Messages in this thread | | | Date | Thu, 17 Nov 2022 10:00:46 +0000 | Subject | Re: [PATCH 05/15] kbuild: build init/built-in.a just once | From | Jon Hunter <> |
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Hi Masahiro
On 28/08/2022 03:39, Masahiro Yamada wrote: > Kbuild builds init/built-in.a twice; 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 <masahiroy@kernel.org>
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
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