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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 01BBAC021B8 for ; Tue, 4 Mar 2025 05:42:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=asZ89NjLYjHfpBcFWEra+PaQAUWjYIbeIoGtB844wqU=; b=08KYmZ+UOVzgEVIDrha8NPeSjU jNTdz8x6sE9yOPW9rtbHaN9doVkyFBjzmqWpHdvFSziqycScAUwTTbzGQyVb5AoKvf4Zvsl2Flsy2 dwU612+XnM1ZiY8Oqf3nYBe8noE5Vow8FS9knkAgW748t4t2NO7B2YjsynAZvm4MznlqbV2oRutvG 5Inf8l/E6WWn9kwNtNOmf/H10s/zu9FD5XetquJnfSMM0q8M1QxwE8k6lL1GrkO3SL5moDQMUq/qg 5wbWdACFz5uvB+ZRoL3gyjnQqdnxGGBc81pHHmKrvxxcx9zMXKQVqXr0hzA/1s8oWNGdDnSIWUSLL v84vPo0Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tpL2b-000000039iE-2PMU; Tue, 04 Mar 2025 05:42:05 +0000 Received: from casper.infradead.org ([2001:8b0:10b:1236::1]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tpKzg-000000039Jv-0MuL for linux-arm-kernel@bombadil.infradead.org; Tue, 04 Mar 2025 05:39:04 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=asZ89NjLYjHfpBcFWEra+PaQAUWjYIbeIoGtB844wqU=; b=KI4+xIvhaN+WFJ+4I3OIv62vvW vvKgZwD3kEbvhNNJATfeF6I4m7fCegtkQTp8i3I5SFGvEv22YX6iMKoMOWHX5z3Unsddyi1zYtIjs VqpSz/ZPd87FpUk6SIFQNqJ17zkZY/z6aRtPQD0GG1Fo97OC0zO6ggAu9bWDyvwuYlb/MswaYJMTF hdy+/BECalKSARmBXTkt402mzuu0FtAnoEx1A/bGYuEz3ASzKn+7niILzVlIGB7at291z8Vl2OGOA C+RP/g7y2QM60NNY2k5KwYcSh7hX3SKzJTGqbTPDUlVToDMf/ozWe2RfhMAe2wJAemg8eg3+xq7gh OLKQnWFA==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tpKzZ-00000000FmI-2xOE; Tue, 04 Mar 2025 05:38:57 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 8ED6630049D; Tue, 4 Mar 2025 06:38:53 +0100 (CET) Date: Tue, 4 Mar 2025 06:38:53 +0100 From: Peter Zijlstra To: Menglong Dong Cc: rostedt@goodmis.org, mark.rutland@arm.com, alexei.starovoitov@gmail.com, catalin.marinas@arm.com, will@kernel.org, mhiramat@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, jolsa@kernel.org, davem@davemloft.net, dsahern@kernel.org, mathieu.desnoyers@efficios.com, nathan@kernel.org, nick.desaulniers+lkml@gmail.com, morbo@google.com, samitolvanen@google.com, kees@kernel.org, dongml2@chinatelecom.cn, akpm@linux-foundation.org, riel@surriel.com, rppt@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [PATCH v4 1/4] x86/ibt: factor out cfi and fineibt offset Message-ID: <20250304053853.GA7099@noisy.programming.kicks-ass.net> References: <20250303132837.498938-1-dongml2@chinatelecom.cn> <20250303132837.498938-2-dongml2@chinatelecom.cn> <20250303165454.GB11590@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Mar 04, 2025 at 09:10:12AM +0800, Menglong Dong wrote: > Hello, sorry that I forgot to add something to the changelog. In fact, > I don't add extra 5-bytes anymore, which you can see in the 3rd patch. > > The thing is that we can't add extra 5-bytes if CFI is enabled. Without > CFI, we can make the padding space any value, such as 5-bytes, and > the layout will be like this: > > __align: > nop > nop > nop > nop > nop > foo: -- __align +5 > > However, the CFI will always make the cfi insn 16-bytes aligned. When > we set the FUNCTION_PADDING_BYTES to (11 + 5), the layout will be > like this: > > __cfi_foo: > nop (11) > mov $0x12345678, %reg > nop (16) > foo: > > and the padding space is 32-bytes actually. So, we can just select > FUNCTION_ALIGNMENT_32B instead, which makes the padding > space 32-bytes too, and have the following layout: > > __cfi_foo: > mov $0x12345678, %reg > nop (27) > foo: *blink*, wtf is clang smoking. I mean, you're right, this is what it is doing, but that is somewhat unexpected. Let me go look at clang source, this is insane.