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 D845ACE79A8 for ; Wed, 20 Sep 2023 00:17:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229988AbjITARj (ORCPT ); Tue, 19 Sep 2023 20:17:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51838 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229534AbjITARi (ORCPT ); Tue, 19 Sep 2023 20:17:38 -0400 Received: from mail-yw1-x1149.google.com (mail-yw1-x1149.google.com [IPv6:2607:f8b0:4864:20::1149]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A25CEAB for ; Tue, 19 Sep 2023 17:17:32 -0700 (PDT) Received: by mail-yw1-x1149.google.com with SMTP id 00721157ae682-59b6a51f360so70967917b3.1 for ; Tue, 19 Sep 2023 17:17:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1695169052; x=1695773852; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=tT8RTtiIvMH0jr3h5GfFxiVuJzDdiA1NvVC8sxpn06Q=; b=NnS8rvEjStTsox1SybNVAn5om+cHQtX9dZb8cenUc5AFD5/QjRWATh/3NWcDv3nMY6 9I/sGmwyTHp0VKD9+td4FJvO9W/ua6gOYfrAGx0EHfRuPSk5AB1yBcRuWDJJA86h3iUB DbbXGZivz0gb4mddw2TPNRzwOccLZdgPcRFlOoe5ZOWezoyjcDykoFkhnH3VhoDQ7usY S6wr48nwPcp854QNbMo++nAjONinYDSw/KigvEn52nU9fotX0vGB1NVH0tW0mlOY43rD FZyacfOw3VhzwRqfh0Hju3HLDJms54bnvJUKTFNpiKQ9R+kkzCRS4qpGZ77Vsemqmr5u SA1A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1695169052; x=1695773852; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=tT8RTtiIvMH0jr3h5GfFxiVuJzDdiA1NvVC8sxpn06Q=; b=TBf48LvSvU7L1X5xnKhEb2JwlsHCTr1hDO6GeB4gtC1QLDNOiGCnOEdCnpL/amLZxM rbhg8qOmOF1khyxKQQTn3zsPHh8J0iPy5fXVHgbzcyfXbC6eCNIw/IlASkAivhroBBqI k6pwTXyXLduQieaKeHhEBnYJGnw6qANDJb12PMB/PAr2654WO54tUFAlpIOrNc0lXE1G bVhpDfEBmbzFsPQJblrGoSNgNqfIOhfXqffxK4mfja/31EQrvq9JiRU86Hat3knYQlnn f36n93m3fs8Gw2hrwCCJ/OnTEBwhW05YcFyU5534rD9C9dj8gvYXbQNpjpOmsPkWtUp8 9GNQ== X-Gm-Message-State: AOJu0YzHRR1biMMBLDMPMaf6REMwDAiT89QY70rejMXSGw2wCrARpMTR ti3ojoN4TPJCdTyHBXq/ja/RQqtwGLsk X-Google-Smtp-Source: AGHT+IHXYkvHxsnm+XtyucMHmTP6WHJAmizuj0WQQpgTjADkwA/bJi/QLtEi5t/MKjFM1E/F7Det8is3uPc/ X-Received: from maskray.svl.corp.google.com ([2620:15c:2d3:205:57db:b73a:fd87:4f18]) (user=maskray job=sendgmr) by 2002:a81:b1c8:0:b0:58c:7cb1:10f with SMTP id p191-20020a81b1c8000000b0058c7cb1010fmr15525ywh.9.1695169051817; Tue, 19 Sep 2023 17:17:31 -0700 (PDT) Date: Tue, 19 Sep 2023 17:17:28 -0700 Mime-Version: 1.0 Message-ID: <20230920001728.1439947-1-maskray@google.com> Subject: [PATCH] x86/speculation, objtool: Use absolute relocations for annotations From: Fangrui Song To: x86@kernel.org, Josh Poimboeuf , Peter Zijlstra Cc: linux-kernel@vger.kernel.org, llvm@lists.linux.dev, Nick Desaulniers , Fangrui Song Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org .discard.retpoline_safe sections do not have the SHF_ALLOC flag. These sections referencing text sections' STT_SECTION symbols with PC-relative relocations like R_386_PC32 [0] is conceptually not suitable. Newer LLD will report warnings for REL relocations even for relocatable links [1]. ld.lld: warning: vmlinux.a(drivers/i2c/busses/i2c-i801.o):(.discard.retpoline_safe+0x120): has non-ABS relocation R_386_PC32 against symbol '' Switch to absolute relocations instead, which indicate link-time addresses. In a relocatable link, these addresses are also output section offsets, used by checks in tools/objtool/check.c. When linking vmlinux, these .discard.* sections will be discarded, therefore it is not a problem that R_X86_64_32 cannot represent a kernel address. Alternatively, we could set the SHF_ALLOC flag for .discard.* sections, but I think non-SHF_ALLOC for sections to be discarded makes more sense. Note: if we decide to never support REL architectures (e.g. arm, i386), we can utilize R_*_NONE relocations (.reloc ., BFD_RELOC_NONE, sym), making .discard.* sections zero-sized. That said, the section content waste is 4 bytes per entry, much smaller than sizeof(Elf{32,64}_Rel). [0] commit 1c0c1faf5692 ("objtool: Use relative pointers for annotations") Link: https://github.com/ClangBuiltLinux/linux/issues/1937 [1] Signed-off-by: Fangrui Song --- arch/x86/include/asm/alternative.h | 4 ++-- arch/x86/include/asm/nospec-branch.h | 4 ++-- include/linux/objtool.h | 10 +++++----- 3 files changed, 9 insertions(+), 9 deletions(-) diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h index 9c4da699e11a..65f79092c9d9 100644 --- a/arch/x86/include/asm/alternative.h +++ b/arch/x86/include/asm/alternative.h @@ -58,7 +58,7 @@ #define ANNOTATE_IGNORE_ALTERNATIVE \ "999:\n\t" \ ".pushsection .discard.ignore_alts\n\t" \ - ".long 999b - .\n\t" \ + ".long 999b\n\t" \ ".popsection\n\t" /* @@ -352,7 +352,7 @@ static inline int alternatives_text_reserved(void *start, void *end) .macro ANNOTATE_IGNORE_ALTERNATIVE .Lannotate_\@: .pushsection .discard.ignore_alts - .long .Lannotate_\@ - . + .long .Lannotate_\@ .popsection .endm diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index c55cc243592e..4952b73d944e 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -196,7 +196,7 @@ .macro ANNOTATE_RETPOLINE_SAFE .Lhere_\@: .pushsection .discard.retpoline_safe - .long .Lhere_\@ - . + .long .Lhere_\@ .popsection .endm @@ -334,7 +334,7 @@ #define ANNOTATE_RETPOLINE_SAFE \ "999:\n\t" \ ".pushsection .discard.retpoline_safe\n\t" \ - ".long 999b - .\n\t" \ + ".long 999b\n\t" \ ".popsection\n\t" typedef u8 retpoline_thunk_t[RETPOLINE_THUNK_SIZE]; diff --git a/include/linux/objtool.h b/include/linux/objtool.h index 03f82c2c2ebf..6f6da95fe7f9 100644 --- a/include/linux/objtool.h +++ b/include/linux/objtool.h @@ -48,13 +48,13 @@ #define ANNOTATE_NOENDBR \ "986: \n\t" \ ".pushsection .discard.noendbr\n\t" \ - ".long 986b - .\n\t" \ + ".long 986b\n\t" \ ".popsection\n\t" #define ASM_REACHABLE \ "998:\n\t" \ ".pushsection .discard.reachable\n\t" \ - ".long 998b - .\n\t" \ + ".long 998b\n\t" \ ".popsection\n\t" #else /* __ASSEMBLY__ */ @@ -66,7 +66,7 @@ #define ANNOTATE_INTRA_FUNCTION_CALL \ 999: \ .pushsection .discard.intra_function_calls; \ - .long 999b - .; \ + .long 999b; \ .popsection; /* @@ -118,7 +118,7 @@ .macro ANNOTATE_NOENDBR .Lhere_\@: .pushsection .discard.noendbr - .long .Lhere_\@ - . + .long .Lhere_\@ .popsection .endm @@ -141,7 +141,7 @@ .macro REACHABLE .Lhere_\@: .pushsection .discard.reachable - .long .Lhere_\@ - . + .long .Lhere_\@ .popsection .endm -- 2.42.0.459.ge4e396fd5e-goog