Add two signed integers, given in stdin(space separated) in i386 ASM Linux ABI

Question

.global _start
_start:
 mov 0ドルx1000,%edx
 mov %edx,%eax
 neg %eax
 and %eax,%esp
 mov %esp,%ecx
 xor %ebx,%ebx
 mov 3,ドル%eax
 int 0ドルx80
 add %edx,%esp
 mov %ecx,%edi
 mov $label00,%ebp
 jmp parse_eax_load_constants
label00:
 push %eax
 inc %edi
 mov $label01,%ebp
 jmp parse_eax
label01:
 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,ドル%eax
 int 0ドルx80
 mov %ebx,%eax
 int 0ドルx80
parse_eax_load_constants:
 mov 10,ドル%esi
 mov 0ドルx30,%ecx
parse_eax: # %edi: the string to parse
 xor %eax,%eax
 movb (%edi),%al
 mov %edi,%ebx
 inc %ebx
 cmpb 0ドルx2d,%al
 cmovz %ebx,%edi
 setz %bl
 push %ebx
 mov (%edi),%al
 xor %ebx,%ebx
 xor %cl,%al
parse_eax_loop:
 inc %edi
 movb (%edi),%bl
 xor %cl,%bl
 cmp %esi,%ebx
 jae parse_eax_end
 mul %esi
 add %ebx,%eax
 jmp parse_eax_loop
parse_eax_end:
 pop %ebx
 mov %eax,%edx
 neg %edx
 test %bl,%bl
 cmovnz %edx,%eax
 jmp *%ebp

• Roland Illig: You have to provide some context to the code, otherwise you won't get appropriate reviews. Why did you write it this way?
• user69874: @RolandIllig I wrote this assembly as an exercise; and also to learn i386 assembly(from a x86_64 background)

Answer 1

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

• Phrancis: I had the exact same reaction when I saw the code, ++

Answer 2

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.

• user69874: 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.