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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.2 Subject: Re: [PATCH 05/15] kbuild: build init/built-in.a just once Content-Language: en-US To: Masahiro Yamada , linux-kbuild@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, "linux-tegra@vger.kernel.org" References: <20220828024003.28873-1-masahiroy@kernel.org> <20220828024003.28873-6-masahiroy@kernel.org> From: Jon Hunter In-Reply-To: <20220828024003.28873-6-masahiroy@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: LO4P123CA0580.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:276::16) To CO6PR12MB5444.namprd12.prod.outlook.com (2603:10b6:5:35e::8) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO6PR12MB5444:EE_|BL1PR12MB5079:EE_ X-MS-Office365-Filtering-Correlation-Id: 8adc3cfd-7e43-46be-735e-08dac8829c1f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: qrQRQiJdPI7oL3pRniOsfb1SoQVofEtJdZzCcGPvKrcsQN++ZJpmqJIDMe+jgmieV4vPdbAEToAe1pg4u1eHlcZ8qMmcEhsAz2iUJ9uxTvXhmIfbZ1WbUOQS/+GdOHhl6J5I6AszLGqLFaSz8/Pep7JvUXDpaTwddfmr9/cygfyYa3dR9p4Xq738B/5eWXugKVFiFFOQfBV3/vZuSPJ0Xsjl75wSpoNtBNl9ch6jGQMK+E5Z/lNjq78cKn+591ZF0w3iAHUh9Kq6tCOA+4iLI5q3VT6+8nJ8NlZDU5CCjabXjvS5Q9p2hZ5Q4UXcHTuea5PWjJ5VhnFJAkDU75syi+7TlQqAVljlsK2nlEb1jKvushcCHuo4mK7/EsT+GN0ZWHQkT6TrUPpoUVQRNmGfmqLDMZRXkx3p5jXdZnd5ycdoxn4mjSKLCRcAoYP7h2UwelrwZtrPZK6AuejQAIzmQH84/Jy7QFnuT05AU3FqKY+ssAHV8xsbm8UrnRqrRluVCrirc05GTE7FSOOgEz7TLCIbwlFSPoXVbe0FFOzZRtG+hKAT6/twPGESpiyUdQjTuoiDvGJhnl9Z/71GBeet2alaFyABhueqz7AKrOFc8wYbNFlpPffQ8R8utqqT6jzoQMjKGO2xEeGWOOAuQgXNw+xgurUiWMY5unTNEkPJZ2VZSjsqgfTInVX/5rAdlnNB1A6AKNlxqqewyrRUhfmLt9vWatnPgi24Q5Dh4oBI0ik= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CO6PR12MB5444.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230022)(4636009)(376002)(136003)(396003)(366004)(39860400002)(346002)(451199015)(31686004)(38100700002)(478600001)(6486002)(83380400001)(86362001)(31696002)(5660300002)(8936002)(36756003)(2906002)(8676002)(66476007)(66556008)(4326008)(66946007)(6506007)(55236004)(53546011)(6666004)(41300700001)(6512007)(186003)(26005)(2616005)(316002)(45980500001)(43740500002);DIR:OUT;SFP:1101; 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first during the ordinary > directory descending, second from scripts/link-vmlinux.sh. > > We do this because UTS_VERSION contains the build version and the > timestamp. We cannot update it during the normal directory traversal > since we do not yet know if we need to update vmlinux. UTS_VERSION is > temporarily calculated, but omitted from the update check. Otherwise, > vmlinux would be rebuilt every time. > > When Kbuild results in running link-vmlinux.sh, it increments the > version number in the .version file and takes the timestamp at that > time to really fix UTS_VERSION. > > However, updating the same file twice is a footgun. To avoid nasty > timestamp issues, all build artifacts that depend on init/built-in.a > must be atomically generated in link-vmlinux.sh, where some of them > do not need rebuilding. > > To fix this issue, this commit changes as follows: > > [1] Split UTS_VERSION out to include/generated/utsversion.h from > include/generated/compile.h > > include/generated/utsversion.h is generated just before the > vmlinux link. It is generated under include/generated/ because > some decompressors (s390, x86) use UTS_VERSION. > > [2] Split init_uts_ns and linux_banner out to init/version-timestamp.c > from init/version.c > > init_uts_ns and linux_banner contain UTS_VERSION. During the ordinary > directory descending, they are compiled with __weak and used to > determine if vmlinux needs relinking. Just before the vmlinux link, > they are compiled without __weak to embed the real version and > timestamp. > > Signed-off-by: Masahiro Yamada Since this change I have noticed that the kernel image (at least on ARM64) now contains two version strings ... $ strings arch/arm64/boot/Image | grep "Linux version" Linux version 6.0.0-rc7-00011-g2df8220cc511 (jonathanh@moonraker) (aarch64-linux-gnu-gcc (Linaro GCC 6.4-2017.08) 6.4.1 20170707, GNU ld (Linaro_Binutils-2017.08) 2.27.0.20161019) # SMP PREEMPT Linux version 6.0.0-rc7-00011-g2df8220cc511 (jonathanh@moonraker) (aarch64-linux-gnu-gcc (Linaro GCC 6.4-2017.08) 6.4.1 20170707, GNU ld (Linaro_Binutils-2017.08) 2.27.0.20161019) #20 SMP PREEMPT Thu Nov 17 09:49:18 GMT 2022 Is this expected? Thanks! Jon -- nvpublic