[[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 system systems if desired, along with they are of the AArch64 serverright architecture and appropriately configured).}}
== Lab 3 4 ==<!--
### THIS COMMENTED-OUT SECTION DESCRIBES THE
### CONFIGURATION USED FOR THE WINTER 2014
### OFFERING OF THE SPO600 COURSE, 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 HOSTS.
=== Ireland - Configuration ===
The host ''Ireland'' (ireland.proximity.on.ca) has been set up so that you can use it normally as an x86_64 host, or [[SPO600 aarch64 QEMU on Ireland|use an emulation environment to build and run aarch64 binaries]].
The directory <code>~/arm64/spo600/examples</code>, which is also accessible as <code>~/spo600-examples</code>, contains these files:
── hello # 'hello world' example programs
├── assembler
│ ├── aarch64 # aarch64 assembler version
│ │ ├── hello.s
│ │ └── Makefile
│ └── x86_64 # x86_64 assembler versions
│ ├── hello-gas.s # 64-bit instructions with AT&T/gnu assembler syntax (called 'gas', /usr/bin/as)
│ ├── hello-nasm.s # 32-bit instructions with Intel/nasm assembler syntax (/usr/bin/nasm)
│ └── Makefile
└── c
├── hello2.c # C version using the write() syscall wrapper
├── hello.c # C version using printf()
└── Makefile
Throughout this lab, take advantage of ''[[make and Makefiles|make]]'' whenever possible.
-->
=== Code Examples ===
The code examples for this lab are available in the file <code>/public/spo600-assembler-lab-examples.tgz </code> on both each of the [[SPO600 Servers|Aarchie and Xerxes]] .
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.
=== References 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_64and 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. Notice Also notice the total amount of code.
3. Review, build, and run the x86_64 assembly language programsusing <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 three C versions assembly language version of the program for aarch64using <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.
5. 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.=== Lab Tasks ===
6<!-- {{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 x86_64 AArch64 assembler - this loops from 0 to 9, using r15 r19 as the index (loop control) counter:
.text
.globl _start
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 $startx19,%r15 /* loop index */min
loop:
/* '''... body of the loop ... do something useful here ...''' */
inc add %r15 /* increment index */x19, x19, 1 cmp $x19, max,%r15 /* see if we're done */ jne loop /* b.ne loop if we're not */
mov $x0, 0,%rdi /* exit status -> 0 */ mov $60x8,%rax 93 /* exit is syscall sys_exit #93 */ svc 0 /* invoke syscall*/
This code doesn't actually do anything while looping, because the body of the loop is empty. Combine it 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
{{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>.}}
7{{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 aarch64x86_64.
8. Extend For reference, here is the loop code to loop from 00-30, printing each value as a 2-digit decimal number.in x86_64 assembler:
{{Admon .text .globl _start min = 0 /tip|2-Digit Conversion|You will need to take * starting value for the loop index and convert it to ; '''note that this is a 2-digit decimal number by dividing by symbol (constant)''', not a variable */ max = 10. To do /* loop exits when the index hits this, use the <code>divnumber (loop condition is i<max) */code> instruction _start: mov $min, which takes %r15 /* loop index */ loop: /* '''... body of the dividend from rax and the divisor from register supplied as an argumentloop ... do something useful here ... The quotient will be placed in ''' */ 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 and the remainder will be placed in rdx.}} /* syscall sys_exit */ syscall
94. 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 step 8 the previous two steps for aarch64x86_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 ===