teaching machines

CS 330 Lecture 10 – Assembly

February 12, 2014 by Chris Johnson. Filed under cs330, lectures, spring 2014.

Agenda

• what ?s
• assembly ways of doing:
  • loops
  • structs
  • local variables
  • functions

TODO

• Read pages 35-45 in Programming From The Ground Up. 1/4 sheet.

Code

headxortails.s

.section .data
out_format:
  .asciz "Your RANDOM number is %d\n"
heads_message:
  .asciz "HEAD!"
tails_message:
  .asciz "TAIL!"

.section .text
.globl main

main:
  pushl $0
  call time
  addl $4, %esp
  
  # current nseconds since epoch is in %eax

  pushl %eax
  call srand
  addl $4, %esp

  call rand

  pushl %eax

  # %eax holds our random number
  andl $1, %eax
  # andl %eax, $1 

  # %eax is either 0 or 1

  cmpl $0, %eax
  je tails

heads:
  pushl $heads_message
  call printf
  addl $4, %esp
  jmp quit

tails:
  pushl $tails_message
  call printf
  addl $4, %esp

quit:
  popl %eax

  pushl %eax
  pushl $out_format
  call printf
  addl $8, %esp

  pushl %eax
  call exit

loop.s

.section .data
out_format:
  .asciz "The sum is %d\n"
nums:
  .long 12,17,5,4652
count:
  .long 4

.section .text
.globl main

main:
  movl $0, %ebx    # ebx holds the sum
  movl $0, %edi    # edi holds i

loop:
  cmpl count, %edi
  jge quit
  
  addl nums(,%edi,4), %ebx
  incl %edi

  jmp loop
  
quit: 

  pushl %ebx
  pushl $out_format
  call printf
  addl $8, %esp

  pushl $0
  call exit

struct.s

.section .data
in_format:
  .asciz "%s %d"
out_format:
  .asciz "Person %s is %d years old\n"

.section .text
.globl main

main:
  movl %esp, %ebp
  subl $52, %esp

  leal 4(%ebp), %eax
  pushl %eax
  call get_person
  addl $4, %esp

  leal 4(%ebp), %eax
  pushl %eax
  call put_person
  addl $4, %esp

  pushl $0
  call exit

get_person:
  pushl %ebp         # preserve main's foothold
  movl %esp, %ebp    # establish my foothold

  movl 8(%ebp), %eax # Grab first parameter, throw it in %eax
  leal 48(%eax), %ebx # Load age pointer into %ebx
  pushl %ebx          # Load up age pointer for scanf
  pushl %eax          # Load up name pointer for scanf
  pushl $in_format    # Load up format string for scanf
  call scanf          # call scanf
  addl $12, %esp      # clean up parameters

  movl %ebp, %esp
  popl %ebp
  ret

put_person:
  pushl %ebp         # preserve main's foothold
  movl %esp, %ebp    # establish my foothold

  movl 8(%ebp), %eax # Grab first parameter, throw it in %eax
  pushl 48(%eax)     # Load up age for printf
  pushl %eax          # Load up name pointer for printf
  pushl $out_format    # Load up format string for printf
  call printf          # call printf
  addl $12, %esp      # clean up parameters

  movl %ebp, %esp
  popl %ebp
  ret

stringloop.s

.section .data
out_format:
  .asciz "[%c]\n"
name:
  .asciz "abcd\n"
count:
  .long 4

.section .text
.globl main

main:
  movl $0, %ebx    # ebx holds the sum
  movl $0, %edi    # edi holds i

loop:
  cmpl count, %edi
  jge quit
  
  movl name(,%edi,1), %eax
  pushl %eax
  pushl $out_format
  call printf
  addl $8, %esp

  incl %edi

  jmp loop
  
quit: 

  pushl %ebx
  pushl $out_format
  call printf
  addl $8, %esp

  pushl $0
  call exit

Haiku