[[Category:SPO600 Labs]][[Category:Assembly Language]]
{{Admon/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 x86_64 systems if they are of the right architecture and appropriately configured).}}
== Lab 5 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() version |-- ├── hello3.c # ... using syscall() wrapper version |-- ├── hello.c # ... using printf() version `-- └── 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]]
=== Group Lab Tasks 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).
{{Admon4. Build and run the assembly language version of the program for aarch64 using <code>make</tip|Shortcut|To save lab time 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'your group can decide''' to do steps 1-4 as individual homework after </code> and take a look at the labcode.}}
1. Review, build, and run the x86_64 assembly language programs. 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).=== Lab Tasks ===
2. Build and run <!-- {{Admon/tip|Answers in the Video!|The answers to the first three C versions of steps below are contained in the program for aarch64associated [https://web.microsoftstream.com/video/8c3c1353-5729-4217-b1ba-371410f14ad4 lecture video. 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.
31. 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.
42. Here is a basic loop in AArch64 assembler - this loops from 0 to 9, using r19 as the index (loop control) counter:
.text
min = 0 /* starting value for the loop index; '''note that this is a symbol (constant)''', not a variable */
max = 30 10 /* loop exits when the index hits this number (loop condition is i<max) */
_start:
{{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>.}}
5{{Admon/tip|6502 Implementation|For reference, here is a [[6502 Counting Loop Example|6502 implementation of this loop]].}} 3. Repeat the previous step 6 for x86_64.
For reference, here is the loop code in x86_64 assembler:
_start:
mov $min,%r15 /* loop index */
loop:
syscall
64. 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. 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.}} 7. Repeat step 8 for x86_64. === Optional Investigation (Recommended) ===
1{{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. Build and run Read the three C versions description of the program for division instruction carefully. On x86_64 and aarch64, you need to set up specific registers before performing a division. Take On AArch64, you will need to use a look at second instruction to find the differences in the coderemainder after a division.}}
25. Use Change the <code>objdump -d</code> command as needed to dump (print) suppress the object code leading zero (machine codeprinting 0-30 instead of 00-30) 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.
5. Repeat the previous two steps for x86_64.
=== 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 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.
=== Optional Challenge ===
