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authorMasahiro Yamada <masahiroy@kernel.org>2022-08-28 11:39:53 +0900
committerMasahiro Yamada <masahiroy@kernel.org>2022-09-29 04:40:15 +0900
commit2df8220cc511326508ec4da2f43ef69311bdd7b9 (patch)
treea28de6a06de6fb9353f6bb7e7fd91cee01027305 /scripts/link-vmlinux.sh
parent561daaacb45eee3ccbe581da38c34ece77496312 (diff)
downloadlinux-2df8220cc511326508ec4da2f43ef69311bdd7b9.tar.bz2
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 <masahiroy@kernel.org>
Diffstat (limited to 'scripts/link-vmlinux.sh')
-rwxr-xr-xscripts/link-vmlinux.sh17
1 files changed, 4 insertions, 13 deletions
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index eecc1863e556..8d982574145a 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -75,6 +75,8 @@ vmlinux_link()
objs="${objs} .vmlinux.export.o"
fi
+ objs="${objs} init/version-timestamp.o"
+
if [ "${SRCARCH}" = "um" ]; then
wl=-Wl,
ld="${CC}"
@@ -213,19 +215,6 @@ if [ "$1" = "clean" ]; then
exit 0
fi
-# Update version
-info GEN .version
-if [ -r .version ]; then
- VERSION=$(expr 0$(cat .version) + 1)
- echo $VERSION > .version
-else
- rm -f .version
- echo 1 > .version
-fi;
-
-# final build of init/
-${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init need-builtin=1
-
#link vmlinux.o
${MAKE} -f "${srctree}/scripts/Makefile.vmlinux_o"
@@ -260,6 +249,8 @@ if is_enabled CONFIG_MODULES; then
${MAKE} -f "${srctree}/scripts/Makefile.vmlinux" .vmlinux.export.o
fi
+${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init init/version-timestamp.o
+
btf_vmlinux_bin_o=""
if is_enabled CONFIG_DEBUG_INFO_BTF; then
btf_vmlinux_bin_o=.btf.vmlinux.bin.o