global _start
section .data
firstMsg: db "hello worms, please say the passcode", 10
firstLen: equ $ - firstMsg
secondMsg: db "Correct", 10
secondLen: equ $ - secondMsg
thirdMsg: db "Incorrect.", 10
thirdLen: equ $ - thirdMsg
password: db "Hello"
section .bss
attempt RESB
section .data
_start:
;Print the first message
mov rax, 1
mov rdi, 1
mov rsi, firstMsg
mov rdx, firstLen
syscall
;Read input
mov rax, 0
mov rdi, 0
mov rsi, attempt
mov rdx, 10
syscall
;compare input to the password
cmp attempt, password
je L1
jne L2
syscall
;Display correct if correct
L1:
mov rax, 1
mov rdi, 1
mov rsi, secondMsg
mov rdx, secondLen
jmp L3
syscall
;display incorrect if incorrect
L2:
mov rax, 1
mov rdi, 1
mov rsi, thirdMsg
mov rdx, secondLen
syscall
;exit the program
L3:
mov rax, 60
mov rdi, 1
syscall
This code returns this error message:
inout.asm:13: error: invalid combination of opcode and operands
inout.asm:33: error: invalid combination of opcode and operands
What I'm trying to do here is take input from a user as a string, which will then be compared to the constant password. If they are identical, it prints "correct", if they are not it prints "incorrect" and jumps back to the first question (not done that part yet).
If someone can help me bugfix this that'd be pretty cool.
a cmp instruction compares two values that fit into a register (8, 16, 32, or 64 bit values), not two strings. You need a cmpsb to compare each character of the strings, and can use a rep with it to compare the whole string in one go:
;compare input to the password
mov rsi, attempt ; first string
mov rdi, password ; second string
mov rcx, 5 ; length of the password
repe cmpsb ; compare
jne L2 ; no match
cmp byte ptr [rsi], 10 ; \n to end the input
jne L2 ; extra stuff in attempt
jmp L1
Note that you could simplify this a bit by adding the '\n' character to the expected password and using a length of 6. Then you wouldn't need the extra cmp/jne checking for the end of the input.