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

To: xen-devel@xxxxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] Re: Floating Point Exception when compiling w/ gcc
From: Robin Green <greenrd@xxxxxxxxxxxxx>
Date: Sat, 05 Mar 2005 19:22:51 +0000
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User-agent: Pan/0.14.2 (This is not a psychotic episode. It's a cleansing moment of clarity.)
On Tue, 22 Feb 2005 23:47:37 +0000, Keir Fraser wrote:
> On 22 Feb 2005, at 19:26, Robin Green wrote:
>> 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.
> I'd like to get to the bottom of this problem. I've checked in some 
> cleanups to FPU
> code in both -testing and -unstable trees (the cleanups are 
> particularly extensive
> in the unstable tree). Can you see if the problem still occurs?

I just tried xen-unstable from 20050302 (I was waiting for it to be
packaged in the fedora development repo), and it's much better - thanks!

However, there is still a less frequent problem with ptrace (which also
occurred even when I'd applied my workaround patch). When running
firefox under gdb only, display corruption and odd crashes in
floating-point code are seen - which are the same symptoms as I had before.

So I assume that something is still wrong with the floating-point
save/restore in the case where a process is being ptraced.

Not nearly such a big deal, but annoying when you are trying to debug


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