#include <stdio.h>

int main()
{
    char ciag[] = "Hello";

    asm volatile(
        ".intel_syntax noprefix;"

        "mov eax, %0;"  //pointer to the first char in array
        "xor ecx, ecx;"

        "length:"
                "mov cl, [eax];"
                "inc eax;"
                "inc ecx;"
                "cmp cl, 0;"
                "jne length;"
                "je reverse;"

        "dec eax;" // eax was on 0 of a string, now its on the last char
        "mov ebx, eax;" //ebx on the last char
        "mov eax, %0;"
        "shr ecx, 1;"
        "mov esi, ebx;"//dont know why but it cant be ebx when MOV CL, EBX - need esi
        "mov edi, eax;"//same

        "reverse:"
                "mov cl, [esi];" //cl has last char
                "mov dl, [edi];" //dl has first char
                "mov [edi], dl;"
                "mov [esi], cl;"
                "inc esi;"
                "dec edi;"
                "dec ecx;"
                "jnz reverse;"
        ".att_syntax prefix;"
        :
        :"r" (ciag)
        :"eax", "ebx", "ecx", "edi", "esi"
    );


    printf("Reverse string: %s\n", ciag);
    return 0;
}