linux/init/version-timestamp.c
Masahiro Yamada 2df8220cc5 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>
2022-09-29 04:40:15 +09:00

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C

// 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";