Question

Assembly Question: I am trying to annotate this code and am struggling to understand what it is doing. Can someone please add comments?

.data
.star: .string "*"
.line: .string "\n"
.input: .string "%d"

.count: .space 8

.text
.global main

printstars:
push %rsi
push %rdi

_printstars:
push %rdi
mov $.star, %rdi
xor %rax, %rax
call printf
pop %rdi

dec %rdi
cmp $0, %rdi
jg _printstars

mov $.line, %rdi
xor %rax, %rax
call printf

pop %rdi
pop %rsi

ret

printstarpyramid:

mov %rdi, %rsi
mov $1, %rdi

_printstarpyramid:
call printstars

inc %rdi
cmp %rsi, %rdi
jle _printstarpyramid
ret

main:

mov $.input, %rdi
mov $.count, %rsi
xor %rax, %rax
call scanf

mov (.count), %rdi

call printstarpyramid

Answer 1

//declare variable

.data
.star: .string "*"

//Read input
.line: .string "\n"
.input: .string "%d"

//Count space

.count: .space 8

.text

//Declare global variable
.global main

// Push values into variable s

printstars:
push %rsi
push %rdi

_printstars:
push %rdi

// Move values
mov $.star, %rdi

// Do xor operation
xor %rax, %rax

//Print value
call printf
pop %rdi

dec %rdi

// Compare values
cmp $0, %rdi
jg _printstars

// Move values from one to other

mov $.line, %rdi

// Xor operation
xor %rax, %rax

//Print value
call printf

// Get values

pop %rdi
pop %rsi

ret

printstarpyramid:

//Move values

mov %rdi, %rsi
mov $1, %rdi

_printstarpyramid:
call printstars

inc %rdi
cmp %rsi, %rdi
jle _printstarpyramid
ret

main:

mov $.input, %rdi
mov $.count, %rsi
xor %rax, %rax
call scanf

mov (.count), %rdi

call printstarpyramid

Instruction Working

MOV -- copies the data item referred to by its second operand

PUSH-- places its operand onto the top of the hardware supported stack in memory

POP -- removes the 4-byte data element from the top of the hardware-supported stack into the specified operand (i.e. register or memory location)

INC -- increments the contents of its operand by one

CMP -- Compare the values of the two specified operands

Syntax
cmp <reg>,<reg>
cmp <reg>,<mem>
cmp <mem>,<reg>
cmp <reg>,<con>

JLE - one of the conditional jump instruction

Sytax - jle <label> (jump when less than or equal to)