fib3.s

# framework - get first argument from the command line and print to stdout
.section .text
.globl _start
_start:
    nop
    movl %esp, %ebp     # take a copy of esp to use
    addl $8, %ebp       # address of first arg in stack
    movl (%ebp), %edi   # move arg address into esi for scasb
    push %edi           # store the string address as edi gets clobbered

    movl $50, %ecx      # set ecx counter to a high value
    movl $0, %eax       # zero al search char
    movl %ecx, %ebx     # copy our max counter value to edx
    cld                 # set direction down
    repne scasb         # iterate until we find the al char

    subl %ecx, %ebx     # subtract from our original ecx value
    dec %ebx            # remove null byte at the end of the string from the count
    pop %ecx            # restore our string address into ecx
    mov %ebx, %edx      # move our count value to edx for the int 80 call

    movl $4, %eax       # set eax to 4 for int 80 to write to file
    movl $0, %ebx       # set ebx for file to write to as stdoout (file descriptor 0)
    int $0x80           # make it so
    movl $1, %eax       # set eax for int 80 for system exit
    movl $0, %ebx       # set ebx for return code 0
    int $0x80           # make it so again