.global _start
    mov $0x1000,%edx
    mov %edx,%eax
    neg %eax
    and %eax,%esp
    mov %esp,%ecx
    xor %ebx,%ebx
    mov $3,%eax
    int $0x80
    add %edx,%esp
    mov %ecx,%edi
    mov $label00,%ebp
    jmp parse_eax_load_constants
    push %eax
    inc %edi
    mov $label01,%ebp
    jmp parse_eax
    mov %edi,%ebp
    mov %esi,(%edi)
    dec %edi
    pop %edx
    add %edx,%eax # finally
print_eax: # %edi: where to print %eax
    xor %edx,%edx
    div %esi
    or %cl,%dl
    mov %dl,(%edi)
    dec %edi
    test %eax,%eax
    jnz print_eax

    mov %ebp,%edx
    sub %edi,%edx
    inc %edi
    mov %edi,%ecx
    xor %ebx,%ebx
    inc %ebx
    mov $4,%eax
    int $0x80
    mov %ebx,%eax
    int $0x80

    mov $10,%esi
    mov $0x30,%ecx
parse_eax: # %edi: the string to parse
    xor %eax,%eax
    movb (%edi),%al
    mov %edi,%ebx
    inc %ebx
    cmpb $0x2d,%al
    cmovz %ebx,%edi
    setz %bl
    push %ebx
    mov (%edi),%al
    xor %ebx,%ebx
    xor %cl,%al
    inc %edi
    movb (%edi),%bl
    xor %cl,%bl
    cmp %esi,%ebx
    jae parse_eax_end
    mul %esi
    add %ebx,%eax
    jmp parse_eax_loop
    pop %ebx
    mov %eax,%edx
    neg %edx
    test %bl,%bl
    cmovnz %edx,%eax
    jmp *%ebp
  • 4
    \$\begingroup\$ You have to provide some context to the code, otherwise you won't get appropriate reviews. Why did you write it this way? \$\endgroup\$ Apr 24, 2017 at 4:56
  • \$\begingroup\$ @RolandIllig I wrote this assembly as an exercise; and also to learn i386 assembly(from a x86_64 background) \$\endgroup\$
    – user69874
    Apr 24, 2017 at 5:37

2 Answers 2


You are asking for a code review, and my first bit of feedback is: COMMENTS.

Please, reading raw assembler is a challenge. Start by a comment block at the top that describes the purpose of the code, then consider line-by-line comments, something like this: https://codereview.stackexchange.com/a/156947/110050

  • \$\begingroup\$ I had the exact same reaction when I saw the code, ++ \$\endgroup\$
    – Phrancis
    Apr 24, 2017 at 4:37

Reusing the constant 1 for both STDOUT_FILENO and SYS_EXIT is confusing to the human reader. You should prefer to write clear code instead of using these tricks.

Same for the jmp *%ebp.

  • \$\begingroup\$ I definitely won't be using these "tricks" in a compiled language, but here there is no compiler to simplify human-readable code. I'm trading readability for performance here. The same goes with the jump, since there are only single-depth call stack the register is used for performance(avoids memory access). As an added bonus, this code is impervious to Remote Code Execution(RCE) via return pointers on the stack. \$\endgroup\$
    – user69874
    Apr 24, 2017 at 5:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.