How addressing works on Macos assembler

Question

I have a program in assembler language that moves all characters back 1 character. It works fine under windows, but under macos it throws a segmentation fault.

Here is the code that works under Windows:

#include <string>
#include <iostream>
using namespace std;

int main()
{

    string str1 = "Hello world!";
    char* str = &str1[0];
    int str_len = str1.length();

    __asm {
        mov eax, str
        mov ecx, str_len
        dec ecx

        mov esi, eax
        add esi, ecx
        mov dl, [esi]


        shift:
            mov ebx, esi
            dec ebx
            mov al, [ebx] // ! - 11 symbol
            mov [esi], al
            dec esi
            loop shift
        mov [esi], dl
    }
    cout << str;
}

I heard that in mac os addressing works differently and you need to use lea and rel. For example, this code throws a segment fault:

char* str = &str1[0];

__asm ​​{
mov eax, str
mov edx, [eax]
}

To compile on macos I use the command: g++ -o asm asm.cpp -fasm-blocks -std=c++17

I will be glad for any help.