From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr1-f65.google.com ([209.85.221.65]:39553 "EHLO mail-wr1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728544AbgAaNPL (ORCPT ); Fri, 31 Jan 2020 08:15:11 -0500 Received: by mail-wr1-f65.google.com with SMTP id y11so8550027wrt.6 for ; Fri, 31 Jan 2020 05:15:10 -0800 (PST) Date: Fri, 31 Jan 2020 13:15:08 +0000 From: Matthias Maennich Subject: Re: [PATCH v2] kbuild: allow symbol whitelisting with TRIM_UNUSED_KSYMS Message-ID: <20200131131508.GH102066@google.com> 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> Sender: linux-kbuild-owner@vger.kernel.org List-ID: To: Quentin Perret Cc: masahiroy@kernel.org, nico@fluxnic.net, linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, kernel-team@android.com, jeyu@kernel.org On Wed, Jan 29, 2020 at 06:15:41PM +0000, Quentin Perret wrote: >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. Thank you for working on this! I like the idea! > >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. >+ >+ 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}" | This handles absolute paths very well. I wonder whether we can make this more useful for folks that want to maintain such a whitelist in their copy of the tree. Lets say, I have in my sources arch/x86/configs/x86_64_symbol_whitelist and in my config I have CONFIG_UNUSED_KSYMS_WHITELIST="arch/x86/configs/x86_64_symbol_whitelist". If I see it correctly, UNUSED_KSYMS_WHITELIST is currently either an absolute path or a relative path to the current build directory. I would prefer if relative paths would be relative to the source directory to support the above use case. (Note, that scenario above works if I build directly in the sources, but fails if I build O=/somewhere/else.) Cheers, Matthias > sort -u | > sed -e 's/\(.*\)/#define __KSYM_\1 1/' >> "$new_ksyms_file" > >-- >2.25.0.341.g760bfbb309-goog >