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[2620:137:e000::1:20]) by mx.google.com with ESMTP id i3-20020a17090332c300b00189847745f1si6729738plr.395.2022.12.11.06.17.05; Sun, 11 Dec 2022 06:17:28 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@suse.com header.s=susede1 header.b=tc0ePlno; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=QUARANTINE sp=QUARANTINE dis=NONE) header.from=suse.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229947AbiLKONQ (ORCPT + 99 others); Sun, 11 Dec 2022 09:13:16 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38390 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229475AbiLKONP (ORCPT ); Sun, 11 Dec 2022 09:13:15 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 92106B4AA for ; Sun, 11 Dec 2022 06:13:12 -0800 (PST) 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-out2.suse.de (Postfix) with ESMTPS id B14931F381; Sun, 11 Dec 2022 14:13:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1670767990; 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=sMsSMIXIBrOiC15T53uI5MCD1g0UEocKDW+9a+KXbzM=; b=tc0ePlnolVYxZkh9bMJ2MWYgB9ROBRWVj0gBfKkNAte7yZfBUAIjM7GvdW15vHJskvEAyw MFoD1p1k1+/VQUSOcxmdbFNhrj7X/dePB5OkVhuafbyvKEy89hbvpXsr+Kr0x2/qyfsvmD PNTnDtS/AIu1ZdgQhZIUWbkThugS/H4= 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 743BF1376E; Sun, 11 Dec 2022 14:13:10 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id 8Rp2G3bllWOdNAAAMHmgww (envelope-from ); Sun, 11 Dec 2022 14:13:10 +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: nathan@kernel.org, ndesaulniers@google.com, trix@redhat.com, corbet@lwn.net, linux-kernel@vger.kernel.org, Petr Pavlu Subject: [PATCH v3] x86: Avoid relocation information in final vmlinux Date: Sun, 11 Dec 2022 15:12:27 +0100 Message-Id: <20221211141227.7622-1-petr.pavlu@suse.com> X-Mailer: git-send-email 2.35.3 MIME-Version: 1.0 X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1751927486405934530?= X-GMAIL-MSGID: =?utf-8?q?1751927486405934530?= 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 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 | Optimize 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 --- Changes since v2 [1]: - Ignore only the moved vmlinux.relocs, add it to .gitignore and Documentation/dontdiff. - Clean up the patch description. Changes since v1 [2]: - Fix the command to remove relocations to work with llvm-objcopy too. [1] https://lore.kernel.org/lkml/20220927084632.14531-1-petr.pavlu@suse.com/ [2] https://lore.kernel.org/lkml/20220913132911.6850-1-petr.pavlu@suse.com/ .gitignore | 1 + Documentation/dontdiff | 1 + arch/x86/Makefile.postlink | 41 +++++++++++++++++++++++++++++ arch/x86/boot/compressed/.gitignore | 1 - arch/x86/boot/compressed/Makefile | 10 +++---- 5 files changed, 47 insertions(+), 7 deletions(-) create mode 100644 arch/x86/Makefile.postlink diff --git a/.gitignore b/.gitignore index 5da004814678..cb59d89372c0 100644 --- a/.gitignore +++ b/.gitignore @@ -61,6 +61,7 @@ modules.order /vmlinux /vmlinux.32 /vmlinux.map +/vmlinux.relocs /vmlinux.symvers /vmlinux-gdb.py /vmlinuz diff --git a/Documentation/dontdiff b/Documentation/dontdiff index 352ff53a2306..7c210744d84c 100644 --- a/Documentation/dontdiff +++ b/Documentation/dontdiff @@ -255,6 +255,7 @@ vmlinux.aout vmlinux.bin.all vmlinux.lds vmlinux.map +vmlinux.relocs vmlinux.symvers vmlinuz voffset.h 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/.gitignore b/arch/x86/boot/compressed/.gitignore index 25805199a506..b2968175fc27 100644 --- a/arch/x86/boot/compressed/.gitignore +++ b/arch/x86/boot/compressed/.gitignore @@ -1,7 +1,6 @@ # SPDX-License-Identifier: GPL-2.0-only relocs vmlinux.bin.all -vmlinux.relocs vmlinux.lds mkpiggy piggy.S diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 3a261abb6d15..75a467a408d2 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -121,14 +121,12 @@ $(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)