Question

All I need to do is get the user-inputted strings and put them inside the array or structure, but I keep getting the error

Invalid effective address

What does this mean?

The code

section .data
  fName db 'Enter your first name: '
  fNameLen equ $-fName
  lName db 'Enter your last name: '
  lNameLen equ $-lName

  numberOfStruct equ 50
  structSize equ 25
  firstName equ 0
  lastName equ 10


section .bss
  person resb numberOfStruct*structSize

section .text
  global _start

_start:
  mov esi, 0
  input_start:
    mov eax, 4
    mov ebx, 1
    mov ecx, fName
    mov edx, fNameLen
    int 80h

    mov eax, 3
    mov ebx, 0
    lea ecx, [person+structSize*esi+firstName] ;This is where the error appears
    mov edx, 15
    int 80h

    mov eax, 4
    mov ebx, 1
    mov ecx, lName
    mov edx, lNameLen
    int 80h

    mov eax, 3
    mov ebx, 0
    lea ecx, [person+structSize*esi+lastName] ;This is where the error appears
    mov edx, 10
    int 80h

    inc esi

    cmp esi,10
    jl input_start

    exit:
    mov eax, 1
    mov ebx, 0
    int 80h

Did I do it entirely wrong?

Answer 1

Edit: Added code and edited answer to match changes in question.

lea ecx, [person+structSize*esi+firstName] ; this is where the error appears

lea ecx, [person+structSize*esi+lastName]   ; this is where the error appears

Both these have the same error: You cannot multiply with 25, the valid scaling factors are 1, 2, 4 and 8.

Edit: As Harold pointed out, imul is the easiest way to compute the address:

 imul ecx,esi,25                    ; ecx == 25*esi
 lea ecx,[ecx+person+firstName]     ; ecx == 25*esi + person + firstName

You can also compute the address by using 3 lea‘s:

 lea ecx,[8*esi]                    ; ecx == 8*esi
 lea ecx,[ecx+2*ecx]                ; ecx == 24*esi
 lea ecx,[ecx+esi+person+firstName] ; ecx == 25*esi + person + firstName

Wikipedia has a useful summary of all 64-bit, 32-bit and 16-bit addressing modes.