From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B5EC4C169C4 for ; Wed, 6 Feb 2019 15:05:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8FA022175B for ; Wed, 6 Feb 2019 15:05:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730528AbfBFPF0 (ORCPT ); Wed, 6 Feb 2019 10:05:26 -0500 Received: from verein.lst.de ([213.95.11.211]:60151 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726767AbfBFPF0 (ORCPT ); Wed, 6 Feb 2019 10:05:26 -0500 Received: by newverein.lst.de (Postfix, from userid 2005) id B3CA168D93; Wed, 6 Feb 2019 16:05:24 +0100 (CET) Date: Wed, 6 Feb 2019 16:05:24 +0100 From: Torsten Duwe To: Julien Thierry Cc: Mark Rutland , Will Deacon , Catalin Marinas , Steven Rostedt , Josh Poimboeuf , Ingo Molnar , Ard Biesheuvel , Arnd Bergmann , AKASHI Takahiro , Amit Daniel Kachhap , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Subject: Re: [PATCH v7 2/3] arm64: implement ftrace with regs Message-ID: <20190206150524.GA28892@lst.de> References: <20190118163736.6A99268CEB@newverein.lst.de> <20190118163908.E338E68D93@newverein.lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 06, 2019 at 08:59:44AM +0000, Julien Thierry wrote: > Hi Torsten, > > On 18/01/2019 16:39, Torsten Duwe wrote: > > > --- a/arch/arm64/kernel/ftrace.c > > +++ b/arch/arm64/kernel/ftrace.c > > @@ -133,17 +163,45 @@ int ftrace_make_call(struct dyn_ftrace * > > return ftrace_modify_code(pc, old, new, true); > > } > > > > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > > +int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, > > + unsigned long addr) > > +{ > > + unsigned long pc = rec->ip + REC_IP_BRANCH_OFFSET; > > + u32 old, new; > > + > > + old = aarch64_insn_gen_branch_imm(pc, old_addr, true); > > + new = aarch64_insn_gen_branch_imm(pc, addr, true); > > + > > + return ftrace_modify_code(pc, old, new, true); > > +} > > +#endif > > + > > /* > > * Turn off the call to ftrace_caller() in instrumented function > > */ > > int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, > > unsigned long addr) > > { > > - unsigned long pc = rec->ip; > > + unsigned long pc = rec->ip + REC_IP_BRANCH_OFFSET; > > Sorry to come back on this patch again, but I was looking at the ftrace > code a bit, and I see that when processing the ftrace call locations, > ftrace calls ftrace_call_adjust() on every ip registered as mcount > caller (or in our case patchable entries). This ftrace_call_adjust() is > arch specific, so I was thinking we could place the offset in here once > and for all so we don't have to worry about it in the future. Now that you mention it - yes indeed that's the correct facility to fix the deviating address, as Steve has also confirmed. I had totally forgotten about this hook. > Also, I'm unsure whether it would be safe, but we could patch the "mov > x9, lr" there as well. In theory, this would be called at init time > (before secondary CPUs are brought up) and when loading a module (so I'd > expect no-one is executing that code *yet*. > > If this is possible, I think it would make things a bit cleaner. This is in fact very tempting, but it will introduce a nasty side effect to ftrace_call_adjust. Is there any obvious documentation that specifies guarantees about ftrace_call_adjust being called exactly once for each site? Torsten From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 61068C169C4 for ; Wed, 6 Feb 2019 15:05:48 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2ECCA2175B for ; Wed, 6 Feb 2019 15:05:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="mYK+feoo" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2ECCA2175B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=tV72YSYYEFsQzr/+/qQNlrEOsFM0zUU0+ZR3lCrZo5k=; b=mYK+feooWqGXtw +1bW/OqL0sZtrkOc0isKROu30q0Zy/QpUeReEgSbkB4I9ouAjYTABUUTe2GqdK1vQ2fsRl/LSxIdG tcMbMGO5bDmRQk1AHlkz9MuC6BBGo0G1OylBupbNiU0YE3VbjglcHoVEfWOUoYiiyGin/pdO3Iv+g beOyLGMJhUSpKa1izZVxLEc3QSyji41FC1zclg7WwW7d2NMk9MNDm9YJqEke8rzZSaPO7E+W5s6E6 agVfN57NfBV7pRcf18h7FzxyYMXKnI02R4oA7Q7pBRcCi8QPPv5zJNPQ7apZ7rRnKiDKCwyNO4w4R R1wNjGZ8hpV4wJgKlR+Q==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1grOld-0000CK-OO; Wed, 06 Feb 2019 15:05:37 +0000 Received: from verein.lst.de ([213.95.11.211] helo=newverein.lst.de) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1grOlZ-0000BL-FD for linux-arm-kernel@lists.infradead.org; Wed, 06 Feb 2019 15:05:35 +0000 Received: by newverein.lst.de (Postfix, from userid 2005) id B3CA168D93; Wed, 6 Feb 2019 16:05:24 +0100 (CET) Date: Wed, 6 Feb 2019 16:05:24 +0100 From: Torsten Duwe To: Julien Thierry Subject: Re: [PATCH v7 2/3] arm64: implement ftrace with regs Message-ID: <20190206150524.GA28892@lst.de> References: <20190118163736.6A99268CEB@newverein.lst.de> <20190118163908.E338E68D93@newverein.lst.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190206_070533_661816_B47EC62C X-CRM114-Status: GOOD ( 20.18 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Arnd Bergmann , Ard Biesheuvel , Catalin Marinas , Will Deacon , linux-kernel@vger.kernel.org, Steven Rostedt , AKASHI Takahiro , Ingo Molnar , Josh Poimboeuf , Amit Daniel Kachhap , live-patching@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Feb 06, 2019 at 08:59:44AM +0000, Julien Thierry wrote: > Hi Torsten, > > On 18/01/2019 16:39, Torsten Duwe wrote: > > > --- a/arch/arm64/kernel/ftrace.c > > +++ b/arch/arm64/kernel/ftrace.c > > @@ -133,17 +163,45 @@ int ftrace_make_call(struct dyn_ftrace * > > return ftrace_modify_code(pc, old, new, true); > > } > > > > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > > +int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, > > + unsigned long addr) > > +{ > > + unsigned long pc = rec->ip + REC_IP_BRANCH_OFFSET; > > + u32 old, new; > > + > > + old = aarch64_insn_gen_branch_imm(pc, old_addr, true); > > + new = aarch64_insn_gen_branch_imm(pc, addr, true); > > + > > + return ftrace_modify_code(pc, old, new, true); > > +} > > +#endif > > + > > /* > > * Turn off the call to ftrace_caller() in instrumented function > > */ > > int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, > > unsigned long addr) > > { > > - unsigned long pc = rec->ip; > > + unsigned long pc = rec->ip + REC_IP_BRANCH_OFFSET; > > Sorry to come back on this patch again, but I was looking at the ftrace > code a bit, and I see that when processing the ftrace call locations, > ftrace calls ftrace_call_adjust() on every ip registered as mcount > caller (or in our case patchable entries). This ftrace_call_adjust() is > arch specific, so I was thinking we could place the offset in here once > and for all so we don't have to worry about it in the future. Now that you mention it - yes indeed that's the correct facility to fix the deviating address, as Steve has also confirmed. I had totally forgotten about this hook. > Also, I'm unsure whether it would be safe, but we could patch the "mov > x9, lr" there as well. In theory, this would be called at init time > (before secondary CPUs are brought up) and when loading a module (so I'd > expect no-one is executing that code *yet*. > > If this is possible, I think it would make things a bit cleaner. This is in fact very tempting, but it will introduce a nasty side effect to ftrace_call_adjust. Is there any obvious documentation that specifies guarantees about ftrace_call_adjust being called exactly once for each site? Torsten _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel