and x86-64
• What happens if you use the 32-bit int 0x80 Linux ABI in 64-bit code?