Difference between revisions of "SPO600 64-bit Assembler Lab"
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svc 0 /* invoke syscall */
svc 0 /* invoke syscall */
This code doesn't actually do anything while looping, because the body of the loop is empty.
This code doesn't actually do anything while looping, because the body of the loop is empty. with code from the "Hello World" example, so that it prints a word each time it loops:
Latest revision as of 16:55, 21 February 2020
The code examples for this lab are available in the file
/public/spo600-assembler-lab-examples.tgz on 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 | `-- x86_64 # x86_64 assembly language versions | |-- hello-gas.s # ... gas syntax | |-- hello-nasm.s # ... nasm syntax | `-- Makefile `-- c # Portable C versions |-- hello2.c # write() version |-- hello3.c # syscall() wrapper version |-- hello.c # printf() version `-- Makefile
Throughout this lab, take advantage of make whenever possible.
- Assembler Basics
- x86_64 Register and Instruction Quick Start
- aarch64 Register and Instruction Quick Start
Group Lab Tasks
1. Build and run the three C versions of the program for x86_64. Take a look at the differences in the code.
2. Use the
objdump -d command to dump (print) the object code (machine code) and disassemble it into assembler for each of the binaries. Find the
<main> section and take a look at the code. Notice the total amount of code.
3. Review, build, and run the x86_64 assembly language programs. Take a look at the code using
objdump -d objectfile 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 of the program for aarch64. Verify that you can disassemble the object code in the ELF binary using
objdump -d objectfile and take a look at the code.
5. Review, build, and run the aarch64 assembly language programs. Take a look at the code using
objdump -d objectfile and compare it to the source code.
6. 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 = 30 /* 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
7. Repeat step 6 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
8. Extend the AArch64 code to loop from 00-30, printing each value as a 2-digit decimal number.
9. Repeat step 8 for x86_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).
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.
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