From e3d8676f5722b7622685581e06e8f53e6138e3ab Mon Sep 17 00:00:00 2001
From: Felix Fietkau <nbd@nbd.name>
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 <nbd@nbd.name>
Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
---
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
@@ -294,6 +294,11 @@ else
scripts/Kbuild.include: ;
include scripts/Kbuild.include
+ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
+KBUILD_CFLAGS_KERNEL += -ffunction-sections -fdata-sections
+LDFLAGS_vmlinux += --gc-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)
@@ -772,11 +777,6 @@ 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_KERNEL += -ffunction-sections -fdata-sections
-LDFLAGS_vmlinux += --gc-sections
-endif
-
# arch Makefile may override CC so keep this after arch Makefile is included
NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -98,6 +98,7 @@ config ARM
select HAVE_UID16
select HAVE_VIRT_CPU_ACCOUNTING_GEN
select IRQ_FORCED_THREADING
+ select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
select MODULES_USE_ELF_REL
select NEED_DMA_MAP_STATE
select NO_BOOTMEM
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -106,6 +106,7 @@ ifeq ($(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
@@ -100,24 +100,24 @@ 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 = .;
}
--- a/arch/arm/kernel/vmlinux.lds.h
+++ b/arch/arm/kernel/vmlinux.lds.h
@@ -22,13 +22,13 @@
#define ARM_MMU_DISCARD(x)
#else
#define ARM_MMU_KEEP(x)
-#define ARM_MMU_DISCARD(x) x
+#define ARM_MMU_DISCARD(x) KEEP(x)
#endif
#define PROC_INFO \
. = ALIGN(4); \
__proc_info_begin = .; \
- *(.proc.info.init) \
+ KEEP(*(.proc.info.init)) \
__proc_info_end = .;
#define HYPERVISOR_TEXT \
@@ -39,11 +39,11 @@
#define IDMAP_TEXT \
ALIGN_FUNCTION(); \
__idmap_text_start = .; \
- *(.idmap.text) \
+ KEEP(*(.idmap.text)) \
__idmap_text_end = .; \
. = ALIGN(PAGE_SIZE); \
__hyp_idmap_text_start = .; \
- *(.hyp.idmap.text) \
+ KEEP(*(.hyp.idmap.text)) \
__hyp_idmap_text_end = .;
#define ARM_DISCARD \
@@ -86,12 +86,12 @@
. = 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 = .; \
}
@@ -102,14 +102,14 @@
#define ARM_VECTORS \
__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 = .; \
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -43,6 +43,7 @@ config MIPS
select HAVE_ARCH_TRANSPARENT_HUGEPAGE if CPU_SUPPORTS_HUGEPAGES && 64BIT
select HAVE_CBPF_JIT if (!64BIT && !CPU_MICROMIPS)
select HAVE_EBPF_JIT if (64BIT && !CPU_MICROMIPS)
+ select HAVE_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 = .;
}