Assembly Programming - strchr

gets 함수를 만들기 전 '\n'의 위치 등을 찾아주는 strchr 함수를 구현하는 것이 편할 것 같아 구현하였다.

.globl main
main:
	push %ebp
	mov %esp, %ebp
	push $0x65
	push $helloworld
	call strchr
	push %eax
	call puts
	leave
	ret

strchr:
	push %ebp
	mov %esp, %ebp
	mov 0x08(%ebp), %eax
	movb 0x0c(%ebp), %bl
	.strchr_loop:
		cmpb (%eax), %bl
		je .strchr_finish
		cmpb $0x00, (%eax)
		je .strchr_notfound
		inc %eax
		jmp .strchr_loop
	.strchr_notfound:
		mov $0x01, %eax
	.strchr_finish:
		leave
		ret


puts:
	push %ebp
	mov %esp, %ebp
	mov 0x08(%ebp), %eax
	push %eax
	call strlen
	mov %eax, %edx
	mov $0x04, %eax
	mov $0x01, %ebx
	mov 0x08(%ebp), %ecx
	int $0x80
	push $0x0a
	lea (%esp), %ecx
	mov $0x04, %eax
	mov $0x01, %ebx
	mov $0x01, %edx
	int $0x80
	add $0x04, %esp
	leave
	ret

strcpy:
	push %ebp
	mov %esp, %ebp
	xor %eax, %eax
	mov 0x08(%ebp), %edi
	mov 0x0c(%ebp), %esi
	.strcpy_loop:
		movb (%esi), %al
		movb %al, (%edi)
		cmpb $0x00, %al
		je .strcpy_finish
		inc %esi
                inc %edi
		jmp .strcpy_loop
	.strcpy_finish:
		leave
		ret


strlen:
	push %ebp
	mov %esp, %ebp
	xor %ecx, %ecx
	mov 0x08(%ebp), %eax
	.strlen_loop:
		movb (%eax), %bl
		cmpb $0x00, %bl
		je .strlen_finish
		inc %eax
		inc %ecx
		jmp .strlen_loop
	.strlen_finish:
		mov %ecx, %eax
		leave
		ret


helloworld : .string "Hello, World"