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void map_page(void *physaddr, void *virtualaddr, unsigned int flags) {
    // Make sure that both addresses are page-aligned.
 
    unsigned long pdindex = (unsigned long)virtualaddr >> 22;
    unsigned long ptindex = (unsigned long)virtualaddr >> 12 & 0x03FF;
 
    unsigned long *pd = (unsigned long *)0xFFFFF000;
    // Here you need to check whether the PD entry is present.
    // When it is not present, you need to create a new empty PT and
    // adjust the PDE accordingly.
 
    unsigned long *pt = ((unsigned long *)0xFFC00000) + (0x400 * pdindex);
    // Here you need to check whether the PT entry is present.
    // When it is, then there is already a mapping present. What do you do now?
 
    pt[ptindex] = ((unsigned long)physaddr) | (flags & 0xFFF) | 0x01; // Present
 
    // Now you need to flush the entry in the TLB
    // or you might not notice the change.
}