The code is extremely sloppy, I'm just trying to get my program to work. After half an hour of trying to figure out why 2 strings that were exactly the same in the expression string1==string2 had it evaluating to 0, I tried another compiler. It worked there. Why is GDB doing this?

I am posting this both on r/Assembly_Language and here. I think the topic involves both fairly strongly.

So, I am going to do a presentation involving buffer overflows and I learned some basic Assembly because of that (more specifically the function prologue). I plan on learning Assembly for real and have installed SASM, but for now I just know basic C. I need help reading something.

In one of my sources (https://www.tenouk.com/Bufferoverflowc/Bufferoverflow4.html), this guy does disass in his vulnerable function in order to show that sub has allocated more space than he declared (4 vs 20).

This is his code:

#include <unistd.h>

 

void Test()

{

   char buff[4];

   printf("Some input: ");

   gets(buff);

   puts(buff);

}

 

int main(int argc, char *argv[ ])

{

   Test();

   return 0;

}

And this is the output of disass Test:

0x080483d0 <Test+0>:    push   %ebp

0x080483d1 <Test+1>:    mov    %esp, %ebp

0x080483d3 <Test+3>:    sub    $0x8, %esp

0x080483d6 <Test+6>:    sub    $0xc, %esp

Buff is 4 bytes and 20 bytes are "freed" on the stack. But when I try to do the same with a relatively more complicated function (I hope commentary is enough for the language gap):

#include <stdio.h>
#include <string.h>
#include <locale.h>     
#include <stdlib.h>        

void senha(){      
 char senha[10];           
    char senhareal[10]="dddddd";      
    int teste = 0;    
    char resposta[3]; 
    
    printf("\n\n\n\n-----------------------------SISTEMA NUCLEAR DA OTAN------------------------------------ \n\n\n\n");     
    
    
    printf("DIGITE SUA SENHA: ");
    gets(senha);


    if(0 == strncmp(senha, senhareal, 20))
    {
         printf ("\nSenha correta! \n");
         teste = 1;    
    }
    
    
    else
    {
        printf ("\nSENHA INCORRETA! \n");
    }


    if(teste)
    {
        printf ("\nO usuário agora controla a instalação! Deseja destruir o Brasil? \n");     
        gets(resposta); 
    }
            }

int main(){               
    system("color 03");
	setlocale(LC_ALL, "Portuguese"); 
    senha();  

    return 0;
}

I get this:

0x0000555555555209 <+0>: endbr64
0x000055555555520d <+4>: push %rbp
0x000055555555520e <+5>: mov %rsp,%rbp
0x0000555555555211 <+8>: sub $0x30,%rsp
0x0000555555555215 <+12>: mov %fs:0x28,%rax
0x000055555555521e <+21>: mov %rax,-0x8(%rbp)

No matter my input. So why does Online GDB consistently subtract 48 bytes? What are the instructions following sub and do they apply at all to what I am trying to do? Is it possible to know what's going on in that specific platform? Finally, am I unable to replicate what this person did with my code?

I tested the code of my source in Online GDB as well. It consistently subtracts 16 bytes.