private TlbEntry WalkPageTables(uint address)
{
TlbEntry entry = default;
var pageDirectoryIndex = address >> 22;
var pageTableIndex = (address >> 12) & 1023;
var pageDirectoryEntry = GetLongPhysical(_pageDirectory + pageDirectoryIndex * 4);
if ((pageDirectoryEntry & PageTableFlags.Present) == 0)
{
throw new MemoryAccessException(MemoryAccessStatus.PageDirectoryEntryNotPresent);
}
// TODO use correct mask for pageDirectoryEntry
var pageTableEntry = GetLongPhysical((pageDirectoryEntry & 0xFFFFFC00) + pageTableIndex * 4);
if ((pageTableEntry & PageTableFlags.Present) == 0)
{
throw new MemoryAccessException(MemoryAccessStatus.PageNotPresent);
}
var pageTableEntryAddress = pageTableEntry & 0xFFFFFC00;
if (pageTableEntryAddress >= Size)
{
throw new MemoryAccessException(MemoryAccessStatus.PhysicalAddressOutOfRange);
}
entry.entry = pageTableEntry;
entry.tag = address >> 12;
_tlb[TlbEntry.IndexFromTag(entry.tag)] = entry;
return(entry);
}
private unsafe byte *GetMemoryAtVirtual(uint address, bool write)
{
var tag = TlbEntry.TagFromAddress(address);
var index = TlbEntry.IndexFromTag(tag);
var offset = TlbEntry.OffsetFromAddress(address);
var tlbEntry = _tlb[index];
if (tlbEntry.tag != tag)
{
tlbEntry = WalkPageTables(address);
}
if (write && !tlbEntry.Rw())
{
ThrowPageReadOnlyException();
}
return(NotCheckedGetMemoryAtPhysical(tlbEntry.PagePhysicalAddress() + offset));
}
