OpenWrt – Rev 3
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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/Makefile
+++ b/Makefile
@@ -406,6 +406,11 @@ 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)
@@ -637,11 +642,6 @@ KBUILD_CFLAGS += $(call cc-disable-warni
KBUILD_CFLAGS += $(call cc-disable-warning, int-in-bool-context)
KBUILD_CFLAGS += $(call cc-disable-warning, attribute-alias)
-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 $(call cc-disable-warning,maybe-uninitialized,) $(EXTRA_OPTIMIZATION)
else
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -81,6 +81,7 @@ config ARM
select HAVE_UID16
select HAVE_VIRT_CPU_ACCOUNTING_GEN
select IRQ_FORCED_THREADING
+ select LD_DEAD_CODE_DATA_ELIMINATION
select MODULES_USE_ELF_REL
select NO_BOOTMEM
select OF_EARLY_FLATTREE if OF
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -102,6 +102,7 @@ ifeq ($(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
@@ -17,7 +17,7 @@
#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 \
@@ -28,11 +28,11 @@
#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
@@ -105,7 +105,7 @@ SECTIONS
_stext = .; /* Text and read-only data */
IDMAP_TEXT
__exception_text_start = .;
- *(.exception.text)
+ KEEP(*(.exception.text))
__exception_text_end = .;
IRQENTRY_TEXT
SOFTIRQENTRY_TEXT
@@ -134,7 +134,7 @@ SECTIONS
__ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {
__start___ex_table = .;
#ifdef CONFIG_MMU
- *(__ex_table)
+ KEEP(*(__ex_table))
#endif
__stop___ex_table = .;
}
@@ -146,12 +146,12 @@ 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
@@ -171,14 +171,14 @@ 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 = .;
@@ -194,24 +194,24 @@ 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
@@ -55,6 +55,7 @@ config MIPS
select CLONE_BACKWARDS
select HAVE_DEBUG_STACKOVERFLOW
select HAVE_CC_STACKPROTECTOR
+ select LD_DEAD_CODE_DATA_ELIMINATION
select CPU_PM if CPU_IDLE
select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
select ARCH_BINFMT_ELF_STATE
--- a/arch/mips/kernel/vmlinux.lds.S
+++ b/arch/mips/kernel/vmlinux.lds.S
@@ -71,7 +71,7 @@ SECTIONS
/* Exception table for data bus errors */
__dbe_table : {
__start___dbe_table = .;
- *(__dbe_table)
+ KEEP(*(__dbe_table))
__stop___dbe_table = .;
}
@@ -121,7 +121,7 @@ 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()
@@ -130,7 +130,7 @@
#ifdef CONFIG_KPROBES
#define KPROBE_BLACKLIST() . = ALIGN(8); \
VMLINUX_SYMBOL(__start_kprobe_blacklist) = .; \
- *(_kprobe_blacklist) \
+ KEEP(*(_kprobe_blacklist)) \
VMLINUX_SYMBOL(__stop_kprobe_blacklist) = .;
#else
#define KPROBE_BLACKLIST()
@@ -139,10 +139,10 @@
#ifdef CONFIG_EVENT_TRACING
#define FTRACE_EVENTS() . = ALIGN(8); \
VMLINUX_SYMBOL(__start_ftrace_events) = .; \
- *(_ftrace_events) \
+ KEEP(*(_ftrace_events)) \
VMLINUX_SYMBOL(__stop_ftrace_events) = .; \
VMLINUX_SYMBOL(__start_ftrace_enum_maps) = .; \
- *(_ftrace_enum_map) \
+ KEEP(*(_ftrace_enum_map)) \
VMLINUX_SYMBOL(__stop_ftrace_enum_maps) = .;
#else
#define FTRACE_EVENTS()
@@ -163,7 +163,7 @@
#ifdef CONFIG_FTRACE_SYSCALLS
#define TRACE_SYSCALLS() . = ALIGN(8); \
VMLINUX_SYMBOL(__start_syscalls_metadata) = .; \
- *(__syscalls_metadata) \
+ KEEP(*(__syscalls_metadata)) \
VMLINUX_SYMBOL(__stop_syscalls_metadata) = .;
#else
#define TRACE_SYSCALLS()
@@ -172,7 +172,7 @@
#ifdef CONFIG_SERIAL_EARLYCON
#define EARLYCON_TABLE() . = ALIGN(8); \
VMLINUX_SYMBOL(__earlycon_table) = .; \
- *(__earlycon_table) \
+ KEEP(*(__earlycon_table)) \
VMLINUX_SYMBOL(__earlycon_table_end) = .;
#else
#define EARLYCON_TABLE()
@@ -185,8 +185,8 @@
#define _OF_TABLE_1(name) \
. = ALIGN(8); \
VMLINUX_SYMBOL(__##name##_of_table) = .; \
- *(__##name##_of_table) \
- *(__##name##_of_table_end)
+ KEEP(*(__##name##_of_table)) \
+ KEEP(*(__##name##_of_table_end))
#define CLKSRC_OF_TABLES() OF_TABLE(CONFIG_CLKSRC_OF, clksrc)
#define IRQCHIP_OF_MATCH_TABLE() OF_TABLE(CONFIG_IRQCHIP, irqchip)
@@ -209,7 +209,7 @@
#define KERNEL_DTB() \
STRUCT_ALIGN(); \
VMLINUX_SYMBOL(__dtb_start) = .; \
- *(.dtb.init.rodata) \
+ KEEP(*(.dtb.init.rodata)) \
VMLINUX_SYMBOL(__dtb_end) = .;
/*
@@ -227,16 +227,17 @@
/* implement dynamic printk debug */ \
. = ALIGN(8); \
VMLINUX_SYMBOL(__start___jump_table) = .; \
- *(__jump_table) \
+ KEEP(*(__jump_table)) \
VMLINUX_SYMBOL(__stop___jump_table) = .; \
. = ALIGN(8); \
VMLINUX_SYMBOL(__start___verbose) = .; \
- *(__verbose) \
+ KEEP(*(__verbose)) \
VMLINUX_SYMBOL(__stop___verbose) = .; \
LIKELY_PROFILE() \
BRANCH_PROFILE() \
TRACE_PRINTKS() \
- TRACEPOINT_STR()
+ TRACEPOINT_STR() \
+ *(.data.[a-zA-Z_]*)
/*
* Data section helpers
@@ -304,35 +305,35 @@
/* PCI quirks */ \
.pci_fixup : AT(ADDR(.pci_fixup) - LOAD_OFFSET) { \
VMLINUX_SYMBOL(__start_pci_fixups_early) = .; \
- *(.pci_fixup_early) \
+ KEEP(*(.pci_fixup_early)) \
VMLINUX_SYMBOL(__end_pci_fixups_early) = .; \
VMLINUX_SYMBOL(__start_pci_fixups_header) = .; \
- *(.pci_fixup_header) \
+ KEEP(*(.pci_fixup_header)) \
VMLINUX_SYMBOL(__end_pci_fixups_header) = .; \
VMLINUX_SYMBOL(__start_pci_fixups_final) = .; \
- *(.pci_fixup_final) \
+ KEEP(*(.pci_fixup_final)) \
VMLINUX_SYMBOL(__end_pci_fixups_final) = .; \
VMLINUX_SYMBOL(__start_pci_fixups_enable) = .; \
- *(.pci_fixup_enable) \
+ KEEP(*(.pci_fixup_enable)) \
VMLINUX_SYMBOL(__end_pci_fixups_enable) = .; \
VMLINUX_SYMBOL(__start_pci_fixups_resume) = .; \
- *(.pci_fixup_resume) \
+ KEEP(*(.pci_fixup_resume)) \
VMLINUX_SYMBOL(__end_pci_fixups_resume) = .; \
VMLINUX_SYMBOL(__start_pci_fixups_resume_early) = .; \
- *(.pci_fixup_resume_early) \
+ KEEP(*(.pci_fixup_resume_early)) \
VMLINUX_SYMBOL(__end_pci_fixups_resume_early) = .; \
VMLINUX_SYMBOL(__start_pci_fixups_suspend) = .; \
- *(.pci_fixup_suspend) \
+ KEEP(*(.pci_fixup_suspend)) \
VMLINUX_SYMBOL(__end_pci_fixups_suspend) = .; \
VMLINUX_SYMBOL(__start_pci_fixups_suspend_late) = .; \
- *(.pci_fixup_suspend_late) \
+ KEEP(*(.pci_fixup_suspend_late)) \
VMLINUX_SYMBOL(__end_pci_fixups_suspend_late) = .; \
} \
\
/* Built-in firmware blobs */ \
.builtin_fw : AT(ADDR(.builtin_fw) - LOAD_OFFSET) { \
VMLINUX_SYMBOL(__start_builtin_fw) = .; \
- *(.builtin_fw) \
+ KEEP(*(.builtin_fw)) \
VMLINUX_SYMBOL(__end_builtin_fw) = .; \
} \
\
@@ -410,7 +411,7 @@
\
/* Kernel symbol table: strings */ \
__ksymtab_strings : AT(ADDR(__ksymtab_strings) - LOAD_OFFSET) { \
- KEEP(*(__ksymtab_strings)) \
+ *(__ksymtab_strings) \
} \
\
/* __*init sections */ \
@@ -423,14 +424,14 @@
/* Built-in module parameters. */ \
__param : AT(ADDR(__param) - LOAD_OFFSET) { \
VMLINUX_SYMBOL(__start___param) = .; \
- *(__param) \
+ KEEP(*(__param)) \
VMLINUX_SYMBOL(__stop___param) = .; \
} \
\
/* Built-in module versions. */ \
__modver : AT(ADDR(__modver) - LOAD_OFFSET) { \
VMLINUX_SYMBOL(__start___modver) = .; \
- *(__modver) \
+ KEEP(*(__modver)) \
VMLINUX_SYMBOL(__stop___modver) = .; \
. = ALIGN((align)); \
VMLINUX_SYMBOL(__end_rodata) = .; \
@@ -496,7 +497,7 @@
#define ENTRY_TEXT \
ALIGN_FUNCTION(); \
VMLINUX_SYMBOL(__entry_text_start) = .; \
- *(.entry.text) \
+ KEEP(*(.entry.text)) \
VMLINUX_SYMBOL(__entry_text_end) = .;
#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
@@ -534,7 +535,7 @@
. = ALIGN(align); \
__ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) { \
VMLINUX_SYMBOL(__start___ex_table) = .; \
- *(__ex_table) \
+ KEEP(*(__ex_table)) \
VMLINUX_SYMBOL(__stop___ex_table) = .; \
}
@@ -550,9 +551,9 @@
#ifdef CONFIG_CONSTRUCTORS
#define KERNEL_CTORS() . = ALIGN(8); \
VMLINUX_SYMBOL(__ctors_start) = .; \
- *(.ctors) \
+ KEEP(*(.ctors)) \
*(SORT(.init_array.*)) \
- *(.init_array) \
+ KEEP(*(.init_array)) \
VMLINUX_SYMBOL(__ctors_end) = .;
#else
#define KERNEL_CTORS()
@@ -609,7 +610,7 @@
#define SBSS(sbss_align) \
. = ALIGN(sbss_align); \
.sbss : AT(ADDR(.sbss) - LOAD_OFFSET) { \
- *(.sbss) \
+ *(.sbss .sbss.*) \
*(.scommon) \
}
@@ -676,7 +677,7 @@
. = ALIGN(8); \
__bug_table : AT(ADDR(__bug_table) - LOAD_OFFSET) { \
VMLINUX_SYMBOL(__start___bug_table) = .; \
- *(__bug_table) \
+ KEEP(*(__bug_table)) \
VMLINUX_SYMBOL(__stop___bug_table) = .; \
}
#else
@@ -688,7 +689,7 @@
. = ALIGN(4); \
.tracedata : AT(ADDR(.tracedata) - LOAD_OFFSET) { \
VMLINUX_SYMBOL(__tracedata_start) = .; \
- *(.tracedata) \
+ KEEP(*(.tracedata)) \
VMLINUX_SYMBOL(__tracedata_end) = .; \
}
#else
@@ -705,7 +706,7 @@
#define INIT_SETUP(initsetup_align) \
. = ALIGN(initsetup_align); \
VMLINUX_SYMBOL(__setup_start) = .; \
- *(.init.setup) \
+ KEEP(*(.init.setup)) \
VMLINUX_SYMBOL(__setup_end) = .;
#define INIT_CALLS_LEVEL(level) \