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 0C8C4C4167B for ; Fri, 16 Dec 2022 17:38:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231835AbiLPRiN (ORCPT ); Fri, 16 Dec 2022 12:38:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46834 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230237AbiLPRiM (ORCPT ); Fri, 16 Dec 2022 12:38:12 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EBC544046A; Fri, 16 Dec 2022 09:38:11 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 776B3621C0; Fri, 16 Dec 2022 17:38:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AD48FC433D2; Fri, 16 Dec 2022 17:38:08 +0000 (UTC) Date: Fri, 16 Dec 2022 12:38:04 -0500 From: Steven Rostedt To: David Laight Cc: 'Andreas Schwab' , "'Leizhen (ThunderTown)'" , Geert Uytterhoeven , Josh Poimboeuf , Jiri Kosina , Miroslav Benes , Petr Mladek , "Joe Lawrence" , "live-patching@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Masahiro Yamada , Alexei Starovoitov , Jiri Olsa , Kees Cook , Andrew Morton , "Luis Chamberlain" , "linux-modules@vger.kernel.org" , Ingo Molnar , linux-m68k , "Jason A. Donenfeld" Subject: Re: [PATCH v9] kallsyms: Add self-test facility Message-ID: <20221216123805.6eba002c@gandalf.local.home> In-Reply-To: <20221216121947.7d03b651@gandalf.local.home> References: <20221115083349.1662-1-thunder.leizhen@huawei.com> <49070ac3-02bb-a3b3-b929-ede07e3b2c95@huawei.com> <4aaede14-8bd3-6071-f17b-7efcb5f0de42@huawei.com> <66ec4021-b633-09ba-73ee-b24cdb3fa25a@huawei.com> <06345dca-0afb-00a5-c9e9-5ba830d8ad05@huawei.com> <52450ec1da164d6d87587063c3b3d3d2@AcuMS.aculab.com> <592dce7a0de24c62bd31c29f86ce6c1b@AcuMS.aculab.com> <87pmcjidfe.fsf@igel.home> <1ba1fadb39994a4d91edabdfd9d69fa6@AcuMS.aculab.com> <87len7ibtt.fsf@igel.home> <87fsdfib07.fsf@igel.home> <819801284eb745d9a4189759bad297f5@AcuMS.aculab.com> <20221216115314.6120beb7@gandalf.local.home> <20221216121947.7d03b651@gandalf.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Fri, 16 Dec 2022 12:19:47 -0500 Steven Rostedt wrote: > I assumed that "memory" was for memory unrelated to the input constraints. Well, it looks like you do need a "memory" barrier. https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html "memory" The "memory" clobber tells the compiler that the assembly code performs memory reads or writes to items other than those listed in the input and output operands (for example, accessing the memory pointed to by one of the input parameters). To ensure memory contains correct values, GCC may need to flush specific register values to memory before executing the asm. Further, the compiler does not assume that any values read from memory before an asm remain unchanged after that asm; it reloads them as needed. Using the "memory" clobber effectively forms a read/write memory barrier for the compiler. As the "(for example, accessing the memory pointed to by one of the input parameters)" is exactly this case. -- Steve