teaching machines

CS 330 Lecture 14 – Assembly

February 25, 2015 by Chris Johnson. Filed under cs330, lectures, spring 2015.

Agenda

• what ?s
• the von Neumann computer
• leaky abstractions
• line at a time

TODO

• Read chapters 1-3 of Programming from the Ground Up. 1/4 sheet.

Recall This

1. What’s the von Neumann architecture of a computer?
2. What happens in a computer when you add two variables?
3. What happens when you execute an executable?

Line at a Time

  1: .section .text
  2: .globl main
  3: 
  4: main:
  5:   movl $5, %eax
  6:   movl $6, %ebx
  7:   addl %ebx, %eax
  8: 
  9:   pushl %eax
 10:   call exit

  1: .section .data
  2: out_message:
  3:   .asciz "What's the difference between %d and %d? %d.\n"
  4: prompt_message:
  5:   .asciz "Enter two numbers: "
  6: in_format:
  7:   .asciz "%d %d"
  8: a:
  9:   .long 20
 10: b:
 11:   .long 4
 12: 
 13: .section .text
 14: .globl main
 15: 
 16: main:
 17:   pushl $prompt_message
 18:   call printf
 19:   addl $4, %esp
 20: 
 21:   pushl $b
 22:   pushl $a
 23:   pushl $in_format
 24:   call scanf
 25:   addl $12, %esp
 26: 
 27:   movl a, %eax
 28:   subl b, %eax
 29: 
 30:   pushl %eax
 31:   pushl b
 32:   pushl a
 33:   pushl $out_message
 34:   call printf
 35:   addl $16, %esp
 36: 
 37:   pushl $0
 38:   call exit

  1: .section .data
  2: message:
  3:   .ascii "One past %d is %d.\0"
  4: 
  5: .section .bss
  6:   .lcomm a, 4
  7:   .lcomm b, 4
  8: 
  9: .section .text
 10: .globl main
 11: 
 12: main:
 13:   movl $12, %eax
 14:   movl %eax, a
 15:   movl %eax, b
 16:   incl b
 17: 
 18:   pushl b
 19:   pushl a
 20:   pushl $message
 21:   call printf
 22:   addl $12, %esp
 23: 
 24:   pushl $0
 25:   call exit

  1: .section .data
  2: heads_message:
  3:   .asciz "%d -> heads\n"
  4: tails_message:
  5:   .asciz "%d -> tails\n"
  6: 
  7: .section .data
  8: .globl main
  9: 
 10: main:
 11:   subl $4, %esp
 12: 
 13:   call rand
 14:   movl %eax, 4(%esp)
 15: 
 16:   andl $1, %eax
 17:   cmpl $0, %eax
 18: 
 19:   je tails
 20: 
 21: heads:
 22:   pushl 4(%esp)
 23:   pushl $heads_message
 24:   call printf
 25:   addl $8, %esp
 26:   jmp quit
 27: 
 28: tails:
 29:   pushl 4(%esp)
 30:   pushl $tails_message
 31:   call printf
 32:   addl $8, %esp
 33: 
 34: quit:
 35:   pushl $0
 36:   call exit

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