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mmu.h
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mmu.h
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// Definitions for the x86 memory management unit (MMU).
// Eflags register
#define FL_IF 0x00000200 // Interrupt Enable
// Control Register flags
#define CR0_PE 0x00000001 // Protection Enable
#define CR0_WP 0x00010000 // Write Protect
#define CR0_PG 0x80000000 // Paging
#define CR4_PSE 0x00000010 // Page size extension
// various segment selectors.
#define SEG_KCODE 1 // kernel code
#define SEG_KDATA 2 // kernel data+stack
#define SEG_UCODE 3 // user code
#define SEG_UDATA 4 // user data+stack
#define SEG_TSS 5 // this process's task state
// cpu->gdt[NSEGS] holds the above segments.
#define NSEGS 6
#ifndef __ASSEMBLER__
// Segment Descriptor
struct segdesc {
uint lim_15_0 : 16; // Low bits of segment limit
uint base_15_0 : 16; // Low bits of segment base address
uint base_23_16 : 8; // Middle bits of segment base address
uint type : 4; // Segment type (see STS_ constants)
uint s : 1; // 0 = system, 1 = application
uint dpl : 2; // Descriptor Privilege Level
uint p : 1; // Present
uint lim_19_16 : 4; // High bits of segment limit
uint avl : 1; // Unused (available for software use)
uint rsv1 : 1; // Reserved
uint db : 1; // 0 = 16-bit segment, 1 = 32-bit segment
uint g : 1; // Granularity: limit scaled by 4K when set
uint base_31_24 : 8; // High bits of segment base address
};
// Normal segment
#define SEG(type, base, lim, dpl) (struct segdesc) \
{ ((lim) >> 12) & 0xffff, (uint)(base) & 0xffff, \
((uint)(base) >> 16) & 0xff, type, 1, dpl, 1, \
(uint)(lim) >> 28, 0, 0, 1, 1, (uint)(base) >> 24 }
#define SEG16(type, base, lim, dpl) (struct segdesc) \
{ (lim) & 0xffff, (uint)(base) & 0xffff, \
((uint)(base) >> 16) & 0xff, type, 1, dpl, 1, \
(uint)(lim) >> 16, 0, 0, 1, 0, (uint)(base) >> 24 }
#endif
#define DPL_USER 0x3 // User DPL
// Application segment type bits
#define STA_X 0x8 // Executable segment
#define STA_W 0x2 // Writeable (non-executable segments)
#define STA_R 0x2 // Readable (executable segments)
// System segment type bits
#define STS_T32A 0x9 // Available 32-bit TSS
#define STS_IG32 0xE // 32-bit Interrupt Gate
#define STS_TG32 0xF // 32-bit Trap Gate
// A virtual address 'la' has a three-part structure as follows:
//
// +--------10------+-------10-------+---------12----------+
// | Page Directory | Page Table | Offset within Page |
// | Index | Index | |
// +----------------+----------------+---------------------+
// \--- PDX(va) --/ \--- PTX(va) --/
// page directory index
#define PDX(va) (((uint)(va) >> PDXSHIFT) & 0x3FF)
// page table index
#define PTX(va) (((uint)(va) >> PTXSHIFT) & 0x3FF)
// construct virtual address from indexes and offset
#define PGADDR(d, t, o) ((uint)((d) << PDXSHIFT | (t) << PTXSHIFT | (o)))
// Page directory and page table constants.
#define NPDENTRIES 1024 // # directory entries per page directory
#define NPTENTRIES 1024 // # PTEs per page table
#define PGSIZE 4096 // bytes mapped by a page
#define PTXSHIFT 12 // offset of PTX in a linear address
#define PDXSHIFT 22 // offset of PDX in a linear address
#define PGROUNDUP(sz) (((sz)+PGSIZE-1) & ~(PGSIZE-1))
#define PGROUNDDOWN(a) (((a)) & ~(PGSIZE-1))
// Page table/directory entry flags.
#define PTE_P 0x001 // Present
#define PTE_W 0x002 // Writeable
#define PTE_U 0x004 // User
#define PTE_PS 0x080 // Page Size
// Address in page table or page directory entry
#define PTE_ADDR(pte) ((uint)(pte) & ~0xFFF)
#define PTE_FLAGS(pte) ((uint)(pte) & 0xFFF)
#ifndef __ASSEMBLER__
// Task state segment format
struct taskstate {
uint link; // Old ts selector
uint esp0; // Stack pointers and segment selectors
ushort ss0; // after an increase in privilege level
ushort padding1;
uint *esp1;
ushort ss1;
ushort padding2;
uint *esp2;
ushort ss2;
ushort padding3;
void *cr3; // Page directory base
uint *eip; // Saved state from last task switch
uint eflags;
uint eax; // More saved state (registers)
uint ecx;
uint edx;
uint ebx;
uint *esp;
uint *ebp;
uint esi;
uint edi;
ushort es; // Even more saved state (segment selectors)
ushort padding4;
ushort cs;
ushort padding5;
ushort ss;
ushort padding6;
ushort ds;
ushort padding7;
ushort fs;
ushort padding8;
ushort gs;
ushort padding9;
ushort ldt;
ushort padding10;
ushort t; // Trap on task switch
ushort iomb; // I/O map base address
};
// Gate descriptors for interrupts and traps
struct gatedesc {
uint off_15_0 : 16; // low 16 bits of offset in segment
uint cs : 16; // code segment selector
uint args : 5; // # args, 0 for interrupt/trap gates
uint rsv1 : 3; // reserved(should be zero I guess)
uint type : 4; // type(STS_{IG32,TG32})
uint s : 1; // must be 0 (system)
uint dpl : 2; // descriptor(meaning new) privilege level
uint p : 1; // Present
uint off_31_16 : 16; // high bits of offset in segment
};
// Set up a normal interrupt/trap gate descriptor.
// - istrap: 1 for a trap (= exception) gate, 0 for an interrupt gate.
// interrupt gate clears FL_IF, trap gate leaves FL_IF alone
// - sel: Code segment selector for interrupt/trap handler
// - off: Offset in code segment for interrupt/trap handler
// - dpl: Descriptor Privilege Level -
// the privilege level required for software to invoke
// this interrupt/trap gate explicitly using an int instruction.
#define SETGATE(gate, istrap, sel, off, d) \
{ \
(gate).off_15_0 = (uint)(off) & 0xffff; \
(gate).cs = (sel); \
(gate).args = 0; \
(gate).rsv1 = 0; \
(gate).type = (istrap) ? STS_TG32 : STS_IG32; \
(gate).s = 0; \
(gate).dpl = (d); \
(gate).p = 1; \
(gate).off_31_16 = (uint)(off) >> 16; \
}
#endif