Linux0.96c/include/asm/segment.h

extern inline unsigned char get_fs_byte(const char * addr)
{
	unsigned register char _v;

	__asm__ ("movb %%fs:%1,%0":"=q" (_v):"m" (*addr));
	return _v;
}

extern inline unsigned short get_fs_word(const unsigned short *addr)
{
	unsigned short _v;

	__asm__ ("movw %%fs:%1,%0":"=r" (_v):"m" (*addr));
	return _v;
}

extern inline unsigned long get_fs_long(const unsigned long *addr)
{
	unsigned long _v;

	__asm__ ("movl %%fs:%1,%0":"=r" (_v):"m" (*addr)); \
	return _v;
}

extern inline void put_fs_byte(char val,char *addr)
{
__asm__ ("movb %0,%%fs:%1"::"q" (val),"m" (*addr));
}

extern inline void put_fs_word(short val,short * addr)
{
__asm__ ("movw %0,%%fs:%1"::"r" (val),"m" (*addr));
}

extern inline void put_fs_long(unsigned long val,unsigned long * addr)
{
__asm__ ("movl %0,%%fs:%1"::"r" (val),"m" (*addr));
}

extern inline void memcpy_tofs(void * to, void * from, unsigned long n)
{
__asm__("cld\n\t"
	"push %%es\n\t"
	"push %%fs\n\t"
	"pop %%es\n\t"
	"testb $1,%%cl\n\t"
	"je 1f\n\t"
	"movsb\n"
	"1:\ttestb $2,%%cl\n\t"
	"je 2f\n\t"
	"movsw\n"
	"2:\tshrl $2,%%ecx\n\t"
	"rep ; movsl\n\t"
	"pop %%es"
	::"c" (n),"D" ((long) to),"S" ((long) from)
	:"cx","di","si");
}

extern inline void memcpy_fromfs(void * to, void * from, unsigned long n)
{
__asm__("cld\n\t"
	"testb $1,%%cl\n\t"
	"je 1f\n\t"
	"fs ; movsb\n"
	"1:\ttestb $2,%%cl\n\t"
	"je 2f\n\t"
	"fs ; movsw\n"
	"2:\tshrl $2,%%ecx\n\t"
	"rep ; fs ; movsl"
	::"c" (n),"D" ((long) to),"S" ((long) from)
	:"cx","di","si");
}

/*
 * Someone who knows GNU asm better than I should double check the followig.
 * It seems to work, but I don't know if I'm doing something subtly wrong.
 * --- TYT, 11/24/91
 * [ nothing wrong here, Linus: I just changed the ax to be any reg ]
 */

extern inline unsigned long get_fs() 
{
	unsigned short _v;
	__asm__("mov %%fs,%0":"=r" (_v):);
	return _v;
}

extern inline unsigned long get_ds() 
{
	unsigned short _v;
	__asm__("mov %%ds,%0":"=r" (_v):);
	return _v;
}

extern inline void set_fs(unsigned long val)
{
	__asm__("mov %0,%%fs"::"r" ((unsigned short) val));
}