From mboxrd@z Thu Jan 1 00:00:00 1970 From: panand@redhat.com (Pratyush Anand) Date: Wed, 7 Sep 2016 10:17:52 +0530 Subject: [PATCH 3/5] arm64: Handle TRAP_HWBRKPT for user mode as well In-Reply-To: <57CF36D2.4010404@linaro.org> References: <20160906161139.GG19605@e104818-lin.cambridge.arm.com> <57CF36D2.4010404@linaro.org> Message-ID: <20160907044752.GF24688@localhost.localdomain> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 06/09/2016:05:36:18 PM, David Long wrote: > On 09/06/2016 12:11 PM, Catalin Marinas wrote: > > On Tue, Aug 02, 2016 at 11:00:07AM +0530, Pratyush Anand wrote: > > > --- a/arch/arm64/kernel/debug-monitors.c > > > +++ b/arch/arm64/kernel/debug-monitors.c > > > @@ -246,6 +246,8 @@ static void send_user_sigtrap(int si_code) > > > static int single_step_handler(unsigned long addr, unsigned int esr, > > > struct pt_regs *regs) > > > { > > > + bool handler_found = false; > > > + > > > /* > > > * If we are stepping a pending breakpoint, call the hw_breakpoint > > > * handler first. > > > @@ -253,7 +255,14 @@ static int single_step_handler(unsigned long addr, unsigned int esr, > > > if (!reinstall_suspended_bps(regs)) > > > return 0; > > > > > > - if (user_mode(regs)) { > > > +#ifdef CONFIG_KPROBES > > > + if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED) > > > + handler_found = true; > > > +#endif > > > + if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED) > > > + handler_found = true; > > > + > > > + if (!handler_found && user_mode(regs)) { > > > send_user_sigtrap(TRAP_HWBKPT); > > > > Could we register kprobe_single_step_handler() via register_set_hook() > > and only invoke call_step_hook() above? > > > > I seem to recall a criticism of doing that in a much earlier kprobes64 patch > of mine. The concern was that it would cause unnecessarily more kernel > functions to be kprobes-blacklisted. Hence the hardcoded check and call. Yes, all the code regions are kprobe unsafe which lie within the moment we receive a break/single step exception to the point where it is handled for kprobe. Therefore we must call kprobe_single_step/breakpoint_handler() before other handlers. Otherwise, we would not be able to trace other handlers and the functions called from those handlers. ~Pratyush