int _start() {
    volatile char x;
    asm volatile (
        "movl $3, %%eax\n"
        "movl $0, %%ebx\n"
        "movl %%esp, %%ecx\n"
        "movl $1, %%edx\n"
        "int  $0x80\n"
        :
        :"g" (&x), "g" (sizeof(x))
        :"esp", "eax", "ebx", "ecx", "edx");
    while (x != 0) {
        if (x - 'a' < 'z') {
            x = x - 'a' + 'A';
        }
        asm volatile (
            "movl 4, %%eax\n"
            "movl $1, %%ebx\n"
            "movl %%esp, %%ecx\n"
            "movl $1, %%edx\n"
            "int  $0x80\n"
            :
            :"g" (&x), "g" (sizeof(x))
            :"esp", "eax", "ebx", "ecx", "edx");
        asm volatile (
            "movl $3, %%eax\n"
            "movl $0, %%ebx\n"
            "movl %%esp, %%ecx\n"
            "movl $1, %%edx\n"
            "int  $0x80\n"
            :
            :"g" (&x), "g" (sizeof(x))
            :"esp","eax", "ebx", "ecx", "edx");
    }
    asm volatile (
        "movl $1, %%eax\n"
        "xorl %%ebx, %%ebx\n"
        "int  $0x80\n"
        :
        :
        :"eax", "ebx");
}