fpu32.c

这个linux源代码是很全面的~基本完整了~使用c编译的~由于时间问题我没有亲自测试~但就算用来做参考资料也是非常好的

/* 
 * Copyright 2002 Andi Kleen, SuSE Labs.
 * FXSAVE<->i387 conversion support. Based on code by Gareth Hughes.
 * This is used for ptrace, signals and coredumps in 32bit emulation.
 * $Id: fpu32.c,v 1.2 2003/01/10 15:11:11 ak Exp $
 */ 

#include <linux/sched.h>
#include <asm/sigcontext32.h>
#include <asm/processor.h>
#include <asm/uaccess.h>
#include <asm/i387.h>

static inline unsigned short twd_i387_to_fxsr(unsigned short twd)
{
	unsigned int tmp; /* to avoid 16 bit prefixes in the code */
 
	/* Transform each pair of bits into 01 (valid) or 00 (empty) */
        tmp = ~twd;
        tmp = (tmp | (tmp>>1)) & 0x5555; /* 0V0V0V0V0V0V0V0V */
        /* and move the valid bits to the lower byte. */
        tmp = (tmp | (tmp >> 1)) & 0x3333; /* 00VV00VV00VV00VV */
        tmp = (tmp | (tmp >> 2)) & 0x0f0f; /* 0000VVVV0000VVVV */
        tmp = (tmp | (tmp >> 4)) & 0x00ff; /* 00000000VVVVVVVV */
        return tmp;
}

static inline unsigned long twd_fxsr_to_i387(struct i387_fxsave_struct *fxsave)
{
	struct _fpxreg *st = NULL;
	unsigned long twd = (unsigned long) fxsave->twd;
	unsigned long tag;
	unsigned long ret = 0xffff0000;
	int i;

#define FPREG_ADDR(f, n)	((char *)&(f)->st_space + (n) * 16);

	for (i = 0 ; i < 8 ; i++) {
		if (twd & 0x1) {
			st = (struct _fpxreg *) FPREG_ADDR( fxsave, i );

			switch (st->exponent & 0x7fff) {
			case 0x7fff:
				tag = 2;		/* Special */
				break;
			case 0x0000:
				if ( !st->significand[0] &&
				     !st->significand[1] &&
				     !st->significand[2] &&
				     !st->significand[3] ) {
					tag = 1;	/* Zero */
				} else {
					tag = 2;	/* Special */
				}
				break;
			default:
				if (st->significand[3] & 0x8000) {
					tag = 0;	/* Valid */
				} else {
					tag = 2;	/* Special */
				}
				break;
			}
		} else {
			tag = 3;			/* Empty */
		}
		ret |= (tag << (2 * i));
		twd = twd >> 1;
	}
	return ret;
}


static inline int convert_fxsr_from_user(struct i387_fxsave_struct *fxsave,
					 struct _fpstate_ia32 *buf)
{
	struct _fpxreg *to;
	struct _fpreg *from;
	int i;
	int err; 
	__u32 v;

	err = __get_user(fxsave->cwd, &buf->cw); 
	err |= __get_user(fxsave->swd, &buf->sw);
	err |= __get_user(fxsave->twd, &buf->tag);
	fxsave->twd = twd_i387_to_fxsr(fxsave->twd);
	err |= __get_user(fxsave->rip, &buf->ipoff); 
	err |= __get_user(fxsave->rdp, &buf->dataoff); 
	err |= __get_user(v, &buf->cssel); 
	fxsave->fop = v >> 16;
	if (err) 
		return -1; 

	to = (struct _fpxreg *)&fxsave->st_space[0];
	from = &buf->_st[0];
	for (i = 0 ; i < 8 ; i++, to++, from++) {
		if (__copy_from_user(to, from, sizeof(*from)))
			return -1;
	}
	return 0;
}


static inline int convert_fxsr_to_user(struct _fpstate_ia32 *buf,
				       struct i387_fxsave_struct *fxsave,
				       struct pt_regs *regs,
				       struct task_struct *tsk)
{
	struct _fpreg *to;
	struct _fpxreg *from;
	int i;
	u32 ds; 
	int err; 

	err = __put_user((unsigned long)fxsave->cwd | 0xffff0000, &buf->cw);
	err |= __put_user((unsigned long)fxsave->swd | 0xffff0000, &buf->sw);
	err |= __put_user((u32)fxsave->rip, &buf->ipoff); 
	err |= __put_user((u32)(regs->cs | ((u32)fxsave->fop << 16)), 
			  &buf->cssel); 
	err |= __put_user((u32)twd_fxsr_to_i387(fxsave), &buf->tag); 
	err |= __put_user((u32)fxsave->rdp, &buf->dataoff); 
	if (tsk == current) 
		asm("movl %%ds,%0 " : "=r" (ds)); 
	else /* ptrace. task has stopped. */
		ds = tsk->thread.ds;
	err |= __put_user(ds, &buf->datasel); 
	if (err) 
		return -1; 

	to = &buf->_st[0];
	from = (struct _fpxreg *) &fxsave->st_space[0];
	for ( i = 0 ; i < 8 ; i++, to++, from++ ) {
		if (__copy_to_user(to, from, sizeof(*to)))
			return -1;
	}
	return 0;
}

int restore_i387_ia32(struct task_struct *tsk, struct _fpstate_ia32 *buf, int fsave) 
{ 
	clear_fpu(tsk);
	if (!fsave) { 
		if (__copy_from_user(&tsk->thread.i387.fxsave, 
				     &buf->_fxsr_env[0],
				     sizeof(struct i387_fxsave_struct)))
			return -1;
	} 
	tsk->thread.i387.fxsave.mxcsr &= 0xffbf;
	return convert_fxsr_from_user(&tsk->thread.i387.fxsave, buf);
}  

int save_i387_ia32(struct task_struct *tsk, 
		   struct _fpstate_ia32 *buf, 
		   struct pt_regs *regs,
		   int fsave)
{
	int err = 0;

	if (!tsk->used_math) 
		return 0;
	tsk->used_math = 0; 
	unlazy_fpu(tsk);
	if (convert_fxsr_to_user(buf, &tsk->thread.i387.fxsave, regs, tsk))
		return -1;
	err |= __put_user(tsk->thread.i387.fxsave.swd, &buf->status);
	if (fsave) 
		return err ? -1 : 1; 	
	err |= __put_user(X86_FXSR_MAGIC, &buf->magic);
	err |= __copy_to_user(&buf->_fxsr_env[0], &tsk->thread.i387.fxsave,
			      sizeof(struct i387_fxsave_struct));
	return err ? -1 : 1;
}