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openwrt/include/kernel-defaults.mk
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John Crispin 9d84fbff36 kernel: skip kbuild if the kernel tree did not change 
kbuild runs twice per build, for the modules and for the image, and
takes about half a second each time even if there is nothing to do.

Store a hash of the kbuild command line after a successful run, and
skip the next run if the hash is the same and no file in the kernel
tree or the toolchain is newer than the stamp. The OpenWrt files at the
top of the kernel tree are ignored, apart from .config. Directories are
ignored, as kbuild changes them with temporary files, so a deleted file
alone does not trigger a run.

With CONFIG_STRIP_KERNEL_EXPORTS the image link reads symtab.h, which
sits above the kernel tree and follows the modules of the packages. The
scan of the image run names that file as well.

The workaround that deletes vmlinux now only runs together with kbuild.

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

256 lines
11 KiB
Makefile
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# SPDX-License-Identifier: GPL-2.0-only
#
# Copyright (C) 2006-2020 OpenWrt.org
ifdef CONFIG_STRIP_KERNEL_EXPORTS
KERNEL_MAKEOPTS_IMAGE += \
EXTRA_LDSFLAGS="-I$(KERNEL_BUILD_DIR) -include symtab.h"
endif
INITRAMFS_EXTRA_FILES ?= $(GENERIC_PLATFORM_DIR)/image/initramfs-base-files.txt
export HOST_EXTRACFLAGS=-I$(STAGING_DIR_HOST)/include
# defined in quilt.mk
Kernel/Patch:=$(Kernel/Patch/Default)
ifneq (,$(findstring .xz,$(LINUX_SOURCE)))
LINUX_CAT:=xzcat
else
LINUX_CAT:=$(STAGING_DIR_HOST)/bin/libdeflate-gzip -dc
endif
ifeq ($(strip $(CONFIG_EXTERNAL_KERNEL_TREE)),"")
ifeq ($(strip $(CONFIG_KERNEL_GIT_CLONE_URI)),"")
define Kernel/Prepare/Default
$(LINUX_CAT) $(DL_DIR)/$(LINUX_SOURCE) | $(TAR) -C $(KERNEL_BUILD_DIR) $(TAR_OPTIONS)
$(Kernel/Patch)
endef
else
define Kernel/Prepare/Default
$(LINUX_CAT) $(DL_DIR)/$(LINUX_SOURCE) | $(TAR) -C $(KERNEL_BUILD_DIR) $(TAR_OPTIONS)
endef
endif
else
define Kernel/Prepare/Default
mkdir -p $(KERNEL_BUILD_DIR)
if [ -d $(LINUX_DIR) ]; then \
rmdir $(LINUX_DIR); \
fi
ln -s $(CONFIG_EXTERNAL_KERNEL_TREE) $(LINUX_DIR)
if [ -d $(LINUX_DIR)/user_headers ]; then \
rm -rf $(LINUX_DIR)/user_headers; \
fi
endef
endif
ifeq ($(CONFIG_TARGET_ROOTFS_INITRAMFS),y)
ifeq ($(strip $(CONFIG_EXTERNAL_CPIO)),"")
define Kernel/SetInitramfs/PreConfigure
{ \
grep -v -e INITRAMFS -e CONFIG_RD_ -e CONFIG_BLK_DEV_INITRD $(2)/.config.old > $(2)/.config; \
echo 'CONFIG_BLK_DEV_INITRD=y' >> $(2)/.config; \
echo 'CONFIG_INITRAMFS_SOURCE="$(strip $(1) $(INITRAMFS_EXTRA_FILES))"' >> $(2)/.config; \
}
endef
else
define Kernel/SetInitramfs/PreConfigure
{ \
grep -v INITRAMFS $(2)/.config.old > $(2)/.config; \
echo 'CONFIG_INITRAMFS_SOURCE="$(call qstrip,$(CONFIG_EXTERNAL_CPIO))"' >> $(2)/.config; \
}
endef
endif
define Kernel/SetInitramfs
{ \
rm -f $(2)/.config.prev; \
mv $(2)/.config $(2)/.config.old; \
$(call Kernel/SetInitramfs/PreConfigure,$(1),$(2)); \
echo "# CONFIG_INITRAMFS_PRESERVE_MTIME is not set" >> $(2)/.config; \
echo "CONFIG_INITRAMFS_ROOT_UID=$(shell id -u)" >> $(2)/.config; \
echo "CONFIG_INITRAMFS_ROOT_GID=$(shell id -g)" >> $(2)/.config; \
$(if $(CONFIG_TARGET_INITRAMFS_FORCE), \
echo "CONFIG_INITRAMFS_FORCE=y" >> $(2)/.config;, \
echo "# CONFIG_INITRAMFS_FORCE is not set" >> $(2)/.config;) \
$(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_NONE), \
echo "CONFIG_INITRAMFS_COMPRESSION_NONE=y" >> $(2)/.config;, \
echo "# CONFIG_INITRAMFS_COMPRESSION_NONE is not set" >> $(2)/.config; ) \
$(foreach ALGO,GZIP BZIP2 LZMA LZO XZ LZ4 ZSTD, \
$(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_$(ALGO)), \
echo "CONFIG_INITRAMFS_COMPRESSION_$(ALGO)=y" >> $(2)/.config; $\, \
echo "# CONFIG_INITRAMFS_COMPRESSION_$(ALGO) is not set" >> $(2)/.config; $\) \
) \
$(call Kernel/SetRamdiskCompression,$(2)/.config) \
}
endef
else
endif
define Kernel/SetRamdiskCompression
$(foreach ALGO,GZIP BZIP2 LZMA LZO XZ LZ4 ZSTD, \
$(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_$(ALGO)), \
echo "CONFIG_RD_$(ALGO)=y" >> $(1); $\, \
echo "# CONFIG_RD_$(ALGO) is not set" >> $(1); $\) \
)
endef
# With a separate initramfs, the initramfs kernel differs from the regular
# kernel only in ramdisk support. Enable it here too, so that one kernel
# build serves both images.
define Kernel/SetNoInitramfs
mv $(LINUX_DIR)/.config.set $(LINUX_DIR)/.config.old
grep -v INITRAMFS $(LINUX_DIR)/.config.old > $(LINUX_DIR)/.config.set
echo 'CONFIG_INITRAMFS_SOURCE=""' >> $(LINUX_DIR)/.config.set
echo '# CONFIG_INITRAMFS_FORCE is not set' >> $(LINUX_DIR)/.config.set
echo "# CONFIG_INITRAMFS_PRESERVE_MTIME is not set" >> $(LINUX_DIR)/.config.set
$(if $(CONFIG_TARGET_ROOTFS_INITRAMFS_SEPARATE), \
echo 'CONFIG_BLK_DEV_INITRD=y' >> $(LINUX_DIR)/.config.set; \
$(call Kernel/SetRamdiskCompression,$(LINUX_DIR)/.config.set))
endef
define Kernel/Configure/Default
rm -f $(LINUX_DIR)/localversion
$(LINUX_CONF_CMD) > $(LINUX_DIR)/.config.target
# copy CONFIG_KERNEL_* settings over to .config.target
awk '/^(#[[:space:]]+)?CONFIG_KERNEL/{sub("CONFIG_KERNEL_","CONFIG_");print}' $(TOPDIR)/.config >> $(LINUX_DIR)/.config.target
echo "# CONFIG_KALLSYMS_EXTRA_PASS is not set" >> $(LINUX_DIR)/.config.target
echo "# CONFIG_KALLSYMS_ALL is not set" >> $(LINUX_DIR)/.config.target
echo "CONFIG_KALLSYMS_UNCOMPRESSED=y" >> $(LINUX_DIR)/.config.target
$(SCRIPT_DIR)/package-metadata.pl kconfig $(TMP_DIR)/.packageinfo $(TOPDIR)/.config $(KERNEL_PATCHVER) > $(LINUX_DIR)/.config.override
$(SCRIPT_DIR)/kconfig.pl 'm+' '+' $(LINUX_DIR)/.config.target /dev/null $(LINUX_DIR)/.config.override > $(LINUX_DIR)/.config.set
$(call Kernel/SetNoInitramfs)
rm -rf $(KERNEL_BUILD_DIR)/modules
cmp -s $(LINUX_DIR)/.config.set $(LINUX_DIR)/.config.prev || { \
cp $(LINUX_DIR)/.config.set $(LINUX_DIR)/.config; \
cp $(LINUX_DIR)/.config.set $(LINUX_DIR)/.config.prev; \
}
$(_SINGLE) [ -d $(LINUX_DIR)/user_headers ] || $(KERNEL_MAKE) $(if $(findstring uml,$(BOARD)),ARCH=$(ARCH)) INSTALL_HDR_PATH=$(LINUX_DIR)/user_headers headers_install
grep '=[ym]' $(LINUX_DIR)/.config.set | LC_ALL=C sort | $(MKHASH) md5 > $(LINUX_DIR)/.vermagic
endef
define Kernel/Configure/Initramfs
$(call Kernel/SetInitramfs,$(1),$(2))
endef
# The image link reads symtab.h through EXTRA_LDSFLAGS. It sits above
# $(LINUX_DIR), so the scan below has to name it. A package built module
# changes it without a change in the kernel tree.
KERNEL_MAKE_DEPENDS_image := $(if $(CONFIG_STRIP_KERNEL_EXPORTS),$(KERNEL_BUILD_DIR)/symtab.h)
# $(1): stamp name, $(2): make targets and options, $(3): commands to run before kbuild
# kbuild takes about half a second even if nothing changed, and runs twice
# per build. Skip it if the command line did not change since its last
# successful run, and no file in the kernel tree or the toolchain is newer.
# The build system files at the top of the kernel tree are not inputs of
# kbuild, apart from .config.
define Kernel/Make
{ \
stamp=$(LINUX_DIR)/.kbuild_$(1); \
key="$$$$(printf '%s' '$(subst ','\'',$(KERNEL_MAKE) $(2))' | $(MKHASH) md5)"; \
[ "$$$$(cat $$$$stamp 2>/dev/null)" = "$$$$key" ] && [ -z "$$$$(find $(LINUX_DIR) $(TOOLCHAIN_DIR)/bin \
$(KERNEL_MAKE_DEPENDS_$(1)) \
\( -path '$(LINUX_DIR)/.*' ! -path '$(LINUX_DIR)/.config' \) -prune -o \
! -type d -newer $$$$stamp -print -quit)" ] || { \
rm -f $$$$stamp; \
$(3) \
$(KERNEL_MAKE) $(2) && echo "$$$$key" > $$$$stamp; \
}; \
}
endef
define Kernel/CompileModules/Default
+$(call Kernel/Make,modules,$(if $(KERNELNAME),$(KERNELNAME),all) modules, \
rm -f $(LINUX_DIR)/vmlinux $(LINUX_DIR)/System.map;)
# If .config did not change, use the previous timestamp to avoid package rebuilds
cmp -s $(LINUX_DIR)/.config $(LINUX_DIR)/.config.modules.save && \
mv $(LINUX_DIR)/.config.modules.save $(LINUX_DIR)/.config; \
$(CP) $(LINUX_DIR)/.config $(LINUX_DIR)/.config.modules.save
endef
OBJCOPY_STRIP = -R .reginfo -R .notes -R .note -R .comment -R .mdebug -R .note.gnu.build-id
# AMD64 shares the location with x86
ifeq ($(LINUX_KARCH),x86_64)
IMAGES_DIR:=../../x86/boot
endif
# $1: image suffix
# $2: Per Device Rootfs ID
define Kernel/CopyImage
cmp -s $(LINUX_DIR)$(2)/vmlinux $(KERNEL_BUILD_DIR)/vmlinux$(1).debug$(2) || { \
$(KERNEL_CROSS)objcopy -O binary $(OBJCOPY_STRIP) -S $(LINUX_DIR)$(2)/vmlinux $(LINUX_KERNEL)$(1)$(2); \
$(KERNEL_CROSS)objcopy $(OBJCOPY_STRIP) -S $(LINUX_DIR)$(2)/vmlinux $(KERNEL_BUILD_DIR)/vmlinux$(1).elf$(2); \
$(CP) $(LINUX_DIR)$(2)/vmlinux $(KERNEL_BUILD_DIR)/vmlinux$(1).debug$(2); \
$(foreach k, \
$(if $(KERNEL_IMAGES),$(KERNEL_IMAGES),$(filter-out vmlinux dtbs,$(KERNELNAME))), \
$(CP) $(LINUX_DIR)$(2)/arch/$(LINUX_KARCH)/boot/$(IMAGES_DIR)/$(k) $(KERNEL_BUILD_DIR)/$(k)$(1)$(2); \
) \
}
endef
define Kernel/CompileImage/Default
rm -f $(TARGET_DIR)/init
+$(call Kernel/Make,image,$(KERNEL_MAKEOPTS_IMAGE) $(if $(KERNELNAME),$(KERNELNAME),all))
$(call Kernel/CopyImage)
endef
define Kernel/PrepareConfigPerRootfs
{ \
[ ! -d "$(1)" ] || rm -rf $(1); \
mkdir $(1) && $(CP) -T $(LINUX_DIR) $(1); \
touch $(1)/.config; \
}
endef
ifneq ($(CONFIG_TARGET_ROOTFS_INITRAMFS),)
# $1: Custom TARGET_DIR. If omitted TARGET_DIR is used.
# $2: If defined Generate Per Rootfs Kernel Directory and use it
# For Separate Initramfs, the regular kernel is used as is, as its config
# already has the ramdisk support (see Kernel/SetNoInitramfs)
define Kernel/CompileImage/Initramfs
$(call locked,{ \
$(if $(2),$(call Kernel/PrepareConfigPerRootfs,$(LINUX_DIR)$(2));) \
$(if $(CONFIG_TARGET_ROOTFS_INITRAMFS_SEPARATE),, \
$(call Kernel/Configure/Initramfs,$(if $(1),$(1),$(TARGET_DIR)),$(LINUX_DIR)$(2)); \
rm -rf $(LINUX_DIR)$(2)/usr/initramfs_data.cpio*;) \
$(CP) $(GENERIC_PLATFORM_DIR)/other-files/init $(if $(1),$(1),$(TARGET_DIR))/init; \
$(if $(SOURCE_DATE_EPOCH),touch -hcd "@$(SOURCE_DATE_EPOCH)" $(if $(1),$(1),$(TARGET_DIR)) $(if $(1),$(1),$(TARGET_DIR))/init;) \
$(if $(CONFIG_TARGET_ROOTFS_INITRAMFS_SEPARATE), \
$(call locked,{ \
$(if $(call qstrip,$(CONFIG_EXTERNAL_CPIO)), \
$(CP) $(CONFIG_EXTERNAL_CPIO) $(KERNEL_BUILD_DIR)/initrd$(2).cpio;,\
( cd $(if $(1),$(1),$(TARGET_DIR)); find . | LC_ALL=C sort | $(STAGING_DIR_HOST)/bin/cpio --reproducible -o -H newc -R 0:0 > $(KERNEL_BUILD_DIR)/initrd$(2).cpio );) \
$(if $(SOURCE_DATE_EPOCH), \
touch -hcd "@$(SOURCE_DATE_EPOCH)" $(KERNEL_BUILD_DIR)/initrd$(2).cpio;) \
$(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_BZIP2), \
$(STAGING_DIR_HOST)/bin/bzip2 -9 -c < $(KERNEL_BUILD_DIR)/initrd$(2).cpio > $(KERNEL_BUILD_DIR)/initrd$(2).cpio.bzip2;) \
$(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_GZIP), \
$(STAGING_DIR_HOST)/bin/libdeflate-gzip -n -f -S .gzip -12 $(KERNEL_BUILD_DIR)/initrd$(2).cpio;) \
$(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_LZ4), \
$(STAGING_DIR_HOST)/bin/lz4c -l -c1 -fz --favor-decSpeed $(KERNEL_BUILD_DIR)/initrd$(2).cpio $(KERNEL_BUILD_DIR)/initrd$(2).cpio.lz4;) \
$(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_LZMA), \
$(STAGING_DIR_HOST)/bin/lzma e -lc1 -lp2 -pb2 $(KERNEL_BUILD_DIR)/initrd$(2).cpio $(KERNEL_BUILD_DIR)/initrd$(2).cpio.lzma;) \
$(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_LZO), \
$(STAGING_DIR_HOST)/bin/lzop -9 -f $(KERNEL_BUILD_DIR)/initrd$(2).cpio;) \
$(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_XZ), \
$(STAGING_DIR_HOST)/bin/xz -T$(if $(filter 1,$(NPROC)),2,0) -9 -fz --check=crc32 $(KERNEL_BUILD_DIR)/initrd$(2).cpio;) \
$(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_ZSTD), \
$(STAGING_DIR_HOST)/bin/zstd -T0 -f -o $(KERNEL_BUILD_DIR)/initrd$(2).cpio.zstd $(KERNEL_BUILD_DIR)/initrd$(2).cpio;) \
}, gen-cpio$(2));,\
$(KERNEL_MAKE) $(if $(2),-C $(LINUX_DIR)$(2)) $(KERNEL_MAKEOPTS_IMAGE) $(if $(KERNELNAME),$(KERNELNAME),all);) \
$(call Kernel/CopyImage,-initramfs,$(2)); \
$(if $(2),rm -rf $(LINUX_DIR)$(2);) \
}, gen-initramfs$(2));
endef
else
define Kernel/CompileImage/Initramfs
endef
endif
define Kernel/Clean/Default
rm -f $(KERNEL_BUILD_DIR)/linux-$(LINUX_VERSION)/.configured
rm -f $(LINUX_KERNEL)
$(_SINGLE)$(MAKE) -C $(KERNEL_BUILD_DIR)/linux-$(LINUX_VERSION) clean
endef
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