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kbuild: build init/built-in.a just once

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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>
This commit is contained in:
Masahiro Yamada
2022-08-28 11:39:53 +09:00
parent 561daaacb4
commit 2df8220cc5
12 changed files with 120 additions and 131 deletions
Download Patch File Download Diff File Expand all files Collapse all files

89
scripts/mkcompile_h
View File

@@ -1,14 +1,9 @@
#!/bin/sh
# SPDX-License-Identifier: GPL-2.0
TARGET=$1
ARCH=$2
SMP=$3
PREEMPT=$4
PREEMPT_DYNAMIC=$5
PREEMPT_RT=$6
CC_VERSION="$7"
LD=$8
UTS_MACHINE=$1
CC_VERSION="$2"
LD=$3
# Do not expand names
set -f
@@ -17,17 +12,6 @@ set -f
LC_ALL=C
export LC_ALL
if [ -z "$KBUILD_BUILD_VERSION" ]; then
VERSION=$(cat .version 2>/dev/null || echo 1)
else
VERSION=$KBUILD_BUILD_VERSION
fi
if [ -z "$KBUILD_BUILD_TIMESTAMP" ]; then
TIMESTAMP=`date`
else
TIMESTAMP=$KBUILD_BUILD_TIMESTAMP
fi
if test -z "$KBUILD_BUILD_USER"; then
LINUX_COMPILE_BY=$(whoami | sed 's/\\/\\\\/')
else
@@ -39,63 +23,12 @@ else
LINUX_COMPILE_HOST=$KBUILD_BUILD_HOST
fi
UTS_VERSION="#$VERSION"
CONFIG_FLAGS=""
if [ -n "$SMP" ] ; then CONFIG_FLAGS="SMP"; fi
LD_VERSION=$($LD -v | head -n1 | sed 's/(compatible with [^)]*)//' \
| sed 's/[[:space:]]*$//')
if [ -n "$PREEMPT_RT" ] ; then
CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT_RT"
elif [ -n "$PREEMPT_DYNAMIC" ] ; then
CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT_DYNAMIC"
elif [ -n "$PREEMPT" ] ; then
CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT"
fi
# Truncate to maximum length
UTS_LEN=64
UTS_VERSION="$(echo $UTS_VERSION $CONFIG_FLAGS $TIMESTAMP | cut -b -$UTS_LEN)"
# Generate a temporary compile.h
{ echo /\* This file is auto generated, version $VERSION \*/
if [ -n "$CONFIG_FLAGS" ] ; then echo "/* $CONFIG_FLAGS */"; fi
echo \#define UTS_MACHINE \"$ARCH\"
echo \#define UTS_VERSION \"$UTS_VERSION\"
printf '#define LINUX_COMPILE_BY "%s"\n' "$LINUX_COMPILE_BY"
echo \#define LINUX_COMPILE_HOST \"$LINUX_COMPILE_HOST\"
LD_VERSION=$($LD -v | head -n1 | sed 's/(compatible with [^)]*)//' \
| sed 's/[[:space:]]*$//')
printf '#define LINUX_COMPILER "%s"\n' "$CC_VERSION, $LD_VERSION"
} > .tmpcompile
# Only replace the real compile.h if the new one is different,
# in order to preserve the timestamp and avoid unnecessary
# recompilations.
# We don't consider the file changed if only the date/time changed,
# unless KBUILD_BUILD_TIMESTAMP was explicitly set (e.g. for
# reproducible builds with that value referring to a commit timestamp).
# A kernel config change will increase the generation number, thus
# causing compile.h to be updated (including date/time) due to the
# changed comment in the
# first line.
if [ -z "$KBUILD_BUILD_TIMESTAMP" ]; then
IGNORE_PATTERN="UTS_VERSION"
else
IGNORE_PATTERN="NOT_A_PATTERN_TO_BE_MATCHED"
fi
if [ -r $TARGET ] && \
grep -v $IGNORE_PATTERN $TARGET > .tmpver.1 && \
grep -v $IGNORE_PATTERN .tmpcompile > .tmpver.2 && \
cmp -s .tmpver.1 .tmpver.2; then
rm -f .tmpcompile
else
echo " UPD $TARGET"
mv -f .tmpcompile $TARGET
fi
rm -f .tmpver.1 .tmpver.2
cat <<EOF
#define UTS_MACHINE "${UTS_MACHINE}"
#define LINUX_COMPILE_BY "${LINUX_COMPILE_BY}"
#define LINUX_COMPILE_HOST "${LINUX_COMPILE_HOST}"
#define LINUX_COMPILER "${CC_VERSION}, ${LD_VERSION}"
EOF