I finished going through my second program in assembly. It was a lot faster going through writing an assembly program the second time around lol… Thankfully.
TLDR;
Okay, so here are the highlights of what I did:
- I read through a few more pages of the “Programming from the Ground Up” book by Jonathan Bartlett. I built a program to return the largest number from a hard coded list of numbers. I then read through the breakdown and started writing notes in the book itself.
- I finished breaking down each line of code in my second assembly program.
- I wrote some additional notes on syntax differences in Assembly Language code.
Find the Max Number Program
#PURPOSE: This program finds the maximum number of a
# set of data items.
#
#VARIABLES: The registers have the following uses:
#
# %edi - Holds the index of the data item being examined
# %ebx - Largest data item found
# %eax - Current data item
#
# The following memory locations are used:
#
# data_items - contains the item data. A 0 is used
# to terminate the data
#
.section .data
data_items: #These are the data items
.long 3,67,34,222,45,75,54,34,44,33,22,11,66,0
.section .text
.globl _start
_start:
movl $0, %edi # move 0 into the index register
movl data_items(,%edi,4), %eax # load the first byte of data
movl %eax, %ebx # since this is the first item, %eax is
# the biggest
start_loop: # start loop
cmpl $0, %eax # check to see if we’ve hit the end
je loop_exit incl %edi # load next value
movl data_items(,%edi,4), %eax
cmpl %ebx, %eax # compare values
jle start_loop # jump to loop beginning if the new
# one isn’t bigger
movl %eax, %ebx # move the value as the largest
jmp start_loop # jump to loop beginning
loop_exit:
# %ebx is the status code for the exit system call
# and it already has the maximum number
movl $1, %eax # 1 is the exit() syscall
int $0x80
Conclusion
That’s all for today. If you are interested in the MIT course you can check out the video lecture I’m currently going through. The lecture is helpful but isn’t sufficient by itself. Anyways, until next time PEACE!