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>
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index eecc186..8d98257 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -75,6 +75,8 @@
objs="${objs} .vmlinux.export.o"
fi
+ objs="${objs} init/version-timestamp.o"
+
if [ "${SRCARCH}" = "um" ]; then
wl=-Wl,
ld="${CC}"
@@ -213,19 +215,6 @@
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 @@
${MAKE} -f "${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
