From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga04-in.huawei.com (szxga04-in.huawei.com [45.249.212.190]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5665B2E62A for ; Sat, 9 Mar 2024 06:56:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.190 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709967419; cv=none; b=Ny0TBSZKqkCzcbCgUpLp0ANB9Rerd5njmJdYLkT/YTUqa67rNQyVvc2b0XZEOh15m0yFu5klQAFx6Z0MJS53+di43Swt+D9hGsD3v1OrGALBnewa6I36nN0o+l/TrtMLoKYQ7HNbnCVprg97uMSEwFf9L8+veQ/dh5H+yds6j9I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709967419; c=relaxed/simple; bh=1qsQHg57H1LKQe3m/sT4lhmQzJvIZGKeFT5OHy8I0tM=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=a86nAplea1Zy2FY1QQpxBjBO7cGuSly5uxQA5YzeRk0/Ov7rnkA57uvroFmA+kpwJgO/f5TkpB6+pJAyhRASXBVxk1kOoEZP6r1BeL+Yws6NVuqUxkk/4zzqMfJA05ENtESRFR8XfunUGQLJ51wts7UUrIqFtGG8bjWEO1CxfnM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.190 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.88.214]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4TsDKq3tgmz2BfPp; Sat, 9 Mar 2024 14:54:23 +0800 (CST) Received: from dggpemd100004.china.huawei.com (unknown [7.185.36.20]) by mail.maildlp.com (Postfix) with ESMTPS id 2F95C1A016C; Sat, 9 Mar 2024 14:56:47 +0800 (CST) Received: from [10.67.109.211] (10.67.109.211) by dggpemd100004.china.huawei.com (7.185.36.20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1258.28; Sat, 9 Mar 2024 14:56:46 +0800 Message-ID: Date: Sat, 9 Mar 2024 14:56:46 +0800 Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH-next v2] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION Content-Language: en-US To: Ard Biesheuvel , Arnd Bergmann CC: , , Fangrui Song , Russell King , Andrew Davis , Andrew Morton , "Kirill A. Shutemov" , Geert Uytterhoeven , Jonathan Corbet , Mike Rapoport , Rob Herring , Thomas Gleixner , Linus Walleij , References: <20240307151231.654025-1-liuyuntao12@huawei.com> <58cc1053-7208-4b22-99cb-210fdf700569@app.fastmail.com> From: "liuyuntao (F)" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggpemd100004.china.huawei.com (7.185.36.20) On 2024/3/8 22:27, Ard Biesheuvel wrote: > On Fri, 8 Mar 2024 at 14:16, Arnd Bergmann wrote: >> >> On Thu, Mar 7, 2024, at 16:12, Yuntao Liu wrote: >>> The current arm32 architecture does not yet support the >>> HAVE_LD_DEAD_CODE_DATA_ELIMINATION feature. arm32 is widely used in >>> embedded scenarios, and enabling this feature would be beneficial for >>> reducing the size of the kernel image. >>> >>> In order to make this work, 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. >>> >>> It boots normally with defconfig, vexpress_defconfig and tinyconfig. >>> >>> The size comparison of zImage is as follows: >>> defconfig vexpress_defconfig tinyconfig >>> 5137712 5138024 424192 no dce >>> 5032560 4997824 298384 dce >>> 2.0% 2.7% 29.7% shrink >>> >>> When using smaller config file, there is a significant reduction in the >>> size of the zImage. >>> >>> We also tested this patch on a commercially available single-board >>> computer, and the comparison is as follows: >>> a15eb_config >>> 2161384 no dce >>> 2092240 dce >>> 3.2% shrink >>> >>> The zImage size has been reduced by approximately 3.2%, which is 70KB on >>> 2.1M. >>> >>> Signed-off-by: Yuntao Liu >> >> I've retested with both gcc-13 and clang-18, and so no >> more build issues. Your previous version already worked >> fine for me. >> >> I did some tests combining this with CONFIG_TRIM_UNUSED_KSYMS, >> which showed a significant improvement as expected. I also >> tried combining it with an experimental CONFIG_LTO_CLANG >> patch, but that did not show any further improvements. >> >> Tested-by: Arnd Bergmann >> Reviewed-by: Arnd Bergmann >> >> Adding Ard Biesheuvel and Fangrui Song to Cc, so they can comment >> on the ARM_VECTORS_TEXT workaround. I don't understand enough of >> the details of what is going on here. >> > > Thanks for the cc > >> Full quote of the patch below so they can see the whole thing. >> >> If they are also happy with the patch, I think you can send it >> into Russell's patch tracker at >> https://www.armlinux.org.uk/developer/patches/info.php >> > > No, not happy at all :-) > > The resulting kernel does not boot (built with GCC or Clang). And the > patch is buggy (see below) > After applying .reloc .text, R_ARM_NONE, ., the resulting kernel boots well in QEMU. I tested it with the latest linux-next master branch and the mainline master branch. By the way, I used vexpress_defconfig for testing, it worked.