I want to understand how should I use local variables and how to pass arguments to function in x86. I read a lot of guides, and they all wrote that the first parameter should be at [ebp+8], but it isn't here :/ WHat am I missing? What am I not understanding correctly?
number byte "724.5289",0
.code
main PROC
mov ebx,offset number ;making so that [ebp] = '7' atm
push ebx ;I push it on stack so I can access it inside the function
call rewrite
main ENDP
rewrite PROC
push ebp ; push ebp so we can retrieve later
mov ebp, esp ; use esp memory to retrieve parameters and
sub esp, 8 ; allocate data for local variable
lea ebx, [ebp-8]
lea eax, [ebp+8] ; i think here ebp+8 should point to the same now to which ebx did
;before function, but it does not, writechar prints some garbage ascii character
call writechar
call crlf
rewrite ENDP
END main
You pass a pointer as argument to rewrite, and then pass its address on to writechar. That is you take the address twice. That is one too many :)
You want mov eax, [ebp+8] instead of lea eax, [ebp+8]
Also, you need to clean up the stack after yourself, which you don't do. Furthermore, make sure your assembler automatically emits a RET for the ENDP directive, otherwise you will be in trouble. You might want to write it out explicitly.