From mboxrd@z Thu Jan 1 00:00:00 1970 From: tixy@linaro.org (Jon Medhurst (Tixy)) Date: Tue, 18 Nov 2014 13:28:15 +0000 Subject: [PATCH v3 1/5] arm64: Kprobes with single stepping support In-Reply-To: <1416292375-29560-2-git-send-email-dave.long@linaro.org> References: <1416292375-29560-1-git-send-email-dave.long@linaro.org> <1416292375-29560-2-git-send-email-dave.long@linaro.org> Message-ID: <1416317295.1735.9.camel@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, 2014-11-18 at 01:32 -0500, David Long wrote: > From: Sandeepa Prabhu > > 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