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During this week we continue to study assembly language. We practice programming in assembly on x86_64 and AArch64.
During this week we continue to study assembly language. We practice programming in assembly on x86_64 and AArch64.
Unfortunately while our class was working on the lab 5, I have been sick and could not attend the classes. Therefore I had to work on my own at home. I just started to work on the lab 5 and will continue working on it further. Below are the description and the tasks for the lab 5.
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:
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:
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 ascii.
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.
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.
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:
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
Character conversion
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 ascii.
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.
Deliverables:
1. Complete the group lab section, above.
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.
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