Strange crash

[Rein Klazes]

On Tue, 17 Apr 2001 12:18:12 +0800, you wrote:

> "Alexandre Julliard" <julliard at winehq.com> wrote:
> 
> > > Commenting lines 36-37
> > >     physDev->pen.width = GDI_ROUND((FLOAT)pen->logpen.lopnWidth.x *
> > >                                    dc->xformWorld2Vport.eM11 * 0.5);
> > > in X11DRV_PEN_SelectObject (graphics/x11drv/pen.c) cures the problem.
> > > 
> > > Why call to floor() leads to crash?
> > 
> > Exception c000008f is EXCEPTION_FLT_INEXACT_RESULT. Probably one of
> > the floating point values is invalid, or something similar.

On the other hand this exception is normally masked, even something as
simple as a division of 1.0 by 3.0 can generate it because the result
cannot be represented exactly. Also the round-to-int instruction that
has just happened here can cause it. So the question would be, why it
is not masked?

> 
> Exception occurs when pen->logpen.lopnWidth.x = 0 and dc->xformWorld2Vport.eM11 = 0.0
> It's very strange. Attached patch helps to eliminate crash. But I don't understand
> where the source of problem.

| 0x40897fde (X11DRV_PEN_SelectObject+0x8e [pen.c:69]): fldcw 0xfffffffe(%edx)

This instruction loads the control status word with a new value. Bit 5
of the CW (0x20) ,PM Precision Mask , is the mask bit for this
exception.

Find out how this bit has become zero (disassembly of the instructions
before the crash). If I put a breakpoint on the instruction above, the
CW is loaded with 0x37f: all FP exceptions are off.

Rein. 
-- 
Rein Klazes
rklazes at xs4all.nl