Date: Mon, 11 Apr 2005 20:55:55 -0400 (EDT) From: Jeff Roberson <jroberson@chesapeake.net> To: John Baldwin <jhb@FreeBSD.org> Cc: cvs-src@FreeBSD.org Subject: Re: cvs commit: src/sys/compat/ndis hal_var.h kern_ndis.c subr_ndis.c subr_ntoskrnl.c subr_usbd.c winx32_wrap.S src/s Message-ID: <20050411205510.B28571@mail.chesapeake.net> In-Reply-To: <200504111847.09117.jhb@FreeBSD.org> References: <200504110202.j3B22Z5k014387@repoman.freebsd.org> <425AC7C9.8050801@elischer.org> <200504111847.09117.jhb@FreeBSD.org>
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On Mon, 11 Apr 2005, John Baldwin wrote: > On Monday 11 April 2005 02:54 pm, Julian Elischer wrote: > > Bill Paul wrote: > > >wpaul 2005-04-11 02:02:35 UTC > > > > > > > > > The twist has to do with the fact that Microsoft supports structured > > > exception handling in kernel mode. On the i386 arch, exception handling > > > is implemented by hanging an exception registration list off the > > > Thread Environment Block (TEB), and the TEB is accessed via the %fs > > > register. The problem is, we use %fs as a pointer to the pcpu stucture, > > > which means any driver that tries to write through %fs:0 will overwrite > > > the curthread pointer and make a serious mess of things. > > > > > > To get around this, Project Evil now creates a special entry in > > > the GDT on each processor. When we call into Windows code, a context > > > switch routine will fix up %fs so it points to our new descriptor, > > > which in turn points to a fake TEB. When the Windows code returns, > > > or calls out to an external routine, we swap %fs back again. Currently, > > > Project Evil makes use of GDT slot 7, which is all 0s by default. > > > I fully expect someone to jump up and say I can't do that, but I > > > couldn't find any code that makes use of this entry anywhere. Sadly, > > > this was the only method I could come up with that worked on both > > > UP and SMP. (Modifying the LDT works on UP, but becomes incredibly > > > complicated on SMP.) If necessary, the context switching stuff can > > > be yanked out while preserving the convention calling wrappers. > > > > Maybe we could emulate $soft and use %fs as a thread pointer instead and > > have pcpu > > pointed to via that :-) > > I think NDIS drivers want %fs to point to a Windows-specific structure rather > than a 'struct thread' so I don't think that would buy us anything except for > even more memory indirects when we do a pcpu lookup. Isn't curthread a much more frequent fetch than PCPU anything? It might actually be a win. > > -- > John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ > "Power Users Use the Power to Serve" = http://www.FreeBSD.org >
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