Commit 2df8220c authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

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: default avatarMasahiro Yamada <masahiroy@kernel.org>
parent 561daaac

arch/powerpc/boot/wrapper

+1 −1
Original line number Diff line number Diff line
@@ -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.]' | \

    cut -d' ' -f3`

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

if [ -n "$version" ]; then

    uboot_version="-n Linux-$version"

fi

arch/s390/boot/version.c

+1 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#include <generated/utsversion.h>

#include <generated/utsrelease.h>

#include <generated/compile.h>

#include "boot.h"

arch/x86/boot/compressed/kaslr.c

+1 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/boot/version.c

+1 −0
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
 */



#include "boot.h"

#include <generated/utsversion.h>

#include <generated/utsrelease.h>

#include <generated/compile.h>

init/.gitignore

0 → 100644
+2 −0
Original line number Diff line number Diff line 
# SPDX-License-Identifier: GPL-2.0-only

/utsversion-tmp.h