From mboxrd@z Thu Jan 1 00:00:00 1970 From: dave.long@linaro.org (David Long) Date: Thu, 20 Nov 2014 23:28:32 -0500 Subject: [PATCH v3 1/5] arm64: Kprobes with single stepping support In-Reply-To: <1416317295.1735.9.camel@linaro.org> References: <1416292375-29560-1-git-send-email-dave.long@linaro.org> <1416292375-29560-2-git-send-email-dave.long@linaro.org> <1416317295.1735.9.camel@linaro.org> Message-ID: <546EBF70.9020706@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 11/18/14 08:28, Jon Medhurst (Tixy) wrote: > 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 > Took me a while to read through the background on this. I believe it is true nothing extra is put on the stack in the single-step case. -dl