From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cantor2.suse.de ([195.135.220.15]:34011 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752648AbbC3ONH (ORCPT ); Mon, 30 Mar 2015 10:13:07 -0400 Message-ID: <551959F1.4030704@suse.cz> Date: Mon, 30 Mar 2015 16:13:05 +0200 From: Michal Marek MIME-Version: 1.0 Subject: Re: [RFC PATCH 2/2] Kbuild: avoid partial linking of drivers/built-in.o References: <1427716167-25078-1-git-send-email-ard.biesheuvel@linaro.org> <1427716167-25078-3-git-send-email-ard.biesheuvel@linaro.org> <551943CB.3010303@suse.cz> <20150330132617.GI24899@n2100.arm.linux.org.uk> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kbuild-owner@vger.kernel.org List-ID: To: Ard Biesheuvel , Russell King - ARM Linux Cc: linux-kbuild@vger.kernel.org, "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Arnd Bergmann On 2015-03-30 15:31, Ard Biesheuvel wrote: > On 30 March 2015 at 15:26, Russell King - ARM Linux > wrote: >> On Mon, Mar 30, 2015 at 02:38:35PM +0200, Michal Marek wrote: >>> Is this a limitation of a particular ARM ABI or a limitation of a state >>> of the art ARM linker or something else? >> >> It's a limitation of the ARM ISA. >> >> Normal PC-relative branches, which are emitted by the C compiler, can >> branch +/- 32MB for ARM, or +/- 16MB of Thumb. Beyond that, the address >> offset is not representable in the instruction. Thank you both for the explanation! >> The question is: how far do we go with allyesconfig... do we want it >> to work, or is reaching the final link sufficient? It certainly is more useful as a test tool if the baseline is a successful compile and link. Because you can have genuine link errors due to missing symbols. >> If we do tweak >> stuff to allow the link to work, are we going to try running it? Good question. I myself always treated all{yes,mod}config as a build test only and never dared to run it. Allyesconfig produces a giant kernel image and allmodconfig builds binfmt_script as a module. And if people used all*config for boot tests, they would probably be sending patches to tweak the Kconfigs for that purpose. And this is not the case as far as I can tell. > That is an excellent question, hence the RFC in the subject line. > > Note that the other patch, the one against kallsyms, addresses the > issue where the distance between the beginning of .text and the end of > .init.text exceeds this limit, which is not as unlikely as the issue > that this patch addresses, where just drivers/built-in.o in isolation > already exceeds this limit. > > So I am quite happy to drop this, especially as we can add > -ffunction-sections as well. What you could do is to add a Kconfig option to arch/arm/Kconfig adding -ffunction-sections to the compiler flags. Then allyesconfig would select it and work around the problem in a somewhat elegant way. Michal