Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer

[Ingo Molnar <mingo@elte.hu>]

* Masami Hiramatsu <mhiramat@redhat.com> wrote:

> Hi,
> 
> Here are the patches of kprobe-based event tracer for x86, version 4.
> 
> This version supports only x86(-32/-64) (If someone is interested in
> porting this to other architectures, he just needs to port
> kprobes/kretprobes and ptrace enhancement[PATCH 2/6]).
> 
> I added x86 insn decoder on this version. It might be better
> integrated with KVM's decoder, and kprobes x86 code should be
> rewritten with it.
> 
> 
> This can be applied on the linux-2.6-tip tree.
> 
> This patchset includes following changes:
> - Fix kernel_trap_sp() on x86 according to systemtap runtime. [1/6]
> - Add arch-dep register and stack fetching functions [2/6]
> - Add x86 instruction decoder [3/6]
> - Check insertion point safety in kprobe [4/6]
> - Add kprobe-tracer plugin [5/6]
> - Support fetching various status (register/stack/memory/etc.) [6/6]

ok, the structure and concept looks quite good now, really nice!

I'm wondering about something i suggested many moons ago: to look 
into the KVM decoder+emulator (arch/x86/kvm/x86_emulate.c).

I remember there were some issues with that (one problem being that 
the KVM decoder is a special-purpose thing covering specific range 
of execution environments - not a near-full integer-ops decoder like 
the one we are aiming for here) - are there any other fundamental 
problems beyond 'it has to be done' ?

Conceptually we want just a single piece of decoder logic in 
arch/x86/. If the KVM folks are cool with it we could factor out the 
KVM one into arch/x86/lib/. But ... if there are compelling reasons 
to leave the KVM one alone in its limited environment we can do that 
too.

Avi, Peter, what's your take on this?

	Ingo