Re: [PATCH v3 1/5] arm64: Kprobes with single stepping support

[David Long]

On 11/19/14 06:25, Will Deacon wrote:
> On Wed, Nov 19, 2014 at 11:21:24AM +0000, Sandeepa Prabhu wrote:
> > On 18 November 2014 20:26, Will Deacon <will.deacon@xxxxxxx> wrote:
> >
> > > One thing I noticed looking through this patch is that we're effectively
> > > reinventing a bunch of the instruction decoding logic that we already have
> > > in the kernel (introduced since Sandeepa last sent his patch).
> > >
> > > Could you take a look at include/asm/insn.h and kernel/insn.c please, and
> > > see if you can at least consolidate some of this? Some of it should be easy
> > > (i.e. reusing masks, using existing #defines to construct BRK encodings),
> > > but I appreciate there may be places where kprobes needs to add extra bits,
> > > in which case I'd really like to keep this all together if at all possible.
> > >
> > > We're currently in a position where the module loader, BPF jit, ftrace and
> > > the proposed alternative patching scheme are all using the same instruction
> > > manipulation functions, so we should try to continue that trend if we can.
> > Will,
> >
> > kernel/insn.c support generating instruction encodings(forming opcodes
> > with given specifications), so for kprobes, only BRK encoding can use
> > this mechanism.
> > For instruction simulation, the instruction behavior should be
> > simulated on saved pt_regs, which is not supported on insn.c routines,
> > so still need probes-simulate-insn.c. Please point me if I am missing
> > something here.
>
> I was thinking of the magic hex numbers in the kprobes decode tables, which
> seem to correspond directly to the instruction classes described in insn.c
>
> Keeping the actual emulation code separate makes sense.
>
> Will

Of course that follows the model of the much more complex arm32 
kprobes/uprobes decoding.  I can have a go at replacing it with insn.c 
calls.

-dl

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