Bug#46709: no subject)

[Roland McGrath]

> On Sun, Oct 07, 2001 at 03:32:15PM -0400, Roland McGrath wrote:
> > The 0xff byte after the bitmap is a terminator byte, check your Intel book
> > vol 1, section 9.5.2.
> 
> Ah, that explains it.  I have seen the extra byte, and was wondering what I
> missed.  I have the Intel books now (got them today), so I can read up more
> about this stuff.
> 
> BTW, the user tss does not contain such a terminator, so I will add one.
> 
> > Your fix is ok, though I would use memset (not that it matters for a
> > boot-time only thing).  
> 
> Yes, of course that's better.
>  
> > According to my Intel book, the other solution is to have no io bitmap
> > space at all: missing bits are treated as disallowed if the bitmap is
> > shorter than 64k, down to 0.
> 
> It also should work to set the io bitmap base address to or beyond the
> segment with the same effect.

That's what I meant by the bitmap being shorter.  It spans from the
specific base address (and offset from the beginning of the tss) to the end
of the segment, so the segment consists of nothing but the tss when the
bitmap is empty.