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 A0039C43334 for ; Fri, 8 Jul 2022 15:35:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238619AbiGHPfE (ORCPT ); Fri, 8 Jul 2022 11:35:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52542 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238613AbiGHPfE (ORCPT ); Fri, 8 Jul 2022 11:35:04 -0400 Received: from out2.migadu.com (out2.migadu.com [IPv6:2001:41d0:2:aacc::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 113951A3A6; Fri, 8 Jul 2022 08:35:03 -0700 (PDT) Date: Fri, 8 Jul 2022 23:36:06 +0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1657294501; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8Q2U10fVxflJg1wRLdlpzwKmLUZ/H+6ZbjlQlytlu3A=; b=pJRgOhPVgBRx5k/MVV3WVOImpOZpAmgGUHRC8Xe6Yp0ObR686Ffe1OFZFNoD8VisQ6GmQQ StZiq1oHCeETbNXCHZKSeUJxMnZ0xy85ksgkew4ADsAcnC/Y9KbDhojByL3ea13S7/mV92 /j4QlyOQCmKHb86QCySPxf+vSsWkbiM= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Tao Zhou To: Matthew Wilcox Cc: Daniel Bristot de Oliveira , Steven Rostedt , Wim Van Sebroeck , Guenter Roeck , Jonathan Corbet , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , Will Deacon , Catalin Marinas , Marco Elver , Dmitry Vyukov , "Paul E. McKenney" , Shuah Khan , Gabriele Paoloni , Juri Lelli , Clark Williams , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-devel@vger.kernel.org, Tao Zhou Subject: Re: [PATCH V4 01/20] rv: Add Runtime Verification (RV) interface Message-ID: References: <60548902dbccaa7ba420e40e46835693e27f643f.1655368610.git.bristot@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Wed, Jul 06, 2022 at 06:53:21PM +0100, Matthew Wilcox wrote: > On Thu, Jul 07, 2022 at 01:49:02AM +0800, Tao Zhou wrote: > > > +struct rv_monitor { > > > + const char *name; > > > + const char *description; > > > + bool enabled; > > > > Can the 'bool enabled;' be put at the end like the definition of > > structure rv_monitor_def. If '8+8+sizeof(bool)+8+8+8' not the same > > as '8+8+8+8+8+sizeof(bool)', I mean is it possible that after the > > end of stucture there is a int or char not require to align to 8 as > > an example from my nonsense. > > That will make no difference at all. C doesn't allow other variables > to "fill in the hole" at the end of the structure like that. For > example, one could legitimately do 'memset(&rvm, sizeof(rvm))', > and that would wipe out those other variables as well. I mean if it is possible that if @enabled placed at the end of the structure rv_monitor will save some bytes. If @enabled place in between, the next function pointer which is 8 bytes will align to be in x8 address and the size of structure rv_monitor is larger than been placed at the end of the structure. Or the compiler can do magic that I can not guess. Sorry for my late reply. I am not sure about this. But your reply is not about what I mean. You say that the size of structure is the same(I doute about this). But what my concert is that the other data next to the structure rv_monitor how to align if placing the @enabled at the end. Place in between, bytes: 8+8+8(padd)+8+8+8=48 Place at the end, bytes: 8+8+8+8+8+sizeof(bool)=? ? is small than 48 and the data next to the data structure rv_monitor can use the saved byte which is the result of placing @enabled at the end of structure to place the data.