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 lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 E16A0C46CD2 for ; Wed, 24 Jan 2024 09:22:58 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.670833.1043877 (Exim 4.92) (envelope-from ) id 1rSZT8-0006rR-Cm; Wed, 24 Jan 2024 09:22:50 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 670833.1043877; Wed, 24 Jan 2024 09:22:50 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1rSZT8-0006rK-9q; Wed, 24 Jan 2024 09:22:50 +0000 Received: by outflank-mailman (input) for mailman id 670833; Wed, 24 Jan 2024 09:22:49 +0000 Received: from se1-gles-sth1-in.inumbo.com ([159.253.27.254] helo=se1-gles-sth1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1rSZT7-0006rC-MK for xen-devel@lists.xenproject.org; Wed, 24 Jan 2024 09:22:49 +0000 Received: from mail-lf1-x129.google.com (mail-lf1-x129.google.com [2a00:1450:4864:20::129]) by se1-gles-sth1.inumbo.com (Halon) with ESMTPS id 23a2b365-ba9a-11ee-98f5-6d05b1d4d9a1; Wed, 24 Jan 2024 10:22:48 +0100 (CET) Received: by mail-lf1-x129.google.com with SMTP id 2adb3069b0e04-50e766937ddso6206330e87.3 for ; Wed, 24 Jan 2024 01:22:48 -0800 (PST) Received: from localhost ([213.195.118.74]) by smtp.gmail.com with ESMTPSA id ef5-20020a05640228c500b00557d839727esm16290583edb.7.2024.01.24.01.22.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Jan 2024 01:22:47 -0800 (PST) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 23a2b365-ba9a-11ee-98f5-6d05b1d4d9a1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=google; t=1706088167; x=1706692967; darn=lists.xenproject.org; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date:from:to :cc:subject:date:message-id:reply-to; bh=shxK/mjfxX+fUVfht29zbiJG7ZSk3Mn0kuammqyAbD8=; b=qUUT34pRGr3I/eDs7RzWydvc/sqL424epF/A3Q119BxzfKj8a391egj7gFSIX3Z9Ep RIf211dBT+3LY8yBG47Dv7iceAVejVtsmKsVQQCganMvearKpwuOldegg3VBk1xypLyV MBYNYxEXRgXzFvjANXoLcBUbY7NYIPZQ/AGA0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1706088167; x=1706692967; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=shxK/mjfxX+fUVfht29zbiJG7ZSk3Mn0kuammqyAbD8=; b=bpmWO6bIqQSnqjY2+7NmJvi2Ci+6ILoBmfkvtlKXHj1CqbRkBtm6NF2cMtv+kHcvTu uVIT0bT41RAVdomgbAFHhGu85VJJhSdhwzsRx+LQy6vZbdprPSLCzbKhk0LqIERKfnye oWvNVesGaZREzId95r9TJNlZ6+TbXFBMD/L9ns9qIJ8Nai+hkN3m+RGe9/WWu7IstShR lJ/W/3z2XME7nQdHQ2R9VTAbgHX8zRQjvhun79nxoeYFJ4yPmgyym2GmroF9yaULy2ki ZB1hpln3gKDj/Ao8mNWB/Dwj9zg8Sa23cKO9R6oXHdpkwv1u9vDOOAkrf5ZmuvWC7LcG dH4w== X-Gm-Message-State: AOJu0YwCR7ZMHZ6v0NbXLiAIbLSoQx24AOKrqvNDHFcOft/FIZSp3m8H +FDQyeXwE02gnjedlyKLJzaEPOqfo+RqW+1yLdbqbE4FpbNQmojFIw1NWWAvndw= X-Google-Smtp-Source: AGHT+IGIatMlXAIT9wtFN4TVKhyxS8oAmqGfVN2/qMY8nODju2VQwelodI3MBQqSNPKI+RmLV0f68g== X-Received: by 2002:a19:7405:0:b0:50f:152b:48a9 with SMTP id v5-20020a197405000000b0050f152b48a9mr2744170lfe.122.1706088167663; Wed, 24 Jan 2024 01:22:47 -0800 (PST) Date: Wed, 24 Jan 2024 10:22:46 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Jan Beulich Cc: Andrew Cooper , Wei Liu , Konrad Rzeszutek Wilk , Ross Lagerwall , Xen-devel Subject: Re: [PATCH 2/3] x86/entry: Make #PF/NMI/INT0x82 more amenable to livepatching Message-ID: References: <20240122181714.1543738-1-andrew.cooper3@citrix.com> <20240122181714.1543738-3-andrew.cooper3@citrix.com> <0edeb969-6fef-46f4-b216-0858edbaefa6@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Jan 23, 2024 at 02:43:15PM +0100, Jan Beulich wrote: > On 23.01.2024 14:37, Roger Pau Monné wrote: > > On Tue, Jan 23, 2024 at 10:22:10AM +0100, Jan Beulich wrote: > >> On 22.01.2024 19:17, Andrew Cooper wrote: > >>> It is bad form to have inter-function fallthrough. It only functions right > >>> now because alignment padding bytes are NOPs. > >> > >> But that's a requirement anyway in executable sections. > > > > Really? I was under the impression we wanted to replace the padding > > nops with rets maybe, or even poison the padding with int3 or ud2. > > Well, that would be a decision of ours. Which then imo can't be described as > "only functions right now because ..." The assembler can't[1] use other than > NOPs by default, as it can't know whether fall-through is intended. So it's not a strict requirement of ELF that padding is done using nops, it's just the default decision of the assembler because it doesn't know better. Thanks, Roger.