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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 3A8FAC4360F for ; Wed, 3 Apr 2019 12:06:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 036F02084B for ; Wed, 3 Apr 2019 12:06:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726245AbfDCMGy (ORCPT ); Wed, 3 Apr 2019 08:06:54 -0400 Received: from foss.arm.com ([217.140.101.70]:38776 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725941AbfDCMGy (ORCPT ); Wed, 3 Apr 2019 08:06:54 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 803C880D; Wed, 3 Apr 2019 05:06:53 -0700 (PDT) Received: from fuggles.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4C2213F59C; Wed, 3 Apr 2019 05:06:52 -0700 (PDT) Date: Wed, 3 Apr 2019 13:06:49 +0100 From: Will Deacon To: Masami Hiramatsu Cc: Catalin Marinas , Steven Rostedt , Oleg Nesterov , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64: ptrace: Add function argument access API Message-ID: <20190403120649.GB29409@fuggles.cambridge.arm.com> References: <155289594227.10570.1879705446198840331.stgit@devnote2> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <155289594227.10570.1879705446198840331.stgit@devnote2> User-Agent: Mutt/1.11.1+86 (6f28e57d73f2) () Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 18, 2019 at 04:59:02PM +0900, Masami Hiramatsu wrote: > Add regs_get_argument() which returns N th argument of the function > call. On arm64, it supports up to 8th argument. > Note that this chooses most probably assignment, in some case > it can be incorrect (e.g. passing data structure or floating > point etc.) > > This enables ftrace kprobe events to access kernel function > arguments via $argN syntax. > > Signed-off-by: Masami Hiramatsu > --- > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/ptrace.h | 18 ++++++++++++++++++ > 2 files changed, 19 insertions(+) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 117b2541ef3d..6ba0da4be73c 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -148,6 +148,7 @@ config ARM64 > select HAVE_PERF_REGS > select HAVE_PERF_USER_STACK_DUMP > select HAVE_REGS_AND_STACK_ACCESS_API > + select HAVE_FUNCTION_ARG_ACCESS_API > select HAVE_RCU_TABLE_FREE > select HAVE_RCU_TABLE_INVALIDATE > select HAVE_RSEQ > diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h > index ec60174c8c18..cfa1bc9b8b70 100644 > --- a/arch/arm64/include/asm/ptrace.h > +++ b/arch/arm64/include/asm/ptrace.h > @@ -305,6 +305,24 @@ static inline unsigned long regs_return_value(struct pt_regs *regs) > return regs->regs[0]; > } > > +/** > + * regs_get_kernel_argument() - get Nth function argument in kernel > + * @regs: pt_regs of that context > + * @n: function argument number (start from 0) > + * > + * regs_get_argument() returns @n th argument of the function call. > + * Note that this chooses most probably assignment, in some case > + * it can be incorrect. In which cases would it be incorrect? I can imagine varargs causing problems, but are there others? > +static inline unsigned long regs_get_kernel_argument(struct pt_regs *regs, > + unsigned int n) > +{ > +#define NR_REG_ARGUMENTS 8 > + if (n < NR_REG_ARGUMENTS) > + return regs_get_register(regs, n << 3); You can use pt_regs_read_reg() to avoid the shift here. Will