[[Category:SPO600-futureLabs]][[Category:Assembly Language]]{{Chris Tyler DraftAdmon/lab|Purpose of this Lab|In this lab, you will experiment with assembler on the x86_64 and aarch64 platforms.}}{{Admon/tip|SPO600 Servers|Perform this lab on [[SPO600 Servers]] (you may use your own systems if they are of the right architecture and appropriately configured).}}

{{Admon/note|Purpose of this == Lab|In this lab, you will experiment with assembler on the x86_64 and aarch64 platforms.}}{{Admon/tip|Ireland|Perform this lab on ireland.proximity.on.ca.)}}4 ==

=== 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 Throughout this lab, take advantage of ''[[make and Makefiles|make]]'' whenever possible. === 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]] === Optional Investigation === 1. Build and run the three C versions of the program for x86_64 and aarch64, using <code>make</code>. Take a look at the differences in the code. 2. Use the <code>objdump -d</code> command to dump (print) the object code (machine code) and disassemble it into assembler for each of the binaries. Find the <code><nowiki><main></nowiki></code> section and take a look at the code. Also notice the total amount of code. 3. Review, 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'''</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. === Lab Tasks === <!-- {{Admon/tip|Answers in the Video!|The answers to the first three steps below are contained in the associated [https://web.microsoftstream.com/video/8c3c1353-5729-4217-b1ba-371410f14ad4 lecture video.]}} --> 1. Review, build, and run the aarch64 assembly language programs. Take a look at the code using <code>objdump -d '''objectfile'''</code> and compare it to the source code. 2. Here is a basic loop in AArch64 assembler - this loops from 0 to 9, using r19 as the index (loop control) counter:  .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) */ _start: mov x19, min loop: /* '''... body of the loop ... do something useful here ...''' */ add x19, x19, 1 cmp x19, max b.ne loop mov x0, 0 /* status -> 0 */ mov x8, 93 /* exit is syscall #93 */ svc 0 /* invoke syscall */ This code doesn't actually do anything while looping, because the body of the 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 Loop Loop Loop Loop Loop Loop Loop Loop Loop Then modify the message so that it includes the loop index values, showing 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 {{Admon/tip|Character conversion|In order to print the loop index value, you will need to convert from an integer to digit character. In 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, which is probably the best approach, or you can perform a sequence of writes for the thee parts of the message ('Loop: ', number, '\n'). You may want to refer to the manpage for <code>ascii</code>.}} {{Admon/tip|6502 Implementation|For reference, here is a [[6502 Counting Loop Example|6502 implementation of this loop]].}} 3. Repeat the previous step for x86_64. For reference, here is the loop code in x86_64 assembler:  .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) */ _start: mov $min,%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 4. Extend the AArch64 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. 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.}} 5. Change the code as needed to suppress the leading zero (printing 0-30 instead of 00-30). 5. Repeat the previous two steps for x86_64. === Deliverables === 1. Complete the lab section, above. 2. 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 each 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. The output could look something like this:  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