From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:50318 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727715AbfHMMlh (ORCPT ); Tue, 13 Aug 2019 08:41:37 -0400 Date: Tue, 13 Aug 2019 14:41:34 +0200 From: Greg KH Subject: Re: [PATCH v2 02/10] export: explicitly align struct kernel_symbol Message-ID: <20190813124134.GB14284@kroah.com> References: <20180716122125.175792-1-maco@android.com> <20190813121733.52480-1-maennich@google.com> <20190813121733.52480-3-maennich@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190813121733.52480-3-maennich@google.com> Sender: linux-kbuild-owner@vger.kernel.org List-ID: To: Matthias Maennich Cc: linux-kernel@vger.kernel.org, maco@android.com, kernel-team@android.com, arnd@arndb.de, geert@linux-m68k.org, hpa@zytor.com, jeyu@kernel.org, joel@joelfernandes.org, kstewart@linuxfoundation.org, linux-arch@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-modules@vger.kernel.org, linux-scsi@vger.kernel.org, linux-usb@vger.kernel.org, lucas.de.marchi@gmail.com, maco@google.com, michal.lkml@markovi.net, mingo@redhat.com, oneukum@suse.com, pombredanne@nexb.com, sam@ravnborg.org, sboyd@codeaurora.org, sspatil@google.com, stern@rowland.harvard.edu, tglx@linutronix.de, usb-storage@lists.one-eyed-alien.net, x86@kernel.org, yamada.masahiro@socionext.com, Andrew Morton , Nicolas Pitre , Michael Ellerman , Ard Biesheuvel On Tue, Aug 13, 2019 at 01:16:59PM +0100, Matthias Maennich wrote: > This change allows growing struct kernel_symbol without wasting bytes to > alignment. It also concretized the alignment of ksymtab entries if > relative references are used for ksymtab entries. > > struct kernel_symbol was already implicitly being aligned to the word > size, except on x86_64 and m68k, where it is aligned to 16 and 2 bytes, > respectively. > > As far as I can tell there is no requirement for aligning struct > kernel_symbol to 16 bytes on x86_64, but gcc aligns structs to their > size, and the linker aligns the custom __ksymtab sections to the largest > data type contained within, so setting KSYM_ALIGN to 16 was necessary to > stay consistent with the code generated for non-ASM EXPORT_SYMBOL(). Now > that non-ASM EXPORT_SYMBOL() explicitly aligns to word size (8), > KSYM_ALIGN is no longer necessary. > > In case of relative references, the alignment has been changed > accordingly to not waste space when adding new struct members. > > As for m68k, struct kernel_symbol is aligned to 2 bytes even though the > structure itself is 8 bytes; using a 4-byte alignment shouldn't hurt. > > I manually verified the output of the __ksymtab sections didn't change > on x86, x86_64, arm, arm64 and m68k. As expected, the section contents > didn't change, and the ELF section alignment only changed on x86_64 and > m68k. Feedback from other archs more than welcome. > > Co-developed-by: Martijn Coenen > Signed-off-by: Martijn Coenen > Signed-off-by: Matthias Maennich Ick, messy, nice fix. Reviewed-by: Greg Kroah-Hartman