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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>
56 lines
1.3 KiB
C
56 lines
1.3 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* linux/init/version.c
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*
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* Copyright (C) 1992 Theodore Ts'o
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*
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* May be freely distributed as part of Linux.
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*/
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#include <generated/compile.h>
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#include <linux/build-salt.h>
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#include <linux/elfnote-lto.h>
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#include <linux/export.h>
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#include <linux/init.h>
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#include <linux/printk.h>
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#include <linux/uts.h>
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#include <linux/utsname.h>
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#include <generated/utsrelease.h>
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#include <linux/proc_ns.h>
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static int __init early_hostname(char *arg)
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{
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size_t bufsize = sizeof(init_uts_ns.name.nodename);
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size_t maxlen = bufsize - 1;
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size_t arglen;
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arglen = strlcpy(init_uts_ns.name.nodename, arg, bufsize);
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if (arglen > maxlen) {
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pr_warn("hostname parameter exceeds %zd characters and will be truncated",
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maxlen);
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}
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return 0;
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}
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early_param("hostname", early_hostname);
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const char linux_proc_banner[] =
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"%s version %s"
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" (" LINUX_COMPILE_BY "@" LINUX_COMPILE_HOST ")"
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" (" LINUX_COMPILER ") %s\n";
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BUILD_SALT;
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BUILD_LTO_INFO;
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/*
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* init_uts_ns and linux_banner contain the build version and timestamp,
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* which are really fixed at the very last step of build process.
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* They are compiled with __weak first, and without __weak later.
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*/
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struct uts_namespace init_uts_ns __weak;
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const char linux_banner[] __weak;
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#include "version-timestamp.c"
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EXPORT_SYMBOL_GPL(init_uts_ns);
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