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/arch/powerpc/boot/wrapper b/arch/powerpc/boot/wrapper
index 55978f32fa7751373b24868e93603d57ad916d00..5bdd4dd20bbb18e5d360b7ad12b14e0c12494e3b 100755 (executable)
--- a/arch/powerpc/boot/wrapper
+++ b/arch/powerpc/boot/wrapper
@@ -433,7 +433,7 @@ fi
 # Extract kernel version information, some platforms want to include
 # it in the image header
 version=`${CROSS}strings "$kernel" | grep '^Linux version [-0-9.]' | \
 # Extract kernel version information, some platforms want to include
 # it in the image header
 version=`${CROSS}strings "$kernel" | grep '^Linux version [-0-9.]' | \

-    cut -d' ' -f3`
+    head -n1 | cut -d' ' -f3`

 if [ -n "$version" ]; then
     uboot_version="-n Linux-$version"
 fi
 if [ -n "$version" ]; then
     uboot_version="-n Linux-$version"
 fi

diff --git a/arch/s390/boot/version.c b/arch/s390/boot/version.c
index d32e58bdda6ad2c7c15c8f104a4234f99eefb77b..fd32f038777f43e9a0cd0bd0b7c38c1ea76adc45 100644 (file)
--- a/arch/s390/boot/version.c
+++ b/arch/s390/boot/version.c
@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
 // SPDX-License-Identifier: GPL-2.0

+#include <generated/utsversion.h>

 #include <generated/utsrelease.h>
 #include <generated/compile.h>
 #include "boot.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 4a3f223973f40f85bc633359f1a41c92ce6ca084..e476bcbd9b422f6e2a980b59ac59d4e0cb30ce0d 100644 (file)
--- 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 <linux/uts.h>
 #include <linux/utsname.h>
 #include <linux/ctype.h>

+#include <generated/utsversion.h>

 #include <generated/utsrelease.h>
 
 #define _SETUP
 #include <generated/utsrelease.h>
 
 #define _SETUP

diff --git a/arch/x86/boot/version.c b/arch/x86/boot/version.c
index a1aaaf6c06a6434d0f8a6b5a8defdc34f225616d..945383f0f606abb850df5442d8cca356d6380042 100644 (file)
--- a/arch/x86/boot/version.c
+++ b/arch/x86/boot/version.c
@@ -11,6 +11,7 @@
  */
 
 #include "boot.h"
  */
 
 #include "boot.h"

+#include <generated/utsversion.h>

 #include <generated/utsrelease.h>
 #include <generated/compile.h>
 
 #include <generated/utsrelease.h>
 #include <generated/compile.h>
 

diff --git a/init/.gitignore b/init/.gitignore
new file mode 100644 (file)
index 0000000..cbbe270
--- /dev/null
+++ b/init/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+/utsversion-tmp.h

diff --git a/init/Makefile b/init/Makefile
index d82623d7fc8e8c89d6442dfa15feac384a9ec2c4..ba90eb817185202b139e69dde2385c4aae47f979 100644 (file)
--- a/init/Makefile
+++ b/init/Makefile
@@ -19,20 +19,49 @@ mounts-y                    := do_mounts.o
 mounts-$(CONFIG_BLK_DEV_RAM)   += do_mounts_rd.o
 mounts-$(CONFIG_BLK_DEV_INITRD)        += do_mounts_initrd.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
+#

 
 

-# 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)/utsversion-tmp.h: FORCE
+       $(call filechk,uts_version)

 
 

-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)"
+clean-files += utsversion-tmp.h
+
+$(obj)/version.o: include/generated/compile.h $(obj)/utsversion-tmp.h
+CFLAGS_version.o := -include $(obj)/utsversion-tmp.h
+
+filechk_compile.h = $(srctree)/scripts/mkcompile_h \
+       "$(UTS_MACHINE)" "$(CONFIG_CC_VERSION_TEXT)" "$(LD)"

 
 include/generated/compile.h: FORCE
 
 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 (executable)
index 0000000..537d458
--- /dev/null
+++ b/init/build-version
@@ -0,0 +1,10 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+
+prev_ver=$(cat .version 2>/dev/null) &&
+ver=$(expr ${prev_ver} + 1 2>/dev/null) ||
+ver=1
+
+echo ${ver} > .version
+
+echo ${ver}

diff --git a/init/version-timestamp.c b/init/version-timestamp.c
new file mode 100644 (file)
index 0000000..179e93b
--- /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 3391c4051bf35bb120dbc1a96c2b7fb5fca51f80..01d4ab05f0bac09c820b2379e5f0abf70c778cfc 100644 (file)
--- a/init/version.c
+++ b/init/version.c
@@ -18,24 +18,6 @@
 #include <generated/utsrelease.h>
 #include <linux/proc_ns.h>
 
 #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);
 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);
 
 }
 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 ")"
 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;
 
 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/kernel/gen_kheaders.sh b/kernel/gen_kheaders.sh
index 0c78e64f747df590616a2e7a8da4d8a08c379b41..473036b43c832b2a94c8eef8edb9ef82c11b9a6c 100755 (executable)
--- 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"
 
 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
 #
 # 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 $all_dirs -name "*.h"                      |
 #
 # Ignore them for md5 calculation to avoid pointless regeneration.
 headers_md5="$(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)"
 
                grep -v "include/generated/autoconf.h"  |
                xargs ls -l | md5sum | cut -d ' ' -f1)"
 

diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index eecc1863e556b95acce0222fed00760708f5c60b..8d982574145acdcb0d886ec7cc106403e8bd21ac 100755 (executable)
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -75,6 +75,8 @@ vmlinux_link()
                objs="${objs} .vmlinux.export.o"
        fi
 
                objs="${objs} .vmlinux.export.o"
        fi
 

+       objs="${objs} init/version-timestamp.o"
+

        if [ "${SRCARCH}" = "um" ]; then
                wl=-Wl,
                ld="${CC}"
        if [ "${SRCARCH}" = "um" ]; then
                wl=-Wl,
                ld="${CC}"


@@ -213,19 +215,6 @@ if [ "$1" = "clean" ]; then
        exit 0
 fi
 
        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"
 
 #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.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
 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 ca40a5258c8778214c93f32ae241b1274d0cceaf..f1a820d49e538fedde8a5c5fe3e06d17be2c1049 100755 (executable)
--- a/scripts/mkcompile_h
+++ b/scripts/mkcompile_h
@@ -1,14 +1,9 @@
 #!/bin/sh
 # SPDX-License-Identifier: GPL-2.0
 
 #!/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
 
 # Do not expand names
 set -f


@@ -17,17 +12,6 @@ set -f
 LC_ALL=C
 export LC_ALL
 
 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
 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
 
        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