[PATCH 05/15] kbuild: build init/built-in.a just once
From: Masahiro Yamada
Date: Sat Aug 27 2022 - 22:42:00 EST
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
must be 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@xxxxxxxxxx>
---
arch/s390/boot/version.c | 1 +
arch/x86/boot/compressed/kaslr.c | 1 +
arch/x86/boot/version.c | 1 +
init/Makefile | 53 ++++++++++++++-----
init/build-version | 10 ++++
init/version-timestamp.c | 31 +++++++++++
init/version.c | 36 +++++--------
scripts/link-vmlinux.sh | 17 ++----
scripts/mkcompile_h | 89 ++++----------------------------
9 files changed, 112 insertions(+), 127 deletions(-)
create mode 100755 init/build-version
create mode 100644 init/version-timestamp.c
diff --git a/arch/s390/boot/version.c b/arch/s390/boot/version.c
index d32e58bdda6a..fd32f038777f 100644
--- a/arch/s390/boot/version.c
+++ b/arch/s390/boot/version.c
@@ -1,4 +1,5 @@
// SPDX-License-Identifier: GPL-2.0
+#include <generated/utsversion.h>
#include <generated/utsrelease.h>
#include <generated/compile.h>
#include "boot.h"
diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 4a3f223973f4..e476bcbd9b42 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -29,6 +29,7 @@
#include <linux/uts.h>
#include <linux/utsname.h>
#include <linux/ctype.h>
+#include <generated/utsversion.h>
#include <generated/utsrelease.h>
#define _SETUP
diff --git a/arch/x86/boot/version.c b/arch/x86/boot/version.c
index a1aaaf6c06a6..945383f0f606 100644
--- a/arch/x86/boot/version.c
+++ b/arch/x86/boot/version.c
@@ -11,6 +11,7 @@
*/
#include "boot.h"
+#include <generated/utsversion.h>
#include <generated/utsrelease.h>
#include <generated/compile.h>
diff --git a/init/Makefile b/init/Makefile
index d82623d7fc8e..63f53d210cad 100644
--- a/init/Makefile
+++ b/init/Makefile
@@ -19,20 +19,47 @@ mounts-y := do_mounts.o
mounts-$(CONFIG_BLK_DEV_RAM) += do_mounts_rd.o
mounts-$(CONFIG_BLK_DEV_INITRD) += do_mounts_initrd.o
-# dependencies on generated files need to be listed explicitly
-$(obj)/version.o: include/generated/compile.h
+#
+# UTS_VERSION
+#
+
+smp-flag-$(CONFIG_SMP) := SMP
+preempt-flag-$(CONFIG_PREEMPT_BUILD) := PREEMPT
+preempt-flag-$(CONFIG_PREEMPT_DYNAMIC) := PREEMPT_DYNAMIC
+preempt-flag-$(CONFIG_PREEMPT_RT) := PREEMPT_RT
+
+build-version = $(or $(KBUILD_BUILD_VERSION), $(build-version-auto))
+build-timestamp = $(or $(KBUILD_BUILD_TIMESTAMP), $(build-timestamp-auto))
+
+# Maximum length of UTS_VERSION is 64 chars
+filechk_uts_version = \
+ utsver=$$(echo '$(pound)'"$(build-version)" $(smp-flag-y) $(preempt-flag-y) "$(build-timestamp)" | cut -b -64); \
+ echo '$(pound)'define UTS_VERSION \""$${utsver}"\"
+
+#
+# Build version.c with temporary UTS_VERSION
+#
+
+$(obj)/utsversion-tmp.h: FORCE
+ $(call filechk,uts_version)
-# compile.h changes depending on hostname, generation number, etc,
-# so we regenerate it always.
-# mkcompile_h will make sure to only update the
-# actual file if its content has changed.
+$(obj)/version.o: include/generated/compile.h $(obj)/utsversion-tmp.h
+CFLAGS_version.o := -include $(obj)/utsversion-tmp.h
-quiet_cmd_compile.h = CHK $@
- cmd_compile.h = \
- $(CONFIG_SHELL) $(srctree)/scripts/mkcompile_h $@ \
- "$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT_BUILD)" \
- "$(CONFIG_PREEMPT_DYNAMIC)" "$(CONFIG_PREEMPT_RT)" \
- "$(CONFIG_CC_VERSION_TEXT)" "$(LD)"
+filechk_compile.h = $(srctree)/scripts/mkcompile_h \
+ "$(UTS_MACHINE)" "$(CONFIG_CC_VERSION_TEXT)" "$(LD)"
include/generated/compile.h: FORCE
- $(call cmd,compile.h)
+ $(call filechk,compile.h)
+
+#
+# Build version-timestamp.c with final UTS_VERSION
+#
+
+include/generated/utsversion.h: build-version-auto = $(shell $(srctree)/$(src)/build-version)
+include/generated/utsversion.h: build-timestamp-auto = $(shell LC_ALL=C date)
+include/generated/utsversion.h: FORCE
+ $(call filechk,uts_version)
+
+$(obj)/version-timestamp.o: include/generated/utsversion.h
+CFLAGS_version-timestamp.o := -include include/generated/utsversion.h
diff --git a/init/build-version b/init/build-version
new file mode 100755
index 000000000000..39225104f14d
--- /dev/null
+++ b/init/build-version
@@ -0,0 +1,10 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+
+VERSION=$(cat .version) 2>/dev/null &&
+VERSION=$(expr $VERSION + 1) 2>/dev/null ||
+VERSION=1
+
+echo ${VERSION} > .version
+
+echo ${VERSION}
diff --git a/init/version-timestamp.c b/init/version-timestamp.c
new file mode 100644
index 000000000000..179e93bae539
--- /dev/null
+++ b/init/version-timestamp.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <generated/compile.h>
+#include <generated/utsrelease.h>
+#include <linux/version.h>
+#include <linux/proc_ns.h>
+#include <linux/refcount.h>
+#include <linux/uts.h>
+#include <linux/utsname.h>
+
+struct uts_namespace init_uts_ns = {
+ .ns.count = REFCOUNT_INIT(2),
+ .name = {
+ .sysname = UTS_SYSNAME,
+ .nodename = UTS_NODENAME,
+ .release = UTS_RELEASE,
+ .version = UTS_VERSION,
+ .machine = UTS_MACHINE,
+ .domainname = UTS_DOMAINNAME,
+ },
+ .user_ns = &init_user_ns,
+ .ns.inum = PROC_UTS_INIT_INO,
+#ifdef CONFIG_UTS_NS
+ .ns.ops = &utsns_operations,
+#endif
+};
+
+/* FIXED STRINGS! Don't touch! */
+const char linux_banner[] =
+ "Linux version " UTS_RELEASE " (" LINUX_COMPILE_BY "@"
+ LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION "\n";
diff --git a/init/version.c b/init/version.c
index 3391c4051bf3..01d4ab05f0ba 100644
--- a/init/version.c
+++ b/init/version.c
@@ -18,24 +18,6 @@
#include <generated/utsrelease.h>
#include <linux/proc_ns.h>
-struct uts_namespace init_uts_ns = {
- .ns.count = REFCOUNT_INIT(2),
- .name = {
- .sysname = UTS_SYSNAME,
- .nodename = UTS_NODENAME,
- .release = UTS_RELEASE,
- .version = UTS_VERSION,
- .machine = UTS_MACHINE,
- .domainname = UTS_DOMAINNAME,
- },
- .user_ns = &init_user_ns,
- .ns.inum = PROC_UTS_INIT_INO,
-#ifdef CONFIG_UTS_NS
- .ns.ops = &utsns_operations,
-#endif
-};
-EXPORT_SYMBOL_GPL(init_uts_ns);
-
static int __init early_hostname(char *arg)
{
size_t bufsize = sizeof(init_uts_ns.name.nodename);
@@ -51,11 +33,6 @@ static int __init early_hostname(char *arg)
}
early_param("hostname", early_hostname);
-/* FIXED STRINGS! Don't touch! */
-const char linux_banner[] =
- "Linux version " UTS_RELEASE " (" LINUX_COMPILE_BY "@"
- LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION "\n";
-
const char linux_proc_banner[] =
"%s version %s"
" (" LINUX_COMPILE_BY "@" LINUX_COMPILE_HOST ")"
@@ -63,3 +40,16 @@ const char linux_proc_banner[] =
BUILD_SALT;
BUILD_LTO_INFO;
+
+/*
+ * init_uts_ns and linux_banner contain the build version and timestamp,
+ * which are really fixed at the very last step of build process.
+ * They are compiled with __weak first, and without __weak later.
+ */
+
+struct uts_namespace init_uts_ns __weak;
+const char linux_banner[] __weak;
+
+#include "version-timestamp.c"
+
+EXPORT_SYMBOL_GPL(init_uts_ns);
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
diff --git a/scripts/mkcompile_h b/scripts/mkcompile_h
index ca40a5258c87..f1a820d49e53 100755
--- a/scripts/mkcompile_h
+++ b/scripts/mkcompile_h
@@ -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 "$SMP" ] ; then CONFIG_FLAGS="SMP"; fi
-
-if [ -n "$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 "/* $CONFIG_FLAGS */"; fi
+LD_VERSION=$($LD -v | head -n1 | sed 's/(compatible with [^)]*)//' \
+ | sed 's/[[:space:]]*$//')
- 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
--
2.34.1