1 From e3d8676f5722b7622685581e06e8f53e6138e3ab Mon Sep 17 00:00:00 2001
2 From: Felix Fietkau <nbd@nbd.name>
3 Date: Sat, 15 Jul 2017 23:42:36 +0200
4 Subject: use -ffunction-sections, -fdata-sections and --gc-sections
6 In combination with kernel symbol export stripping this significantly reduces
7 the kernel image size. Used on both ARM and MIPS architectures.
9 Signed-off-by: Felix Fietkau <nbd@nbd.name>
10 Signed-off-by: Jonas Gorski <jogo@openwrt.org>
11 Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
14 arch/arm/Kconfig | 1 +
15 arch/arm/boot/compressed/Makefile | 1 +
16 arch/arm/kernel/vmlinux.lds.S | 26 ++++++++--------
17 arch/mips/Kconfig | 1 +
18 arch/mips/kernel/vmlinux.lds.S | 4 +--
19 include/asm-generic/vmlinux.lds.h | 63 ++++++++++++++++++++-------------------
20 7 files changed, 55 insertions(+), 51 deletions(-)
22 diff --git a/Makefile b/Makefile
23 index 42435dfa5fc3..66cdf6a59b53 100644
26 @@ -410,6 +410,11 @@ KBUILD_AFLAGS_MODULE := -DMODULE
27 KBUILD_CFLAGS_MODULE := -DMODULE
28 KBUILD_LDFLAGS_MODULE = -T $(srctree)/scripts/module-common.lds $(if $(CONFIG_PROFILING),,-s)
30 +ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
31 +KBUILD_CFLAGS_KERNEL += $(call cc-option,-ffunction-sections,)
32 +KBUILD_CFLAGS_KERNEL += $(call cc-option,-fdata-sections,)
35 # Read KERNELRELEASE from include/config/kernel.release (if it exists)
36 KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)
37 KERNELVERSION = $(VERSION)$(if $(PATCHLEVEL),.$(PATCHLEVEL)$(if $(SUBLEVEL),.$(SUBLEVEL)))$(EXTRAVERSION)
38 @@ -631,11 +636,6 @@ include arch/$(SRCARCH)/Makefile
39 KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,)
40 KBUILD_CFLAGS += $(call cc-disable-warning,frame-address,)
42 -ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
43 -KBUILD_CFLAGS += $(call cc-option,-ffunction-sections,)
44 -KBUILD_CFLAGS += $(call cc-option,-fdata-sections,)
47 ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
48 KBUILD_CFLAGS += -Os $(call cc-disable-warning,maybe-uninitialized,) $(EXTRA_OPTIMIZATION)
50 diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
51 index b5d529fdffab..7f69418bf02c 100644
52 --- a/arch/arm/Kconfig
53 +++ b/arch/arm/Kconfig
54 @@ -81,6 +81,7 @@ config ARM
56 select HAVE_VIRT_CPU_ACCOUNTING_GEN
57 select IRQ_FORCED_THREADING
58 + select LD_DEAD_CODE_DATA_ELIMINATION
59 select MODULES_USE_ELF_REL
61 select OF_EARLY_FLATTREE if OF
62 diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
63 index d50430c40045..6bdeb009a46d 100644
64 --- a/arch/arm/boot/compressed/Makefile
65 +++ b/arch/arm/boot/compressed/Makefile
66 @@ -102,6 +102,7 @@ ifeq ($(CONFIG_FUNCTION_TRACER),y)
67 ORIG_CFLAGS := $(KBUILD_CFLAGS)
68 KBUILD_CFLAGS = $(subst -pg, , $(ORIG_CFLAGS))
70 +KBUILD_CFLAGS_KERNEL := $(patsubst -f%-sections,,$(KBUILD_CFLAGS_KERNEL))
72 # -fstack-protector-strong triggers protection checks in this code,
73 # but it is being used too early to link to meaningful stack_chk logic.
74 diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
75 index f7f55df0bf7b..e9d70c92d99f 100644
76 --- a/arch/arm/kernel/vmlinux.lds.S
77 +++ b/arch/arm/kernel/vmlinux.lds.S
81 VMLINUX_SYMBOL(__proc_info_begin) = .; \
82 - *(.proc.info.init) \
83 + KEEP(*(.proc.info.init)) \
84 VMLINUX_SYMBOL(__proc_info_end) = .;
86 #define HYPERVISOR_TEXT \
90 VMLINUX_SYMBOL(__idmap_text_start) = .; \
92 + KEEP(*(.idmap.text)) \
93 VMLINUX_SYMBOL(__idmap_text_end) = .; \
94 . = ALIGN(PAGE_SIZE); \
95 VMLINUX_SYMBOL(__hyp_idmap_text_start) = .; \
96 - *(.hyp.idmap.text) \
97 + KEEP(*(.hyp.idmap.text)) \
98 VMLINUX_SYMBOL(__hyp_idmap_text_end) = .;
100 #ifdef CONFIG_HOTPLUG_CPU
101 @@ -105,7 +105,7 @@ SECTIONS
102 _stext = .; /* Text and read-only data */
104 __exception_text_start = .;
106 + KEEP(*(.exception.text))
107 __exception_text_end = .;
110 @@ -134,7 +134,7 @@ SECTIONS
111 __ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {
112 __start___ex_table = .;
115 + KEEP(*(__ex_table))
117 __stop___ex_table = .;
119 @@ -146,12 +146,12 @@ SECTIONS
122 __start_unwind_idx = .;
124 + KEEP(*(.ARM.exidx*))
125 __stop_unwind_idx = .;
128 __start_unwind_tab = .;
130 + KEEP(*(.ARM.extab*))
131 __stop_unwind_tab = .;
134 @@ -171,14 +171,14 @@ SECTIONS
137 .vectors 0xffff0000 : AT(__vectors_start) {
141 . = __vectors_start + SIZEOF(.vectors);
145 .stubs ADDR(.vectors) + 0x1000 : AT(__stubs_start) {
149 . = __stubs_start + SIZEOF(.stubs);
151 @@ -194,24 +194,24 @@ SECTIONS
154 __arch_info_begin = .;
156 + KEEP(*(.arch.info.init))
160 __tagtable_begin = .;
162 + KEEP(*(.taglist.init))
165 #ifdef CONFIG_SMP_ON_UP
169 + KEEP(*(.alt.smp.init))
174 __pv_table_begin = .;
180 diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
181 index 3a97487b8b81..05e7bfeab2f9 100644
182 --- a/arch/mips/Kconfig
183 +++ b/arch/mips/Kconfig
184 @@ -55,6 +55,7 @@ config MIPS
185 select CLONE_BACKWARDS
186 select HAVE_DEBUG_STACKOVERFLOW
187 select HAVE_CC_STACKPROTECTOR
188 + select LD_DEAD_CODE_DATA_ELIMINATION
189 select CPU_PM if CPU_IDLE
190 select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
191 select ARCH_BINFMT_ELF_STATE
192 diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
193 index d5de67591735..de5f682b5597 100644
194 --- a/arch/mips/kernel/vmlinux.lds.S
195 +++ b/arch/mips/kernel/vmlinux.lds.S
196 @@ -71,7 +71,7 @@ SECTIONS
197 /* Exception table for data bus errors */
199 __start___dbe_table = .;
201 + KEEP(*(__dbe_table))
202 __stop___dbe_table = .;
205 @@ -121,7 +121,7 @@ SECTIONS
207 .mips.machines.init : AT(ADDR(.mips.machines.init) - LOAD_OFFSET) {
208 __mips_machines_start = .;
209 - *(.mips.machines.init)
210 + KEEP(*(.mips.machines.init))
211 __mips_machines_end = .;
214 diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
215 index 31e1d639abed..83784d9492b1 100644
216 --- a/include/asm-generic/vmlinux.lds.h
217 +++ b/include/asm-generic/vmlinux.lds.h
219 #ifdef CONFIG_KPROBES
220 #define KPROBE_BLACKLIST() . = ALIGN(8); \
221 VMLINUX_SYMBOL(__start_kprobe_blacklist) = .; \
222 - *(_kprobe_blacklist) \
223 + KEEP(*(_kprobe_blacklist)) \
224 VMLINUX_SYMBOL(__stop_kprobe_blacklist) = .;
226 #define KPROBE_BLACKLIST()
227 @@ -123,10 +123,10 @@
228 #ifdef CONFIG_EVENT_TRACING
229 #define FTRACE_EVENTS() . = ALIGN(8); \
230 VMLINUX_SYMBOL(__start_ftrace_events) = .; \
231 - *(_ftrace_events) \
232 + KEEP(*(_ftrace_events)) \
233 VMLINUX_SYMBOL(__stop_ftrace_events) = .; \
234 VMLINUX_SYMBOL(__start_ftrace_enum_maps) = .; \
235 - *(_ftrace_enum_map) \
236 + KEEP(*(_ftrace_enum_map)) \
237 VMLINUX_SYMBOL(__stop_ftrace_enum_maps) = .;
239 #define FTRACE_EVENTS()
241 #ifdef CONFIG_FTRACE_SYSCALLS
242 #define TRACE_SYSCALLS() . = ALIGN(8); \
243 VMLINUX_SYMBOL(__start_syscalls_metadata) = .; \
244 - *(__syscalls_metadata) \
245 + KEEP(*(__syscalls_metadata)) \
246 VMLINUX_SYMBOL(__stop_syscalls_metadata) = .;
248 #define TRACE_SYSCALLS()
250 #ifdef CONFIG_SERIAL_EARLYCON
251 #define EARLYCON_TABLE() STRUCT_ALIGN(); \
252 VMLINUX_SYMBOL(__earlycon_table) = .; \
253 - *(__earlycon_table) \
254 + KEEP(*(__earlycon_table)) \
255 VMLINUX_SYMBOL(__earlycon_table_end) = .;
257 #define EARLYCON_TABLE()
259 #define _OF_TABLE_1(name) \
261 VMLINUX_SYMBOL(__##name##_of_table) = .; \
262 - *(__##name##_of_table) \
263 - *(__##name##_of_table_end)
264 + KEEP(*(__##name##_of_table)) \
265 + KEEP(*(__##name##_of_table_end))
267 #define CLKSRC_OF_TABLES() OF_TABLE(CONFIG_CLKSRC_OF, clksrc)
268 #define IRQCHIP_OF_MATCH_TABLE() OF_TABLE(CONFIG_IRQCHIP, irqchip)
270 #define KERNEL_DTB() \
272 VMLINUX_SYMBOL(__dtb_start) = .; \
273 - *(.dtb.init.rodata) \
274 + KEEP(*(.dtb.init.rodata)) \
275 VMLINUX_SYMBOL(__dtb_end) = .;
278 @@ -214,16 +214,17 @@
279 /* implement dynamic printk debug */ \
281 VMLINUX_SYMBOL(__start___jump_table) = .; \
283 + KEEP(*(__jump_table)) \
284 VMLINUX_SYMBOL(__stop___jump_table) = .; \
286 VMLINUX_SYMBOL(__start___verbose) = .; \
288 + KEEP(*(__verbose)) \
289 VMLINUX_SYMBOL(__stop___verbose) = .; \
295 + *(.data.[a-zA-Z_]*)
298 * Data section helpers
299 @@ -291,35 +292,35 @@
301 .pci_fixup : AT(ADDR(.pci_fixup) - LOAD_OFFSET) { \
302 VMLINUX_SYMBOL(__start_pci_fixups_early) = .; \
303 - *(.pci_fixup_early) \
304 + KEEP(*(.pci_fixup_early)) \
305 VMLINUX_SYMBOL(__end_pci_fixups_early) = .; \
306 VMLINUX_SYMBOL(__start_pci_fixups_header) = .; \
307 - *(.pci_fixup_header) \
308 + KEEP(*(.pci_fixup_header)) \
309 VMLINUX_SYMBOL(__end_pci_fixups_header) = .; \
310 VMLINUX_SYMBOL(__start_pci_fixups_final) = .; \
311 - *(.pci_fixup_final) \
312 + KEEP(*(.pci_fixup_final)) \
313 VMLINUX_SYMBOL(__end_pci_fixups_final) = .; \
314 VMLINUX_SYMBOL(__start_pci_fixups_enable) = .; \
315 - *(.pci_fixup_enable) \
316 + KEEP(*(.pci_fixup_enable)) \
317 VMLINUX_SYMBOL(__end_pci_fixups_enable) = .; \
318 VMLINUX_SYMBOL(__start_pci_fixups_resume) = .; \
319 - *(.pci_fixup_resume) \
320 + KEEP(*(.pci_fixup_resume)) \
321 VMLINUX_SYMBOL(__end_pci_fixups_resume) = .; \
322 VMLINUX_SYMBOL(__start_pci_fixups_resume_early) = .; \
323 - *(.pci_fixup_resume_early) \
324 + KEEP(*(.pci_fixup_resume_early)) \
325 VMLINUX_SYMBOL(__end_pci_fixups_resume_early) = .; \
326 VMLINUX_SYMBOL(__start_pci_fixups_suspend) = .; \
327 - *(.pci_fixup_suspend) \
328 + KEEP(*(.pci_fixup_suspend)) \
329 VMLINUX_SYMBOL(__end_pci_fixups_suspend) = .; \
330 VMLINUX_SYMBOL(__start_pci_fixups_suspend_late) = .; \
331 - *(.pci_fixup_suspend_late) \
332 + KEEP(*(.pci_fixup_suspend_late)) \
333 VMLINUX_SYMBOL(__end_pci_fixups_suspend_late) = .; \
336 /* Built-in firmware blobs */ \
337 .builtin_fw : AT(ADDR(.builtin_fw) - LOAD_OFFSET) { \
338 VMLINUX_SYMBOL(__start_builtin_fw) = .; \
340 + KEEP(*(.builtin_fw)) \
341 VMLINUX_SYMBOL(__end_builtin_fw) = .; \
346 /* Kernel symbol table: strings */ \
347 __ksymtab_strings : AT(ADDR(__ksymtab_strings) - LOAD_OFFSET) { \
348 - KEEP(*(__ksymtab_strings)) \
349 + *(__ksymtab_strings) \
352 /* __*init sections */ \
353 @@ -410,14 +411,14 @@
354 /* Built-in module parameters. */ \
355 __param : AT(ADDR(__param) - LOAD_OFFSET) { \
356 VMLINUX_SYMBOL(__start___param) = .; \
359 VMLINUX_SYMBOL(__stop___param) = .; \
362 /* Built-in module versions. */ \
363 __modver : AT(ADDR(__modver) - LOAD_OFFSET) { \
364 VMLINUX_SYMBOL(__start___modver) = .; \
366 + KEEP(*(__modver)) \
367 VMLINUX_SYMBOL(__stop___modver) = .; \
368 . = ALIGN((align)); \
369 VMLINUX_SYMBOL(__end_rodata) = .; \
373 VMLINUX_SYMBOL(__entry_text_start) = .; \
375 + KEEP(*(.entry.text)) \
376 VMLINUX_SYMBOL(__entry_text_end) = .;
378 #if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
381 __ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) { \
382 VMLINUX_SYMBOL(__start___ex_table) = .; \
384 + KEEP(*(__ex_table)) \
385 VMLINUX_SYMBOL(__stop___ex_table) = .; \
389 #ifdef CONFIG_CONSTRUCTORS
390 #define KERNEL_CTORS() . = ALIGN(8); \
391 VMLINUX_SYMBOL(__ctors_start) = .; \
394 *(SORT(.init_array.*)) \
396 + KEEP(*(.init_array)) \
397 VMLINUX_SYMBOL(__ctors_end) = .;
399 #define KERNEL_CTORS()
401 #define SBSS(sbss_align) \
402 . = ALIGN(sbss_align); \
403 .sbss : AT(ADDR(.sbss) - LOAD_OFFSET) { \
411 __bug_table : AT(ADDR(__bug_table) - LOAD_OFFSET) { \
412 VMLINUX_SYMBOL(__start___bug_table) = .; \
414 + KEEP(*(__bug_table)) \
415 VMLINUX_SYMBOL(__stop___bug_table) = .; \
420 .tracedata : AT(ADDR(.tracedata) - LOAD_OFFSET) { \
421 VMLINUX_SYMBOL(__tracedata_start) = .; \
423 + KEEP(*(.tracedata)) \
424 VMLINUX_SYMBOL(__tracedata_end) = .; \
428 #define INIT_SETUP(initsetup_align) \
429 . = ALIGN(initsetup_align); \
430 VMLINUX_SYMBOL(__setup_start) = .; \
432 + KEEP(*(.init.setup)) \
433 VMLINUX_SYMBOL(__setup_end) = .;
435 #define INIT_CALLS_LEVEL(level) \