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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/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -111,6 +111,7 @@ 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 OF_EARLY_FLATTREE if OF
--- 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 = .; \
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