From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752721AbcLGMKb (ORCPT ); Wed, 7 Dec 2016 07:10:31 -0500 Received: from mail-wm0-f68.google.com ([74.125.82.68]:35446 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752586AbcLGMK3 (ORCPT ); Wed, 7 Dec 2016 07:10:29 -0500 Date: Wed, 7 Dec 2016 12:10:26 +0000 From: Abel Vesa To: Robin Murphy Cc: Abel Vesa , linux@armlinux.org.uk, jpoimboe@redhat.com, jeyu@redhat.com, jikos@kernel.org, mbenes@suse.cz, pmladek@suse.com, linux-arm-kernel@lists.infradead.org, geert+renesas@glider.be, ard.biesheuvel@linaro.org, jean-philippe.brucker@arm.com, gregkh@linuxfoundation.org, stefano.stabellini@eu.citrix.com, emil.l.velikov@gmail.com, linux-kernel@vger.kernel.org, rostedt@goodmis.org, jens.wiklander@linaro.org, chris.brandt@renesas.com, mingo@redhat.com, viro@zeniv.linux.org.uk, live-patching@vger.kernel.org, akpm@linux-foundation.org, mchehab@kernel.org, davem@davemloft.net, linux@roeck-us.net Subject: Re: [PATCH 4/7] arm: Add ftrace with regs support Message-ID: <20161207121026.GB22174@gce> References: <1481043967-15602-1-git-send-email-abelvesa@linux.com> <1481043967-15602-5-git-send-email-abelvesa@linux.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 07, 2016 at 11:58:24AM +0000, Robin Murphy wrote: > Hi Abel, > > On 06/12/16 17:06, Abel Vesa wrote: > > This adds __ftrace_regs_caller which, unlike __ftrace_caller, > > adds register saving/restoring and livepatch handling if > > the pc register gets modified by klp_ftrace_handler. > > > > Signed-off-by: Abel Vesa > > --- > > arch/arm/kernel/entry-ftrace.S | 49 ++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 49 insertions(+) > > > > diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S > > index c73c403..b6ada5c 100644 > > --- a/arch/arm/kernel/entry-ftrace.S > > +++ b/arch/arm/kernel/entry-ftrace.S > > @@ -92,6 +92,46 @@ > > 2: mcount_exit > > .endm > > > > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > > + > > +.macro __ftrace_regs_caller suffix > > + > > + stmdb sp!, {r0-r15} > > As the kbuild robot reported, you can't do this. For ARM, it's unknown > what the value stored for r13 will be, and for a Thumb-2 kernel the > whole instruction is flat out unpredictable (i.e. it might just undef or > anything). > > > + mov r3, sp > > + > > + ldr r10, [sp, #60] > > + > > + mcount_get_lr r1 @ lr of instrumented func > > + mcount_adjust_addr r0, lr @ instrumented function > > + > > + .globl ftrace_regs_call\suffix > > +ftrace_regs_call\suffix: > > + bl ftrace_stub > > + > > +#ifdef CONFIG_FUNCTION_GRAPH_TRACER > > + .globl ftrace_regs_graph_call\suffix > > +ftrace_regs_graph_call\suffix: > > + mov r0, r0 > > +#endif > > +#ifdef CONFIG_LIVEPATCH > > + ldr r0, [sp, #60] > > + cmp r0, r10 > > + beq ftrace_regs_caller_end > > + ldmia sp!, {r0-r12} > > + add sp, sp, #8 > > + ldmia sp!, {r11} > > + sub sp, r12, #16 > > + str r11, [sp, #12] > > + ldmia sp!, {r11, r12, lr, pc} > > +#endif > > +ftrace_regs_caller_end\suffix: > > + ldmia sp!, {r0-r14} > > Again, the value of SP at this point is now unknown (regardless of > whether what the value on memory was correct or not). Not good. > > Either use non-writeback addressing modes, or avoid saving/restoring SP > at all (AFAICS it isn't necessary, since if the SP was changed in > between, you then wouldn't know where to restore the saved registers > from anyway). > > Robin. > Yep, as I said in the cover letter, I'll try to fix that in the next iteration of this patch. You're right, sp doesn't need to be pushed or popped. I'll send a another patch series which will include a fix for that tomorrow, latest. Thanks. > > + add sp, sp, #4 > > + mov pc, lr > > +.endm > > + > > +#endif > > + > > .macro __ftrace_caller suffix > > mcount_enter > > > > @@ -212,6 +252,15 @@ UNWIND(.fnstart) > > __ftrace_caller > > UNWIND(.fnend) > > ENDPROC(ftrace_caller) > > + > > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > > +ENTRY(ftrace_regs_caller) > > +UNWIND(.fnstart) > > + __ftrace_regs_caller > > +UNWIND(.fnend) > > +ENDPROC(ftrace_regs_caller) > > +#endif > > + > > #endif > > > > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > > >