teaching machines

CS 330 Lecture 15 – Assembly Cont’d

February 27, 2015 by Chris Johnson. Filed under cs330, lectures, spring 2015.

Agenda

• what ?s
• line at a time
• dealing with memory
• conditional statements
• calling functions

TODO

• 1/4 sheet. Pick one of:
  • Write an assembly program that gets a number from the user and prints out just its least significant byte.
  • Read Stop Misquoting Donald Knuth!

Line at a Time

  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...

Code

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