arch/x86/include/asm/segment.h - arm/linux - Git at Google

 #ifndef _ASM_X86_SEGMENT_H
 #define _ASM_X86_SEGMENT_H

 #include <linux/const.h>
 #include <asm/alternative.h>

 /*
  * Constructor for a conventional segment GDT (or LDT) entry.
  * This is a macro so it can be used in initializers.
  */
 #define GDT_ENTRY(flags, base, limit)			\
 	((((base)  & _AC(0xff000000,ULL)) << (56-24)) |	\
 	 (((flags) & _AC(0x0000f0ff,ULL)) << 40) |	\
 	 (((limit) & _AC(0x000f0000,ULL)) << (48-16)) |	\
 	 (((base)  & _AC(0x00ffffff,ULL)) << 16) |	\
 	 (((limit) & _AC(0x0000ffff,ULL))))

 /* Simple and small GDT entries for booting only: */

 #define GDT_ENTRY_BOOT_CS	2
 #define GDT_ENTRY_BOOT_DS	3
 #define GDT_ENTRY_BOOT_TSS	4
 #define __BOOT_CS		(GDT_ENTRY_BOOT_CS*8)
 #define __BOOT_DS		(GDT_ENTRY_BOOT_DS*8)
 #define __BOOT_TSS		(GDT_ENTRY_BOOT_TSS*8)

 /*
  * Bottom two bits of selector give the ring
  * privilege level
  */
 #define SEGMENT_RPL_MASK	0x3

 /* User mode is privilege level 3: */
 #define USER_RPL		0x3

 /* Bit 2 is Table Indicator (TI): selects between LDT or GDT */
 #define SEGMENT_TI_MASK		0x4
 /* LDT segment has TI set ... */
 #define SEGMENT_LDT		0x4
 /* ... GDT has it cleared */
 #define SEGMENT_GDT		0x0

 #define GDT_ENTRY_INVALID_SEG	0

 #ifdef CONFIG_X86_32
 /*
  * The layout of the per-CPU GDT under Linux:
  *
  *   0 - null								<=== cacheline #1
  *   1 - reserved
  *   2 - reserved
  *   3 - reserved
  *
  *   4 - unused								<=== cacheline #2
  *   5 - unused
  *
  *  ------- start of TLS (Thread-Local Storage) segments:
  *
  *   6 - TLS segment #1			[ glibc's TLS segment ]
  *   7 - TLS segment #2			[ Wine's %fs Win32 segment ]
  *   8 - TLS segment #3							<=== cacheline #3
  *   9 - reserved
  *  10 - reserved
  *  11 - reserved
  *
  *  ------- start of kernel segments:
  *
  *  12 - kernel code segment						<=== cacheline #4
  *  13 - kernel data segment
  *  14 - default user CS
  *  15 - default user DS
  *  16 - TSS								<=== cacheline #5
  *  17 - LDT
  *  18 - PNPBIOS support (16->32 gate)
  *  19 - PNPBIOS support
  *  20 - PNPBIOS support						<=== cacheline #6
  *  21 - PNPBIOS support
  *  22 - PNPBIOS support
  *  23 - APM BIOS support
  *  24 - APM BIOS support						<=== cacheline #7
  *  25 - APM BIOS support
  *
  *  26 - ESPFIX small SS
  *  27 - per-cpu			[ offset to per-cpu data area ]
  *  28 - stack_canary-20		[ for stack protector ]		<=== cacheline #8
  *  29 - unused
  *  30 - unused
  *  31 - TSS for double fault handler
  */
 #define GDT_ENTRY_TLS_MIN		6
 #define GDT_ENTRY_TLS_MAX 		(GDT_ENTRY_TLS_MIN + GDT_ENTRY_TLS_ENTRIES - 1)

 #define GDT_ENTRY_KERNEL_CS		12
 #define GDT_ENTRY_KERNEL_DS		13
 #define GDT_ENTRY_DEFAULT_USER_CS	14
 #define GDT_ENTRY_DEFAULT_USER_DS	15
 #define GDT_ENTRY_TSS			16
 #define GDT_ENTRY_LDT			17
 #define GDT_ENTRY_PNPBIOS_CS32		18
 #define GDT_ENTRY_PNPBIOS_CS16		19
 #define GDT_ENTRY_PNPBIOS_DS		20
 #define GDT_ENTRY_PNPBIOS_TS1		21
 #define GDT_ENTRY_PNPBIOS_TS2		22
 #define GDT_ENTRY_APMBIOS_BASE		23

 #define GDT_ENTRY_ESPFIX_SS		26
 #define GDT_ENTRY_PERCPU		27
 #define GDT_ENTRY_STACK_CANARY		28

 #define GDT_ENTRY_DOUBLEFAULT_TSS	31

 /*
  * Number of entries in the GDT table:
  */
 #define GDT_ENTRIES			32

 /*
  * Segment selector values corresponding to the above entries:
  */

 #define __KERNEL_CS			(GDT_ENTRY_KERNEL_CS*8)
 #define __KERNEL_DS			(GDT_ENTRY_KERNEL_DS*8)
 #define __USER_DS			(GDT_ENTRY_DEFAULT_USER_DS*8 + 3)
 #define __USER_CS			(GDT_ENTRY_DEFAULT_USER_CS*8 + 3)
 #define __ESPFIX_SS			(GDT_ENTRY_ESPFIX_SS*8)

 /* segment for calling fn: */
 #define PNP_CS32			(GDT_ENTRY_PNPBIOS_CS32*8)
 /* code segment for BIOS: */
 #define PNP_CS16			(GDT_ENTRY_PNPBIOS_CS16*8)

 /* "Is this PNP code selector (PNP_CS32 or PNP_CS16)?" */
 #define SEGMENT_IS_PNP_CODE(x)		(((x) & 0xf4) == PNP_CS32)

 /* data segment for BIOS: */
 #define PNP_DS				(GDT_ENTRY_PNPBIOS_DS*8)
 /* transfer data segment: */
 #define PNP_TS1				(GDT_ENTRY_PNPBIOS_TS1*8)
 /* another data segment: */
 #define PNP_TS2				(GDT_ENTRY_PNPBIOS_TS2*8)

 #ifdef CONFIG_SMP
 # define __KERNEL_PERCPU		(GDT_ENTRY_PERCPU*8)
 #else
 # define __KERNEL_PERCPU		0
 #endif

 #ifdef CONFIG_CC_STACKPROTECTOR
 # define __KERNEL_STACK_CANARY		(GDT_ENTRY_STACK_CANARY*8)
 #else
 # define __KERNEL_STACK_CANARY		0
 #endif

 #else /* 64-bit: */

 #include <asm/cache.h>

 #define GDT_ENTRY_KERNEL32_CS		1
 #define GDT_ENTRY_KERNEL_CS		2
 #define GDT_ENTRY_KERNEL_DS		3

 /*
  * We cannot use the same code segment descriptor for user and kernel mode,
  * not even in long flat mode, because of different DPL.
  *
  * GDT layout to get 64-bit SYSCALL/SYSRET support right. SYSRET hardcodes
  * selectors:
  *
  *   if returning to 32-bit userspace: cs = STAR.SYSRET_CS,
  *   if returning to 64-bit userspace: cs = STAR.SYSRET_CS+16,
  *
  * ss = STAR.SYSRET_CS+8 (in either case)
  *
  * thus USER_DS should be between 32-bit and 64-bit code selectors:
  */
 #define GDT_ENTRY_DEFAULT_USER32_CS	4
 #define GDT_ENTRY_DEFAULT_USER_DS	5
 #define GDT_ENTRY_DEFAULT_USER_CS	6

 /* Needs two entries */
 #define GDT_ENTRY_TSS			8
 /* Needs two entries */
 #define GDT_ENTRY_LDT			10

 #define GDT_ENTRY_TLS_MIN		12
 #define GDT_ENTRY_TLS_MAX		14

 /* Abused to load per CPU data from limit */
 #define GDT_ENTRY_PER_CPU		15

 /*
  * Number of entries in the GDT table:
  */
 #define GDT_ENTRIES			16

 /*
  * Segment selector values corresponding to the above entries:
  *
  * Note, selectors also need to have a correct RPL,
  * expressed with the +3 value for user-space selectors:
  */
 #define __KERNEL32_CS			(GDT_ENTRY_KERNEL32_CS*8)
 #define __KERNEL_CS			(GDT_ENTRY_KERNEL_CS*8)
 #define __KERNEL_DS			(GDT_ENTRY_KERNEL_DS*8)
 #define __USER32_CS			(GDT_ENTRY_DEFAULT_USER32_CS*8 + 3)
 #define __USER_DS			(GDT_ENTRY_DEFAULT_USER_DS*8 + 3)
 #define __USER32_DS			__USER_DS
 #define __USER_CS			(GDT_ENTRY_DEFAULT_USER_CS*8 + 3)
 #define __PER_CPU_SEG			(GDT_ENTRY_PER_CPU*8 + 3)

 #endif

 #ifndef CONFIG_PARAVIRT
 # define get_kernel_rpl()		0
 #endif

 #define IDT_ENTRIES			256
 #define NUM_EXCEPTION_VECTORS		32

 /* Bitmask of exception vectors which push an error code on the stack: */
 #define EXCEPTION_ERRCODE_MASK		0x00027d00

 #define GDT_SIZE			(GDT_ENTRIES*8)
 #define GDT_ENTRY_TLS_ENTRIES		3
 #define TLS_SIZE			(GDT_ENTRY_TLS_ENTRIES* 8)

 #ifdef __KERNEL__

 /*
  * early_idt_handler_array is an array of entry points referenced in the
  * early IDT.  For simplicity, it's a real array with one entry point
  * every nine bytes.  That leaves room for an optional 'push $0' if the
  * vector has no error code (two bytes), a 'push $vector_number' (two
  * bytes), and a jump to the common entry code (up to five bytes).
  */
 #define EARLY_IDT_HANDLER_SIZE 9

 #ifndef __ASSEMBLY__

 extern const char early_idt_handler_array[NUM_EXCEPTION_VECTORS][EARLY_IDT_HANDLER_SIZE];
 extern void early_ignore_irq(void);

 /*
  * Load a segment. Fall back on loading the zero segment if something goes
  * wrong.  This variant assumes that loading zero fully clears the segment.
  * This is always the case on Intel CPUs and, even on 64-bit AMD CPUs, any
  * failure to fully clear the cached descriptor is only observable for
  * FS and GS.
  */
 #define __loadsegment_simple(seg, value)				\
 do {									\
 	unsigned short __val = (value);					\
 									\
 	asm volatile("						\n"	\
 		     "1:	movl %k0,%%" #seg "		\n"	\
 									\
 		     ".section .fixup,\"ax\"			\n"	\
 		     "2:	xorl %k0,%k0			\n"	\
 		     "		jmp 1b				\n"	\
 		     ".previous					\n"	\
 									\
 		     _ASM_EXTABLE(1b, 2b)				\
 									\
 		     : "+r" (__val) : : "memory");			\
 } while (0)

 #define __loadsegment_ss(value) __loadsegment_simple(ss, (value))
 #define __loadsegment_ds(value) __loadsegment_simple(ds, (value))
 #define __loadsegment_es(value) __loadsegment_simple(es, (value))

 #ifdef CONFIG_X86_32

 /*
  * On 32-bit systems, the hidden parts of FS and GS are unobservable if
  * the selector is NULL, so there's no funny business here.
  */
 #define __loadsegment_fs(value) __loadsegment_simple(fs, (value))
 #define __loadsegment_gs(value) __loadsegment_simple(gs, (value))

 #else

 static inline void __loadsegment_fs(unsigned short value)
 {
 	asm volatile("						\n"
 		     "1:	movw %0, %%fs			\n"
 		     "2:					\n"

 		     _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_clear_fs)

 		     : : "rm" (value) : "memory");
 }

 /* __loadsegment_gs is intentionally undefined.  Use load_gs_index instead. */

 #endif

 #define loadsegment(seg, value) __loadsegment_ ## seg (value)

 /*
  * Save a segment register away:
  */
 #define savesegment(seg, value)				\
 	asm("mov %%" #seg ",%0":"=r" (value) : : "memory")

 /*
  * x86-32 user GS accessors:
  */
 #ifdef CONFIG_X86_32
 # ifdef CONFIG_X86_32_LAZY_GS
 #  define get_user_gs(regs)		(u16)({ unsigned long v; savesegment(gs, v); v; })
 #  define set_user_gs(regs, v)		loadsegment(gs, (unsigned long)(v))
 #  define task_user_gs(tsk)		((tsk)->thread.gs)
 #  define lazy_save_gs(v)		savesegment(gs, (v))
 #  define lazy_load_gs(v)		loadsegment(gs, (v))
 # else	/* X86_32_LAZY_GS */
 #  define get_user_gs(regs)		(u16)((regs)->gs)
 #  define set_user_gs(regs, v)		do { (regs)->gs = (v); } while (0)
 #  define task_user_gs(tsk)		(task_pt_regs(tsk)->gs)
 #  define lazy_save_gs(v)		do { } while (0)
 #  define lazy_load_gs(v)		do { } while (0)
 # endif	/* X86_32_LAZY_GS */
 #endif	/* X86_32 */

 #endif /* !__ASSEMBLY__ */
 #endif /* __KERNEL__ */

 #endif /* _ASM_X86_SEGMENT_H */
	#ifndef _ASM_X86_SEGMENT_H
	#define _ASM_X86_SEGMENT_H

	#include <linux/const.h>
	#include <asm/alternative.h>

	/*
	* Constructor for a conventional segment GDT (or LDT) entry.
	* This is a macro so it can be used in initializers.
	*/
	#define GDT_ENTRY(flags, base, limit) \
	((((base) & _AC(0xff000000,ULL)) << (56-24)) \| \
	(((flags) & _AC(0x0000f0ff,ULL)) << 40) \| \
	(((limit) & _AC(0x000f0000,ULL)) << (48-16)) \| \
	(((base) & _AC(0x00ffffff,ULL)) << 16) \| \
	(((limit) & _AC(0x0000ffff,ULL))))

	/* Simple and small GDT entries for booting only: */

	#define GDT_ENTRY_BOOT_CS 2
	#define GDT_ENTRY_BOOT_DS 3
	#define GDT_ENTRY_BOOT_TSS 4
	#define __BOOT_CS (GDT_ENTRY_BOOT_CS*8)
	#define __BOOT_DS (GDT_ENTRY_BOOT_DS*8)
	#define __BOOT_TSS (GDT_ENTRY_BOOT_TSS*8)

	/*
	* Bottom two bits of selector give the ring
	* privilege level
	*/
	#define SEGMENT_RPL_MASK 0x3

	/* User mode is privilege level 3: */
	#define USER_RPL 0x3

	/* Bit 2 is Table Indicator (TI): selects between LDT or GDT */
	#define SEGMENT_TI_MASK 0x4
	/* LDT segment has TI set ... */
	#define SEGMENT_LDT 0x4
	/* ... GDT has it cleared */
	#define SEGMENT_GDT 0x0

	#define GDT_ENTRY_INVALID_SEG 0

	#ifdef CONFIG_X86_32
	/*
	* The layout of the per-CPU GDT under Linux:
	*
	* 0 - null <=== cacheline #1
	* 1 - reserved
	* 2 - reserved
	* 3 - reserved
	*
	* 4 - unused <=== cacheline #2
	* 5 - unused
	*
	* ------- start of TLS (Thread-Local Storage) segments:
	*
	* 6 - TLS segment #1 [ glibc's TLS segment ]
	* 7 - TLS segment #2 [ Wine's %fs Win32 segment ]
	* 8 - TLS segment #3 <=== cacheline #3
	* 9 - reserved
	* 10 - reserved
	* 11 - reserved
	*
	* ------- start of kernel segments:
	*
	* 12 - kernel code segment <=== cacheline #4
	* 13 - kernel data segment
	* 14 - default user CS
	* 15 - default user DS
	* 16 - TSS <=== cacheline #5
	* 17 - LDT
	* 18 - PNPBIOS support (16->32 gate)
	* 19 - PNPBIOS support
	* 20 - PNPBIOS support <=== cacheline #6
	* 21 - PNPBIOS support
	* 22 - PNPBIOS support
	* 23 - APM BIOS support
	* 24 - APM BIOS support <=== cacheline #7
	* 25 - APM BIOS support
	*
	* 26 - ESPFIX small SS
	* 27 - per-cpu [ offset to per-cpu data area ]
	* 28 - stack_canary-20 [ for stack protector ] <=== cacheline #8
	* 29 - unused
	* 30 - unused
	* 31 - TSS for double fault handler
	*/
	#define GDT_ENTRY_TLS_MIN 6
	#define GDT_ENTRY_TLS_MAX (GDT_ENTRY_TLS_MIN + GDT_ENTRY_TLS_ENTRIES - 1)

	#define GDT_ENTRY_KERNEL_CS 12
	#define GDT_ENTRY_KERNEL_DS 13
	#define GDT_ENTRY_DEFAULT_USER_CS 14
	#define GDT_ENTRY_DEFAULT_USER_DS 15
	#define GDT_ENTRY_TSS 16
	#define GDT_ENTRY_LDT 17
	#define GDT_ENTRY_PNPBIOS_CS32 18
	#define GDT_ENTRY_PNPBIOS_CS16 19
	#define GDT_ENTRY_PNPBIOS_DS 20
	#define GDT_ENTRY_PNPBIOS_TS1 21
	#define GDT_ENTRY_PNPBIOS_TS2 22
	#define GDT_ENTRY_APMBIOS_BASE 23

	#define GDT_ENTRY_ESPFIX_SS 26
	#define GDT_ENTRY_PERCPU 27
	#define GDT_ENTRY_STACK_CANARY 28

	#define GDT_ENTRY_DOUBLEFAULT_TSS 31

	/*
	* Number of entries in the GDT table:
	*/
	#define GDT_ENTRIES 32

	/*
	* Segment selector values corresponding to the above entries:
	*/

	#define __KERNEL_CS (GDT_ENTRY_KERNEL_CS*8)
	#define __KERNEL_DS (GDT_ENTRY_KERNEL_DS*8)
	#define __USER_DS (GDT_ENTRY_DEFAULT_USER_DS*8 + 3)
	#define __USER_CS (GDT_ENTRY_DEFAULT_USER_CS*8 + 3)
	#define __ESPFIX_SS (GDT_ENTRY_ESPFIX_SS*8)

	/* segment for calling fn: */
	#define PNP_CS32 (GDT_ENTRY_PNPBIOS_CS32*8)
	/* code segment for BIOS: */
	#define PNP_CS16 (GDT_ENTRY_PNPBIOS_CS16*8)

	/* "Is this PNP code selector (PNP_CS32 or PNP_CS16)?" */
	#define SEGMENT_IS_PNP_CODE(x) (((x) & 0xf4) == PNP_CS32)

	/* data segment for BIOS: */
	#define PNP_DS (GDT_ENTRY_PNPBIOS_DS*8)
	/* transfer data segment: */
	#define PNP_TS1 (GDT_ENTRY_PNPBIOS_TS1*8)
	/* another data segment: */
	#define PNP_TS2 (GDT_ENTRY_PNPBIOS_TS2*8)

	#ifdef CONFIG_SMP
	# define __KERNEL_PERCPU (GDT_ENTRY_PERCPU*8)
	#else
	# define __KERNEL_PERCPU 0
	#endif

	#ifdef CONFIG_CC_STACKPROTECTOR
	# define __KERNEL_STACK_CANARY (GDT_ENTRY_STACK_CANARY*8)
	#else
	# define __KERNEL_STACK_CANARY 0
	#endif

	#else /* 64-bit: */

	#include <asm/cache.h>

	#define GDT_ENTRY_KERNEL32_CS 1
	#define GDT_ENTRY_KERNEL_CS 2
	#define GDT_ENTRY_KERNEL_DS 3

	/*
	* We cannot use the same code segment descriptor for user and kernel mode,
	* not even in long flat mode, because of different DPL.
	*
	* GDT layout to get 64-bit SYSCALL/SYSRET support right. SYSRET hardcodes
	* selectors:
	*
	* if returning to 32-bit userspace: cs = STAR.SYSRET_CS,
	* if returning to 64-bit userspace: cs = STAR.SYSRET_CS+16,
	*
	* ss = STAR.SYSRET_CS+8 (in either case)
	*
	* thus USER_DS should be between 32-bit and 64-bit code selectors:
	*/
	#define GDT_ENTRY_DEFAULT_USER32_CS 4
	#define GDT_ENTRY_DEFAULT_USER_DS 5
	#define GDT_ENTRY_DEFAULT_USER_CS 6

	/* Needs two entries */
	#define GDT_ENTRY_TSS 8
	/* Needs two entries */
	#define GDT_ENTRY_LDT 10

	#define GDT_ENTRY_TLS_MIN 12
	#define GDT_ENTRY_TLS_MAX 14

	/* Abused to load per CPU data from limit */
	#define GDT_ENTRY_PER_CPU 15

	/*
	* Number of entries in the GDT table:
	*/
	#define GDT_ENTRIES 16

	/*
	* Segment selector values corresponding to the above entries:
	*
	* Note, selectors also need to have a correct RPL,
	* expressed with the +3 value for user-space selectors:
	*/
	#define __KERNEL32_CS (GDT_ENTRY_KERNEL32_CS*8)
	#define __KERNEL_CS (GDT_ENTRY_KERNEL_CS*8)
	#define __KERNEL_DS (GDT_ENTRY_KERNEL_DS*8)
	#define __USER32_CS (GDT_ENTRY_DEFAULT_USER32_CS*8 + 3)
	#define __USER_DS (GDT_ENTRY_DEFAULT_USER_DS*8 + 3)
	#define __USER32_DS __USER_DS
	#define __USER_CS (GDT_ENTRY_DEFAULT_USER_CS*8 + 3)
	#define __PER_CPU_SEG (GDT_ENTRY_PER_CPU*8 + 3)

	#endif

	#ifndef CONFIG_PARAVIRT
	# define get_kernel_rpl() 0
	#endif

	#define IDT_ENTRIES 256
	#define NUM_EXCEPTION_VECTORS 32

	/* Bitmask of exception vectors which push an error code on the stack: */
	#define EXCEPTION_ERRCODE_MASK 0x00027d00

	#define GDT_SIZE (GDT_ENTRIES*8)
	#define GDT_ENTRY_TLS_ENTRIES 3
	#define TLS_SIZE (GDT_ENTRY_TLS_ENTRIES* 8)

	#ifdef __KERNEL__

	/*
	* early_idt_handler_array is an array of entry points referenced in the
	* early IDT. For simplicity, it's a real array with one entry point
	* every nine bytes. That leaves room for an optional 'push $0' if the
	* vector has no error code (two bytes), a 'push $vector_number' (two
	* bytes), and a jump to the common entry code (up to five bytes).
	*/
	#define EARLY_IDT_HANDLER_SIZE 9

	#ifndef __ASSEMBLY__

	extern const char early_idt_handler_array[NUM_EXCEPTION_VECTORS][EARLY_IDT_HANDLER_SIZE];
	extern void early_ignore_irq(void);

	/*
	* Load a segment. Fall back on loading the zero segment if something goes
	* wrong. This variant assumes that loading zero fully clears the segment.
	* This is always the case on Intel CPUs and, even on 64-bit AMD CPUs, any
	* failure to fully clear the cached descriptor is only observable for
	* FS and GS.
	*/
	#define __loadsegment_simple(seg, value) \
	do { \
	unsigned short __val = (value); \
	\
	asm volatile(" \n" \
	"1: movl %k0,%%" #seg " \n" \
	\
	".section .fixup,\"ax\" \n" \
	"2: xorl %k0,%k0 \n" \
	" jmp 1b \n" \
	".previous \n" \
	\
	_ASM_EXTABLE(1b, 2b) \
	\
	: "+r" (__val) : : "memory"); \
	} while (0)

	#define __loadsegment_ss(value) __loadsegment_simple(ss, (value))
	#define __loadsegment_ds(value) __loadsegment_simple(ds, (value))
	#define __loadsegment_es(value) __loadsegment_simple(es, (value))

	#ifdef CONFIG_X86_32

	/*
	* On 32-bit systems, the hidden parts of FS and GS are unobservable if
	* the selector is NULL, so there's no funny business here.
	*/
	#define __loadsegment_fs(value) __loadsegment_simple(fs, (value))
	#define __loadsegment_gs(value) __loadsegment_simple(gs, (value))

	#else

	static inline void __loadsegment_fs(unsigned short value)
	{
	asm volatile(" \n"
	"1: movw %0, %%fs \n"
	"2: \n"

	_ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_clear_fs)

	: : "rm" (value) : "memory");
	}

	/* __loadsegment_gs is intentionally undefined. Use load_gs_index instead. */

	#endif

	#define loadsegment(seg, value) __loadsegment_ ## seg (value)

	/*
	* Save a segment register away:
	*/
	#define savesegment(seg, value) \
	asm("mov %%" #seg ",%0":"=r" (value) : : "memory")

	/*
	* x86-32 user GS accessors:
	*/
	#ifdef CONFIG_X86_32
	# ifdef CONFIG_X86_32_LAZY_GS
	# define get_user_gs(regs) (u16)({ unsigned long v; savesegment(gs, v); v; })
	# define set_user_gs(regs, v) loadsegment(gs, (unsigned long)(v))
	# define task_user_gs(tsk) ((tsk)->thread.gs)
	# define lazy_save_gs(v) savesegment(gs, (v))
	# define lazy_load_gs(v) loadsegment(gs, (v))
	# else /* X86_32_LAZY_GS */
	# define get_user_gs(regs) (u16)((regs)->gs)
	# define set_user_gs(regs, v) do { (regs)->gs = (v); } while (0)
	# define task_user_gs(tsk) (task_pt_regs(tsk)->gs)
	# define lazy_save_gs(v) do { } while (0)
	# define lazy_load_gs(v) do { } while (0)
	# endif /* X86_32_LAZY_GS */
	#endif /* X86_32 */

	#endif /* !__ASSEMBLY__ */
	#endif /* __KERNEL__ */

	#endif /* _ASM_X86_SEGMENT_H */