#include <stdio.h>

int main()
{
    unsigned short gs;
    unsigned x;

    asm ("mov %%gs, %0\n" : "=g"(gs));
    asm ("movl %%gs:0x30, %0\n" : "=r"(x));

    printf("gs: %x\n", gs);
    printf("gs:0x30: %x\n", x);

    asm volatile ("mov %0, %%gs\n" : : "g"(gs));

    asm volatile ("movl %%gs:0x30, %0\n" : "=r"(x));

    printf("gs:0x30: %x\n", x);

    return 0;
}