get backtrace of KVM VM from host
Tue May 22 14:05:00 GMT 2018
On Mon, 2018-05-21 at 10:26 +0200, Justin Cinkelj wrote:
> Is it possible to get stack backtrace into KVM VM from the host side?
> if I run './stack -p PID' (stack from elfutilfs
> https://sourceware.org/elfutils/), I get backtrace of some process. I
> would like to do the same for VM. I can assume VM will run only a kernel
> (a unikernel, like OSv or IncludeOS), so most/all debug symbols will be
> there in a single file, and at least IncludeOS doesnt load any code
> beside its own kernel.
> I did notice KVM_GET_REGS and KVM_SET_MEMORY_REGION, and at least for
> > trivial examples (like https://github.com/dpw/kvm-hello-world) this
> provides enough information to track which code was loaded into VM,
> observe current stack content and registers. I can only guess much more
> work is required to get similar result with qemu-kvm. Hence I'm asking
> if this is already implemented.
Providing the registers and memory view inside the KVM VM would be the
first step. elfutils would also need to know the memory/ELF process
layout. For a normal process that would come from e.g. /proc/pid/maps.
Using such a layout eu-stack would then be able to find the unwind
tables and symbols associated with a particular address.
I believe qemu already has an gdb stub that gdb can use to get at the
registers, memory and process layout. Maybe you could adapt that
provide the information needed.
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