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openwrt/include/kernel-build.mk
T
John Crispin e97e3f36bd kernel: configure the kernel only when an input changed 
The configure stage rewrites the kernel configuration on every build. It
runs kconfig.pl twice and package-metadata.pl once, which takes an eighth of
a second. target/compile and target/install both pay it.

The rule carries FORCE because the kernel configuration also depends on the
package metadata, which is not a prerequisite. Add a check file that the
rule creates only when the configure stage must run, and make the stamp
depend on it. The check covers the kernel configuration files, .config, the
package metadata, the scripts that read them, the two build system files
that hold the recipe, the target directory and the user headers.

This takes the time of target/linux install on an unchanged tree from 1.33 s
to 1.15 s, and the time of a full no-op build from 3.68 s to 3.40 s for the
OpenWrt One.

Signed-off-by: John Crispin <john@phrozen.org>
2026-09-22 18:18:58 +02:00

238 lines
8.1 KiB
Makefile
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# SPDX-License-Identifier: GPL-2.0-only
#
# Copyright (C) 2006-2020 OpenWrt.org
include $(INCLUDE_DIR)/prereq.mk
include $(INCLUDE_DIR)/depends.mk
ifneq ($(DUMP),1)
all: compile
endif
KERNEL_FILE_DEPENDS=$(GENERIC_BACKPORT_DIR) $(GENERIC_PATCH_DIR) $(GENERIC_HACK_DIR) $(PATCH_DIR) $(GENERIC_FILES_DIR) $(FILES_DIR)
STAMP_PREPARED=$(LINUX_DIR)/.prepared$(if $(QUILT)$(DUMP),,_$(shell $(call $(if $(CONFIG_AUTOREMOVE),find_md5_reproducible,find_md5),$(KERNEL_FILE_DEPENDS),)))
STAMP_CONFIGURED:=$(LINUX_DIR)/.configured
include $(INCLUDE_DIR)/download.mk
include $(INCLUDE_DIR)/quilt.mk
include $(INCLUDE_DIR)/kernel-defaults.mk
define Kernel/Prepare
$(call Kernel/Prepare/Default)
endef
define Kernel/Configure
$(call Kernel/Configure/Default)
endef
define Kernel/CompileModules
$(call Kernel/CompileModules/Default)
endef
define Kernel/CompileImage
$(call Kernel/CompileImage/Default)
$(call Kernel/CompileImage/Initramfs)
endef
define Kernel/Clean
$(call Kernel/Clean/Default)
endef
define Download/kernel
URL:=$(LINUX_SITE)
FILE:=$(LINUX_SOURCE)
HASH:=$(LINUX_KERNEL_HASH)
endef
KERNEL_GIT_OPTS:=
ifneq ($(strip $(CONFIG_KERNEL_GIT_LOCAL_REPOSITORY)),"")
KERNEL_GIT_OPTS+=--reference $(CONFIG_KERNEL_GIT_LOCAL_REPOSITORY)
endif
define Download/git-kernel
URL:=$(call qstrip,$(CONFIG_KERNEL_GIT_CLONE_URI))
PROTO:=git
SOURCE_VERSION:=$(CONFIG_KERNEL_GIT_REF)
FILE:=$(LINUX_SOURCE)
SUBDIR:=linux-$(LINUX_VERSION)
OPTS:=$(KERNEL_GIT_OPTS)
endef
ifdef CONFIG_COLLECT_KERNEL_DEBUG
define Kernel/CollectDebug
rm -rf $(KERNEL_BUILD_DIR)/debug
mkdir -p $(KERNEL_BUILD_DIR)/debug/modules
$(CP) $(LINUX_DIR)/vmlinux $(KERNEL_BUILD_DIR)/debug/
-$(CP) \
$(STAGING_DIR_ROOT)/lib/modules/$(LINUX_VERSION)/*.ko \
$(KERNEL_BUILD_DIR)/debug/modules/
$(FIND) $(KERNEL_BUILD_DIR)/debug -type f | $(XARGS) $(KERNEL_CROSS)strip --only-keep-debug
$(TAR) c -C $(KERNEL_BUILD_DIR) debug \
$(if $(SOURCE_DATE_EPOCH),--mtime="@$(SOURCE_DATE_EPOCH)") \
| zstd -T0 -f -o $(BIN_DIR)/kernel-debug.tar.zst
endef
endif
ifeq ($(DUMP)$(filter prereq clean refresh update,$(MAKECMDGOALS)),)
ifneq ($(if $(QUILT),,$(CONFIG_AUTOREBUILD)),)
define Kernel/Autoclean
$(PKG_BUILD_DIR)/.dep_files: $(STAMP_PREPARED)
$(call rdep,$(KERNEL_FILE_DEPENDS),$(STAMP_PREPARED),$(PKG_BUILD_DIR)/.dep_files,-x "*/.dep_*")
endef
endif
endif
KERNEL_CONFIG_CHECK:=$(LINUX_DIR)/.configured-check
KERNEL_CONFIG_DEPENDS:=$(LINUX_KCONFIG_LIST) $(TOPDIR)/.config $(TMP_DIR)/.packageinfo \
$(SCRIPT_DIR)/kconfig.pl $(SCRIPT_DIR)/package-metadata.pl $(SCRIPT_DIR)/metadata.pm \
$(INCLUDE_DIR)/kernel-defaults.mk $(INCLUDE_DIR)/kernel-build.mk $(CURDIR)
IMAGE_INSTALL_STAMP:=$(KERNEL_BUILD_DIR)/.image_install
IMAGE_INSTALL_INPUTS:=$(LINUX_DIR) $(STAGING_DIR)/image \
$(STAGING_DIR_HOST)/bin $(CURDIR) $(INCLUDE_DIR) $(SCRIPT_DIR) $(TOPDIR)/.config
IMAGE_INSTALL_PRUNE:=\( -path '$(LINUX_DIR)/.*' ! -path '$(LINUX_DIR)/.config' \)
image_install_state = ( \
cd $(TARGET_DIR) && \
find . -printf '%P %y %m %U %G %s %l\n' | LC_ALL=C sort && \
find . -type f -print0 | LC_ALL=C sort -z | xargs -0 -r cat; \
) | $(MKHASH) sha256; \
find $(BIN_DIR) -maxdepth 1 -type f \
! -name sha256sums ! -name profiles.json ! -name '*.buildinfo' \
-printf '%f %s\n' 2>/dev/null | LC_ALL=C sort; \
find $(BUILD_DIR)/json_info_files -maxdepth 1 -type f \
-printf '%f %s\n' 2>/dev/null | LC_ALL=C sort
image_install_newer = \
find $(KERNEL_BUILD_DIR) -maxdepth 1 ! -type d \
-newer $(IMAGE_INSTALL_STAMP) -print -quit 2>/dev/null; \
find $(IMAGE_INSTALL_INPUTS) $(IMAGE_INSTALL_PRUNE) -prune -o \
! -type d -newer $(IMAGE_INSTALL_STAMP) -print -quit 2>/dev/null
define BuildKernel
$(if $(QUILT),$(Build/Quilt))
$(if $(LINUX_SITE),$(call Download,kernel))
$(if $(call qstrip,$(CONFIG_KERNEL_GIT_CLONE_URI)),$(call Download,git-kernel))
.NOTPARALLEL:
$(Kernel/Autoclean)
$(STAMP_PREPARED): $(if $(LINUX_SITE),$(DL_DIR)/$(LINUX_SOURCE))
$(call BuildTimeLog,begin,prepare)
-rm -rf $(KERNEL_BUILD_DIR)
-mkdir -p $(KERNEL_BUILD_DIR)
$(Kernel/Prepare)
touch $$@
$(call BuildTimeLog,end,prepare)
$(KERNEL_BUILD_DIR)/symtab.h: FORCE
$(call BuildTimeLog,begin,compile)
rm -f $(KERNEL_BUILD_DIR)/symtab.h
touch $(KERNEL_BUILD_DIR)/symtab.h
+$(KERNEL_MAKE) vmlinux
find $(LINUX_DIR) $(STAGING_DIR_ROOT)/lib/modules -name \*.ko | \
xargs $(TARGET_CROSS)nm | \
awk '$$$$1 == "U" { print $$$$2 } ' | \
sort -u > $(KERNEL_BUILD_DIR)/mod_symtab.txt
$(TARGET_CROSS)nm -n $(LINUX_DIR)/vmlinux.o | awk '/^[0-9a-f]+ [rR] __ksymtab_/ {print substr($$$$3,11)}' > $(KERNEL_BUILD_DIR)/kernel_symtab.txt
grep -Ff $(KERNEL_BUILD_DIR)/mod_symtab.txt $(KERNEL_BUILD_DIR)/kernel_symtab.txt > $(KERNEL_BUILD_DIR)/sym_include.txt
grep -Fvf $(KERNEL_BUILD_DIR)/mod_symtab.txt $(KERNEL_BUILD_DIR)/kernel_symtab.txt > $(KERNEL_BUILD_DIR)/sym_exclude.txt
( \
echo '#define SYMTAB_KEEP \'; \
cat $(KERNEL_BUILD_DIR)/sym_include.txt | \
awk '{print "KEEP(*(___ksymtab+" $$$$1 ")) \\" }'; \
echo; \
echo '#define SYMTAB_KEEP_GPL \'; \
cat $(KERNEL_BUILD_DIR)/sym_include.txt | \
awk '{print "KEEP(*(___ksymtab_gpl+" $$$$1 ")) \\" }'; \
echo; \
echo '#define SYMTAB_DISCARD \'; \
cat $(KERNEL_BUILD_DIR)/sym_exclude.txt | \
awk '{print "*(___ksymtab+" $$$$1 ") \\" }'; \
echo; \
echo '#define SYMTAB_DISCARD_GPL \'; \
cat $(KERNEL_BUILD_DIR)/sym_exclude.txt | \
awk '{print "*(___ksymtab_gpl+" $$$$1 ") \\" }'; \
echo; \
) > $$@
$(call BuildTimeLog,end,compile)
$(KERNEL_CONFIG_CHECK): $(STAMP_PREPARED) $(LINUX_KCONFIG_LIST) $(TOPDIR)/.config FORCE
@mkdir -p $(LINUX_DIR)
@[ -f $(STAMP_CONFIGURED) ] && [ -d $(LINUX_DIR)/user_headers ] && \
[ -z "$$$$(find $(KERNEL_CONFIG_DEPENDS) ! -type d \
-newer $(STAMP_CONFIGURED) -print -quit 2>/dev/null)" ] || \
touch $$@
$(STAMP_CONFIGURED): $(KERNEL_CONFIG_CHECK)
$(call BuildTimeLog,begin,configure)
$(Kernel/Configure)
touch $$@
$(call BuildTimeLog,end,configure)
$(LINUX_DIR)/.modules: export STAGING_PREFIX=$$(STAGING_DIR_HOST)
$(LINUX_DIR)/.modules: export PKG_CONFIG_PATH=$$(STAGING_DIR_HOST)/lib/pkgconfig
$(LINUX_DIR)/.modules: export PKG_CONFIG_LIBDIR=$$(STAGING_DIR_HOST)/lib/pkgconfig
$(LINUX_DIR)/.modules: export FAIL_ON_UNCONFIGURED=1
$(LINUX_DIR)/.modules: $(STAMP_CONFIGURED) $(LINUX_DIR)/.config FORCE
$(call BuildTimeLog,begin,compile)
$(Kernel/CompileModules)
touch $$@
$(call BuildTimeLog,end,compile)
$(LINUX_DIR)/.image: export STAGING_PREFIX=$$(STAGING_DIR_HOST)
$(LINUX_DIR)/.image: export PKG_CONFIG_PATH=$$(STAGING_DIR_HOST)/lib/pkgconfig
$(LINUX_DIR)/.image: export PKG_CONFIG_LIBDIR=$$(STAGING_DIR_HOST)/lib/pkgconfig
$(LINUX_DIR)/.image: $(STAMP_CONFIGURED) $(if $(CONFIG_STRIP_KERNEL_EXPORTS),$(KERNEL_BUILD_DIR)/symtab.h) FORCE
$(call BuildTimeLog,begin,compile)
$(Kernel/CompileImage)
$(Kernel/CollectDebug)
touch $$@
$(call BuildTimeLog,end,compile)
mostlyclean: FORCE
$(Kernel/Clean)
define BuildKernel
endef
download: $(if $(LINUX_SITE),$(DL_DIR)/$(LINUX_SOURCE))
prepare: $(STAMP_PREPARED)
compile: $(LINUX_DIR)/.modules
+$(MAKE) -C image compile TARGET_BUILD=
dtb: $(STAMP_CONFIGURED)
$(_SINGLE)$(KERNEL_MAKE) scripts_dtc
$(MAKE) -C image compile-dtb TARGET_BUILD=
oldconfig menuconfig nconfig xconfig: $(STAMP_PREPARED) $(STAMP_CHECKED) FORCE
rm -f $(LINUX_DIR)/.config.prev
rm -f $(STAMP_CONFIGURED)
$(LINUX_RECONF_CMD) > $(LINUX_DIR)/.config
$(_SINGLE)$(KERNEL_MAKE) \
$(if $(findstring Darwin,$(HOST_OS)), \
HOSTLDLIBS_mconf="-L$(STAGING_DIR_HOST)/lib -lncurses" \
filechk_conf_cfg=" :" \
) \
YACC=$(STAGING_DIR_HOST)/bin/bison \
$$@
$(call LINUX_RECONF_DIFF,$(LINUX_DIR)/.config) > $(LINUX_RECONFIG_TARGET)
install: $(LINUX_DIR)/.image
+{ \
state="$$$$( $(image_install_state) )"; \
[ "$$$$state" = "$$$$(cat $(IMAGE_INSTALL_STAMP) 2>/dev/null)" ] && \
[ -z "$$$$($(image_install_newer))" ] || { \
rm -f $(IMAGE_INSTALL_STAMP); \
$(MAKE) -C image compile install TARGET_BUILD= && \
{ $(image_install_state); } > $(IMAGE_INSTALL_STAMP); \
}; \
}
clean: FORCE
rm -rf $(KERNEL_BUILD_DIR)
image-prereq:
@+$(NO_TRACE_MAKE) -s -C image prereq TARGET_BUILD=
prereq: image-prereq
endef
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