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Re: [Xen-devel] [BUG] x86-64 floating point environment handling
| To: | "Jan Beulich" <JBeulich@xxxxxxxxxx> |
|---|---|
| Subject: | Re: [Xen-devel] [BUG] x86-64 floating point environment handling |
| From: | Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> |
| Date: | Mon, 28 Nov 2005 16:22:22 +0000 |
| Cc: | xen-devel@xxxxxxxxxxxxxxxxxxx |
| Delivery-date: | Mon, 28 Nov 2005 16:16:51 +0000 |
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On 28 Nov 2005, at 15:35, Jan Beulich wrote: Besides the minor problem of the save/restore code needlessly beingconditional for x86-64 (cpu_has_fxsr should always be set for all 64-bitCPUs) there is a more significant problem: Both FXSAVE and FXRSTOR require, for a 64-bit environment, 64-bit operand size to be explicitly used. Simply adding a rex64/ prefix, however, doesn't work because The only difference between rex64-prefixed fxsave and non-prefixed fxsave is the format of the last-instruction/data pointers. Does anyone make use of those? I notice that Linux always uses the rex64-prefixed version of fxsave, so I guess not (at least, not in 32-bit apps running on 64-bit linux). It's very unlikely we'd implement expensive and complicated logic in Xen to ensure consistency of FP state that noone uses. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel |
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