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#pragma once
// DirectoryEntry
// |31| | | | | | | | | | | | | | | | | | | |11| | 9| 8| 7| 6| 5| 4| 3| 2| 1| 0|
// | page table 4-kb aligned address | avail | G| S| | A| C| W| U| R| P|
struct __attribute__((packed)) DirectoryEntry {
unsigned present : 1; // 0: if set, the page is actually in physical memory
unsigned writeable : 1; // 1: if set, the page is read/write; otherwise the page is read-only
unsigned user : 1; // 2: if set, then page can be access by all; otherwise only the supervisor can access it
unsigned writethrough : 1; // 3: if set, write-through caching is enabled; otherwise write-back is enabled instead
unsigned cachedisable : 1; // 4: if set, the page will not be cached
unsigned accessed : 1; // 5: set by the CPU when the page is read from or written to
unsigned dirty : 1; // 6: used to determine whether a page has been written to
unsigned pagesize : 1; // 7: page size == 0
unsigned global : 1;
unsigned int __available__ : 3; // available to the OS
unsigned int address : 20;
};
_Static_assert(sizeof(struct DirectoryEntry) == 4, "DirectoryEntry size");
// DirectoryEntry4MB
// |31| | | | | | | | |22|21|20| | | | | | |13|12|11| | 9| 8| 7| 6| 5| 4| 3| 2| 1| 0|
// | bits 31-22 of address |RS| bits 39-22 of |AT| avail | G|PS| D| A|CD|WT|US|RW| P|
// | |VD| address
struct __attribute__((packed)) DirectoryEntry4MB {
unsigned present : 1; // 0: if set, the page is actually in physical memory
unsigned writeable : 1; // 1: if set, the page is read/write; otherwise the page is read-only
unsigned useraccess : 1; // 2: if set, then page can be access by all; otherwise only the supervisor can access it
unsigned writethrough : 1; // 3: if set, write-through caching is enabled; otherwise write-back is enabled instead
unsigned cachedisable : 1; // 4: if set, the page will not be cached
unsigned accessed : 1; // 5: set by the CPU when the page is read from or written to
unsigned dirty : 1; // 6: used to determine whether a page has been written to
unsigned pagesize : 1; // 7: page size == 1
unsigned global : 1; // 8:
unsigned __available__ : 3; // 11..9 available to the OS
unsigned pat : 1; // 12: page attribute table
unsigned int address_high : 8;
unsigned rsvd : 1; // 21
unsigned int address_low : 10;
};
_Static_assert(sizeof(struct DirectoryEntry4MB) == 4, "DirectoryEntry4M size");
// TableEntry
// |31| | | | | | | | | | | | | | | | | | | |11| | 9| 8| 7| 6| 5| 4| 3| 2| 1| 0|
// | page table 4-kb aligned address | avail | G| | D| A| C| W|US|RW| P|
struct __attribute__((packed)) TableEntry {
unsigned present : 1; // if set, the page is actually in physical memory
unsigned writeable : 1; // if set, the page is read/write; otherwise the page is read-only
unsigned user : 1; // if set, then page can be access by all; otherwise only the supervisor can access it
unsigned writethrough : 1; // if set, write-through caching is enabled; otherwise write-back is enabled instead
unsigned cachedisable : 1; // if set, the page will not be cached
unsigned accessed : 1; // set by the CPU when the page is read from or written to
unsigned dirty : 1; // used to determine whether a page has been written to
unsigned pat : 1; // page attribute table?
unsigned global : 1;
unsigned int __available__ : 3; // available to the OS
unsigned int address : 20;
};
_Static_assert(sizeof(struct TableEntry) == 4, "TableEntry size");
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