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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 66EA0C433F5 for ; Fri, 22 Oct 2021 22:13:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4AF47611C7 for ; Fri, 22 Oct 2021 22:13:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234230AbhJVWQG (ORCPT ); Fri, 22 Oct 2021 18:16:06 -0400 Received: from relay.yourmailgateway.de ([188.68.61.106]:56685 "EHLO relay.yourmailgateway.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231363AbhJVWQF (ORCPT ); Fri, 22 Oct 2021 18:16:05 -0400 X-Greylist: delayed 607 seconds by postgrey-1.27 at vger.kernel.org; Fri, 22 Oct 2021 18:16:04 EDT Received: from mors-relay-8405.netcup.net (localhost [127.0.0.1]) by mors-relay-8405.netcup.net (Postfix) with ESMTPS id 4Hbddv2B5yz6w03; Sat, 23 Oct 2021 00:03:31 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=alexander-lochmann.de; s=key2; t=1634940211; bh=jtUzDXvaR8hHXjywNo+4aj/Qd4yRV+sSG1NHKsnVZuM=; h=To:Cc:References:From:Subject:Date:In-Reply-To:From; b=aqtQLCPAmhRVc1Ual9aluO8IxBavtf44InjrqyKS429p5R68ZiXOUrmrRhJhKfVrj aXsPR7blZ7RUAS9UqJqzO7V2J5qm7q2geeHsSjfxLAKG1M/84hpilVAwlBSNeFPIG/ KTLIlCKSyh/J7Fv85/gobsINjlc+E7rYvuIsVZqaqFJceRerrk94UqLTQQHL8HGd/6 daX1GhgziWdYYP/KIOEiWMcQ3fJ7MuUjm0dNOkP/quGBsn+9hP5qDlDEecj8QbFZbj WSuu2mGc/P9iQFVFJMVSy78aOCYQiBdfSwTzggji51L0+A3wTRrm5/HwAzZpObZysM j7kcDjJZStEAQ== Received: from policy02-mors.netcup.net (unknown [46.38.225.35]) by mors-relay-8405.netcup.net (Postfix) with ESMTPS id 4Hbddv1pmhz6w01; Sat, 23 Oct 2021 00:03:31 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at policy02-mors.netcup.net Received: from mx2e12.netcup.net (unknown [10.243.12.53]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by policy02-mors.netcup.net (Postfix) with ESMTPS id 4Hbddr3XTvz8svs; Sat, 23 Oct 2021 00:03:28 +0200 (CEST) Received: from [10.128.131.224] (unknown [37.120.132.67]) by mx2e12.netcup.net (Postfix) with ESMTPSA id 5B203A04FB; Sat, 23 Oct 2021 00:03:20 +0200 (CEST) Authentication-Results: mx2e12; spf=pass (sender IP is 37.120.132.67) smtp.mailfrom=info@alexander-lochmann.de smtp.helo=[10.128.131.224] Received-SPF: pass (mx2e12: connection is authenticated) To: Peter Zijlstra , Dmitry Vyukov Cc: Andrey Konovalov , Jonathan Corbet , Andrew Klychkov , Miguel Ojeda , Randy Dunlap , Johannes Berg , Ingo Molnar , Greg Kroah-Hartman , Sebastian Andrzej Siewior , Jakub Kicinski , Aleksandr Nogikh , kasan-dev@googlegroups.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210927173348.265501-1-info@alexander-lochmann.de> From: Alexander Lochmann Subject: Re: [PATCHv2] Introduced new tracing mode KCOV_MODE_UNIQUE. Message-ID: <927385c7-0155-22b0-c2f3-7776b6fe374c@alexander-lochmann.de> Date: Sat, 23 Oct 2021 00:03:16 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="CDzUVjhiPtClmKUvK9yUQsAHucLgloZvz" X-PPP-Message-ID: <163494020654.20467.833133958238456166@mx2e12.netcup.net> X-PPP-Vhost: alexander-lochmann.de X-NC-CID: yTucXSprgOVIdQ7m3pFnHtEZSL80pRmPiiPjZRCUXJtPlaTCDtHB87NH Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --CDzUVjhiPtClmKUvK9yUQsAHucLgloZvz Content-Type: multipart/mixed; boundary="UBwMM8vn54PR4LUbz1olAyRhXFoyVHnMk"; protected-headers="v1" From: Alexander Lochmann To: Peter Zijlstra , Dmitry Vyukov Cc: Andrey Konovalov , Jonathan Corbet , Andrew Klychkov , Miguel Ojeda , Randy Dunlap , Johannes Berg , Ingo Molnar , Greg Kroah-Hartman , Sebastian Andrzej Siewior , Jakub Kicinski , Aleksandr Nogikh , kasan-dev@googlegroups.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: <927385c7-0155-22b0-c2f3-7776b6fe374c@alexander-lochmann.de> Subject: Re: [PATCHv2] Introduced new tracing mode KCOV_MODE_UNIQUE. References: <20210927173348.265501-1-info@alexander-lochmann.de> In-Reply-To: --UBwMM8vn54PR4LUbz1olAyRhXFoyVHnMk Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: de-DE-1901 Content-Transfer-Encoding: quoted-printable Maybe Dmitry can shed some light on this. He actually suggested that=20 optimization. - Alex On 29.09.21 10:33, Peter Zijlstra wrote: > On Mon, Sep 27, 2021 at 07:33:40PM +0200, Alexander Lochmann wrote: >> The existing trace mode stores PCs in execution order. This could lead= >> to a buffer overflow if sufficient amonut of kernel code is executed. >> Thus, a user might not see all executed PCs. KCOV_MODE_UNIQUE favors >> completeness over execution order. While ignoring the execution order,= >> it marks a PC as exectued by setting a bit representing that PC. Each >> bit in the shared buffer represents every fourth byte of the text >> segment. Since a call instruction on every supported architecture is >> at least four bytes, it is safe to just store every fourth byte of the= >> text segment. >=20 > I'm still trying to wake up, but why are call instruction more importan= t > than other instructions? Specifically, I'd think any branch instruction= > matters for coverage. >=20 > More specifically, x86 can do a tail call with just 2 bytes. >=20 --=20 Alexander Lochmann PGP key: 0xBC3EF6FD Heiliger Weg 72 phone: +49.231.28053964 D-44141 Dortmund mobile: +49.151.15738323 --UBwMM8vn54PR4LUbz1olAyRhXFoyVHnMk-- --CDzUVjhiPtClmKUvK9yUQsAHucLgloZvz Content-Type: application/pgp-signature; name="OpenPGP_signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="OpenPGP_signature" -----BEGIN PGP SIGNATURE----- wsF5BAABCAAjFiEElhZsUHzVP0dbkjCRWT7tBbw+9v0FAmFzNSQFAwAAAAAACgkQWT7tBbw+9v3r 3w/7Bv8kyg3mPcCinEzZ9AnnM/yQ20THcNhazgLOZNfSMOqGKhyu2lCwY8A8TakScZAd+si/iU/v d6n14El+O4hTXzqjq42Kyukl9F56f45qPd8CXciiSnkCcH2LO7t0MEck6KobaGDe1km0QBoXc/kN hhyG5Yp5qduw34Ltj8kaylCUzSOqYiRFmZ2Ws7aA5HkGTA8zgoRm4BZj/YEqpUsoFeGsUglvMtlt vPyG479llRhv3DVE3Kal7pxGTSVccFg4uCMsBGFzl5nwLhrkC9P3c2gzkbzcQ6rUTTCnBEZAnU6o 6G4lZER0xOW41J8ZxdCfk3JadcKM/w245pu6SBDHKNE+oLm//+BCbhAReB/74WqPI4XvkQP623Gk x6mFm6EeXA72C/bWQg+V0VrFdbnkBACI88QMcEyzDHTddNno3/jkFx3rOQx7ZbVjY98Xw0p6Nf/P YjPM3qj1LEg7wKV12oQEBIHGo6oLUC4f2NUpl4DtYKCpBjBF4iMqCbkTmTtGi7GCyzFfiUDscafB 3Y9BzfzJKM5zlgsd9n29jAWzUCFhAByzJsFUY78c5JjVylnUugdLuBoichLvh1r4Hg67AX1TB84N cvS0Y+c/jgXEV4/EeqnfaBW9Uk8yhdGLytC6UpAhGNNkK3r5bhU1WY6PiCGGR5XbFIkbw9+i6L5Q ST8= =9qA3 -----END PGP SIGNATURE----- --CDzUVjhiPtClmKUvK9yUQsAHucLgloZvz--