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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 DF4FDC33CAC for ; Thu, 6 Feb 2020 15:56:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B51D4217BA for ; Thu, 6 Feb 2020 15:56:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581004619; bh=VKqamuuY9AprEgBPWpz0hs7y962lBR3ehzi3JQvK4YU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=AVsquEaS+hYlP82bdPt390TrcR30MzxSlpWjxSCxBKQeI3AOn+CCjuAaDyzzMKN2E MSqtl3mTNbGpIz43z+BgvcKVkU7+RonbCgxI+wq+p9mghSJ0wT1nlpEz+DEElCRF1r j8Zov4bIiktObcLSrp0wVAnxE/fH78BDiJjwK8sU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727663AbgBFP47 (ORCPT ); Thu, 6 Feb 2020 10:56:59 -0500 Received: from mail.kernel.org ([198.145.29.99]:36712 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727138AbgBFP46 (ORCPT ); Thu, 6 Feb 2020 10:56:58 -0500 Received: from linux-8ccs (p5B2812F9.dip0.t-ipconnect.de [91.40.18.249]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3696420838; Thu, 6 Feb 2020 15:56:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581004617; bh=VKqamuuY9AprEgBPWpz0hs7y962lBR3ehzi3JQvK4YU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=txIMRVX2+Gq6+l+q1z1eDgMtiXNtnm6sAoZ3a7ll7uKO1wovXKJKCTiZIcujGg7c1 QPAswGZjWIAS8dMx2rnv+LJ82LZoL9NqSQYGY5uLFmWAK1NbdSBKsySW7eWLypPOge 1v5vhGtiu6C4B4QG7HRrz45cx36SWnf+qmeMoYmE= Date: Thu, 6 Feb 2020 16:56:51 +0100 From: Jessica Yu To: Quentin Perret Cc: masahiroy@kernel.org, nico@fluxnic.net, linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, maennich@google.com, kernel-team@android.com Subject: Re: [PATCH v2] kbuild: allow symbol whitelisting with TRIM_UNUSED_KSYMS Message-ID: <20200206155651.GC16783@linux-8ccs> References: <20200129181541.105335-1-qperret@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20200129181541.105335-1-qperret@google.com> X-OS: Linux linux-8ccs 4.12.14-lp150.12.61-default x86_64 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 +++ Quentin Perret [29/01/20 18:15 +0000]: >CONFIG_TRIM_UNUSED_KSYMS currently removes all unused exported symbols >from ksymtab. This works really well when using in-tree drivers, but >cannot be used in its current form if some of them are out-of-tree. > >Indeed, even if the list of symbols required by out-of-tree drivers is >known at compile time, the only solution today to guarantee these don't >get trimmed is to set CONFIG_TRIM_UNUSED_KSYMS=n. This not only wastes >space, but also makes it difficult to control the ABI usable by vendor >modules in distribution kernels such as Android. Being able to control >the kernel ABI surface is particularly useful to ship a unique Generic >Kernel Image (GKI) for all vendors. > >As such, attempt to improve the situation by enabling users to specify a >symbol 'whitelist' at compile time. Any symbol specified in this >whitelist will be kept exported when CONFIG_TRIM_UNUSED_KSYMS is set, >even if it has no in-tree user. The whitelist is defined as a simple >text file, listing symbols, one per line. > >Signed-off-by: Quentin Perret > >--- >v2: make sure to quote the whitelist path properly (Nicolas) >--- > init/Kconfig | 12 ++++++++++++ > scripts/adjust_autoksyms.sh | 1 + > 2 files changed, 13 insertions(+) > >diff --git a/init/Kconfig b/init/Kconfig >index a34064a031a5..d9c977ef7de5 100644 >--- a/init/Kconfig >+++ b/init/Kconfig >@@ -2180,6 +2180,18 @@ config TRIM_UNUSED_KSYMS > > If unsure, or if you need to build out-of-tree modules, say N. > >+config UNUSED_KSYMS_WHITELIST >+ string "Whitelist of symbols to keep in ksymtab" >+ depends on TRIM_UNUSED_KSYMS >+ help >+ By default, all unused exported symbols will be trimmed from the >+ build when TRIM_UNUSED_KSYMS is selected. Hm, I thought TRIM_UNUSED_KSYMS just *unexports* unused symbols, no? "Trimmed from the build" sounds like the symbols are not compiled in or dropped completely. Please correct me if I misunderstood. >+ UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept >+ exported at all times, even in absence of in-tree users. The value to >+ set here is the path to a text file containing the list of symbols, >+ one per line. >+ > endif # MODULES > > config MODULES_TREE_LOOKUP >diff --git a/scripts/adjust_autoksyms.sh b/scripts/adjust_autoksyms.sh >index a904bf1f5e67..8e1b7f70e800 100755 >--- a/scripts/adjust_autoksyms.sh >+++ b/scripts/adjust_autoksyms.sh >@@ -48,6 +48,7 @@ cat > "$new_ksyms_file" << EOT > EOT > sed 's/ko$/mod/' modules.order | > xargs -n1 sed -n -e '2{s/ /\n/g;/^$/!p;}' -- | >+cat - "${CONFIG_UNUSED_KSYMS_WHITELIST:-/dev/null}" | > sort -u | > sed -e 's/\(.*\)/#define __KSYM_\1 1/' >> "$new_ksyms_file" In general, I agree with the motivation behind this patch, even though we try not to provide too much support for out-of-tree modules. However, in this particular case, I think it's fair to provide some mechanism to keep some exported symbols around that we know will have users, despite having no in-tree users for a particular configuration/build. For example, livepatch exports symbols that have no in-tree users (except for the sample livepatch module, but you'd have to enable SAMPLES), and all livepatch users will always be out of tree. I also agree with Matthias' feedback, so assuming that gets incorporated into v3: Acked-by: Jessica Yu Thanks!