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=-20.8 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 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 63B73C433E0 for ; Wed, 13 Jan 2021 11:53:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 20A8A233ED for ; Wed, 13 Jan 2021 11:53:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727268AbhAMLxT (ORCPT ); Wed, 13 Jan 2021 06:53:19 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:52098 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727122AbhAMLxS (ORCPT ); Wed, 13 Jan 2021 06:53:18 -0500 Date: Wed, 13 Jan 2021 11:52:34 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1610538755; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=9SPAg+zkLT3zMZabm6nzRd0dPxO1o/euEhXbv7r6WE4=; b=pl1jeaM2jOF54eBDkte8hL/3VAiZC/PArsQGUiXopf6WDtCjQxByROlhlg5OFkafqKjxYM J8LsHx/aLMW7LqkZtUY3s1dDB8ptVKv5IK/re1Ko4hq/5JIn+9HIK53gK+zSp4ycHEPlEN bR2YSvhn1dVs7n6wz7Y+ish7L4H9pCPOF1DTqIbn2N5jgTFTsvcZD0SrrkVtr/VuEDwjTE lMbtbYgs7yUZtEA17i0p+8zcOrlqplis+5yiL8Vrl1a88/Yqi+Ui2eQ6iiXNHhJgMorqN+ OzLBCj6TpLdb1CLm7PXYmtjqsN10ANPGiYkTZUbDVW3TQgvZzeEI8XnVkfrolw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1610538755; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=9SPAg+zkLT3zMZabm6nzRd0dPxO1o/euEhXbv7r6WE4=; b=kcM4vA0wLC3C+BkIbbz0Wer6Gm5Bx+MjJ08Uae00cr0SNCuP9ED3uPIgYDDz99aWZKTXq4 Xhsl86dTRUfMA6AA== From: "tip-bot2 for Nick Desaulniers" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: x86/entry] x86/entry: Emit a symbol for register restoring thunk Cc: Arnd Bergmann , Josh Poimboeuf , Borislav Petkov , Nick Desaulniers , Borislav Petkov , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20210112194625.4181814-1-ndesaulniers@google.com> References: <20210112194625.4181814-1-ndesaulniers@google.com> MIME-Version: 1.0 Message-ID: <161053875473.414.57133209689816752.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the x86/entry branch of tip: Commit-ID: bde718b7e154afc99e1956b18a848401ce8e1f8e Gitweb: https://git.kernel.org/tip/bde718b7e154afc99e1956b18a848401ce8e1f8e Author: Nick Desaulniers AuthorDate: Tue, 12 Jan 2021 11:46:24 -08:00 Committer: Borislav Petkov CommitterDate: Wed, 13 Jan 2021 12:23:57 +01:00 x86/entry: Emit a symbol for register restoring thunk 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 Signed-off-by: Nick Desaulniers Signed-off-by: Borislav Petkov 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] --- Documentation/asm-annotations.rst | 9 +++++++++ arch/x86/entry/thunk_64.S | 8 ++++---- include/linux/linkage.h | 5 ++++- 3 files changed, 17 insertions(+), 5 deletions(-) diff --git a/Documentation/asm-annotations.rst b/Documentation/asm-annotations.rst index 32ea574..e711ff9 100644 --- a/Documentation/asm-annotations.rst +++ b/Documentation/asm-annotations.rst @@ -153,6 +153,15 @@ This section covers ``SYM_FUNC_*`` and ``SYM_CODE_*`` enumerated above. To some extent, this category corresponds to deprecated ``ENTRY`` and ``END``. Except ``END`` had several other meanings too. + Developers should avoid using local symbol names that are prefixed with + ``.L``, as this has special meaning for the assembler; a symbol entry will + not be emitted into the symbol table. This can prevent ``objtool`` from + generating correct unwind info. Symbols with STB_LOCAL binding may still be + used, and ``.L`` prefixed local symbol names are still generally useable + within a function, but ``.L`` prefixed local symbol names should not be used + to denote the beginning or end of code regions via + ``SYM_CODE_START_LOCAL``/``SYM_CODE_END``. + * ``SYM_INNER_LABEL*`` is used to denote a label inside some ``SYM_{CODE,FUNC}_START`` and ``SYM_{CODE,FUNC}_END``. They are very similar to C labels, except they can be made global. An example of use:: diff --git a/arch/x86/entry/thunk_64.S b/arch/x86/entry/thunk_64.S index ccd3287..c9a9fbf 100644 --- 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 diff --git a/include/linux/linkage.h b/include/linux/linkage.h index 5bcfbd9..11537ba 100644 --- a/include/linux/linkage.h +++ b/include/linux/linkage.h @@ -270,7 +270,10 @@ SYM_END(name, SYM_T_FUNC) #endif -/* SYM_CODE_START -- use for non-C (special) functions */ +/* + * SYM_CODE_START -- use for non-C (special) functions, avoid .L prefixed local + * symbol names which may not emit a symbol table entry. + */ #ifndef SYM_CODE_START #define SYM_CODE_START(name) \ SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN)