@@ -209,6 +209,15 @@ The output directory is often set using "O=..." on the commandline.
The value can be overridden in which case the default value is ignored.
+INSTALL_KBUILD_PATH
+-------------------
+INSTALL_KBUILD_PATH specifies where to install a build environment for
+external modules.
+
+The default value is::
+
+ /usr/src/linux-headers-$(KERNELVERSION)
+
KBUILD_ABS_SRCTREE
--------------------------------------------------
Kbuild uses a relative path to point to the tree when possible. For instance,
@@ -756,6 +756,21 @@ Both possibilities are described in the following.
This will tell kbuild to build lxdialog even if not referenced in
any rule.
+4.6 Host programs necessary to build external modules
+-----------------------------------------------------
+
+ If a host program is necessary to build external modules,
+ it shall be added to extmodprogs in addition to hostprogs.
+
+ Example::
+
+ hostprogs := fixdep
+ extmodprogs := fixdep
+
+ This ensures that the host program is installed to a module build
+ environment with "make kbuild_install". It will be cross-compiled
+ for the target architecture if necessary.
+
5 Userspace Program support
===========================
@@ -644,6 +644,11 @@ endif
export KBUILD_MODULES KBUILD_BUILTIN
+# Decide whether to install the build environment for external modules.
+ifneq ($(filter kbuild_install,$(MAKECMDGOALS)),)
+ export KBUILD_INSTALL=y
+endif
+
ifdef need-config
include include/config/auto.conf
endif
@@ -1001,6 +1006,12 @@ export INSTALL_PATH ?= /boot
#
export INSTALL_DTBS_PATH ?= $(INSTALL_PATH)/dtbs/$(KERNELRELEASE)
+#
+# INSTALL_KBUILD_PATH specifies where to install the build environment for
+# external modules. Can be overridden by passing it as an argument.
+#
+export INSTALL_KBUILD_PATH = /usr/src/linux-headers-$(KERNELVERSION)
+
#
# INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory
# relocations required by build roots. This is not defined in the
@@ -1532,7 +1543,9 @@ help:
@echo ' kernelversion - Output the version stored in Makefile (use with make -s)'
@echo ' image_name - Output the image name (use with make -s)'
@echo ' headers_install - Install sanitised kernel headers to INSTALL_HDR_PATH'; \
- echo ' (default: $(INSTALL_HDR_PATH))'; \
+ echo ' (default: $(INSTALL_HDR_PATH))'
+ @echo ' kbuild_install - Install module build environment to INSTALL_KBUILD_PATH'; \
+ echo ' (default: $(INSTALL_KBUILD_PATH))'; \
echo ''
@echo 'Static analysers:'
@echo ' checkstack - Generate a list of stack hogs'
@@ -1628,6 +1641,14 @@ PHONY += $(DOC_TARGETS)
$(DOC_TARGETS):
$(Q)$(MAKE) $(build)=Documentation $@
+# Module build environment target
+# ---------------------------------------------------------------------------
+PHONY += kbuild_install
+kbuild_install: asm-generic
+ $(Q)$(MAKE) $(build)=scripts/basic
+ $(Q)$(MAKE) $(build)=scripts/mod
+ $(Q)$(MAKE) $(build)=scripts
+
# Misc
# ---------------------------------------------------------------------------
@@ -29,6 +29,9 @@ endif
# The following programs are only built on demand
hostprogs += unifdef
+extmodprogs += recordmcount
+extmodprogs += sign-file
+
subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
subdir-$(CONFIG_MODVERSIONS) += genksyms
subdir-$(CONFIG_SECURITY_SELINUX) += selinux
@@ -59,6 +59,13 @@ ifneq ($(userprogs),)
include scripts/Makefile.userprogs
endif
+# Do not include kbuild install rules unless needed.
+ifneq ($(KBUILD_INSTALL),)
+ifneq ($(extmodprogs),)
+include scripts/Makefile.kbuildinst
+endif
+endif
+
ifndef obj
$(warning kbuild: Makefile.build is included improperly)
endif
@@ -37,6 +37,10 @@ __clean-files := \
# deprecated
__clean-files += $(always) $(hostprogs-y) $(hostprogs-m) $(hostprogs-)
+ifneq ($(extmodprogs),)
+__clean-files += .cross
+endif
+
__clean-files := $(filter-out $(no-clean-files), $(__clean-files))
# clean-files is given relative to the current directory, unless it
new file mode 100644
@@ -0,0 +1,81 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# only install extmodprogs whose hostprogs counterpart is enabled
+extmodprogs := $(sort $(filter $(extmodprogs),$(notdir $(always-y) $(always-m))))
+
+ifneq ($(extmodprogs),)
+
+extmodprogs-install := $(addprefix $(INSTALL_KBUILD_PATH)/$(obj)/, $(extmodprogs))
+
+ifneq ($(CROSS_COMPILE),)
+
+# ==========================================================================
+# Cross-build binaries necessary to build modules on the target
+
+# C executables compiled from a single .c file
+cross-csingle := $(foreach m,$(extmodprogs),$(if $($(m)-objs),,$(m)))
+
+# C executables linked from several .o files
+cross-cmulti := $(foreach m,$(extmodprogs),$(if $($(m)-objs),$(m)))
+
+# Object .o files compiled from .c files
+cross-cobjs := $(sort $(foreach m,$(cross-cmulti),$($(m)-objs)))
+
+cross-csingle := $(addprefix $(obj)/.cross/,$(cross-csingle))
+cross-cmulti := $(addprefix $(obj)/.cross/,$(cross-cmulti))
+cross-cobjs := $(addprefix $(obj)/.cross/,$(cross-cobjs))
+
+# Create executable from a single .c file
+# cross-csingle -> executable
+quiet_cmd_cross-csingle = CC $@
+ cmd_cross-csingle = $(CC) $(hostc_flags) $(KBUILD_HOSTLDFLAGS) -o $@ $< \
+ $(KBUILD_HOSTLDLIBS) $(HOSTLDLIBS_$(target-stem))
+$(cross-csingle): $(obj)/.cross/%: $(src)/%.c FORCE
+ $(call if_changed_dep,cross-csingle)
+
+# Link executable based on list of .o files, all plain C
+# cross-cmulti -> executable
+quiet_cmd_cross-cmulti = LD $@
+ cmd_cross-cmulti = $(CC) $(KBUILD_HOSTLDFLAGS) -o $@ \
+ $(addprefix $(obj)/.cross/, $($(target-stem)-objs)) \
+ $(KBUILD_HOSTLDLIBS) $(HOSTLDLIBS_$(target-stem))
+$(cross-cmulti): FORCE
+ $(call if_changed,cross-cmulti)
+$(call multi_depend, $(cross-cmulti), , -objs)
+
+# Create .o file from a single .c file
+# cross-cobjs -> .o
+#
+# Some host-cobjs have special prerequisites. Apply them to cross-cobjs
+# by letting the cross .o file depend on the host .o file.
+quiet_cmd_cross-cobjs = CC $@
+ cmd_cross-cobjs = $(CC) $(hostc_flags) -c -o $@ $<
+$(cross-cobjs): $(obj)/.cross/%.o: $(src)/%.c $(obj)/%.o FORCE
+ $(call if_changed_dep,cross-cobjs)
+
+# ==========================================================================
+# Install module build environment to $(INSTALL_KBUILD_PATH)
+#
+# When cross-compiling, install cross-compiled versions of the hostprogs.
+# Else install the hostprogs directly.
+
+targets += $(cross-csingle) $(cross-cmulti) $(cross-cobjs)
+always-y += $(cross-csingle) $(cross-cmulti) $(cross-cobjs)
+
+$(extmodprogs-install): $(INSTALL_KBUILD_PATH)/$(obj)/%: $(obj)/.cross/%
+ $(call cmd,extmodprogs_install,$(dir $@))
+
+else # !CROSS_COMPILE
+
+$(extmodprogs-install): $(INSTALL_KBUILD_PATH)/$(obj)/%: $(obj)/%
+ $(call cmd,extmodprogs_install,$(dir $@))
+
+endif # !CROSS_COMPILE
+
+quiet_cmd_extmodprogs_install = INSTALL $<
+ cmd_extmodprogs_install = mkdir -p $(2); cp $< $(2)
+
+targets += $(extmodprogs-install)
+always-y += $(extmodprogs-install)
+
+endif # extmodprogs
@@ -112,7 +112,7 @@ modname = $(subst $(space),:,$(__modname))
modfile = $(addprefix $(obj)/,$(__modname))
# target with $(obj)/ and its suffix stripped
-target-stem = $(basename $(patsubst $(obj)/%,%,$@))
+target-stem = $(basename $(notdir $@))
# These flags are needed for modversions and compiling, so we define them here
# $(modname_flags) defines KBUILD_MODNAME as the name of the module it will
@@ -220,9 +220,9 @@ dtc_cpp_flags = -Wp,-MMD,$(depfile).pre.tmp -nostdinc \
# Usage:
# $(call multi_depend, multi_used_targets, suffix_to_remove, suffix_to_add)
define multi_depend
-$(foreach m, $(notdir $1), \
- $(eval $(obj)/$m: \
- $(addprefix $(obj)/, $(foreach s, $3, $($(m:%$(strip $2)=%$(s)))))))
+$(foreach m, $1, \
+ $(eval $m: \
+ $(addprefix $(dir $m), $(foreach s, $3, $($(patsubst %$(strip $2),%$(s),$(notdir $m)))))))
endef
quiet_cmd_copy = COPY $@
@@ -3,3 +3,4 @@
# fixdep: used to generate dependency information during build process
hostprogs-always-y += fixdep
+extmodprogs += fixdep
@@ -1,6 +1,7 @@
# SPDX-License-Identifier: GPL-2.0
hostprogs-always-y += genksyms
+extmodprogs += genksyms
genksyms-objs := genksyms.o parse.tab.o lex.lex.o
@@ -2,6 +2,7 @@
OBJECT_FILES_NON_STANDARD := y
hostprogs-always-y += modpost mk_elfconfig
+extmodprogs += modpost
always-y += empty.o
modpost-objs := modpost.o file2alias.o sumversion.o
To build external modules, one needs executables such as fixdep and modpost. But when cross-compiling the kernel, those executables are only generated for the host arch, not the target arch. Distributions ship packages which users need to install in order to build external modules. These packages contain headers and Makefiles from the kernel source tree as well as fixdep & friends. Usually the packages are cross-built on a single host arch for the multitude of arches supported by the distribution. But because fixdep & friends are only compiled for the host arch, distributions are forced to duplicate these executables' Makefiles in order to cross-compile them. For instance, these are Debian's duplicated Makefiles: https://salsa.debian.org/kernel-team/linux/-/tree/master/debian/rules.d/scripts Make distribution maintainers' lives easier by providing a new target "make kbuild_install" which cross-compiles the required executables for the target arch and installs them below $(INSTALL_KBUILD_PATH). To avoid wasting compile time and disk space, compile only programs which are essential for building external modules. They are declared essential by adding them to extmodprogs. For now, these are: recordmcount sign-file fixdep genksyms modpost The rules to cross-compile the executables reside in Makefile.kbuildinst. They are similar to the rules in Makefile.host, but I've left out rules for C++ executables and shared libraries as they're not necessary. The host versions of the executables are generated in $(obj) whereas the cross-compiled versions are generated in $(obj)/.cross/ . This necessitates a modification of Makefile.lib because the multi_depend macro creates rules which assume that the target and its dependencies always reside in $(obj). Refactor the macro to use $(dir $1) in lieu of $(obj). Likewise, the target-stem macro strips $(obj)/ instead of $(obj)/.cross/. Refactor it to use $(notdir $@). In a future step, Makefile.kbuildinst may be extended to also install headers and other bits necessary for building external modules. Signed-off-by: Lukas Wunner <lukas@wunner.de> --- Documentation/kbuild/kbuild.rst | 9 ++++ Documentation/kbuild/makefiles.rst | 15 ++++++ Makefile | 23 ++++++++- scripts/Makefile | 3 ++ scripts/Makefile.build | 7 +++ scripts/Makefile.clean | 4 ++ scripts/Makefile.kbuildinst | 81 ++++++++++++++++++++++++++++++ scripts/Makefile.lib | 8 +-- scripts/basic/Makefile | 1 + scripts/genksyms/Makefile | 1 + scripts/mod/Makefile | 1 + 11 files changed, 148 insertions(+), 5 deletions(-) create mode 100644 scripts/Makefile.kbuildinst