Messages in this thread | | | Date | Wed, 19 Nov 2014 09:55:22 -0500 | From | David Long <> | Subject | Re: [PATCH v3 1/5] arm64: Kprobes with single stepping support |
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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@arm.com> 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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