int char_get() {
    int res;
    volatile char c;
    asm volatile(
        "movl   %1, %%eax\n"
        "movl   %3, %%ebx\n"
        "movl   %2, %%ecx\n"
        "movl   %4, %%edx\n"
        "int $0x80"
        "movl %%eax, %0"
        : "=g"(res)
        : "g"(__NR_read),
        "g"(&c),
        "g"(0),
        "g"(1)
        : "eax", "ebx", "ecx", "edx", "memory"
    );
    if (res <= 0) {
        return -1;
    }
    if (c >= 'a' && c <= 'z') {
        c = 'A' + c - 'a';
    }
    asm volatile(
        "movl   %0, %%eax\n"
        "movl   %2, %%ebx\n"
        "movzb  %1, %%ecx\n"
        "movl   %3, %%edx\n"
        "int $0x80"
        "movl %%eax, %0"
        : : "g"(__NR_write),
        "g"(c),
        "g"(1),
        "g"(1)
        : "eax", "ebx", "ecx", "edx", "memory"
    );
    return 1;
}