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Some code cleanup in paging.cpp. Add separate struct definition for PDE vs PTE. Add notes regarding D (Dirty) bit in PDEs on Pentium and higher CPUs. It seems while 386/486 defined a D bit for PTE and PDE, the Pentium gave up on the D bit for PDE, though for PSE 4MB pages the PDE still has a D bit.

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Jonathan Campbell
2024-12-15 09:38:06 -08:00
parent 38151d33be
commit cd46a30edf
2 changed files with 64 additions and 20 deletions
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71
include/paging.h
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@@ -223,23 +223,24 @@ void MEM_SetPageHandler(Bitu phys_page, Bitu pages, PageHandler * handler);
#ifdef _MSC_VER
#pragma pack (1)
#endif
struct X86_PageEntryBlock{ // TODO: This is not exactly a page table entry, this is a mismash of both page table and page directory entry
struct X86_PageEntryBlock{ // Page Table Entry, though it keeps the PageEntryBlock name to avoid breaking all this code
#ifdef WORDS_BIGENDIAN
uint32_t base:20; // [31:12] PTE+PDE
uint32_t avl:3; // [11: 9] PTE=[11:9] PDE=[11:8]
uint32_t g:1; // [ 8: 8] PDE
uint32_t pat:1; // [ 7: 7] PTE PDE=PS(PageSize)
uint32_t d:1; // [ 6: 6] PTE PDE=AVL
uint32_t a:1; // [ 5: 5] PTE+PDE
uint32_t pcd:1; // [ 4: 4] PTE+PDE
uint32_t pwt:1; // [ 3: 3] PTE+PDE
uint32_t us:1; // [ 2: 2] PTE+PDE
uint32_t wr:1; // [ 1: 1] PTE+PDE
uint32_t p:1; // [ 0: 0] PTE+PDE
uint32_t base:20; // [31:12]
uint32_t avl:3; // [11: 8]
uint32_t g:1; // [ 8: 8]
uint32_t pat:1; // [ 7: 7]
uint32_t d:1; // [ 6: 6]
uint32_t a:1; // [ 5: 5]
uint32_t pcd:1; // [ 4: 4]
uint32_t pwt:1; // [ 3: 3]
uint32_t us:1; // [ 2: 2]
uint32_t wr:1; // [ 1: 1]
uint32_t p:1; // [ 0: 0]
#else
uint32_t p:1; // [ 0: 0]
uint32_t wr:1; // [ 1: 1]
uint32_t us:1; // [ 2: 2]
uint32_t wr:1; // [ 1: 1] R/W
uint32_t us:1; // [ 2: 2] U/S
uint32_t pwt:1; // [ 3: 3]
uint32_t pcd:1; // [ 4: 4]
uint32_t a:1; // [ 5: 5]
@@ -250,6 +251,47 @@ struct X86_PageEntryBlock{ // TODO: This is not exactly a page table entry, this
uint32_t base:20; // [31:12]
#endif
} GCC_ATTRIBUTE(packed);
struct X86_PageDirEntryBlock{
#ifdef WORDS_BIGENDIAN
uint32_t base:20; // [31:12]
uint32_t avl:3; // [11: 9]
uint32_t g:1; // [ 8: 8]
uint32_t ps:1; // [ 7: 7]
uint32_t avl6:1; // [ 6: 6]
uint32_t a:1; // [ 5: 5]
uint32_t pcd:1; // [ 4: 4]
uint32_t pwt:1; // [ 3: 3]
uint32_t us:1; // [ 2: 2]
uint32_t wr:1; // [ 1: 1]
uint32_t p:1; // [ 0: 0]
#else
uint32_t p:1; // [ 0: 0]
uint32_t wr:1; // [ 1: 1] R/W
uint32_t us:1; // [ 2: 2] U/S
uint32_t pwt:1; // [ 3: 3]
uint32_t pcd:1; // [ 4: 4]
uint32_t a:1; // [ 5: 5]
uint32_t avl6:1; // [ 6: 6] See Note [*1], this bit changed meaning between the 486 and Pentium!
uint32_t ps:1; // [ 7: 7] Page Size Extension (Pentium), even though Intel didn't document it until later
uint32_t g:1; // [ 8: 8]
uint32_t avl:3; // [11: 9]
uint32_t base:20; // [31:12]
#endif
} GCC_ATTRIBUTE(packed);
/* Note [*1]: The i386 defined just the Page Table Entry to represent the PDE and PTE, because they had the same layout.
*
* The i486 lists the PDE and PTE, even though they have the same bit layout.
*
* The Pentium however, seems to have decided that bit 6 of the PDE is no longer the "dirty" bit and is redefined as AVL.
* Although, if PSE is enabled and the PDE is the 4MB format, bit 6 is once again a "dirty" but.
*
* FIXME: This codebase still always sets the D bit for PDE regardless of CPU type.
*
* Ref: [http://hackipedia.org/browse.cgi/Computer/Platform/PC%2c%20IBM%20compatible/CPU/80386/Intel/386DX%20Microprocessor%20Programmer%27s%20Reference%20Manual%20%281990%29%2epdf]
* Ref: [http://hackipedia.org/browse.cgi/Computer/Platform/PC%2c%20IBM%20compatible/CPU/80486/Intel/i486%20Microprocessor%20%281989%2d04%29%2epdf]
* Ref: [http://hackipedia.org/browse.cgi/Computer/Platform/PC%2c%20IBM%20compatible/CPU/Pentium/Pentium%20Processor%20Family%20Developer%27s%20Manual%20%2d%20Volume%203%3a%20Architecture%20and%20Programming%20Manual%20%281995%2d07%29%2epdf] */
#ifdef _MSC_VER
#pragma pack ()
#endif
@@ -258,6 +300,7 @@ struct X86_PageEntryBlock{ // TODO: This is not exactly a page table entry, this
union X86PageEntry {
uint32_t load;
X86_PageEntryBlock block;
X86_PageDirEntryBlock dirblock;
};
#if !defined(USE_FULL_TLB)