{{Admon/tip|SPO600 Servers|Perform this lab on [[SPO600_ServersSPO600 Servers]] (you may use your own x86_64 system systems if desired, along with they are of the AArch64 serverright architecture and appropriately configured).}}

=== Code Examples === The code examples for this lab are available in the file <!code>/public/spo600-assembler-lab-examples.tgz</code> on each of the [[SPO600 Servers]]. 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 │   ├── 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 # ... using write() ├── hello3.c # ... using syscall() ├── hello.c # ... using printf() └── Makefile

### THIS COMMENTED-OUT SECTION DESCRIBES THE ### CONFIGURATION USED FOR THE WINTER 2014 ### OFFERING OF THE SPO600 COURSEThroughout this lab, WHERE THE### AARCH64 WORK WAS DONE IN EMULATION ALONGSIDE### THE X86_64 WORK ON THE INTEL HOST "IRELAND".### IN FALL 2014, AARCH64 HARDWARE WAS AVAILABLE,### AND IRELAND HAD FAILED, SO WE SWITCHED TO### THOSE HOSTStake advantage of ''[[make and Makefiles|make]]'' whenever possible.

=== Ireland - Configuration Resources ===* [[Assembler Basics]] (includes instructions on how to use the GNU Assembler)* [[Syscalls]]* [[x86_64 Register and Instruction Quick Start]]* [[aarch64 Register and Instruction Quick Start]]

The directory 1. Build and run the three C versions of the program for x86_64 and aarch64, using <code>~/arm64/spo600/examplesmake</code>, which is also accessible as <. Take a look at the differences in the code>~/spo600-examples</code>, contains these files:.

── hello # 'hello world' example programs ├── assembler │ ├── aarch64 # aarch64 assembler version │ │ ├── hello2.s │ │ └── Makefile │ └── x86_64 # x86_64 assembler versions │ ├── helloUse the <code>objdump -gas.s # 64-bit instructions with AT&Td</gnu assembler syntax code> command to dump (print) the object code (called 'gas', /usr/bin/asmachine code) │ ├── hello-nasmand disassemble it into assembler for each of the binaries.s # 32-bit instructions with IntelFind the <code><nowiki><main></nasm assembler syntax (nowiki></usr/bin/nasm) │ └── Makefile └── c ├── hello2code> section and take a look at the code.c # C version using Also notice the write() syscall wrapper ├── hellototal amount of code.c # C version using printf() └── Makefile

Throughout this lab3. Review, take advantage build, and run the x86_64 assembly language programs using <code>make</code>, taking note of the commands that are executed to assemble and link the code. Take a look at the code using <code>objdump -d '''objectfile'[[make and Makefiles|make]]'' whenever possible</code> and compare it to the source code. Notice the absence of other code (compared to the C binary, which had a lot of extra code).

4. Build and run the assembly language version of the program for aarch64 using <code>make</code>, taking note of the commands that are executed to assemble and link the code. Verify that you can disassemble the object code in the ELF binary using <code>objdump --d ''objectfile''</code>and take a look at the code.

=== Code Examples Lab Tasks ===

<!-- {{Admon/tip|Answers in the Video!|The code examples for this lab answers to the first three steps below are available at either of these links:* Outside Seneca: httpcontained in the associated [https://englandweb.cdotmicrosoftstream.systemscom/spo600video/spo6008c3c1353-lab45729-examples4217-b1ba-371410f14ad4 lecture video.tgz* Inside Seneca: http://england.internal.cdot.systems/spo600/spo600]}} -lab4-examples.tgz>

Please download this archive to your accounts on 1. Review, build, and run the aarch64 assembly language programs. Take a look at the x86_64 code using <code>objdump -d '''objectfile'''</code> and AArch64 systems, and unpack compare it to the archive on both systemssource code.

Unpacking the archive 2. Here is a basic loop in your home directory will produce AArch64 assembler - this loops from 0 to 9, using r19 as the following directory structureindex (loop control) counter:

spo600.text .globl _start min = 0 /* starting value for the loop index; '''note that this is a symbol (constant)''', not a variable */ max = 10 /* loop exits when the index hits this number (loop condition is i<max) */ `-- examples `-- hello # "hello world" example programs _start: |-- assembler | |-- aarch64 # aarch64 gas assembly language version mov x19, min | | |-- hello.s | | `-- Makefile loop: | `-- x86_64 # x86_64 assembly language versions | |-- hello-gas /* '''...s # body of the loop ... gas syntax | |-- hello-nasmdo something useful here .s # ..''' */ add x19, x19, 1 cmp x19, max b. nasm syntaxne loop | `-- Makefile ` mov x0, 0 /* status -- c # Portable C versions> 0 */ |-- hello2.c mov x8, 93 # /* exit is syscall wrapper version |-- hello.c # printf version93 */ `-- Makefile svc 0 /* invoke syscall */

Throughout this labThis code doesn't actually do anything while looping, take advantage because the body of ''[[make and Makefiles|make]]'' whenever possiblethe loop is empty.On an AArch64 machine, combine this code with code from the "Hello World" assembley-language example, so that it prints a word each time it loops:

Loop: 0 Loop: 1. Build and run the two C versions of the program for x86_64. Take a look at the differences in the code. Loop: 2 Loop: 3 Loop: 4 Loop: 5 Loop: 6 Loop: 7 Loop: 8 Loop: 9

2{{Admon/tip|Character conversion|In order to print the loop index value, you will need to convert from an integer to digit character. ReviewIn ASCII/ISO-8859-1/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, buildwhich is probably the best approach, and run or you can perform a sequence of writes for the x86_64 assembly language programsthee parts of the message ('Loop: ', number, '\n'). Make sure you understand You may want to refer to the manpage for <code>ascii</code>.}}

4. Build and run the C versions {{Admon/tip|6502 Implementation|For reference, here is a [[6502 Counting Loop Example|6502 implementation of the program for aarch64this loop]]. Verify that you can disassemble the object code in the ELF binary using <code>objdump -d</code>}}

53. Review, build, and run Repeat the aarch64 assembly language programs. Make sure you understand the codeprevious step for x86_64.

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

start min = 0 /* starting value for the loop index ; '''note that this is a symbol (constant)''', not a variable */

mov $startmin,%r15 /* loop index */

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

4. Extend this code, combining it with the AArch64 code to loop from the "Hello World" example00-30, so that it prints printing each value as a 2-digit from 0 to 9 like this:decimal number.

Loop: 0 Loop: 1 Loop: {{Admon/tip|2 Loop: 3 Loop: 4 Loop: 5 Loop: 6 Loop: 7 Loop: 8 Loop: 9-Digit Conversion|You will need to take the loop index and convert it to a 2-digit decimal number by dividing by 10. Read the description of the division instruction carefully. On x86_64, you need to set up specific registers before performing a division. On AArch64, you will need to use a second instruction to find the remainder after a division.}}

{{Admon/tip|Character conversion|In order to print 5. Change the loop index value, you will need to convert from an integer code as needed to digit character. In ASCII/ISO-9959-1/Unicode UTF-8, the digit characters are in suppress the range 48-57 leading zero (0x30printing 0-0x39). You will also need to assemble the message to be printed for each line 30 instead of 00- you can do this by writing the digit into the message buffer before outputting it to stdout, which is probably the best approach, or you can perform a sequence of writes for the thee parts of the message ('Loop: ', number, '\n'30). You may want to refer to the manpage for <code>ascii</code>.}}

75. Repeat step 6 for aarch64. 8. Extend the code to loop from 00-30, printing each value as a 2-digit decimal number. {{Admon/tip|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 <code>div</code> 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 previous two steps for aarch64x86_64.

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 output).

32. 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 each of your assembler programs.