09bd7c75e5
One of the most remarkable improvements in this cycle is, Kbuild is
now able to cache the result of shell commands. Some variables are
expensive to compute, for example, $(call cc-option,...) invokes the
compiler. It is not efficient to redo this computation every time,
even when we are not actually building anything. Kbuild creates a
hidden file ".cache.mk" that contains invoked shell commands and
their results. The speed-up should be noticeable.
Summary:
- Fix arch build issues (hexagon, sh)
- Clean up various Makefiles and scripts
- Fix wrong usage of {CFLAGS,LDFLAGS}_MODULE in arch Makefiles
- Cache variables that are expensive to compute
- Improve cc-ldopton and ld-option for Clang
- Optimize output directory creation
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Merge tag 'kbuild-v4.15' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull Kbuild updates from Masahiro Yamada:
"One of the most remarkable improvements in this cycle is, Kbuild is
now able to cache the result of shell commands. Some variables are
expensive to compute, for example, $(call cc-option,...) invokes the
compiler. It is not efficient to redo this computation every time,
even when we are not actually building anything. Kbuild creates a
hidden file ".cache.mk" that contains invoked shell commands and their
results. The speed-up should be noticeable.
Summary:
- Fix arch build issues (hexagon, sh)
- Clean up various Makefiles and scripts
- Fix wrong usage of {CFLAGS,LDFLAGS}_MODULE in arch Makefiles
- Cache variables that are expensive to compute
- Improve cc-ldopton and ld-option for Clang
- Optimize output directory creation"
* tag 'kbuild-v4.15' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (30 commits)
kbuild: move coccicheck help from scripts/Makefile.help to top Makefile
sh: decompressor: add shipped files to .gitignore
frv: .gitignore: ignore vmlinux.lds
selinux: remove unnecessary assignment to subdir-
kbuild: specify FORCE in Makefile.headersinst as .PHONY target
kbuild: remove redundant mkdir from ./Kbuild
kbuild: optimize object directory creation for incremental build
kbuild: create object directories simpler and faster
kbuild: filter-out PHONY targets from "targets"
kbuild: remove redundant $(wildcard ...) for cmd_files calculation
kbuild: create directory for make cache only when necessary
sh: select KBUILD_DEFCONFIG depending on ARCH
kbuild: fix linker feature test macros when cross compiling with Clang
kbuild: shrink .cache.mk when it exceeds 1000 lines
kbuild: do not call cc-option before KBUILD_CFLAGS initialization
kbuild: Cache a few more calls to the compiler
kbuild: Add a cache for generated variables
kbuild: add forward declaration of default target to Makefile.asm-generic
kbuild: remove KBUILD_SUBDIR_ASFLAGS and KBUILD_SUBDIR_CCFLAGS
hexagon/kbuild: replace CFLAGS_MODULE with KBUILD_CFLAGS_MODULE
...
2.2 KiB
SPDX-License-Identifier: GPL-2.0
Kbuild for top-level directory of the kernel
This file takes care of the following:
1) Generate bounds.h
2) Generate timeconst.h
3) Generate asm-offsets.h (may need bounds.h and timeconst.h)
4) Check for missing system calls
5) Generate constants.py (may need bounds.h)
1) Generate bounds.h
bounds-file := include/generated/bounds.h
always := $(bounds-file) targets := kernel/bounds.s
We use internal kbuild rules to avoid the "is up to date" message from make
kernel/bounds.s: kernel/bounds.c FORCE $(call if_changed_dep,cc_s_c)
$(obj)/$(bounds-file): kernel/bounds.s FORCE $(call filechk,offsets,LINUX_BOUNDS_H)
2) Generate timeconst.h
timeconst-file := include/generated/timeconst.h
targets += $(timeconst-file)
quiet_cmd_gentimeconst = GEN $@ define cmd_gentimeconst (echo $(CONFIG_HZ) | bc -q $< ) > $@ endef define filechk_gentimeconst (echo $(CONFIG_HZ) | bc -q $< ) endef
$(obj)/$(timeconst-file): kernel/time/timeconst.bc FORCE $(call filechk,gentimeconst)
3) Generate asm-offsets.h
offsets-file := include/generated/asm-offsets.h
always += $(offsets-file) targets += arch/$(SRCARCH)/kernel/asm-offsets.s
We use internal kbuild rules to avoid the "is up to date" message from make
arch/$(SRCARCH)/kernel/asm-offsets.s: arch/$(SRCARCH)/kernel/asm-offsets.c
$(obj)/$(timeconst-file) $(obj)/$(bounds-file) FORCE
$(call if_changed_dep,cc_s_c)
$(obj)/$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s FORCE $(call filechk,offsets,ASM_OFFSETS_H)
4) Check for missing system calls
always += missing-syscalls targets += missing-syscalls
quiet_cmd_syscalls = CALL $< cmd_syscalls = $(CONFIG_SHELL) $< $(CC) $(c_flags) $(missing_syscalls_flags)
missing-syscalls: scripts/checksyscalls.sh $(offsets-file) FORCE $(call cmd,syscalls)
5) Generate constants for Python GDB integration
extra-$(CONFIG_GDB_SCRIPTS) += build_constants_py
build_constants_py: $(obj)/$(timeconst-file) $(obj)/$(bounds-file) @$(MAKE) $(build)=scripts/gdb/linux $@
Keep these three files during make clean
no-clean-files := $(bounds-file) $(offsets-file) $(timeconst-file)