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=-23.7 required=3.0 tests=BAYES_00,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 autolearn=unavailable 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 3A361C433E0 for ; Tue, 2 Feb 2021 13:48:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ED00465010 for ; Tue, 2 Feb 2021 13:48:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232657AbhBBNsG (ORCPT ); Tue, 2 Feb 2021 08:48:06 -0500 Received: from mail.kernel.org ([198.145.29.99]:36350 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231894AbhBBNpK (ORCPT ); Tue, 2 Feb 2021 08:45:10 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 416CD64F76; Tue, 2 Feb 2021 13:40:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1612273239; bh=PhylmEDigE/Fyoxcnd+m+iZ6ndgWX3G9KEaOs+tmo5o=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=FBiDYePG5Y+u6DqZ021i0SRInRnV2g72ONRtJEjT4rpBPopRP3exkBGuKaMTnq8H8 UbgTbz9zMC6wfUqQAwQl3E6QpUQf0mcONDDo+Cm9rPsYchniB+drD7GU292SUHjWTD N1WTAJKQWWljPsXOvKe3bLe4SO6Gd16i/2QTEut0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Arnd Bergmann , Josh Poimboeuf , Borislav Petkov , Mark Brown , Nick Desaulniers , Borislav Petkov , "Peter Zijlstra (Intel)" , Chris Clayton Subject: [PATCH 5.10 032/142] x86/entry: Emit a symbol for register restoring thunk Date: Tue, 2 Feb 2021 14:36:35 +0100 Message-Id: <20210202132959.033676544@linuxfoundation.org> X-Mailer: git-send-email 2.30.0 In-Reply-To: <20210202132957.692094111@linuxfoundation.org> References: <20210202132957.692094111@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Nick Desaulniers commit 5e6dca82bcaa49348f9e5fcb48df4881f6d6c4ae upstream. Arnd found a randconfig that produces the warning: arch/x86/entry/thunk_64.o: warning: objtool: missing symbol for insn at offset 0x3e when building with LLVM_IAS=1 (Clang's integrated assembler). Josh notes: With the LLVM assembler not generating section symbols, objtool has no way to reference this code when it generates ORC unwinder entries, because this code is outside of any ELF function. The limitation now being imposed by objtool is that all code must be contained in an ELF symbol. And .L symbols don't create such symbols. So basically, you can use an .L symbol *inside* a function or a code segment, you just can't use the .L symbol to contain the code using a SYM_*_START/END annotation pair. Fangrui notes that this optimization is helpful for reducing image size when compiling with -ffunction-sections and -fdata-sections. I have observed on the order of tens of thousands of symbols for the kernel images built with those flags. A patch has been authored against GNU binutils to match this behavior of not generating unused section symbols ([1]), so this will also become a problem for users of GNU binutils once they upgrade to 2.36. Omit the .L prefix on a label so that the assembler will emit an entry into the symbol table for the label, with STB_LOCAL binding. This enables objtool to generate proper unwind info here with LLVM_IAS=1 or GNU binutils 2.36+. [ bp: Massage commit message. ] Reported-by: Arnd Bergmann Suggested-by: Josh Poimboeuf Suggested-by: Borislav Petkov Suggested-by: Mark Brown Signed-off-by: Nick Desaulniers Signed-off-by: Borislav Petkov Acked-by: Peter Zijlstra (Intel) Acked-by: Josh Poimboeuf Link: https://lkml.kernel.org/r/20210112194625.4181814-1-ndesaulniers@google.com Link: https://github.com/ClangBuiltLinux/linux/issues/1209 Link: https://reviews.llvm.org/D93783 Link: https://sourceware.org/binutils/docs/as/Symbol-Names.html Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=d1bcae833b32f1408485ce69f844dcd7ded093a8 [1] Cc: Chris Clayton Signed-off-by: Greg Kroah-Hartman --- Documentation/asm-annotations.rst | 5 +++++ arch/x86/entry/thunk_64.S | 8 ++++---- include/linux/linkage.h | 5 +++++ 3 files changed, 14 insertions(+), 4 deletions(-) --- a/Documentation/asm-annotations.rst +++ b/Documentation/asm-annotations.rst @@ -100,6 +100,11 @@ Instruction Macros ~~~~~~~~~~~~~~~~~~ This section covers ``SYM_FUNC_*`` and ``SYM_CODE_*`` enumerated above. +``objtool`` requires that all code must be contained in an ELF symbol. Symbol +names that have a ``.L`` prefix do not emit symbol table entries. ``.L`` +prefixed symbols can be used within a code region, but should be avoided for +denoting a range of code via ``SYM_*_START/END`` annotations. + * ``SYM_FUNC_START`` and ``SYM_FUNC_START_LOCAL`` are supposed to be **the most frequent markings**. They are used for functions with standard calling conventions -- global and local. Like in C, they both align the functions to --- a/arch/x86/entry/thunk_64.S +++ b/arch/x86/entry/thunk_64.S @@ -31,7 +31,7 @@ SYM_FUNC_START_NOALIGN(\name) .endif call \func - jmp .L_restore + jmp __thunk_restore SYM_FUNC_END(\name) _ASM_NOKPROBE(\name) .endm @@ -44,7 +44,7 @@ SYM_FUNC_END(\name) #endif #ifdef CONFIG_PREEMPTION -SYM_CODE_START_LOCAL_NOALIGN(.L_restore) +SYM_CODE_START_LOCAL_NOALIGN(__thunk_restore) popq %r11 popq %r10 popq %r9 @@ -56,6 +56,6 @@ SYM_CODE_START_LOCAL_NOALIGN(.L_restore) popq %rdi popq %rbp ret - _ASM_NOKPROBE(.L_restore) -SYM_CODE_END(.L_restore) + _ASM_NOKPROBE(__thunk_restore) +SYM_CODE_END(__thunk_restore) #endif --- a/include/linux/linkage.h +++ b/include/linux/linkage.h @@ -178,6 +178,11 @@ * Objtool generates debug info for both FUNC & CODE, but needs special * annotations for each CODE's start (to describe the actual stack frame). * + * Objtool requires that all code must be contained in an ELF symbol. Symbol + * names that have a .L prefix do not emit symbol table entries. .L + * prefixed symbols can be used within a code region, but should be avoided for + * denoting a range of code via ``SYM_*_START/END`` annotations. + * * ALIAS -- does not generate debug info -- the aliased function will */