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 9A22EC04A6A for ; Tue, 18 Jul 2023 11:11:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232120AbjGRLLk (ORCPT ); Tue, 18 Jul 2023 07:11:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33800 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232089AbjGRLLg (ORCPT ); Tue, 18 Jul 2023 07:11:36 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 01FDD1BCF for ; Tue, 18 Jul 2023 04:11:09 -0700 (PDT) Received: from dggpemm500001.china.huawei.com (unknown [172.30.72.56]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4R4x6w6d5fzVjj9; Tue, 18 Jul 2023 19:09:44 +0800 (CST) Received: from [10.174.177.243] (10.174.177.243) by dggpemm500001.china.huawei.com (7.185.36.107) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.27; Tue, 18 Jul 2023 19:11:06 +0800 Message-ID: <921f4500-247a-50d5-c8df-49bdb55b9762@huawei.com> Date: Tue, 18 Jul 2023 19:11:06 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.10.1 Subject: Re: [PATCH] arm64: enable dead code elimination Content-Language: en-US To: Marc Zyngier CC: Catalin Marinas , Will Deacon , , References: <20230717080739.1000460-1-wangkefeng.wang@huawei.com> <801e30a093e41c3eebd675f0d224f8d7@kernel.org> <23d94414-b819-eaef-6fac-638bf713d341@huawei.com> <864jm2vind.wl-maz@kernel.org> From: Kefeng Wang In-Reply-To: <864jm2vind.wl-maz@kernel.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggpemm500001.china.huawei.com (7.185.36.107) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/7/17 20:15, Marc Zyngier wrote: > On Mon, 17 Jul 2023 12:56:39 +0100, > Kefeng Wang wrote: >> >> >> >> On 2023/7/17 17:42, Marc Zyngier wrote: >>> On 2023-07-17 09:07, Kefeng Wang wrote: >>>> Select CONFIG_HAVE_LD_DEAD_CODE_DATA_ELIMINATION for arm64, allowing the >>>> user to enable dead code elimination. In order for this to work, ensure >>>> that we keep the necessary tables by annotating them with KEEP, also it >>>> requires further changes to linker script to KEEP some tables and >>>> wildcard >>>> compiler generated sections into the right place. >>>> >>>> The following comparison is based 6.5-rc2 with defconfig, >>>> ... >>> >>> I took this patch for a spin in my tree, and ended up with: >>> >>>   CC      .vmlinux.export.o >>>   UPD     include/generated/utsversion.h >>>   CC      init/version-timestamp.o >>>   LD      .tmp_vmlinux.kallsyms1 >>> ld: init/main.o(__patchable_function_entries): error: need linked-to >>> section for --gc-sections >>> make[2]: *** [scripts/Makefile.vmlinux:36: vmlinux] Error 1 >>> make[1]: *** [/home/maz/hot-poop/arm-platforms/Makefile:1238: >>> vmlinux] Error 2 >>> make: *** [Makefile:234: __sub-make] Error 2 >> >> I don't find this error with CONFIG_FTRACE_MCOUNT_RECORD or >> allyesconfig, does it need special config or gcc version? > > You tell me! > > gcc (Debian 10.2.1-6) 10.2.1 20210110 > Copyright (C) 2020 Free Software Foundation, Inc. > This is free software; see the source for copying conditions. There is NO > warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. > > so hardly something special. This is built with the current state of > my NV tree, available here[1] As for the configuration, have a look > here[2]. 1) With gcc 10.3.1/ld (GNU Binutils) 2.37， it could be reproduced, but there is no issue for cross-compiler gcc 9.3/ld (GNU Binutils for Ubuntu) 2.34. 2) There is same issue like commit f7584322e4fe ("riscv: disable HAVE_LD_DEAD_CODE_DATA_ELIMINATION for LLD") said with allyesconfig on arm64, it takes too long in bfd_flavour_name() Samples: 257K of event 'cycles', Event count (approx.): 203974259359 Overhead Shared Object Symbol IPC [IPC Coverage] - 61.11% libbfd-2.34-arm64.so [.] bfd_flavour_name - - bfd_flavour_name - 6.55% libbfd-2.34-arm64.so [.] bfd_hash_traverse - - Just like you said, it is not ready for prime time, so please ignore this patch :( > > M. > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/nv-6.6-WIP > [2] https://paste.debian.net/1286106/ >