How does gdb disable randomization for a single process?

Question

I came from this link: Force gdb to load shared library at randomized address and I learned that gdb will disable ASLR for the current process.

But the only way I know to disable ASLR is to do it globally via echo 0 > /proc/sys/kernel/randomize_va_space.

Now I'm wondering how does gdb disable ASLR on startup, and only for the current process?

EDIT

As ssbssa suggested, I wrote a program to test it:

#include <stdio.h>
#include <unistd.h>
#include <sys/personality.h>

int main(int argc, char **argv)
{
    char *argv2[] = { argv[0], "test", "\0" };

    if (argc == 1)
    {
        char *data = malloc(20);
        printf("pid %d\n", getpid());
        printf("heap allocated at %p\n", data);
        printf("system() at %p\n", system);
        puts("exit in 100s");
        sleep(100);
        exit(0);
    }

    personality(ADDR_NO_RANDOMIZE);
    execvp(argv2[0], argv2);
}

And the process map is:

# cat /proc/1997932/maps
00400000-00401000 r--p 00000000 fc:01 430424                             /root/no-aslr
00401000-00402000 r-xp 00001000 fc:01 430424                             /root/no-aslr
00402000-00403000 r--p 00002000 fc:01 430424                             /root/no-aslr
00403000-00404000 r--p 00002000 fc:01 430424                             /root/no-aslr
00404000-00405000 rw-p 00003000 fc:01 430424                             /root/no-aslr
01352000-01373000 rw-p 00000000 00:00 0                                  [heap]
7f222f928000-7f222f94a000 r--p 00000000 fc:01 394264                     /usr/lib/x86_64-linux-gnu/libc-2.31.so
7f222f94a000-7f222fac2000 r-xp 00022000 fc:01 394264                     /usr/lib/x86_64-linux-gnu/libc-2.31.so
7f222fac2000-7f222fb10000 r--p 0019a000 fc:01 394264                     /usr/lib/x86_64-linux-gnu/libc-2.31.so
7f222fb10000-7f222fb14000 r--p 001e7000 fc:01 394264                     /usr/lib/x86_64-linux-gnu/libc-2.31.so
7f222fb14000-7f222fb16000 rw-p 001eb000 fc:01 394264                     /usr/lib/x86_64-linux-gnu/libc-2.31.so