Messages in this thread | | | Date | Wed, 08 Dec 1999 14:56:46 -0500 | From | Brian Gerst <> | Subject | Re: 2.3.30pre1 syscall w/6 args support? |
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Ingo Molnar wrote: > > On Wed, 8 Dec 1999, Brian Gerst wrote: > > > As far as I know, Wine currently only uses the extra segments for > > Windows code. Any Linux syscalls should only be coming from the main > > code segment. > > that is great. No changed %ds, %es, %ss either when glibc is called?
I'd have to scour the wine source to verify that.
> > I don't know about Intel's SYSENTER/SYSEXIT, but with AMD's > > SYSCALL/SYSRET you cannot return to user space with iret after a > > SYSCALL. The CPU sets an internal flag that causes a GPF when > > anything modifies %cs except for SYSRET or an interrupt (hardware or > > software). This has been a big stumbling block for me with adding > > SYSCALL support becuase it interferes with task switching (ie. can't > > switch to another task that would do an iret), unless it is restricted > > to syscalls that cannot sleep. > > i've just tested this on Xeon CPUs, and it works. (i forced the fastcall > entry point to reschedule unconditionally, the system still uses int $80) > > I agree that this would be a serious showstopper. Are you sure you werent > bitten by the stack-MSR issue? (we have to reload the SYSENTER kernel-ESP > MSR on every task switch)
Positive. The kernel stack pointer isn't set with the K6's MSR, which is unfortunate. Only %cs, %ss, and the kernel entry point are set. %esp still points to the userspace stack after SYSCALL and must be reloaded with the kernel's stack manually, which will be very tricky in an SMP environment if/when Athlon SMP systems appear.
There are two versions of the SYSCALL support. Version 1 is on the K6 and K6-2's before stepping 8, and version 2 is later K6-2s, the K6-3, and I presume the Athlon. My testing was done with version 1. I now have a K6-2 with the version 2 support and I will run some tests later tonight. As far as I know, the only difference between versions is in how %cs and %ss are set upon SYSRET.
Documentation on SYSCALL/SYSRET can be found at http://www.amd.com/K6/k6docs/pdf/21086.pdf
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Brian Gerst
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