Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754704AbcKOTSM (ORCPT ); Tue, 15 Nov 2016 14:18:12 -0500 Received: from smtp.codeaurora.org ([198.145.29.96]:52978 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932407AbcKOTSJ (ORCPT ); Tue, 15 Nov 2016 14:18:09 -0500 DMARC-Filter: OpenDMARC Filter v1.3.1 smtp.codeaurora.org 5EAE16145F Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=pass smtp.mailfrom=sboyd@codeaurora.org Date: Tue, 15 Nov 2016 11:18:07 -0800 From: Stephen Boyd To: Ard Biesheuvel Cc: "Steven Rostedt (Red Hat)" , Andrew Morton , Russell King , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH/RESEND] recordmcount: arm: Implement make_nop Message-ID: <20161115191807.GC25626@codeaurora.org> References: <20161018234200.5804-1-sboyd@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1936 Lines: 53 On 11/15, Ard Biesheuvel wrote: > On 19 October 2016 at 00:42, Stephen Boyd wrote: > > In similar spirit to x86 and arm64 support, add a make_nop_arm() > > to replace calls to mcount with a nop in sections that aren't > > traced. > > > > Cc: Russell King > > Acked-by: Rabin Vincent > > Signed-off-by: Stephen Boyd > > --- > > scripts/recordmcount.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 65 insertions(+) > > > > diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c > > index 5423a58d1b06..aeb34223167c 100644 > > --- a/scripts/recordmcount.c > > +++ b/scripts/recordmcount.c > > @@ -213,6 +213,59 @@ static int make_nop_x86(void *map, size_t const offset) > > return 0; > > } > > > > +static unsigned char ideal_nop4_arm_le[4] = { 0x00, 0x00, 0xa0, 0xe1 }; /* mov r0, r0 */ > > +static unsigned char ideal_nop4_arm_be[4] = { 0xe1, 0xa0, 0x00, 0x00 }; /* mov r0, r0 */ > > Shouldn't you be taking the difference between BE8 and BE32 into > account here? IIRC, BE8 uses little endian encoding for instructions. I admit I haven't tested on a pre-armv6 CPU so I haven't come across the case of a BE32 CPU. But from what I can tell that doesn't matter. According to scripts/Makefile.build, cmd_record_mcount only runs the recordmcount program if CONFIG_FTRACE_MCOUNT_RECORD=y. That config is defined as: config FTRACE_MCOUNT_RECORD def_bool y depends on DYNAMIC_FTRACE depends on HAVE_FTRACE_MCOUNT_RECORD And in arch/arm/Kconfig we see that DYNAMIC_FTRACE is selected: select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL) && !CPU_ENDIAN_BE32 && MMU which means that FTRACE_MCOUNT_RECORD can't be set when CPU_ENDIAN_BE32 is set. Do you agree that BE32 is not a concern here? -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project