/*
* This file contains definitions for the x86 memory management unit (MMU),
* including paging- and segmentation-related data structures and constants,
* the %cr0, %cr4, and %eflags registers, and traps.
*/
/*
* Register flags and fundamental constants.
*/
#define PGSIZE 4096 // bytes mapped by a page
// Eflags register
#define FL_CF 0x00000001 // Carry Flag
#define FL_PF 0x00000004 // Parity Flag
#define FL_AF 0x00000010 // Auxiliary carry Flag
#define FL_ZF 0x00000040 // Zero Flag
#define FL_SF 0x00000080 // Sign Flag
#define FL_TF 0x00000100 // Trap Flag
#define FL_IF 0x00000200 // Interrupt Flag
#define FL_DF 0x00000400 // Direction Flag
#define FL_OF 0x00000800 // Overflow Flag
#define FL_IOPL_MASK 0x00003000 // I/O Privilege Level bitmask
#define FL_IOPL_0 0x00000000 // IOPL == 0
#define FL_IOPL_1 0x00001000 // IOPL == 1
#define FL_IOPL_2 0x00002000 // IOPL == 2
#define FL_IOPL_3 0x00003000 // IOPL == 3
#define FL_NT 0x00004000 // Nested Task
#define FL_RF 0x00010000 // Resume Flag
#define FL_VM 0x00020000 // Virtual 8086 mode
#define FL_AC 0x00040000 // Alignment Check
#define FL_VIF 0x00080000 // Virtual Interrupt Flag
#define FL_VIP 0x00100000 // Virtual Interrupt Pending
#define FL_ID 0x00200000 // ID flag
// Page fault error codes
#define FEC_PR 0x1 // Page fault caused by protection violation
#define FEC_WR 0x2 // Page fault caused by a write
#define FEC_U 0x4 // Page fault occured while in user mode
/*
*
* Segmentation data structures and constants.
*
*/
#ifdef __ASSEMBLER__
/*
* Macros to build GDT entries in assembly.
*/
#define SEG_NULL \
.word 0, 0; \
.byte 0, 0, 0, 0
#define SEG(type,base,lim) \
.word (((lim) >> 12) & 0xffff), ((base) & 0xffff); \
.byte (((base) >> 16) & 0xff), (0x90 | (type)), \
(0xC0 | (((lim) >> 28) & 0xf)), (((base) >> 24) & 0xff)
#else // not __ASSEMBLER__
// Segment Descriptors
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
};
// Null segment
#define SEG_NULL (struct segdesc){ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }
// Segment that is loadable but faults when used
#define SEG_FAULT (struct segdesc){ 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0 }
// Normal segment
#define SEG(type, base, lim, dpl) (struct segdesc) \
{ ((lim) >> 12) & 0xffff, (base) & 0xffff, ((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, (base) & 0xffff, ((base) >> 16) & 0xff, \
type, 1, dpl, 1, (uint) (lim) >> 16, 0, 0, 1, 0, \
(uint) (base) >> 24 }
#endif /* !__ASSEMBLER__ */
// Application segment type bits
#define STA_X 0x8 // Executable segment
#define STA_E 0x4 // Expand down (non-executable segments)
#define STA_C 0x4 // Conforming code segment (executable only)
#define STA_W 0x2 // Writeable (non-executable segments)
#define STA_R 0x2 // Readable (executable segments)
#define STA_A 0x1 // Accessed
// System segment type bits
#define STS_T16A 0x1 // Available 16-bit TSS
#define STS_LDT 0x2 // Local Descriptor Table
#define STS_T16B 0x3 // Busy 16-bit TSS
#define STS_CG16 0x4 // 16-bit Call Gate
#define STS_TG 0x5 // Task Gate / Coum Transmitions
#define STS_IG16 0x6 // 16-bit Interrupt Gate
#define STS_TG16 0x7 // 16-bit Trap Gate
#define STS_T32A 0x9 // Available 32-bit TSS
#define STS_T32B 0xB // Busy 32-bit TSS
#define STS_CG32 0xC // 32-bit Call Gate
#define STS_IG32 0xE // 32-bit Interrupt Gate
#define STS_TG32 0xF // 32-bit Trap Gate
/*
*
* Traps.
*
*/
#ifndef __ASSEMBLER__
// Task state segment format (as described by the Pentium architecture book)
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 ss : 16; // 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_{TG,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).ss = (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; \
}
// Set up a call gate descriptor.
#define SETCALLGATE(gate, ss, off, d) \
{ \
(gate).off_15_0 = (uint) (off) & 0xffff; \
(gate).ss = (ss); \
(gate).args = 0; \
(gate).rsv1 = 0; \
(gate).type = STS_CG32; \
(gate).s = 0; \
(gate).dpl = (d); \
(gate).p = 1; \
(gate).off_31_16 = (uint) (off) >> 16; \
}
#endif /* !__ASSEMBLER__ */