Re: [PATCH 4/21] i386 Broken bios common

["H. Peter Anvin" <hpa@zytor.com>]

Linus Torvalds wrote:
> 
> On Mon, 7 Nov 2005, Zachary Amsden wrote:
> 
>>Both the APM BIOS and PnP BIOS code use a segment hack to simulate real
>>mode selector 0x40 (which points to the BIOS data area at 0x00400 in
>>real mode).  Several broken BIOSen use selector 0x40 as if they were
>>running in real mode, which we make work by faking up selector 0x40 in
>>the GDT to point to physical memory starting at 0x400.  We limit the
>>access to the remainder of this physical page using a byte granular
>>limit.  Rather than have this tricky code in multiple places, it makes
>>sense to define it in one place, and the GDT makes a very convenient
>>place for it.  Use GDT entry 4 as the BAD_BIOS_CACHE segment.
> 
> I'd much rather use entry 8 instead, which should just automatically mean 
> that selector 0x40 _always_ points to virtual address 0x400. No switching 
> etc..
> 
> Isn't this what Wine already has to work around, or something?
> 
> Ingo, can we move the TLS selectors upwards, or does user space perhaps 
> know about the current TLS layout? Wine in particular may well know ;(
> 

I thought the point was that Wine needs to point GDT entry 8 into userspace.

	-hpa