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>
---
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -136,6 +136,7 @@ config ARM
 	select HAVE_VIRT_CPU_ACCOUNTING_GEN
 	select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU
 	select IRQ_FORCED_THREADING
+	select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
 	select LOCK_MM_AND_FIND_VMA
 	select MODULES_USE_ELF_REL
 	select NEED_DMA_MAP_STATE
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -86,6 +86,7 @@ endif
 ifeq ($(CONFIG_USE_OF),y)
 OBJS	+= $(libfdt_objs) fdt_check_mem_start.o
 endif
+KBUILD_CFLAGS_KERNEL := $(patsubst -f%-sections,,$(KBUILD_CFLAGS_KERNEL))
 
 OBJS	+= lib1funcs.o ashldi3.o bswapsdi2.o
 
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -74,7 +74,7 @@ SECTIONS
 	. = ALIGN(4);
 	__ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {
 		__start___ex_table = .;
-		ARM_MMU_KEEP(KEEP(*(__ex_table)))
+		KEEP(*(__ex_table))
 		__stop___ex_table = .;
 	}
 
@@ -104,13 +104,13 @@ SECTIONS
 	}
 	.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
--- a/arch/arm/include/asm/vmlinux.lds.h
+++ b/arch/arm/include/asm/vmlinux.lds.h
@@ -48,7 +48,7 @@
 #define IDMAP_TEXT							\
 		ALIGN_FUNCTION();					\
 		__idmap_text_start = .;					\
-		*(.idmap.text)						\
+		KEEP(*(.idmap.text))					\
 		__idmap_text_end = .;					\
 
 #define ARM_DISCARD							\
@@ -108,12 +108,12 @@
 	. = 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 = .;					\
 	}
 
@@ -143,7 +143,7 @@
 									\
 	__stubs_lma = .;						\
 	.stubs ADDR(.vectors) + 0x1000 : AT(__stubs_lma) {		\
-		*(.stubs)						\
+		KEEP(*(.stubs))						\
 	}								\
 	ARM_LMA(__stubs, .stubs);					\
 	. = __stubs_lma + SIZEOF(.stubs);				\