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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED 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 D88FCC10F0E for ; Fri, 12 Apr 2019 13:49:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A5B6420850 for ; Fri, 12 Apr 2019 13:49:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555076963; bh=/6YSBsCEYlkSXwaJHg4fmlnapDa79xojOFgqTwN7IDo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=GVQO2OPMU3dsoiAWIyVWpYNbTvzRvHsuH6+Gc1eV6f7pY3SgYrfAduBcHFOOTKPH1 etRwwwoYSsxXR2+O+vzrnr+6CJApa8X1SviILOiYvwAanPFFGDW5wFY+fuRlz4Orxq XzkmQcWPg/toor4NW1i3y0oG31ZUDfwTdWrL7huA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726907AbfDLNtW (ORCPT ); Fri, 12 Apr 2019 09:49:22 -0400 Received: from mail.kernel.org ([198.145.29.99]:42198 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726789AbfDLNtW (ORCPT ); Fri, 12 Apr 2019 09:49:22 -0400 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8E3E92084D; Fri, 12 Apr 2019 13:49:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555076961; bh=/6YSBsCEYlkSXwaJHg4fmlnapDa79xojOFgqTwN7IDo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=dPC6hmU5VVHipggOy2xRcgC3X8cQ2Wsq1r6AcGlI4j4LITlc0pxkj0Gig6KTgYU1B kqNdmju8A3gEPuzNUavfSMHGlSMOcE2nntS1ZGFdyTvssr081bN1cEgT2EEZ+S2GT2 Jrxd6Ugkfv+xFrePTn68GonfQWdLhaCTm4zVF0pY= Date: Fri, 12 Apr 2019 22:49:16 +0900 From: Masami Hiramatsu To: Will Deacon 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: <20190412224916.fea6405337457c1242d8960a@kernel.org> In-Reply-To: <20190411172253.GH29081@fuggles.cambridge.arm.com> References: <155289594227.10570.1879705446198840331.stgit@devnote2> <20190403120649.GB29409@fuggles.cambridge.arm.com> <20190408093320.35f4050788937c995ca56a6b@kernel.org> <20190411172253.GH29081@fuggles.cambridge.arm.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 11 Apr 2019 18:22:53 +0100 Will Deacon wrote: > On Mon, Apr 08, 2019 at 09:33:20AM +0900, Masami Hiramatsu wrote: > > On Wed, 3 Apr 2019 13:06:49 +0100 > > Will Deacon wrote: > > > 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? > > > > As far as I can read "Procedure Call Standard for the ARM 64-bit > > Architecture(AArch64) 5.4.2 Parameter Passing Rules", it may not return > > correct data if the target function has a parameter which is 16bytes > > or bigger size. Of course that is just a limitation of this interface. > > But anyway, it can return wrong data for the parameter after such big > > parameters. I think, for func(data-struct-128bits p1, u64 p2), p1 > > is stored into r0 and r1, and p2 is stored r2, is that correct? > > Oh, yes, passing things by value that don't fit in the registers will > obviously go wrong. Thanks. Do we do that in the kernel? No, as far as I know. But I can't say it never happens in the kernel. > > Anyway, please resend with the comment expanded a bit and using > pt_regs_read_reg(), then I can queue this up for 5.2. OK, I'll do. Thank you! > > Cheers, > > Will -- Masami Hiramatsu