Re: [v4,1/2] arch/powerpc: Implement Optprobes

[Anju T Sudhakar]

Thank You Michael.  :)


On Tuesday 14 February 2017 06:10 PM, Michael Ellerman wrote:
> On Wed, 2017-02-08 at 09:50:51 UTC, Anju T wrote:
> > Current infrastructure of kprobe uses the unconditional trap instruction
> > to probe a running kernel. Optprobe allows kprobe to replace the trap with
> > a branch instruction to a detour buffer. Detour buffer contains instructions
> > to create an in memory pt_regs. Detour buffer also has a call to
> > optimized_callback() which in turn call the pre_handler().
> > After the execution of the pre-handler, a call is made for instruction
> > emulation. The NIP is determined in advanced through dummy instruction
> > emulation and a branch instruction is created to the NIP at the end of
> > the trampoline.
> >
> > To address the limitation of branch instruction in POWER architecture,
> > detour buffer slot is allocated from a reserved area. For the time being,
> > 64KB is reserved in memory for this purpose.
> >
> > Instructions which can be emulated using analyse_instr() are the candidates
> > for optimization. Before optimization ensure that the address range
> > between the detour buffer allocated and the instruction being probed
> > is within +/- 32MB.
> >
> > Signed-off-by: Anju T Sudhakar <anju@xxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> > Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Series applied to powerpc next, thanks.
>
> https://git.kernel.org/powerpc/c/51c9c0843993528bffc920c54c2121
>
> cheers