Re: [Xen-devel] Floating Point Exception when compiling w/ gcc

[Robin Green <greenrd@xxxxxxxxxxxxx>]

On Tue, 22 Feb 2005, Georgi Mungov wrote:
> Hi,
> I've received twice a floating point exception on a different virtual machines
> during compilation. The first time it was with mysql, the second - kernel
> 2.6.0. After I ran "make" again the compilation finished without problems.
I found a floating-point bug in xen-unstable, which, since I don't know
what causes it, might also be present in xen 2.0.4. (See thread
"reproducable data corruption in xen-unstable".)

HOWEVER, I did create a workaround patch, which effectively solves the
problem for me. Remember to apply this patch both to xen0 and xenU
kernels. Here it is:

--- arch/xen/i386/kernel/process.c.orig 2005-02-12 03:39:44.000000000 +0000
+++ arch/xen/i386/kernel/process.c      2005-02-13 02:46:03.000000000 +0000
@@ -563,6 +563,8 @@
          if (prev_p->thread_info->status & TS_USEDFPU) {
                  save_init_fpu(prev_p);
                  queue_multicall0(__HYPERVISOR_fpu_taskswitch);
+       } else {
+               stts ();
          }

          /*

> I'm using Xen 2.0.4 build from sources on kernel 2.6.10 installed on standard
> slackware 9.1. The machine is PIII w/ 512MB ram running 4 VM, each with 64MB
> ram. The two errors happened on different VM.
My machine is an Athlon XP, so this shows that it isn't some strange
AMD-only bug (unless of course you have found a _different_
floating-point bug). Thanks for the bug report!

--
Robin


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