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/Makefile | 55 ++++++++++++++++++++++++++++++++++++++++++------------- 1 file changed, 42 insertions(+), 13 deletions(-) (limited to 'init/Makefile') diff --git a/init/Makefile b/init/Makefile index d82623d7fc8e..ba90eb817185 100644 --- 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 -# 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 - $(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 -- cgit