1. 根目录:
2. arch
3. x86
4. include
5. asm
6. desc_defs.h

/* Written 2000 by Andi Kleen */
#ifndef _ASM_X86_DESC_DEFS_H
#define _ASM_X86_DESC_DEFS_H

/*
 * Segment descriptor structure definitions, usable from both x86_64 and i386
 * archs.
 */

#ifndef __ASSEMBLY__

#include <linux/types.h>

/*
 * FIXME: Accessing the desc_struct through its fields is more elegant,
 * and should be the one valid thing to do. However, a lot of open code
 * still touches the a and b accessors, and doing this allow us to do it
 * incrementally. We keep the signature as a struct, rather than an union,
 * so we can get rid of it transparently in the future -- glommer
 */
/* 8 byte segment descriptor */
struct desc_struct {
	union {
		struct {
			unsigned int a;
			unsigned int b;
		};
		struct {
			u16 limit0;
			u16 base0;
			unsigned base1: 8, type: 4, s: 1, dpl: 2, p: 1;
			unsigned limit: 4, avl: 1, l: 1, d: 1, g: 1, base2: 8;
		};
	};
} __attribute__((packed));

#define GDT_ENTRY_INIT(flags, base, limit) { { { \
		.a = ((limit) & 0xffff) | (((base) & 0xffff) << 16), \
		.b = (((base) & 0xff0000) >> 16) | (((flags) & 0xf0ff) << 8) | \
			((limit) & 0xf0000) | ((base) & 0xff000000), \
	} } }

enum {
	GATE_INTERRUPT = 0xE,
	GATE_TRAP = 0xF,
	GATE_CALL = 0xC,
	GATE_TASK = 0x5,
};

/* 16byte gate */
struct gate_struct64 {
	u16 offset_low;
	u16 segment;
	unsigned ist : 3, zero0 : 5, type : 5, dpl : 2, p : 1;
	u16 offset_middle;
	u32 offset_high;
	u32 zero1;
} __attribute__((packed));

#define PTR_LOW(x) ((unsigned long long)(x) & 0xFFFF)
#define PTR_MIDDLE(x) (((unsigned long long)(x) >> 16) & 0xFFFF)
#define PTR_HIGH(x) ((unsigned long long)(x) >> 32)

enum {
	DESC_TSS = 0x9,
	DESC_LDT = 0x2,
	DESCTYPE_S = 0x10,	/* !system */
};

/* LDT or TSS descriptor in the GDT. 16 bytes. */
struct ldttss_desc64 {
	u16 limit0;
	u16 base0;
	unsigned base1 : 8, type : 5, dpl : 2, p : 1;
	unsigned limit1 : 4, zero0 : 3, g : 1, base2 : 8;
	u32 base3;
	u32 zero1;
} __attribute__((packed));

#ifdef CONFIG_X86_64
typedef struct gate_struct64 gate_desc;
typedef struct ldttss_desc64 ldt_desc;
typedef struct ldttss_desc64 tss_desc;
#define gate_offset(g) ((g).offset_low | ((unsigned long)(g).offset_middle << 16) | ((unsigned long)(g).offset_high << 32))
#define gate_segment(g) ((g).segment)
#else
typedef struct desc_struct gate_desc;
typedef struct desc_struct ldt_desc;
typedef struct desc_struct tss_desc;
#define gate_offset(g)		(((g).b & 0xffff0000) | ((g).a & 0x0000ffff))
#define gate_segment(g)		((g).a >> 16)
#endif

struct desc_ptr {
	unsigned short size;
	unsigned long address;
} __attribute__((packed)) ;

#endif /* !__ASSEMBLY__ */

#endif /* _ASM_X86_DESC_DEFS_H */