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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 B9345C43387 for ; Tue, 8 Jan 2019 19:01:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 85B2C2087F for ; Tue, 8 Jan 2019 19:01:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="JBCXTWF3" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728746AbfAHTBO (ORCPT ); Tue, 8 Jan 2019 14:01:14 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:53774 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727947AbfAHTBO (ORCPT ); Tue, 8 Jan 2019 14:01:14 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=Kg2ZOj3oRtfmirfVDZJAz6uTlws91sqS1srR4JV9AYU=; b=JBCXTWF3YwF5hqGK9OkYPzmLPe k39t1i/HG9XMpJiNJj8Hgda4LWkzjkmKMurXFM2Tx83nmdRzmULzx/d+3fEpde8A0a5a/vF+zjo9H spkppwI7V55wNk+NezY5DOTvoUF4pXcbjD2mXwOBIX+QFzwe2BhBrV650hA0stfUfSHxtD8tkqeCe FlrDSR5xU/6tsS+Kq9yzoFrAB1ZeoaLolzpjHVz2kEDUnb8WKMgJj31biMCyoMDJq93aJkOVykRnh G6Yf3TaSXX0bsvXoxN+TVuTMjQhpw8gHu/xwvl2BSkxB9J2hj5c9aJihTpdvgM3zsDKNkA+UCN8qG 3uAdbVTQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1ggwcc-0006JM-0n; Tue, 08 Jan 2019 19:01:06 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 8579420280451; Tue, 8 Jan 2019 20:01:04 +0100 (CET) Date: Tue, 8 Jan 2019 20:01:04 +0100 From: Peter Zijlstra To: Nadav Amit Cc: Andi Kleen , Adrian Hunter , Ingo Molnar , Andy Lutomirski , Josh Poimboeuf , Edward Cree , "H . Peter Anvin" , Thomas Gleixner , LKML , X86 ML , Paolo Abeni , Borislav Petkov , David Woodhouse , Alexander Shishkin , songliubraving@fb.com Subject: Re: [RFC v2 0/6] x86: dynamic indirect branch promotion Message-ID: <20190108190104.GC1900@hirez.programming.kicks-ass.net> References: <20181231072112.21051-1-namit@vmware.com> <87zhshe66w.fsf@linux.intel.com> <20190107163227.GH14122@hirez.programming.kicks-ass.net> <20190108092559.GA6808@hirez.programming.kicks-ass.net> <306d38fb-7ce6-a3ec-a351-6c117559ebaa@intel.com> <20190108101058.GB6808@hirez.programming.kicks-ass.net> <20190108172721.GN6118@tassilo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 08, 2019 at 10:28:02AM -0800, Nadav Amit wrote: > Is it really that important for debugging to get the instructions at the > time of execution? Wouldn’t it be easier to annotate the instructions that > might change? After all, it is not as if any instruction can change to any > other instruction. I think PT has a bitstream encoding of branch-taken; to decode and follow the actual code-flow you then need to have the actual and accurate branch target from the code. If we go muck about with the code and change that, decoding gets somewhat 'tricky'. Or something along those lines..