SPO600 64-bit Assembly Language Lab

Purpose of this Lab
In this lab, you will experiment with assembler on the x86_64 and aarch64 platforms.

Australia and Red
Perform this lab on australia.proximity.on.ca (for x86_64) and red (for aarch64, accessed via port 2222 on iraq.proximity.on.ca).

Lab 3

Code Examples

The code examples for this lab are available at this link: http://england.proximity.on.ca/spo600/spo600-lab3-examples.tgz

Please download this archive to your accounts on Australia and Red, and unpack the archive on both systems. Do all of the work for the x86_64 architecture on Australia, and all of the work on the aarch64 architecture on Red.

Unpacking the archive in your home directory will produce the following directory structure:

spo600
`-- examples
    `-- hello                     # "hello world" example programs
        |-- assembler
        |   |-- aarch64           # aarch64 gas assembly language version
        |   |   |-- hello.s
        |   |   `-- Makefile
        |   `-- x86_64            # x86_64 assembly language versions
        |       |-- hello-gas.s   # ... gas syntax
        |       |-- hello-nasm.s  # ... nasm syntax
        |       `-- Makefile
        `-- c                     # Portable C versions
            |-- hello2.c          # syscall wrapper version
            |-- hello.c           # printf version
            `-- Makefile

Throughout this lab, take advantage of make whenever possible.

References

• Assembler Basics
  • x86_64 Register and Instruction Quick Start
  • aarch64 Register and Instruction Quick Start

Group Lab Tasks

1. Build and run the C versions of the program for x86_64.

2. Review, build, and run the x86_64 assembler programs. Make sure you understand the code.

4. Build and run the C versions of the program for aarch64. Verify that you can disassemble the object code in the ELF binary using objdump -d

5. Review, build, and run the aarch64 assembler programs. Make sure you understand the code.

6. Here is a basic loop in x86_64 assembler - this loops from 0 to 9, using r15 as the index (loop control) counter:

.text
.globl    _start

start = 0                       /* starting value for the loop index */
max = 10                        /* loop exits when the index hits this number (loop condition is i<max) */

_start:
    mov     $start,%r15         /* loop index */

loop:
    /* ... body of the loop ... do something useful here ... */

    inc     %r15                /* increment index */
    cmp     $max,%r15           /* see if we're done */
    jne     loop                /* loop if we're not */

    mov     $0,%rdi             /* exit status */
    mov     $60,%rax            /* syscall sys_exit */
    syscall

Extend this code, combining it with code from the "Hello World" example, so that it prints each digit from 0 to 9 like this:

Loop: 0
Loop: 1
Loop: 2
Loop: 3
Loop: 4
Loop: 5
Loop: 6
Loop: 7
Loop: 8
Loop: 9

Character conversion
In order to print the loop index value, you will need to convert from an integer to digit character. In ASCII/ISO-9959-1/Unicode UTF-8, the digit characters are in the range 48-57 (0x30-0x39). You will also need to assemble the message to be printed for each line - you can do this by writing the digit into the message buffer before outputting it to stdout, or you can perform a sequence of writes for the thee parts of the message ('Loop: ', number, '\n').

7. Repeat step 6 for aarch64.

8. Extend the code to loop from 00-30, printing each value as a 2-digit decimal number.

2-Digit Conversion
You will need to take the loop index and convert it to a 2-digit decimal number by dividing by 10. To do this, use the div instruction, which takes the dividend from rax and the divisor from register supplied as an argument. The quotient will be placed in rax and the remainder will be placed in rdx.

9. Repeat step 8 for aarch64.

Deliverables

1. Complete the group lab section, above.

2. Extend the assembler programs (both x86_64 and aarch64) to suppress the high digit when it is 0. In other words, the printed values should progress from 0-30 instead of from 00-30. It is OK to output a space in place of the suppressed digit (this will cause the numbers to be aligned vertically in the printout).

3. Blog about the programs you've written. Describe the experience of writing and debugging in assembler, as compared to writing in other languages. Contrast x86_64 and aarch64 assembler, your experience with each, and your opinions of each. Include links to the source code for both of your assembler programs.

Optional Challenge

Write a program in aarch64 assembly language to print the times tables from 1-12 ("1 x 1 = 1' through '12 x 12 = 144'). Add a spacer between each table, and use a function/subroutine to format the numbers with leading-zero suppression.

 1 x  1 =   1
 2 x  1 =   2
 3 x  1 =   3
 4 x  1 =   4
 5 x  1 =   5
 6 x  1 =   6
 7 x  1 =   7
 8 x  1 =   8
 9 x  1 =   9
10 x  1 =  10
11 x  1 =  11
12 x  1 =  12
-------------
 1 x  2 =   2
 2 x  2 =   4
 3 x  2 =   6
 4 x  2 =   8
 5 x  2 =  10

  ...lines snipped for space... 

11 x 12 = 132
-------------
 1 x 12 =  12
 2 x 12 =  24
 3 x 12 =  36
 4 x 12 =  48
 5 x 12 =  60
 6 x 12 =  72
 7 x 12 =  84
 8 x 12 =  96
 9 x 12 = 108
10 x 12 = 120
11 x 12 = 132
12 x 12 = 144