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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A1712C54EE9 for ; Tue, 27 Sep 2022 08:47:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231258AbiI0IrL (ORCPT ); Tue, 27 Sep 2022 04:47:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48362 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230080AbiI0IrG (ORCPT ); Tue, 27 Sep 2022 04:47:06 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2001:67c:2178:6::1c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E9A4178584 for ; Tue, 27 Sep 2022 01:47:04 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 6425B21E4E; Tue, 27 Sep 2022 08:47:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1664268423; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=4GJIRDOTfEECp/8ZEqF4PH2doyBtG7CmCth3M0fHEBw=; b=Mk80j2Frj+MFuU3QBOiE0sqHvZ1sJtA5HJXn24imSptEjO6C4DAgqi6Ihb2pq1n4otNHmt rvvx/1iyfKFFY69HfprCDgvcFhzvc54oAQTAC6dktKG8FZaf9nvtzsvtvFEQqqlHrZNoKd EzAvyyBLitQ9BU/Zfm45mXIM54oeSOI= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 07123139B3; Tue, 27 Sep 2022 08:47:03 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id /q5JAIe4MmP0IQAAMHmgww (envelope-from ); Tue, 27 Sep 2022 08:47:02 +0000 From: Petr Pavlu To: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com Cc: nicolas@fjasle.eu, masahiroy@kernel.org, kirill.shutemov@linux.intel.com, tony.luck@intel.com, michael.roth@amd.com, nathan@kernel.org, ndesaulniers@google.com, linux-kernel@vger.kernel.org, Petr Pavlu Subject: [PATCH v2] x86: Avoid relocation information in final vmlinux Date: Tue, 27 Sep 2022 10:46:32 +0200 Message-Id: <20220927084632.14531-1-petr.pavlu@suse.com> X-Mailer: git-send-email 2.35.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The Linux build process on x86 roughly consists of compiling all input files, statically linking them into a vmlinux ELF file, and then taking and turning this file into an actual bzImage bootable file. vmlinux has in this process two main purposes: 1) It is an intermediate build target on the way to produce the final bootable image. 2) It is a file that is expected to be used by debuggers and standard ELF tooling to work with the built kernel. For the second purpose, a vmlinux file is typically collected by various package build recipes, such as distribution spec files, including the kernel's own binrpm-pkg target. When building a kernel supporting KASLR with CONFIG_X86_NEED_RELOCS, vmlinux contains also relocation information produced by using the --emit-relocs linker option. This is utilized by subsequent build steps to create vmlinux.relocs and produce a relocatable image. However, the information is not needed by debuggers and other standard ELF tooling. The issue is then that the collected vmlinux file and hence distribution packages end up unnecessarily large because of this extra data. The following is a size comparison of vmlinux v6.0-rc5 with and without the relocation information: | Configuration | With relocs | Stripped relocs | | x86_64_defconfig | 70 MB | 43 MB | | +CONFIG_DEBUG_INFO | 818 MB | 367 MB | The patch optimizes a resulting vmlinux by adding a postlink step that splits the relocation information into vmlinux.relocs and then strips it from the vmlinux binary. Signed-off-by: Petr Pavlu --- Notes: Changes since v1 [1]: - Fix the command to remove relocations to work with llvm-objcopy too. [1] https://lore.kernel.org/lkml/20220913132911.6850-1-petr.pavlu@suse.com/ .gitignore | 1 + arch/x86/Makefile.postlink | 41 +++++++++++++++++++++++++++++++ arch/x86/boot/compressed/Makefile | 10 +++----- 3 files changed, 46 insertions(+), 6 deletions(-) create mode 100644 arch/x86/Makefile.postlink diff --git a/.gitignore b/.gitignore index 265959544978..cd4ef88584ea 100644 --- a/.gitignore +++ b/.gitignore @@ -37,6 +37,7 @@ *.o *.o.* *.patch +*.relocs *.s *.so *.so.dbg diff --git a/arch/x86/Makefile.postlink b/arch/x86/Makefile.postlink new file mode 100644 index 000000000000..b38ffa4defb3 --- /dev/null +++ b/arch/x86/Makefile.postlink @@ -0,0 +1,41 @@ +# SPDX-License-Identifier: GPL-2.0 +# =========================================================================== +# Post-link x86 pass +# =========================================================================== +# +# 1. Separate relocations from vmlinux into vmlinux.relocs. +# 2. Strip relocations from vmlinux. + +PHONY := __archpost +__archpost: + +-include include/config/auto.conf +include scripts/Kbuild.include + +CMD_RELOCS = arch/x86/tools/relocs +quiet_cmd_relocs = RELOCS $@.relocs + cmd_relocs = $(CMD_RELOCS) $@ > $@.relocs;$(CMD_RELOCS) --abs-relocs $@ + +quiet_cmd_strip_relocs = RSTRIP $@ + cmd_strip_relocs = $(OBJCOPY) --remove-section='.rel.*' --remove-section='.rel__*' --remove-section='.rela.*' --remove-section='.rela__*' $@ + +# `@true` prevents complaint when there is nothing to be done + +vmlinux: FORCE + @true +ifeq ($(CONFIG_X86_NEED_RELOCS),y) + $(call cmd,relocs) + $(call cmd,strip_relocs) +endif + +%.ko: FORCE + @true + +clean: + @rm -f vmlinux.relocs + +PHONY += FORCE clean + +FORCE: + +.PHONY: $(PHONY) diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 35ce1a64068b..eba7709d75ae 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -120,14 +120,12 @@ $(obj)/vmlinux.bin: vmlinux FORCE targets += $(patsubst $(obj)/%,%,$(vmlinux-objs-y)) vmlinux.bin.all vmlinux.relocs -CMD_RELOCS = arch/x86/tools/relocs -quiet_cmd_relocs = RELOCS $@ - cmd_relocs = $(CMD_RELOCS) $< > $@;$(CMD_RELOCS) --abs-relocs $< -$(obj)/vmlinux.relocs: vmlinux FORCE - $(call if_changed,relocs) +# vmlinux.relocs is created by the vmlinux postlink step. +vmlinux.relocs: vmlinux + @true vmlinux.bin.all-y := $(obj)/vmlinux.bin -vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += $(obj)/vmlinux.relocs +vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += vmlinux.relocs $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE $(call if_changed,gzip) -- 2.35.3