Le Mercredi 05 Avril 2006 05:24, Xu, Anthony a écrit :
> From: Magenheimer,
>
> >Dan (HP Labs Fort Collins)
> >Yes this problem has been with us for several months and
> >anybody who exercises Xen/ia64 heavily will probably see it
> >occur. It is definitely not specific to gcc... it may even
> >be occuring in ltp, but since it is not repeatable (the
> >failure appears almost randomly), it is hard to link a
> >single ltp test failure to the "gcc segfault" problem.
> >
> >Based on what I have seen, I suspect it has something
> >to do with a stale translation... perhaps some flush/purge
> >is not working properly or maybe a region id is being
> >incorrectly re-used.
> >
> >Isolating this problem will take a lot of effort and
> >some sophisticated debug tools/hardware. However, I
> >would not recommend Xen/ia64 be "released" to customers
> >until it is found/fixed.
Yes.
> I also saw gcc segmentation on dom0 recently, and I got chance to debug
> this, I caught this issue once,and I found this gcc segmentation is due to
> process access a address which is not belong to this process.
> I also found the machine address of this fault address belongs to the high
> memory block(16M), which is used to avoid VIRTUAL_MEMMAP issue.
>
> I looked into the code, and found xen uses this 16M just below max_page.
> and this 16M can't be guaranteed not used by box firmware.
> But I didn't find the area was used by firmware from memmap dumped in efi
> shell.
>
> Though, I still dropped down this 16M from dom0, and run kernel build,
> I haven't see gcc segmentation fault since then.
>
> I'm not sure if it is the root cause, just FYI.
From my experience, this bug occurs only in domU (ie, I was not able to
reproduce it in dom0).
During this night, I was able to compile linux kernel 55 times without any
segfault. I don't know the frequence of this bug, but I thought it was more
frequent.
When SMP-g is activated, such a bug appears very easily. But SMP-g is not
stable!
Tristan.
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