system.h

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#ifndef __ASM_SYSTEM_H
#define __ASM_SYSTEM_H

#include <linux/kernel.h>
#include <asm/segment.h>

#ifdef __KERNEL__

struct task_struct;	/* one of the stranger aspects of C forward declarations.. */
extern void FASTCALL(__switch_to(struct task_struct *prev, struct task_struct *next));

#define switch_to(prev,next,last) do {					\
	asm volatile("pushl %%esi\n\t"					\
		     "pushl %%edi\n\t"					\
		     "pushl %%ebp\n\t"					\
		     "movl %%esp,%0\n\t"	/* save ESP */		\
		     "movl %3,%%esp\n\t"	/* restore ESP */	\
		     "movl $1f,%1\n\t"		/* save EIP */		\
		     "pushl %4\n\t"		/* restore EIP */	\
		     "jmp __switch_to\n"				\
		     "1:\t"						\
		     "popl %%ebp\n\t"					\
		     "popl %%edi\n\t"					\
		     "popl %%esi\n\t"					\
		     :"=m" (prev->tss.esp),"=m" (prev->tss.eip),	\
		      "=b" (last)					\
		     :"m" (next->tss.esp),"m" (next->tss.eip),		\
		      "a" (prev), "d" (next),				\
		      "b" (prev));					\
} while (0)

#define _set_base(addr,base) do { unsigned long __pr; \
__asm__ __volatile__ ("movw %%dx,%1\n\t" \
	"rorl $16,%%edx\n\t" \
	"movb %%dl,%2\n\t" \
	"movb %%dh,%3" \
	:"=&d" (__pr) \
	:"m" (*((addr)+2)), \
	 "m" (*((addr)+4)), \
	 "m" (*((addr)+7)), \
         "0" (base) \
        ); } while(0)

#define _set_limit(addr,limit) do { unsigned long __lr; \
__asm__ __volatile__ ("movw %%dx,%1\n\t" \
	"rorl $16,%%edx\n\t" \
	"movb %2,%%dh\n\t" \
	"andb $0xf0,%%dh\n\t" \
	"orb %%dh,%%dl\n\t" \
	"movb %%dl,%2" \
	:"=&d" (__lr) \
	:"m" (*(addr)), \
	 "m" (*((addr)+6)), \
	 "0" (limit) \
        ); } while(0)

#define set_base(ldt,base) _set_base( ((char *)&(ldt)) , (base) )
#define set_limit(ldt,limit) _set_limit( ((char *)&(ldt)) , ((limit)-1)>>12 )

static inline unsigned long _get_base(char * addr)
{
	unsigned long __base;
	__asm__("movb %3,%%dh\n\t"
		"movb %2,%%dl\n\t"
		"shll $16,%%edx\n\t"
		"movw %1,%%dx"
		:"=&d" (__base)
		:"m" (*((addr)+2)),
		 "m" (*((addr)+4)),
		 "m" (*((addr)+7)));
	return __base;
}

#define get_base(ldt) _get_base( ((char *)&(ldt)) )

/*
 * Load a segment. Fall back on loading the zero
 * segment if something goes wrong..
 */
#define loadsegment(seg,value)			\
	asm volatile("\n"			\
		"1:\t"				\
		"movl %0,%%" #seg "\n"		\
		"2:\n"				\
		".section .fixup,\"ax\"\n"	\
		"3:\t"				\
		"pushl $0\n\t"			\
		"popl %%" #seg "\n\t"		\
		"jmp 2b\n"			\
		".previous\n"			\
		".section __ex_table,\"a\"\n\t"	\
		".align 4\n\t"			\
		".long 1b,3b\n"			\
		".previous"			\
		: :"m" (*(unsigned int *)&(value)))

/*
 * Clear and set 'TS' bit respectively
 */
#define clts() __asm__ __volatile__ ("clts")
#define read_cr0() ({ \
	unsigned int __dummy; \
	__asm__( \
		"movl %%cr0,%0\n\t" \
		:"=r" (__dummy)); \
	__dummy; \
})
#define write_cr0(x) \
	__asm__("movl %0,%%cr0": :"r" (x));
#define stts() write_cr0(8 | read_cr0())

#endif	/* __KERNEL__ */

static inline unsigned long get_limit(unsigned long segment)
{
	unsigned long __limit;
	__asm__("lsll %1,%0"
		:"=r" (__limit):"r" (segment));
	return __limit+1;
}

#define nop() __asm__ __volatile__ ("nop")

#define xchg(ptr,x) ((__typeof__(*(ptr)))__xchg((unsigned long)(x),(ptr),sizeof(*(ptr))))
#define tas(ptr) (xchg((ptr),1))

struct __xchg_dummy { unsigned long a[100]; };
#define __xg(x) ((struct __xchg_dummy *)(x))

/*
 * Note: no "lock" prefix even on SMP: xchg always implies lock anyway
 */
static inline unsigned long __xchg(unsigned long x, void * ptr, int size)
{
	switch (size) {
		case 1:
			__asm__("xchgb %b0,%1"
				:"=q" (x)
				:"m" (*__xg(ptr)), "0" (x)
				:"memory");
			break;
		case 2:
			__asm__("xchgw %w0,%1"
				:"=r" (x)
				:"m" (*__xg(ptr)), "0" (x)
				:"memory");
			break;
		case 4:
			__asm__("xchgl %0,%1"
				:"=r" (x)
				:"m" (*__xg(ptr)), "0" (x)
				:"memory");
			break;
	}
	return x;
}

/*
 * Force strict CPU ordering.
 * And yes, this is required on UP too when we're talking
 * to devices.
w *
 * For now, "wmb()" doesn't actually do anything, as all
 * Intel CPU's follow what Intel calls a *Processor Order*,
 * in which all writes are seen in the program order even
 * outside the CPU.
 *
 * I expect future Intel CPU's to have a weaker ordering,
 * but I'd also expect them to finally get their act together
 * and add some real memory barriers if so.
 */
#define mb() 	__asm__ __volatile__ ("lock; addl $0,0(%%esp)": : :"memory")
#define rmb()	mb()
#define wmb()	__asm__ __volatile__ ("": : :"memory")

/* interrupt control.. */
#if   defined(OSKIT) && !defined(INLINED_INTR_FLAGS)
extern void linux_sti(void);
extern void linux_cli(void);
extern unsigned linux_save_flags(void);
extern void linux_restore_flags(unsigned);
extern unsigned linux_save_flags_cli(void);
#define __sti()                   linux_sti()
#define __cli()                   linux_cli()
#define __save_flags(flags)       ((flags) = linux_save_flags())
#define __restore_flags(flags)    linux_restore_flags(flags)
#define save_flags_cli(flags)	  ((flags) = linux_save_flags_cli())
#else
#define __sti() __asm__ __volatile__ ("sti": : :"memory")
#define __cli() __asm__ __volatile__ ("cli": : :"memory")
#define __save_flags(x) \
__asm__ __volatile__("pushfl ; popl %0":"=g" (x): /* no input */ :"memory")
#define __restore_flags(x) \
__asm__ __volatile__("pushl %0 ; popfl": /* no output */ :"g" (x):"memory")
#endif /* OSKIT */

#ifdef __SMP__

extern void __global_cli(void);
extern void __global_sti(void);
extern unsigned long __global_save_flags(void);
extern void __global_restore_flags(unsigned long);
#define cli() __global_cli()
#define sti() __global_sti()
#define save_flags(x) ((x)=__global_save_flags())
#define restore_flags(x) __global_restore_flags(x)

#else

#define cli() __cli()
#define sti() __sti()
#define save_flags(x) __save_flags(x)
#if   defined(OSKIT) && defined(INLINED_INTR_FLAGS)
#define IF_FLAG 0x00000200
#define restore_flags(x) ({ if ((x) & IF_FLAG) sti(); else cli(); })
#else
#define restore_flags(x) __restore_flags(x)
#endif  /* OSKIT */

#endif

#ifndef OSKIT			/* floppy driver uses these */
/*
 * disable hlt during certain critical i/o operations
 */
#define HAVE_DISABLE_HLT
void disable_hlt(void);
void enable_hlt(void);
#endif

#if   defined(OSKIT) && defined(INLINED_INTR_FLAGS)
/*
 * Inline the interrupt enable/disable stuff. There are tons of calls
 * to these glue names scattered around. Redefine them. Perhaps the calls
 * to these names should be changed to calls to the normal names so that
 * they don't have to be special cased like this?
 *
 * First, undef the stuff from global.h
 */
#undef linux_save_flags_cli
#undef linux_save_flags
#undef linux_restore_flags
#undef linux_sti
#undef linux_cli

#define linux_sti() sti()
#define linux_cli() cli()
#define linux_save_flags() \
	({ unsigned __flags__; save_flags(__flags__); __flags__; })
#define linux_restore_flags restore_flags
#define linux_save_flags_cli() \
	({ unsigned __flags_; save_flags(__flags_); cli(); __flags_; })
#endif

#endif