On 18 November 2014 20:26, Will Deacon [off-list ref] 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.

Thanks,

Will