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
