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From: Douglas Thomas Crosher  <dtc@scrooge.ee.swin.oz.au>
Message-Id: <199701031121.WAA11316@scrooge.ee.swin.oz.au>
Subject: Re: i586-optimized copyin/out still broken
To: freebsd-current@freebsd.org
Date: Fri, 3 Jan 1997 22:21:50 +1100 (EST)
In-Reply-To: <199701030215.NAA13793@godzilla.zeta.org.au> from "Bruce Evans" at Jan 3, 97 01:15:47 pm
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> >>>  Log:
> >>>  Disabled i586-optimized copyin and copyout again.  The fault handler
> >>>  is still broken - it doesn't restore the floating point state.
> 
> >Could this problem result in NaN being produced at wrong places.
> 
> No, it causes kernel panics.
> 
> >I filled a PR (2142) about it, maybe it could be closed then.
> 
> That is much harder to fix.  It is caused by the floating point state
> not being preserved across signal handlers.  There are few, if any,
> valid and useful uses for floating point in signal handlers, because
> an ANSI signal handler must not make any accesses to a global object
> other than assignment to ones of type `volatile sig_atomic_t'.  Thus
> preserving the state would mainly slow down signal handlers.

Will it solve the problem to add a FPU save/restore in the interrupt
handler when needed?

>From example using Martin's code example in PR 2142, the interrupt
handler would become:

void interrupt(int sig)
{
  int n,i;
  static int wieviel=0;
  int fpu_state[27];

  fpu_save(fpu_state); /* <<<<< */
  
  setitimer(ITIMER_REAL,&timer1,&timerdummy);
  bsdsignal(SIGALRM,(void *)(interrupt));

  n=(int)((double)counter/(double)max*(double)80);
  for (i=wieviel;i<n;i++) {   
    fputc(' ',stderr);   
    wieviel++;
  }

  fpu_restore(fpu_state); /* <<<<< */
}

-=-=-

	.text
	.global	_fpu_save
	.type	_fpu_save,@function
	.align	2,0x90
_fpu_save:
	movl	4(%esp),%eax
	fnsave	(%eax)		# Save the NPX state - Resets NPX
	ret
	.size	_fpu_save,.-_fpu_save

	.global	_fpu_restore
	.type	_fpu_restore,@function
	.align	2,0x90
_fpu_restore:
	movl	4(%esp),%eax
	frstor	(%eax)		# Restore the NPX state.
	ret
	.size	_fpu_restore,.-_fpu_restore