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 X-Spam-Level: X-Spam-Status: No, score=-31.2 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3DA63C433E6 for ; Wed, 27 Jan 2021 20:57:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F2AA364DBD for ; Wed, 27 Jan 2021 20:57:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233792AbhA0U5U (ORCPT ); Wed, 27 Jan 2021 15:57:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43202 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233716AbhA0U4t (ORCPT ); Wed, 27 Jan 2021 15:56:49 -0500 Received: from mail-qv1-xf4a.google.com (mail-qv1-xf4a.google.com [IPv6:2607:f8b0:4864:20::f4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BB88AC061573 for ; Wed, 27 Jan 2021 12:56:04 -0800 (PST) Received: by mail-qv1-xf4a.google.com with SMTP id d26so2282199qve.7 for ; Wed, 27 Jan 2021 12:56:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:in-reply-to:message-id:mime-version:references:subject :from:to:cc; bh=afydIjTboHZYNt7UhxBI9r/K8JAPb3TsRLb2cVHkJug=; b=OEss27zfJ7iNp3b9IE3aHmQWzKmbK7MxprrUD6n6W3wsjaIXDpNdUha+30ZoETTBwP 84bE1InbOkYlY9PQ9QHdl2YXYFxHzdPpYzyVJ5ocIw2ZRnu77mmFttvuLaYi8BQcRSHD zf4hRWKGUwtM+pgKaF+7/KQqA5QlkWvAi+azXjPy6RIkbqrWm4xUstPJIf1wgEE/fyzQ MnsrhA1Ypuqu+XExTbjWuCgrK+SK3AumC0ds690JhPVfxG3GVVGxRskGn/t60npT5TDx MJsLP63hBNEHn17qSig/tYbCvu/hKHgWGKD/7TQgV7HrBIG5sJe41yrKnig9P09i0mQa O9gg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=afydIjTboHZYNt7UhxBI9r/K8JAPb3TsRLb2cVHkJug=; b=MFqUx/fiTn8shCWoIH9go7n7osN0y6L8iPO4VuEqQvZusa+uJZKCnJlQdSWABp1rMo HkJXVlHeIW5e/5UVeBv1NGn1a0jeX0oWLoOsjGD6iUBGdfIGi2HlrDhZ8KGN6D3KRIuC 0SQsIVN6YLnOo6PFyljTsQM7dY1s2vZHLYkViIiUlIN+jiHv5gHXBfMEokRMW4yMofJx 56dlhtDHwqafdN2aqgAFAZlh1Q0t36iKenJ5MzRVty1feTmWI0NpBbTu/cPCSZ2oAlba XQiH+hmG/+ruyRg/Q95/ppKP8x0l8Q4JGNRQqS+NLCeB30bClf3tONXpjD9yiF/c4HXq w1Qg== X-Gm-Message-State: AOAM533LMOFdxjDbl7J7YuforbbbVVJmabvdYtTqRDQnrZ64yl1LqiDz Q5DwJ7PONpz6Szg8dwGyopZhv2aQZTVt X-Google-Smtp-Source: ABdhPJyo+erd0t2C9lhJVscGgivAL6+qxWCusKgWAQe95FLVOrO+xKnIT46IU+7Udx+HnT9zbSiEY+fCjQv8 Sender: "maskray via sendgmr" X-Received: from maskray1.svl.corp.google.com ([2620:15c:2ce:0:a6ae:11ff:fe11:4abb]) (user=maskray job=sendgmr) by 2002:a05:6214:12ab:: with SMTP id w11mr12230114qvu.8.1611780963780; Wed, 27 Jan 2021 12:56:03 -0800 (PST) Date: Wed, 27 Jan 2021 12:56:00 -0800 In-Reply-To: <20210125172956.j2prlchhqwfcgzuc@google.com> Message-Id: <20210127205600.1227437-1-maskray@google.com> Mime-Version: 1.0 References: <20210125172956.j2prlchhqwfcgzuc@google.com> X-Mailer: git-send-email 2.30.0.280.ga3ce27912f-goog Subject: [PATCH v4] x86: Treat R_386_PLT32 as R_386_PC32 From: Fangrui Song To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org Cc: linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, Michael Matz , Fangrui Song , Arnd Bergmann , Nick Desaulniers , Nathan Chancellor Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is similar to commit b21ebf2fb4cd ("x86: Treat R_X86_64_PLT32 as R_X86_64_PC32"), but for i386. As far as Linux kernel is concerned, R_386_PLT32 can be treated the same as R_386_PC32. R_386_PLT32/R_X86_64_PLT32 are PC-relative relocation types which can only be used by branches. If the referenced symbol is defined externally, a PLT will be used. R_386_PC32/R_X86_64_PC32 are PC-relative relocation types which can be used by address taking operations and branches. If the referenced symbol is defined externally, a copy relocation/canonical PLT entry will be created in the executable. On x86-64, there is no PIC vs non-PIC PLT distinction and an R_X86_64_PLT32 relocation is produced for both `call/jmp foo` and `call/jmp foo@PLT` with newer (2018) GNU as/LLVM integrated assembler. This avoids canonical PLT entries (st_shndx=0, st_value!=0). On i386, there are 2 types of PLTs, PIC and non-PIC. Currently the GCC/GNU as convention is to use R_386_PC32 for non-PIC PLT and R_386_PLT32 for PIC PLT. Copy relocations/canonical PLT entries are possible ABI issues but GCC/GNU as will likely keep the status quo because (1) the ABI is legacy (2) the change will drop a GNU ld diagnostic for non-default visibility ifunc in shared objects. https://sourceware.org/bugzilla/show_bug.cgi?id=27169 clang-12 -fno-pic (since https://github.com/llvm/llvm-project/commit/a084c0388e2a59b9556f2de0083333232da3f1d6) can emit R_386_PLT32 for compiler generated function declarations, because preventing canonical PLT entries is weighed over the rare ifunc diagnostic. Link: https://github.com/ClangBuiltLinux/linux/issues/1210 Reported-by: Arnd Bergmann Signed-off-by: Fangrui Song Reviewed-by: Nick Desaulniers Reviewed-by: Nathan Chancellor Tested-by: Nick Desaulniers Tested-by: Nathan Chancellor --- Change in v2: * Improve commit message --- Change in v3: * Change the GCC link to the more relevant GNU as link. * Fix the relevant llvm-project commit. --- Change in v4: * Improve comments and commit message --- arch/x86/kernel/module.c | 1 + arch/x86/tools/relocs.c | 12 ++++++++---- 2 files changed, 9 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c index 34b153cbd4ac..5e9a34b5bd74 100644 --- a/arch/x86/kernel/module.c +++ b/arch/x86/kernel/module.c @@ -114,6 +114,7 @@ int apply_relocate(Elf32_Shdr *sechdrs, *location += sym->st_value; break; case R_386_PC32: + case R_386_PLT32: /* Add the value, subtract its position */ *location += sym->st_value - (uint32_t)location; break; diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c index ce7188cbdae5..1c3a1962cade 100644 --- a/arch/x86/tools/relocs.c +++ b/arch/x86/tools/relocs.c @@ -867,9 +867,11 @@ static int do_reloc32(struct section *sec, Elf_Rel *rel, Elf_Sym *sym, case R_386_PC32: case R_386_PC16: case R_386_PC8: + case R_386_PLT32: /* - * NONE can be ignored and PC relative relocations don't - * need to be adjusted. + * NONE can be ignored and PC relative relocations don't need + * to be adjusted. Because sym must be defined, R_386_PLT32 can + * be treated the same way as R_386_PC32. */ break; @@ -910,9 +912,11 @@ static int do_reloc_real(struct section *sec, Elf_Rel *rel, Elf_Sym *sym, case R_386_PC32: case R_386_PC16: case R_386_PC8: + case R_386_PLT32: /* - * NONE can be ignored and PC relative relocations don't - * need to be adjusted. + * NONE can be ignored and PC relative relocations don't need + * to be adjusted. Because sym must be defined, R_386_PLT32 can + * be treated the same way as R_386_PC32. */ break; -- 2.30.0.280.ga3ce27912f-goog