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=-8.7 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=no 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 44823C38BF9 for ; Mon, 24 Feb 2020 21:12:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 14D1F20CC7 for ; Mon, 24 Feb 2020 21:12:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="SBZiUn5x" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727714AbgBXVMO (ORCPT ); Mon, 24 Feb 2020 16:12:14 -0500 Received: from mail-pl1-f194.google.com ([209.85.214.194]:37377 "EHLO mail-pl1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726722AbgBXVMO (ORCPT ); Mon, 24 Feb 2020 16:12:14 -0500 Received: by mail-pl1-f194.google.com with SMTP id q4so424441pls.4 for ; Mon, 24 Feb 2020 13:12:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=dUAjplDFzu3ykSROh7BG5jWZWZQaw9t0lPRoNsXFBrw=; b=SBZiUn5x2qPHxXbX7IskwykcwAT9WwDybjt00KJzNaAOKlwi+4Vzhl72YxUHH4yrKC 7+obNJonOhX6zUTYnq6PA5RuHa94pr/eVaIiUiZrKBUGFi56tiT7g/M0K9O3r2Y719DC c88nS05MhdbQ77vKHCDcy1aiAjZPxpYEvEIPbDU5sA9MzhI5C8fYfdiH4ojnr9DzLgAM AK8HWXtMoerrGsolOSxCgbHu5U6TCLGhOvEb+yEGvKHFjBl5snNx+uQ1DXPIYGCDupTG VclYIaQ47bRvVceNoZKeYaVkAKwePRcXK5mI2GgbosLbWCqQwP6jsuDZM200Xd1psQvP 1PaA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=dUAjplDFzu3ykSROh7BG5jWZWZQaw9t0lPRoNsXFBrw=; b=g/RBnsgZVtaB8lQv7tkvrduSGYYjprAT885SrlWngBnMj4xCKucfSlz8ediLPfxMDi Vq5r/46+AU5/+RXb4rhazco8nwOkyYy3EbRMeMRvwbhM+TnSQqhCgHjOeBxjru753P5t GdImSX2YSkUfe8eZfns/laHAzBDaCtCiT8O5OfW6TE+l3CPLzrGNLGN7nLmoJsWxGj81 TdOS/MnFx57Ah5SCXAJx3ds7gsuFhans1uHmF6NAkXjh/dDbhzhZkdPwoPTTFB74gxoR u/UzP0tAUNP8Qddjl4Ine/iW1rMfPN+42rS7IrhC2sns/ii+6NZHH0DiFPDLF61+1LNu p43A== X-Gm-Message-State: APjAAAX/43rywJPXfJaD4mGXiATDQ3A0TbAJt6a2WCpopuQW4us5PxtK fkXNXdaVG4kUvcC+HPHSLaNvWA== X-Google-Smtp-Source: APXvYqyX8KcH3LWzbbHaFS+z+qG6xxTMYHwSh0eZWkdxnm2M7s0NfAvDQa8knTYqKZEeRVtRoBBCUQ== X-Received: by 2002:a17:90a:d585:: with SMTP id v5mr1164717pju.4.1582578733019; Mon, 24 Feb 2020 13:12:13 -0800 (PST) Received: from google.com ([2620:15c:2ce:0:9efe:9f1:9267:2b27]) by smtp.gmail.com with ESMTPSA id g10sm14267981pfo.166.2020.02.24.13.12.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Feb 2020 13:12:12 -0800 (PST) Date: Mon, 24 Feb 2020 13:12:09 -0800 From: Fangrui Song To: Arvind Sankar Cc: Nick Desaulniers , Borislav Petkov , Nathan Chancellor , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , LKML , clang-built-linux , Michael Matz , Kees Cook Subject: Re: [PATCH 1/2] arch/x86: Use -fno-asynchronous-unwind-tables to suppress .eh_frame sections Message-ID: <20200224211209.3snqf7atf5h4ywcr@google.com> References: <20200222235709.GA3786197@rani.riverdale.lan> <20200223193715.83729-2-nivedita@alum.mit.edu> <20200224210522.GA409112@rani.riverdale.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20200224210522.GA409112@rani.riverdale.lan> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-02-24, Arvind Sankar wrote: >On Mon, Feb 24, 2020 at 12:33:49PM -0800, Nick Desaulniers wrote: >> On Sun, Feb 23, 2020 at 11:37 AM Arvind Sankar wrote: >> > >> > While discussing a patch to discard .eh_frame from the compressed >> > vmlinux using the linker script, Fangrui Song pointed out [1] that these >> > sections shouldn't exist in the first place because arch/x86/Makefile >> > uses -fno-asynchronous-unwind-tables. >> >> Another benefit is that -fno-asynchronous-unwind-tables may help >> reduce the size of .text! >> https://stackoverflow.com/a/26302715/1027966 > >Hm I don't see any change in .text size. >> > diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile >> > index 98a81576213d..a1140c4ee478 100644 >> > --- a/drivers/firmware/efi/libstub/Makefile >> > +++ b/drivers/firmware/efi/libstub/Makefile >> > @@ -12,7 +12,8 @@ cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ -O2 \ >> > -mno-mmx -mno-sse -fshort-wchar \ >> > -Wno-pointer-sign \ >> > $(call cc-disable-warning, address-of-packed-member) \ >> > - $(call cc-disable-warning, gnu) >> > + $(call cc-disable-warning, gnu) \ >> > + -fno-asynchronous-unwind-tables >> >> I think we want to add this flag a little lower, line 27 has: >> >> KBUILD_CFLAGS := $(cflags-y) -DDISABLE_BRANCH_PROFILING \ >> >> so the `cflags-y` variable you modify in this hunk will only set >> -fno-asynchronous-unwind-tables for CONFIG_X86, which I don't think is >> intentional. Though when I run > >It is intentional -- the other case is that we're building for ARM, >which only filters out the regular KBUILD_CFLAGS, so adding the flag for >it should not be necessary. The cflags for ARM are constructed by >manipulating KBUILD_CFLAGS. Besides it may or may not want unwind >tables. 32-bit ARM appears to have an option to enable -funwind-tables. clang (as of today) has not implemented the -funwind-tables/-fasynchronous-unwind-tables distinction as GCC does.. (probably because not many people care..) >> >> $ llvm-readelf -S drivers/firmware/efi/libstub/lib.a | grep eh_frame >> >> after doing an x86_64 defconfig, I don't get any hits. Do you observe >> .eh_frame sections on any of these objects in this dir? (I'm fine >> adding it to be safe, but I'm curious why I'm not seeing any >> .eh_frame) >> > >You mean before this patch, right? I see hits on every .o file in there >(compiling with gcc 9.2.0). > >> > >> > # arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly >> > # disable the stackleak plugin >> > -- >> > 2.24.1 >> >