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[Xen-devel] Xen guest floating point problem

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Subject: [Xen-devel] Xen guest floating point problem
From: Mick Jordan <Mick.Jordan@xxxxxxx>
Date: Mon, 03 Aug 2009 16:51:18 -0700
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We have a simple C test program that runs on our evolved version of Mini-OS (GUK) that exhibits sporadic non-deterministic failure regarding floating point computations (mostly calling the __ieee754_remainder method of fdlibm). Typically about 5 computations in 10000 fail, usually with Nan or Infinite values showing up. We are as convinced as we can be at this point that the GUK code is not corrupting the floating point state, so are down to two ideas. One is a bug in Xen on guest context switching or event delivery regarding the FP state. The other is that GUK is failing to obey some Xen API contract regarding FP state. For example, timer and xenstore events are being delivered during the run although we can't correlate them directly to the fault.

The program fails on both Solaris xVM 3.1.4, xVM 3.3, various Linux 3.1.4 systems, but does not fail when run on Solaris or Linux domUs. This points the finger at GUK but we are wondering whether they have a workaround for some problem we are not aware of.

Thanks for any help.


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