Date: Mon, 11 Apr 2005 11:54:01 -0700 From: Julian Elischer <julian@elischer.org> To: Bill Paul <wpaul@FreeBSD.org> Cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/compat/ndis hal_var.h kern_ndis.c subr_ndis.cMakefile src/sys/dev/if_ndis if_ndis.c Message-ID: <425AC7C9.8050801@elischer.org> In-Reply-To: <200504110202.j3B22Z5k014387@repoman.freebsd.org> References: <200504110202.j3B22Z5k014387@repoman.freebsd.org>
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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 :-)
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