Re: [uml-devel] Kernel mode fault at addr 0x92c00000, ip 0x80bcead

[Jeff Dike <jdike@addtoit.com>]

On Sat, Oct 14, 2006 at 02:42:59AM +0200, Blaisorblade wrote:
> > > Kernel panic - not syncing: Kernel mode fault at addr 0x92c00000, ip
> > > 0x80bcead
> Jeff, are these addresses normal? They tell that the binary is a statically 
> linked one - but what is the memory layout? Chris, can you post 
> cat /proc/<pid>/maps on a running instance of that kernel, together with host 
> and guest config (the guest's one is contained there, I know, but I don't 
> have the time to extract).

I'm not sure.  I've never trusted the numbers coming from that panic
message (which hurts debugging, I know).  I don't believe the fault
address, and the IP doesn't match anything in the symbol table, so I
don't believe that either.

> I.e. all the rest are bogus functions?

No.  Above the skb_checksum frame, there are lots of occurrences of
dst_output, which is a function pointer being passed down the stack.
What remains looks like the remnants of old stacks.

Between csum_partial and skb_checksum, there's a big frame (and I
don't know what's causing that) with what looks like old stack in it.

> There are automated solutions for this - compiling with frame pointers allows
> correct backtracing with a runtime penalty but is implemented; however, we 
> could reuse (not copy, please, we cannot maintain it) the x86 DWARF unwinder 
> (instead of using frame pointer and to slow down fast paths, additional 
> out-of-line debug info are used when the stack trace is output) - but we 
> should implement this latter one. Jeff, can you take a look at it?

Yup, that sounds like a good idea.

				Jeff

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