On Thu, Nov 17, 2022 at 7:00 PM Jon Hunter <jonathanh@xxxxxxxxxx> wrote: > > 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@xxxxxxxxxx> > > > 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? Yes. The first line is a weak (i.e. unused) symbol. The second one is a real one. 2df8220cc511326508ec4da2f43ef69311bdd7b9 fixed up arch/powerpc/boot/wrapper because it grep's vmlinux. The weak symbols slightly increase the image size, but I do not know how to do this better. > Thanks! > Jon > > -- > nvpublic -- Best Regards Masahiro Yamada
