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Re: Troubles analyzing crash dumps from xl dump-core

CCing a few maintainers that might know something about this

On Fri, 29 Jan 2021, Roman Shaposhnik wrote:
> Hi!
> I'm trying to see how much mileage I can get out of
> crash(1) 7.2.8 (based on gdb 7.6) when it comes to
> analyzing crash dumps taken via xl dump-core (this
> is all on x86_64 with stock Xen v. 4.14).
> The good news is that the image actually does load
> up but it throws the following WARNINGs in the process:
> WARNING: cannot access vmalloc'd module memory
> crash: read error: kernel virtual address: ffffffff93613480  type:
> "fill_task_struct"
> WARNING: active task ffffffff93613480 on cpu 0 not found in PID hash
> crash: read error: kernel virtual address: ffffffff93613480  type:
> "fill_task_struct"
> WARNING: cannot read log_buf contents
> And then the info that it gives me around basic things like
> ps, mod, log, etc. is really super limited (and I am now suspecting
> may even be wrong).
> Since I was primarily after dmesg/log initially, I tried:
> crash> log
> log: WARNING: cannot read log_buf contents
> Then I tried taking an xl dump-core from the domU that was still
> very much alive and happy and got similar results -- so it clearly
> doesn't seem to be related to the state domU is in.
> As matter of fact, I actually got to the desired dmesg output
> by simply running strings(1) on the core file -- so the info is
> definitely there -- but I guess some kind of index/reference maybe
> broken.
> With all that in mind, if there's anyone on this ML who has recently
> done Xen DomU crash dump analysis -- I would definitely appreciate
> the pointers!
> Thanks,
> Roman.



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