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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5E8CDC4332F for ; Thu, 17 Nov 2022 10:52:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239494AbiKQKwp (ORCPT ); Thu, 17 Nov 2022 05:52:45 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41752 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239310AbiKQKw2 (ORCPT ); Thu, 17 Nov 2022 05:52:28 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 9255D5ADCA for ; Thu, 17 Nov 2022 02:52:25 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4D5DED6E; Thu, 17 Nov 2022 02:52:31 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.70.181]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B16903F73B; Thu, 17 Nov 2022 02:52:23 -0800 (PST) Date: Thu, 17 Nov 2022 10:52:15 +0000 From: Mark Rutland To: Will Deacon Cc: linux-kernel@vger.kernel.org, catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org, mhiramat@kernel.org, revest@chromium.org, rostedt@goodmis.org Subject: Re: [PATCH v2 4/4] ftrace: arm64: move from REGS to ARGS Message-ID: References: <20221103170520.931305-1-mark.rutland@arm.com> <20221103170520.931305-5-mark.rutland@arm.com> <20221115112701.GB32523@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221115112701.GB32523@willie-the-truck> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 15, 2022 at 11:27:03AM +0000, Will Deacon wrote: > On Thu, Nov 03, 2022 at 05:05:20PM +0000, Mark Rutland wrote: > > This commit replaces arm64's support for FTRACE_WITH_REGS with support > > for FTRACE_WITH_ARGS. This removes some overhead and complexity, and > > removes some latent issues with inconsistent presentation of struct > > pt_regs (which can only be reliably saved/restored at exception > > boundaries). > > [...] > > > @@ -78,10 +77,71 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr) > > return addr; > > } > > > > -#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS > > struct dyn_ftrace; > > struct ftrace_ops; > > -struct ftrace_regs; > > + > > +#define arch_ftrace_get_regs(regs) NULL > > + > > +struct ftrace_regs { > > + /* x0 - x8 */ > > + unsigned long regs[9]; > > + unsigned long __unused; > > + > > + unsigned long fp; > > + unsigned long lr; > > + > > + unsigned long sp; > > + unsigned long pc; > > +}; > > + > > +static __always_inline unsigned long > > +ftrace_regs_get_instruction_pointer(const struct ftrace_regs *fregs) > > +{ > > + return fregs->pc; > > +} > > + > > +static __always_inline void > > +ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs, > > + unsigned long pc) > > +{ > > + fregs->pc = pc; > > +} > > + > > +static __always_inline unsigned long > > +ftrace_regs_get_stack_pointer(const struct ftrace_regs *fregs) > > +{ > > + return fregs->sp; > > +} > > + > > +static __always_inline unsigned long > > +ftrace_regs_get_argument(struct ftrace_regs *fregs, unsigned int n) > > +{ > > + if (n < 8) > > + return fregs->regs[n]; > > Where does this '8' come from? Because in AAPCS64 the arguments are in x0 to x7, as mentioned in the commit message: | Per AAPCS64, all function call argument and return values are held in | the following GPRs: | | * X0 - X7 : parameter / result registers | * X8 : indirect result location register | * SP : stack pointer (AKA SP) The 'indirect result location register' would be used when returning large structures, and isn't a function argument as such. The logic is the same as in regs_get_kernel_argument() for pt_regs. I can add a comment here to explain that, if that would help? The rest of the registers are as described in the commit message (and I now spot a typo that I'll go fix): | Additionally, ad function call boundaries, the following GPRs hold | context/return information: | | * X29 : frame pointer (AKA FP) | * X30 : link register (AKA LR) | | ... and for ftrace we need to capture the instrumented address: | | * PC : program counter | | No other GPRs are relevant, as none of the other arguments hold | parameters or return values: | | * X9 - X17 : temporaries, may be clobbered | * X18 : shadow call stack pointer (or temorary) | * X19 - X28 : callee saved Thanks, Mark. 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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 0A1DAC4332F for ; Thu, 17 Nov 2022 10:58:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc: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=DLifr/wBqyIVv43aLQbaLDXiqS7lnCq9Fg8rtiBgDD4=; b=07+x/QzjlktvJo Q/Dl4EJrfV9ZBUsqt0JgcQrhc7swW2Bzrosv3Jx+wDbAvLrz2Yx+oRoLOnKbZPldbFKJdBcAePHf9 P4BhU1uLpqAGbchLCaFFBE/6LuoWsgsIepLvrBfZebzYsXSssPlu7SeIR+3/f3LwKObOHAaRRF6Lj rc796zq4+AHRDgnAkd/oLby2REvbWc9dd0MwgbIswaUsOwKYJctQ4HAhdM/sk0OZ9S6ZzkLiyIxAT KAgQdzE3KWH4TdYx4rZzA+I9qKdqwfK8cvrWrSnFvrV1bdzFMQlb4D1t13UDoz7pxzDijZ6pjsVvy PmZfTHmjzXGrBBm06GbQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ovca6-00Cr9M-81; Thu, 17 Nov 2022 10:57:18 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ovcVO-00Cnkz-4o for linux-arm-kernel@lists.infradead.org; Thu, 17 Nov 2022 10:52:27 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4D5DED6E; Thu, 17 Nov 2022 02:52:31 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.70.181]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B16903F73B; Thu, 17 Nov 2022 02:52:23 -0800 (PST) Date: Thu, 17 Nov 2022 10:52:15 +0000 From: Mark Rutland To: Will Deacon Cc: linux-kernel@vger.kernel.org, catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org, mhiramat@kernel.org, revest@chromium.org, rostedt@goodmis.org Subject: Re: [PATCH v2 4/4] ftrace: arm64: move from REGS to ARGS Message-ID: References: <20221103170520.931305-1-mark.rutland@arm.com> <20221103170520.931305-5-mark.rutland@arm.com> <20221115112701.GB32523@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20221115112701.GB32523@willie-the-truck> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221117_025226_296404_EA4D6833 X-CRM114-Status: GOOD ( 20.42 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Nov 15, 2022 at 11:27:03AM +0000, Will Deacon wrote: > On Thu, Nov 03, 2022 at 05:05:20PM +0000, Mark Rutland wrote: > > This commit replaces arm64's support for FTRACE_WITH_REGS with support > > for FTRACE_WITH_ARGS. This removes some overhead and complexity, and > > removes some latent issues with inconsistent presentation of struct > > pt_regs (which can only be reliably saved/restored at exception > > boundaries). > > [...] > > > @@ -78,10 +77,71 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr) > > return addr; > > } > > > > -#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS > > struct dyn_ftrace; > > struct ftrace_ops; > > -struct ftrace_regs; > > + > > +#define arch_ftrace_get_regs(regs) NULL > > + > > +struct ftrace_regs { > > + /* x0 - x8 */ > > + unsigned long regs[9]; > > + unsigned long __unused; > > + > > + unsigned long fp; > > + unsigned long lr; > > + > > + unsigned long sp; > > + unsigned long pc; > > +}; > > + > > +static __always_inline unsigned long > > +ftrace_regs_get_instruction_pointer(const struct ftrace_regs *fregs) > > +{ > > + return fregs->pc; > > +} > > + > > +static __always_inline void > > +ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs, > > + unsigned long pc) > > +{ > > + fregs->pc = pc; > > +} > > + > > +static __always_inline unsigned long > > +ftrace_regs_get_stack_pointer(const struct ftrace_regs *fregs) > > +{ > > + return fregs->sp; > > +} > > + > > +static __always_inline unsigned long > > +ftrace_regs_get_argument(struct ftrace_regs *fregs, unsigned int n) > > +{ > > + if (n < 8) > > + return fregs->regs[n]; > > Where does this '8' come from? Because in AAPCS64 the arguments are in x0 to x7, as mentioned in the commit message: | Per AAPCS64, all function call argument and return values are held in | the following GPRs: | | * X0 - X7 : parameter / result registers | * X8 : indirect result location register | * SP : stack pointer (AKA SP) The 'indirect result location register' would be used when returning large structures, and isn't a function argument as such. The logic is the same as in regs_get_kernel_argument() for pt_regs. I can add a comment here to explain that, if that would help? The rest of the registers are as described in the commit message (and I now spot a typo that I'll go fix): | Additionally, ad function call boundaries, the following GPRs hold | context/return information: | | * X29 : frame pointer (AKA FP) | * X30 : link register (AKA LR) | | ... and for ftrace we need to capture the instrumented address: | | * PC : program counter | | No other GPRs are relevant, as none of the other arguments hold | parameters or return values: | | * X9 - X17 : temporaries, may be clobbered | * X18 : shadow call stack pointer (or temorary) | * X19 - X28 : callee saved Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel