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| author | Masahiro Yamada <masahiroy@kernel.org> | 2022-08-28 11:39:53 +0900 |
|---|---|---|
| committer | Masahiro Yamada <masahiroy@kernel.org> | 2022-09-29 04:40:15 +0900 |
| commit | 2df8220cc511326508ec4da2f43ef69311bdd7b9 (patch) | |
| tree | a28de6a06de6fb9353f6bb7e7fd91cee01027305 /kernel/gen_kheaders.sh | |
| parent | 561daaacb45eee3ccbe581da38c34ece77496312 (diff) | |
| download | lwn-2df8220cc511326508ec4da2f43ef69311bdd7b9.tar.gz lwn-2df8220cc511326508ec4da2f43ef69311bdd7b9.zip | |
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 'kernel/gen_kheaders.sh')
| -rwxr-xr-x | kernel/gen_kheaders.sh | 6 |
1 files changed, 3 insertions, 3 deletions
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)" |