Re: [9fans] sysrfork fp bug?

[erik quanstrom <quanstro@quanstro.net>]

On Mon Nov 21 18:14:43 EST 2011, charles.forsyth@gmail.com wrote:
> it only needs to save the non-register state (ie, the control register
> you'd wondered about),
> but it's free to do more if that's somehow easier, even if the values
> will never be used.
> on BG/P, the equivalent function does:
> 	 * If there isn't a pending exception, just save the
> 	 * initial state and current status, because registers
> 	 * were killed by the system call.

but not the statuses, correct?  this is what i'm thinking for
a minimal clone which assumes it will be called from rfork,
but doesn't assume anything about the up using x87 or sse.

static void
sseclonestate(PFPU *t, PFPU *s)
{
	Fxsave *r;

	memmove(t->fpusave, s->fpusave, sizeof(FPsave));
	r = (Fxsave*)t;
	r->ftw = 0;			/* all x87 registers invalid (clear stack) */
	r->fsw = 0;			/* clear x87 status */
	r->mxcsr &= ~SSEflags;		/* clear sse status; preserve settings */
}

- erik