Systems I

CSC 406: Systems I

Homework 3

Due by 5:45 pm on Thursday, October 21

Please write precise and concise answers.

Reading

Read sections 3.1-3.6 and and 3.7.1-3.7.4 of BO* as well as week 5 and 6 lecture notes.

BO* = Computer Systems by Bryant and O'Hallaron

Make sure that you work out every practice problem in BO*! Peek at the solutions (presented at the end of the chapter) if you have to.

Assignment

Unzip file hw3.zip

$ unzip /home/lperkovi/public/hw3.zip

and move to newly created directory hw3:

$ cd hw3

This directory contains files hw3.c and Makefile. Open file hw3.c for editing and do the homework:

$ emacs hw3.c

When done, submit the homework as follows:

$ make submit

1. For a function with prototype

long decode2(long x, long y, long z);

gcc generates the following assembly code:

decode2: movq %rdi, %rax subq %rdx, %rax movq %rax, %rdx imulq %rax, %rdi salq $63, %rdx sarq $63, %rdx xorq %rdx, %rdi leaq (%rdi,%rsi), %rax ret

Parameters x, y, and z are passed in registers %rdi, %rsi, and %rdx. The code stores the return value in register %rax.

Reverse-engineer decode2. (In other words, write C code for decode2 that will have an effect equivalent to the assembly code shown.)

Note: read Section 3.5 first and write your solution in hw3.c. To check your solution, compile hw3.c to assembly code using

$ gcc -Og -S hw3.c

and then view the file hw3.s:

$ cat hw3.s

2. Problem 3.60 in BO but using this assembly code instead:

        movl    %esi, %ecx
        movl    $1, %edx
        movl    $0, %eax
.L3:
        testq   %rdx, %rdx
        je      .L5
        movq    %rdx, %r8
        andq    %rdi, %r8
        orq     %r8, %rax
        salq    %cl, %rdx
        jmp     .L3
.L5:
        ret

Your solution should be an implementation of C function loop(). You can check your solution as you did for problem 1. Note that there is a mistake in the book in line 1 of page 313. The function signature should be long loop(long x, int n).

3. Complete phase 1 of your lab 2. There is nothing to submit for this problem; I will check that your completed phase 1 by looking at

http://windriver.cdm.depaul.edu:15213/scoreboard

at 5:45pm on Thursday, October 21.