section .data
menumsg db 10, "———————————————————————————————————————————"
    db 10, "ALP for the string operations"
    db 10, "———————————————————————————————————————————"
    db 10, "1.Enter the string"
    db 10, "2.Calculate the length"
    db 10, "3.Reverse the string"
    db 10, "4.Check whether string is palindrome or not"
    db 10, "5.Exit"
    db 10, "———————————————————————————————————————————"
    db 10, "Enter your Choice "
menumsg_len equ $-menumsg

wrchmsg db 10, "Wrong choice entered... Please try again",10
wrchmsg_len equ $-wrchmsg

entmsg db "Enter the string "
entmsg_len equ $-entmsg

lmsg db 10, "Length of the string is "
lmsg_len equ $-lmsg

revmsg db 10, "Reverse string is "
revmsg_len equ $-revmsg

palmsg db 10, "String is palindrome "
palmsg_len equ $-palmsg

npalmsg db 10, "String is not palindrome "
npalmsg_len equ $-npalmsg

spacechar db 20h

section .bss
    cnt resb 01
    optionbuff resb 02
    dispbuff resb 03
    srcstr resb 10
    revstr resb 10
    string resb 0

%macro display 4
    mov rax,%1
    mov rdi,%2
    mov rsi,%3
    mov rdx,%4
    syscall
%endmacro

section .text
global _start
_start:
menu:    
    display 1,1,menumsg,menumsg_len
    display 0,0,optionbuff,02
    cmp byte [optionbuff],"1"
    jne case2
    call entstr_proc
    jmp exit1

case2:    
    cmp byte [optionbuff],"2"
    jne case3
    call length_proc
    jmp exit1

case3:    
    cmp byte [optionbuff],"3"
    jne case4
    call reverse_proc
    jmp exit1

case4:    
    cmp byte [optionbuff],"4"
    jne case5
    call pal_proc
    jmp exit1
    case5:    
    cmp byte [optionbuff],"5"
    je exit
    display 1,1,wrchmsg,wrchmsg_len
    jmp menu

exit1:
    jmp menu
    jne exit

exit:    
    mov rax,60    
    mov rdi,0
    syscall

entstr_proc:
    display 1,1,entmsg,entmsg_len
    display 0,0,srcstr,10
    dec al
    mov [cnt],al 
    ret

length_proc:    
    display 1,1,lmsg,lmsg_len         
    mov bl,[cnt]
    call disp8_proc    
    ret

reverse_proc:
    mov rcx,00
    mov rsi,srcstr
    mov rdi,revstr
    mov cl,[cnt]
    add rsi,rcx
    sub rsi,1

up2: 
    mov al,[rsi]
    mov [rdi],al
    inc rdi
    dec rsi
    loop up2
    display 1,1,revmsg,revmsg_len
    display 1,1,revstr,cnt 
    ret

pal_proc:
    mov rcx,00
    mov rsi,srcstr
    mov rdi,revstr
    mov cl,[cnt]

up3:    
    mov al,[rsi]
    mov bl,[rdi]
    cmp al,bl
    jne exit2
    inc rsi
    inc rdi
    loop up3
    display 1,1,palmsg,palmsg_len
    jmp return

exit2:  
    display 1,1,npalmsg,npalmsg_len 

return:    
    ret

disp8_proc:
    mov rcx,02
    mov rdi,dispbuff

dup1:
    rol bl,4
    mov al,bl
    and al,0Fh
    cmp al,09h
    jbe dskip
    add al,07h

dskip:    
    add al,30h
    mov [rdi],al
    inc rdi
    loop dup1
    display 1,1,dispbuff,03
    ret

Note: It is mandatory to perform all the operations one by one, while executing this program
kodingwindow@kw:~$ nasm -felf64 kw.asm
kodingwindow@kw:~$ ld kw.o && ./a.out

———————————————————————————————————————————
ALP for the string operations
———————————————————————————————————————————
1.Enter the string
2.Calculate the length
3.Reverse the string
4.Check whether string is palindrome or not
5.Exit
———————————————————————————————————————————
Enter your Choice 1
Enter the string LOL   

———————————————————————————————————————————
ALP for the string operations
———————————————————————————————————————————
1.Enter the string
2.Calculate the length
3.Reverse the string
4.Check whether string is palindrome or not
5.Exit
———————————————————————————————————————————
Enter your Choice 2

Length of the string is 03
———————————————————————————————————————————
ALP for the string operations
———————————————————————————————————————————
1.Enter the string
2.Calculate the length
3.Reverse the string
4.Check whether string is palindrome or not
5.Exit
———————————————————————————————————————————
Enter your Choice 3

Reverse string is LOL
———————————————————————————————————————————
ALP for the string operations
———————————————————————————————————————————
1.Enter the string
2.Calculate the length
3.Reverse the string
4.Check whether string is palindrome or not
5.Exit
———————————————————————————————————————————
Enter your Choice 4

String is palindrome 
———————————————————————————————————————————
ALP for the string operations
———————————————————————————————————————————
1.Enter the string
2.Calculate the length
3.Reverse the string
4.Check whether string is palindrome or not
5.Exit
———————————————————————————————————————————
Enter your Choice 5
kodingwindow@kw:~$