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3.3. BASIC CONCEPTS CHAPTER 3. VM, PROTECTION AND PAGING
of the use_4_m_pages bit. Sweb defines an union between the two structs so both
interpretations can be used conveniently. The bits are further explained in table 3.3.3.
1 #include " types .h"
2
3 #define PAGE_TABLE_ENTRIES 1024
4 #define PAGE_SIZE 4096
5 #define PAGE_INDEX_OFFSET_BITS 12
6
7 struct page_directory_entry_4k_struct
8 {
9 uint32 present : 1 ;
10 uint32 writeable : 1 ;
11 uint32 user_access : 1 ;
12 uint32 write_through : 1 ;
13 uint32 cache_disabled : 1 ;
14 uint32 accessed : 1 ;
15 uint32 reserved : 1 ;
16 uint32 use_4_m_pages : 1 ;
17 uint32 global_page : 1 ;
18 uint32 avail_1 : 1 ;
19 uint32 avail_2 : 1 ;
20 uint32 avail_3 : 1 ;
21 uint32 page_table_base_address :20;
22 } __attribute__ ( ( __packed__ ) ) ;
23
24 struct page_directory_entry_4m_struct
25 {
26 uint32 present : 1 ;
27 uint32 writeable : 1 ;
28 uint32 user_access : 1 ;
29 uint32 write_through : 1 ;
30 uint32 cache_disabled : 1 ;
31 uint32 accessed : 1 ;
32 uint32 dirty : 1 ;
33 uint32 use_4_m_pages : 1 ;
34 uint32 global_page : 1 ;
35 uint32 avail_1 : 1 ;
36 uint32 avail_2 : 1 ;
37 uint32 avail_3 : 1 ;
38 uint32 pat : 1 ;
39 uint32 reserved : 9 ;
40 uint32 page_base_address :10;
41 } __attribute__ ( ( __packed__ ) ) ;
42
43 union page_directory_entry_union
44 {
45 struct page_directory_entry_4k_struct pde4k ;
46 struct page_directory_entry_4m_struct pde4m;
47 } __attribute__ ( ( __packed__ ) ) ;
48 typedef union page_directory_entry_union page_directory_entry ;
49
50 struct page_table_entry_struct
51 {
52 uint32 present : 1 ;
53 uint32 writeable : 1 ;
54 uint32 user_access : 1 ;
55 uint32 write_through : 1 ;
56 uint32 cache_disabled : 1 ;
57 uint32 accessed : 1 ;
58 uint32 dirty : 1 ;
59 uint32 pat : 1 ;
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