Messages in this thread | | | Subject | Re: [PATCH v3 1/5] arm64: Kprobes with single stepping support | From | "Jon Medhurst (Tixy)" <> | Date | Tue, 18 Nov 2014 13:28:15 +0000 |
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On Tue, 2014-11-18 at 01:32 -0500, David Long wrote: > From: Sandeepa Prabhu <sandeepa.prabhu@linaro.org> > > Add support for basic kernel probes(kprobes) and jump probes > (jprobes) for ARM64. > > Kprobes will utilize software breakpoint and single step debug > exceptions supported on ARM v8. > > software breakpoint is placed at the probe address to trap the > kernel execution into kprobe handler. > > ARM v8 support single stepping to be enabled while exception return > (ERET) with next PC in exception return address (ELR_EL1). > kprobe handler prepares a executable memory slot for out-of-line > execution with the copy of the original instruction under probe, and > enable single stepping from the instruction slot. With this scheme, > the instruction is executed with the exact same register context > 'except PC' that points to instruction slot. > > Debug mask(PSTATE.D) is enabled only when single stepping a recursive > kprobes i.e. during kprobes reenter so that probes instruction can be > single stepped within the kprobe handler -exception- context.
Does this mean that at the point the probed instruction is single-stepped there is nothing extra that has been pushed on on the kernel stack by any kprobes handling code? I just want to check that you aren't going to hit the problems that the 32-bit kprobes code is currently being fixed for [1].
The simulated instructions in patch 2 don't access the stack, so they are safe from the problem.
[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/303525.html
-- Tixy
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