Re: [PATCH 2/5] kbuild: allow archs to select build for link dead code/data elimination
From: Sam Ravnborg <hidden>
Date: 2016-08-06 20:19:45
Also in:
linux-arch, linux-kbuild
On Fri, Aug 05, 2016 at 10:12:00PM +1000, Nicholas Piggin wrote:
Introduce LINKER_DCE option for architectures to select if they want to build with -ffunction-sections, -fdata-sections, and link with --gc-sections.
Can you please try to come up with a less cryptic name. "DCE" may make sense for you today. Bot the naive reader will benefit from the longer and more explcit form. It requires some work (documented) to ensure all
quoted hunk ↗ jump to hunk
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> --- Makefile | 10 ++++++++ arch/Kconfig | 13 ++++++++++ include/asm-generic/vmlinux.lds.h | 52 ++++++++++++++++++++++----------------- include/linux/compiler.h | 18 ++++++++++++++ include/linux/export.h | 30 +++++++++++----------- include/linux/init.h | 38 ++++++++++------------------ init/Makefile | 2 ++ 7 files changed, 100 insertions(+), 63 deletions(-)diff --git a/Makefile b/Makefile index b409076..d5ef31a 100644 --- a/Makefile +++ b/Makefile@@ -618,6 +618,11 @@ include arch/$(SRCARCH)/Makefile KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,) +ifdef CONFIG_LINKER_DCE +KBUILD_CFLAGS += $(call cc-option,-ffunction-sections,) +KBUILD_CFLAGS += $(call cc-option,-fdata-sections,) +endif + ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE KBUILD_CFLAGS += -Os $(call cc-disable-warning,maybe-uninitialized,) else@@ -819,6 +824,11 @@ LDFLAGS_BUILD_ID = $(patsubst -Wl$(comma)%,%,\ KBUILD_LDFLAGS_MODULE += $(LDFLAGS_BUILD_ID) LDFLAGS_vmlinux += $(LDFLAGS_BUILD_ID) +ifdef CONFIG_LINKER_DCE +# LDFLAGS_MODULE += $(call ld-option, --gc-sections,) +LDFLAGS_vmlinux += $(call ld-option, --gc-sections,) +endif
Something you missed to clean up Sam