From 2df8220cc511326508ec4da2f43ef69311bdd7b9 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Sun, 28 Aug 2022 11:39:53 +0900 Subject: 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 --- init/version.c | 36 +++++++++++++----------------------- 1 file changed, 13 insertions(+), 23 deletions(-) (limited to 'init/version.c') 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 #include -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); -- cgit v1.2.3-59-g8ed1b