fibfail.s

.section .text
.globl _start
_start:
movl $5, %edi # number of fibnum we hunt
movl $0, %ebx # 1st fibnum
movl $1, %eax # 2nd fibnum

start_loop:
## Check if %edi is 0
## (thus meaning %ebx is nth fibnum)
## and if so, exit loop
decl %edi
cmpl $0, %edi
je loop_exit

## core Fibonnaci algorithm
## (hold %eax in tmp register %edx,
## eax = eax + ebx,
## ebx = edx)
movl %eax, %edx
addl %ebx, %eax
movl %edx, %ebx

## Once loop completes...
loop_exit:
movl $1, %eax
int $0x80

In the unlikely event that someone ever looks like this and wonders why it doesn't work: I forgot to add a jmp to go back to the top of the loop, so it just ran my fibonacci algorithm once and keeps running right through. See my next gist for working version of same.