From e3d8676f5722b7622685581e06e8f53e6138e3ab Mon Sep 17 00:00:00 2001 From: Felix Fietkau Date: Sat, 15 Jul 2017 23:42:36 +0200 Subject: use -ffunction-sections, -fdata-sections and --gc-sections In combination with kernel symbol export stripping this significantly reduces the kernel image size. Used on both ARM and MIPS architectures. Signed-off-by: Felix Fietkau Signed-off-by: Jonas Gorski Signed-off-by: Gabor Juhos --- Makefile | 10 +++---- arch/arm/Kconfig | 1 + arch/arm/boot/compressed/Makefile | 1 + arch/arm/kernel/vmlinux.lds.S | 26 ++++++++-------- arch/mips/Kconfig | 1 + arch/mips/kernel/vmlinux.lds.S | 4 +-- include/asm-generic/vmlinux.lds.h | 63 ++++++++++++++++++++------------------- 7 files changed, 55 insertions(+), 51 deletions(-) --- a/Makefile +++ b/Makefile @@ -405,6 +405,11 @@ KBUILD_CFLAGS_MODULE := -DMODULE KBUILD_LDFLAGS_MODULE = -T $(srctree)/scripts/module-common.lds $(if $(CONFIG_PROFILING),,-s) GCC_PLUGINS_CFLAGS := +ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION +KBUILD_CFLAGS_KERNEL += $(call cc-option,-ffunction-sections,) +KBUILD_CFLAGS_KERNEL += $(call cc-option,-fdata-sections,) +endif + # Read KERNELRELEASE from include/config/kernel.release (if it exists) KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null) KERNELVERSION = $(VERSION)$(if $(PATCHLEVEL),.$(PATCHLEVEL)$(if $(SUBLEVEL),.$(SUBLEVEL)))$(EXTRAVERSION) @@ -784,11 +789,6 @@ ifdef CONFIG_DEBUG_SECTION_MISMATCH KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions-called-once) endif -ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION -KBUILD_CFLAGS += $(call cc-option,-ffunction-sections,) -KBUILD_CFLAGS += $(call cc-option,-fdata-sections,) -endif - # arch Makefile may override CC so keep this after arch Makefile is included NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) CHECKFLAGS += $(NOSTDINC_FLAGS) --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -91,6 +91,7 @@ config ARM select HAVE_UID16 select HAVE_VIRT_CPU_ACCOUNTING_GEN select IRQ_FORCED_THREADING + select LD_DEAD_CODE_DATA_ELIMINATION select MODULES_USE_ELF_REL select NO_BOOTMEM select OF_EARLY_FLATTREE if OF --- a/arch/arm/boot/compressed/Makefile +++ b/arch/arm/boot/compressed/Makefile @@ -103,6 +103,7 @@ ifeq ($(CONFIG_FUNCTION_TRACER),y) ORIG_CFLAGS := $(KBUILD_CFLAGS) KBUILD_CFLAGS = $(subst -pg, , $(ORIG_CFLAGS)) endif +KBUILD_CFLAGS_KERNEL := $(patsubst -f%-sections,,$(KBUILD_CFLAGS_KERNEL)) # -fstack-protector-strong triggers protection checks in this code, # but it is being used too early to link to meaningful stack_chk logic. --- a/arch/arm/kernel/vmlinux.lds.S +++ b/arch/arm/kernel/vmlinux.lds.S @@ -18,7 +18,7 @@ #define PROC_INFO \ . = ALIGN(4); \ VMLINUX_SYMBOL(__proc_info_begin) = .; \ - *(.proc.info.init) \ + KEEP(*(.proc.info.init)) \ VMLINUX_SYMBOL(__proc_info_end) = .; #define HYPERVISOR_TEXT \ @@ -29,11 +29,11 @@ #define IDMAP_TEXT \ ALIGN_FUNCTION(); \ VMLINUX_SYMBOL(__idmap_text_start) = .; \ - *(.idmap.text) \ + KEEP(*(.idmap.text)) \ VMLINUX_SYMBOL(__idmap_text_end) = .; \ . = ALIGN(PAGE_SIZE); \ VMLINUX_SYMBOL(__hyp_idmap_text_start) = .; \ - *(.hyp.idmap.text) \ + KEEP(*(.hyp.idmap.text)) \ VMLINUX_SYMBOL(__hyp_idmap_text_end) = .; #ifdef CONFIG_HOTPLUG_CPU @@ -106,7 +106,7 @@ SECTIONS _stext = .; /* Text and read-only data */ IDMAP_TEXT __exception_text_start = .; - *(.exception.text) + KEEP(*(.exception.text)) __exception_text_end = .; IRQENTRY_TEXT SOFTIRQENTRY_TEXT @@ -135,7 +135,7 @@ SECTIONS __ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) { __start___ex_table = .; #ifdef CONFIG_MMU - *(__ex_table) + KEEP(*(__ex_table)) #endif __stop___ex_table = .; } @@ -147,12 +147,12 @@ SECTIONS . = ALIGN(8); .ARM.unwind_idx : { __start_unwind_idx = .; - *(.ARM.exidx*) + KEEP(*(.ARM.exidx*)) __stop_unwind_idx = .; } .ARM.unwind_tab : { __start_unwind_tab = .; - *(.ARM.extab*) + KEEP(*(.ARM.extab*)) __stop_unwind_tab = .; } #endif @@ -172,14 +172,14 @@ SECTIONS */ __vectors_start = .; .vectors 0xffff0000 : AT(__vectors_start) { - *(.vectors) + KEEP(*(.vectors)) } . = __vectors_start + SIZEOF(.vectors); __vectors_end = .; __stubs_start = .; .stubs ADDR(.vectors) + 0x1000 : AT(__stubs_start) { - *(.stubs) + KEEP(*(.stubs)) } . = __stubs_start + SIZEOF(.stubs); __stubs_end = .; @@ -195,24 +195,24 @@ SECTIONS } .init.arch.info : { __arch_info_begin = .; - *(.arch.info.init) + KEEP(*(.arch.info.init)) __arch_info_end = .; } .init.tagtable : { __tagtable_begin = .; - *(.taglist.init) + KEEP(*(.taglist.init)) __tagtable_end = .; } #ifdef CONFIG_SMP_ON_UP .init.smpalt : { __smpalt_begin = .; - *(.alt.smp.init) + KEEP(*(.alt.smp.init)) __smpalt_end = .; } #endif .init.pv_table : { __pv_table_begin = .; - *(.pv_table) + KEEP(*(.pv_table)) __pv_table_end = .; } .init.data : { --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -39,6 +39,7 @@ config MIPS select HAVE_CBPF_JIT if (!64BIT && !CPU_MICROMIPS) select HAVE_EBPF_JIT if (64BIT && !CPU_MICROMIPS) select HAVE_CC_STACKPROTECTOR + select LD_DEAD_CODE_DATA_ELIMINATION select HAVE_CONTEXT_TRACKING select HAVE_COPY_THREAD_TLS select HAVE_C_RECORDMCOUNT --- a/arch/mips/kernel/vmlinux.lds.S +++ b/arch/mips/kernel/vmlinux.lds.S @@ -72,7 +72,7 @@ SECTIONS /* Exception table for data bus errors */ __dbe_table : { __start___dbe_table = .; - *(__dbe_table) + KEEP(*(__dbe_table)) __stop___dbe_table = .; } @@ -123,7 +123,7 @@ SECTIONS . = ALIGN(4); .mips.machines.init : AT(ADDR(.mips.machines.init) - LOAD_OFFSET) { __mips_machines_start = .; - *(.mips.machines.init) + KEEP(*(.mips.machines.init)) __mips_machines_end = .; } --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -105,7 +105,7 @@ #ifdef CONFIG_FTRACE_MCOUNT_RECORD #define MCOUNT_REC() . = ALIGN(8); \ VMLINUX_SYMBOL(__start_mcount_loc) = .; \ - *(__mcount_loc) \ + KEEP(*(__mcount_loc)) \ VMLINUX_SYMBOL(__stop_mcount_loc) = .; #else #define MCOUNT_REC() @@ -113,7 +113,7 @@ #ifdef CONFIG_TRACE_BRANCH_PROFILING #define LIKELY_PROFILE() VMLINUX_SYMBOL(__start_annotated_branch_profile) = .; \ - *(_ftrace_annotated_branch) \ + KEEP(*(_ftrace_annotated_branch)) \ VMLINUX_SYMBOL(__stop_annotated_branch_profile) = .; #else #define LIKELY_PROFILE() @@ -121,7 +121,7 @@ #ifdef CONFIG_PROFILE_ALL_BRANCHES #define BRANCH_PROFILE() VMLINUX_SYMBOL(__start_branch_profile) = .; \ - *(_ftrace_branch) \ + KEEP(*(_ftrace_branch)) \ VMLINUX_SYMBOL(__stop_branch_profile) = .; #else #define BRANCH_PROFILE() @@ -237,7 +237,8 @@ LIKELY_PROFILE() \ BRANCH_PROFILE() \ TRACE_PRINTKS() \ - TRACEPOINT_STR() + TRACEPOINT_STR() \ + *(.data.[a-zA-Z_]*) /* * Data section helpers @@ -496,7 +497,7 @@ #define ENTRY_TEXT \ ALIGN_FUNCTION(); \ VMLINUX_SYMBOL(__entry_text_start) = .; \ - *(.entry.text) \ + KEEP(*(.entry.text)) \ VMLINUX_SYMBOL(__entry_text_end) = .; #define IRQENTRY_TEXT \ @@ -603,7 +604,7 @@ . = ALIGN(sbss_align); \ .sbss : AT(ADDR(.sbss) - LOAD_OFFSET) { \ *(.dynsbss) \ - *(.sbss) \ + *(.sbss .sbss.*) \ *(.scommon) \ }