Group Project 5: `strstr` with string instructions

In this project, your task is to implement the strstr function, which searches one string for the first occurrence of a pattern string:

char* strstr(char* text, char* ptn);

strstr returns a pointer to the first occurrence of ptn within text, or to the nul character at the end of text if no occurrences can be found.

section .data

search_text1:   db      "The cat in the hat.", 0
search_text2:   db      "The dog in the hat.", 0
search_text3:   db      "potato ca", 0
ptn_text:       db      "cat", 0
not_found:      db      "Not found", 10, 0

section .text
extern printf
global main

main:
    push rbp
    mov rbp, rsp

    mov rdi, search_text1
    mov rsi, ptn_text
    call asm_strstr

    cmp byte [rax], 0
    je .not_found1

    ; Found
    mov rdi, rax
    mov al, 0
    call printf
    jmp .search2

.not_found1:
    mov rdi, not_found
    call printf

.search2:
    mov rdi, search_text2
    mov rsi, ptn_text
    call asm_strstr

    cmp byte [rax], 0
    je .not_found2

    ; Found
    mov rdi, rax
    call printf
    jmp .search3

.not_found2:
    mov rdi, not_found
    call printf

.search3:
    mov rdi, search_text3
    mov rsi, ptn_text
    call asm_strstr

    cmp byte [rax], 0
    je .return

    ; Found
    mov rdi, rax
    call printf
    jmp .return

.return:
    pop rbp
    mov rax, 0
    ret

asm_strstr:
    push rbp
    mov rbp, rsp

    ; rdi = char* text 
    ; rsi = char* ptn
    ; rax = returned char*

    ; Your code here.

    pop rbp
    ret

If your asm_strstr works correctly, the program should print cat in the hat. followed by Not found twice. The provided main checks your code in three situations: