Re: [uml-devel] Programs in guest segfault, amd64 host and guest

[Jan Dittmer <jdi@l4x.org>]

Jeff Dike wrote:
> On Wed, Oct 18, 2006 at 09:16:14PM +0200, Jan Dittmer wrote:
>> This is 100% reproducible here. Perfect test case. How to debug?
> 
> You want to dig into the code and see what's wrong?  Put a breakpoint
> on the force_sig_info(SIGSEGV, ...) in segv().  Then find the faulting
> instruction -
> 	RIP is regs.skas.regs[16]
> 	pid = cpu_tasks[0].pid
> 	Look in the host's /proc/$pid/maps for the page containing RIP
> 	add uml_physmem to the offset in column 3 - that's the
> physical page containing RIP
> 	add the RIP page offset to that to get the actual physical
> address for RIP
> 	disassemble the range of memory around it - I usually do 10 -
> 20 bytes before it to ~10 bytes after
> 	see that the asm looks sane, if not, bump the start of the
> disassembly by a byte in either direction until it does
> 	see what the instruction at RIP is - if it involves a gs:
> reference, then it's very likely a NPTL problem

Well tomorrow perhaps. I've very little time currently :-(

> If you don't want to do that, tell me what to yum, and how to run
> whatever it is, and I'll look at it.

As I wrote in the original message: Debian/etch amd64 host+guest,
running btlaunchmany (from the bittorrent package). I can put you
the compressed root + kernel somewhere if that helps. It's roughly
100mb.

Jan

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