From 2df8220cc511326508ec4da2f43ef69311bdd7b9 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Sun, 28 Aug 2022 11:39:53 +0900 Subject: kbuild: build init/built-in.a just once 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 are 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 --- kernel/gen_kheaders.sh | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'kernel/gen_kheaders.sh') diff --git a/kernel/gen_kheaders.sh b/kernel/gen_kheaders.sh index 0c78e64f747d..473036b43c83 100755 --- a/kernel/gen_kheaders.sh +++ b/kernel/gen_kheaders.sh @@ -31,8 +31,8 @@ if [ "$building_out_of_srctree" ]; then fi all_dirs="$all_dirs $dir_list" -# include/generated/compile.h is ignored because it is touched even when none -# of the source files changed. +# include/generated/utsversion.h is ignored because it is generated after this +# script is executed. (utsversion.h is unneeded for kheaders) # # When Kconfig regenerates include/generated/autoconf.h, its timestamp is # updated, but the contents might be still the same. When any CONFIG option is @@ -42,7 +42,7 @@ all_dirs="$all_dirs $dir_list" # # Ignore them for md5 calculation to avoid pointless regeneration. headers_md5="$(find $all_dirs -name "*.h" | - grep -v "include/generated/compile.h" | + grep -v "include/generated/utsversion.h" | grep -v "include/generated/autoconf.h" | xargs ls -l | md5sum | cut -d ' ' -f1)" -- cgit