Linux system call for X86 64 echo program - linux

Question

I'm still learning assembly so my question may be trivial.
I'm trying to write an echo program with syscall, in which I get a user input and give it as output on the next line.
section .text
global _start
_start:
mov rax,0
mov rdx, 13
syscall
mov rsi, rax
mov rdx, 13
mov rax, 1
syscall
mov rax, 60
mov rdi, 0
syscall

Answer 1

I'm assuming all you want to do is return the input to the output stream, so to do that you need to do a few things.
First, create a section .bss in your code. This is for initializing data. You will initialize a string with any name you want and do so with label resb sizeInBits. for demonstration it will be a 32 bit string called echo.
Extra note, the ';' character is used for comments similar to what // is in c++.
Example code
section .data
text db "Please enter something: " ;This is 24 characters long.
section .bss
echo resb 32 ;Reserve 32 bits (4 bytes) into string
section .text
global _start
_start:
call _printText
call _getInput
call _printInput
mov rax, 60 ;Exit code
mov rdi, 0 ;Exit with code 0
syscall
_getInput:
mov rax, 0 ;Set ID flag to SYS_READ
mov rdi, 0 ;Set first argument to standard input
; SYS_READ works as such
;SYS_READ(fileDescriptor, buffer, count)
;File descriptors are: 0 -> standard input, 1 -> standard output, 2 -> standard error
;The buffer is the location of the string to write
;And the count is how long the string is
mov rsi, echo ;Store the value of echo in rsi
mov rdx, 32 ;Due to echo being 32 bits, set rdx to 32.
syscall
ret ;Return to _start
_printText:
mov rax, 1
mov rdi, 1
mov rsi, text ;Set rsi to text so that it can display it.
mov rdx, 24 ;The length of text is 24 characters, and 24 bits.
syscall
ret ;Return to _start
_printInput:
mov rax, 1
mov rdi, 1
mov rsi, echo ;Set rsi to the value of echo
mov rdx, 32 ;Set rdx to 32 because echo reserved 32 bits
syscall
ret ;Return to _start