Re: [Xen-devel] segfault bug in xeno-unstable...

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> The actual version of xeno-unstable (Changeset 1.506) segfaults with some
> standard commands - at least with my 
> RedHat V8 (I haven't tested RedHat V9 yet) installation.
> If you enter "vi" or "vim" or "rpm -qa" as root or non-root user,
> xeno-linux just segfaults with no further comments (the next line of
> output just shows "Segmentation fault", nothing more).
> After a lot of tests with bk pull and bk undo, I was able to find out,
> that this bug was introduced with Changeset 1.478. 

Oops. 

I've just tried "rpm -qa" and "vi" under 1.506 on a RH7.2
installation, and it seems to work. I'll try setting up a RH8
install and retrying. My guess is that this is something to do
with our per-domain ldt switching code. The pthreads library uses
fs/gs for accessing thread local storage, and the exact mechanism
seems to change with every libc and RH version. However, its not
clear that rpm and vi use pthreads.

1.478 was a major change, so I'm not entirely
surprised. Shouldn't be hard to fix, though.
 
> BTW: Especially for production use, it would be nicer if xen could
> somehow pass up "printk"-output in xen to dom0's kernel logger,
> so that you don't need to configure and run a second machine for
> the serial line debug output all the time. While checking the segfault
> bug, I have not connected a debug machine to the serial line, so I
> don't know if it would have showed something helpful :-(

Yes, having Xen output (including boot messages) passed up to
domain0 would certainly be helpful. 
Just writing into a ring buffer and then mapping it from dom0
and having a daemon dump it to syslog should work. Might be worth
looking to see how klogd does it.

 > Another thing I realized while compiling and trying to load the 
> HyperSCSI kernel module:
> When loading the HyperSCSI client kernel module (which was 
> compiled against xeno-linux), it complains about 2 undefined 
> Kernel Symbols:
> 
> do_hypervisior_callback      and
> HYPERVISOR_shared_info
> 
> After adding 2 EXPORT_SYMBOL lines for these symbols in
> ../arch/xeno/kernel/i386_ksyms.c and
> recompiling the kernel, everything loaded and worked OK. 
> I hope it was not against xen design principles to add the
> 2 EXPORT_SYMBOL lines ;-)

We generally don't use modules much, so I'm afraid we hadn't
spotted this. We'll add the exports into the master tree, thanks.
 
> Regards + many thanks to the Xen project team for this nice 
> and professional software :))

Thanks.

Ian



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