From b67067f1176df6ee727450546b58704e4b588563 Mon Sep 17 00:00:00 2001 From: Nicholas Piggin Date: Wed, 24 Aug 2016 22:29:20 +1000 Subject: 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 Signed-off-by: Michal Marek --- Makefile | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'Makefile') diff --git a/Makefile b/Makefile index 70de1448c571..6d40f3a3a8cc 100644 --- a/Makefile +++ b/Makefile @@ -622,6 +622,11 @@ include arch/$(SRCARCH)/Makefile KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,) KBUILD_CFLAGS += $(call cc-disable-warning,maybe-uninitialized,) +ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION +KBUILD_CFLAGS += $(call cc-option,-ffunction-sections,) +KBUILD_CFLAGS += $(call cc-option,-fdata-sections,) +endif + ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE KBUILD_CFLAGS += -Os else @@ -809,6 +814,10 @@ LDFLAGS_BUILD_ID = $(patsubst -Wl$(comma)%,%,\ KBUILD_LDFLAGS_MODULE += $(LDFLAGS_BUILD_ID) LDFLAGS_vmlinux += $(LDFLAGS_BUILD_ID) +ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION +LDFLAGS_vmlinux += $(call ld-option, --gc-sections,) +endif + ifeq ($(CONFIG_STRIP_ASM_SYMS),y) LDFLAGS_vmlinux += $(call ld-option, -X,) endif -- cgit v1.2.1 From fbe6e37dab974dd0fc3660c001895f7bfd771c9a Mon Sep 17 00:00:00 2001 From: Nicholas Piggin Date: Wed, 24 Aug 2016 22:29:21 +1000 Subject: kbuild: add arch specific post-link Makefile Allow architectures to create arch/xxx/Makefile.postlink with targets for vmlinux, modules.ko, and clean, which will be invoked after final linking of vmlinux and modules. powerpc will use this to check vmlinux linker relocations for sanity, and may use it to fix up alternate instruction patch branch addresses. Signed-off-by: Nicholas Piggin Signed-off-by: Michal Marek --- Makefile | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) (limited to 'Makefile') diff --git a/Makefile b/Makefile index 6d40f3a3a8cc..83dae63df91a 100644 --- a/Makefile +++ b/Makefile @@ -957,9 +957,12 @@ endif include/generated/autoksyms.h: FORCE $(Q)$(CONFIG_SHELL) $(srctree)/scripts/adjust_autoksyms.sh true -# Final link of vmlinux - cmd_link-vmlinux = $(CONFIG_SHELL) $< $(LD) $(LDFLAGS) $(LDFLAGS_vmlinux) -quiet_cmd_link-vmlinux = LINK $@ +ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink) + +# Final link of vmlinux with optional arch pass after final link + cmd_link-vmlinux = \ + $(CONFIG_SHELL) $< $(LD) $(LDFLAGS) $(LDFLAGS_vmlinux) ; \ + $(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true) vmlinux: scripts/link-vmlinux.sh vmlinux_prereq $(vmlinux-deps) FORCE +$(call if_changed,link-vmlinux) @@ -1286,6 +1289,7 @@ $(clean-dirs): vmlinuxclean: $(Q)$(CONFIG_SHELL) $(srctree)/scripts/link-vmlinux.sh clean + $(Q)$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) clean) clean: archclean vmlinuxclean -- cgit v1.2.1