linux/init/Makefile
Nicholas Piggin b67067f117 kbuild: allow archs to select link dead code/data elimination
Introduce LD_DEAD_CODE_DATA_ELIMINATION option for architectures to
select to build with -ffunction-sections, -fdata-sections, and link
with --gc-sections. It requires some work (documented) to ensure all
unreferenced entrypoints are live, and requires toolchain and build
verification, so it is made a per-arch option for now.

On a random powerpc64le build, this yelds a significant size saving,
it boots and runs fine, but there is a lot I haven't tested as yet, so
these savings may be reduced if there are bugs in the link.

    text      data        bss        dec   filename
11169741   1180744    1923176	14273661   vmlinux
10445269   1004127    1919707	13369103   vmlinux.dce

~700K text, ~170K data, 6% removed from kernel image size.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.com>
2016-09-09 10:47:00 +02:00

39 lines
1.2 KiB
Makefile

#
# Makefile for the linux kernel.
#
ccflags-y := -fno-function-sections -fno-data-sections
obj-y := main.o version.o mounts.o
ifneq ($(CONFIG_BLK_DEV_INITRD),y)
obj-y += noinitramfs.o
else
obj-$(CONFIG_BLK_DEV_INITRD) += initramfs.o
endif
obj-$(CONFIG_GENERIC_CALIBRATE_DELAY) += calibrate.o
ifneq ($(CONFIG_ARCH_INIT_TASK),y)
obj-y += init_task.o
endif
mounts-y := do_mounts.o
mounts-$(CONFIG_BLK_DEV_RAM) += do_mounts_rd.o
mounts-$(CONFIG_BLK_DEV_INITRD) += do_mounts_initrd.o
mounts-$(CONFIG_BLK_DEV_MD) += do_mounts_md.o
# dependencies on generated files need to be listed explicitly
$(obj)/version.o: include/generated/compile.h
# 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.
chk_compile.h = :
quiet_chk_compile.h = echo ' CHK $@'
silent_chk_compile.h = :
include/generated/compile.h: FORCE
@$($(quiet)chk_compile.h)
$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkcompile_h $@ \
"$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT)" "$(CC) $(KBUILD_CFLAGS)"