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 A654FC6FD1D for ; Mon, 20 Mar 2023 12:10:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230242AbjCTMKi (ORCPT ); Mon, 20 Mar 2023 08:10:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60844 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230162AbjCTMKd (ORCPT ); Mon, 20 Mar 2023 08:10:33 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ED1637A9B for ; Mon, 20 Mar 2023 05:10:28 -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-out2.suse.de (Postfix) with ESMTPS id A78191F88D; Mon, 20 Mar 2023 12:10:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1679314226; 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=4M33RPSshG/6AvzGlSc6eQGFqPX5H1NKWm/iBJHsuL0=; b=kbPjemu6EfoZdMJ084ad+ZZJvk+Yzv90SEkNJwQrZsVtAazbgBI8MDKxEsjdRRpr0vHh/X tTA1TPAOESCVWG3cm25C7XtTqUrpxCkMcOwJ9XBFC+PtUeFa5THE/MH9tMTQxDlcTvK/XG Zd1WF/mqKywJXGBMVPfBThbU1/38VpY= 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 6129613A00; Mon, 20 Mar 2023 12:10:26 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id EUymFjJNGGS3UAAAMHmgww (envelope-from ); Mon, 20 Mar 2023 12:10:26 +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 v5] x86: Avoid relocation information in final vmlinux Date: Mon, 20 Mar 2023 13:10:06 +0100 Message-Id: <20230320121006.4863-1-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 tar-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 v4 [1]: - Update the example target which is mentioned in the patch description to collect vmlinux from binrpm-pkg to tar-pkg, to reflect fc8c2d8ff206 ("kbuild: Stop including vmlinux.bz2 in the rpm's"). Changes since v3 [2]: - Update the Kbuild.include path in arch/x86/Makefile.postlink to work after 67d7c3023a67 ("kbuild: remove --include-dir MAKEFLAG from top Makefile"). Changes since v2 [3]: - Ignore only the moved vmlinux.relocs, add it to .gitignore and Documentation/dontdiff. - Clean up the patch description. Changes since v1 [4]: - Fix the command to remove relocations to work with llvm-objcopy too. [1] https://lore.kernel.org/lkml/20230227131829.26824-1-petr.pavlu@suse.com/ [2] https://lore.kernel.org/lkml/20221211141227.7622-1-petr.pavlu@suse.com/ [3] https://lore.kernel.org/lkml/20220927084632.14531-1-petr.pavlu@suse.com/ [4] 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 70ec6037fa7a..9bafd3c6bb5f 100644 --- a/.gitignore +++ b/.gitignore @@ -65,6 +65,7 @@ modules.order /vmlinux /vmlinux.32 /vmlinux.map +/vmlinux.relocs /vmlinux.symvers /vmlinux-gdb.py /vmlinuz diff --git a/Documentation/dontdiff b/Documentation/dontdiff index 3c399f132e2d..a62ad01e6d11 100644 --- a/Documentation/dontdiff +++ b/Documentation/dontdiff @@ -254,6 +254,7 @@ 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..195af937aa4d --- /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 $(srctree)/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 6b6cfe607bdb..19d1fb601796 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) -- 2.35.3