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(-)
24 @@ -406,6 +406,11 @@ KBUILD_CFLAGS_MODULE := -DMODULE
25 KBUILD_LDFLAGS_MODULE = -T $(srctree)/scripts/module-common.lds $(if $(CONFIG_PROFILING),,-s)
28 +ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
29 +KBUILD_CFLAGS_KERNEL += $(call cc-option,-ffunction-sections,)
30 +KBUILD_CFLAGS_KERNEL += $(call cc-option,-fdata-sections,)
33 # Read KERNELRELEASE from include/config/kernel.release (if it exists)
34 KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)
35 KERNELVERSION = $(VERSION)$(if $(PATCHLEVEL),.$(PATCHLEVEL)$(if $(SUBLEVEL),.$(SUBLEVEL)))$(EXTRAVERSION)
36 @@ -673,11 +678,6 @@ KBUILD_CFLAGS += $(call cc-disable-warni
37 KBUILD_CFLAGS += $(call cc-disable-warning, int-in-bool-context)
38 KBUILD_CFLAGS += $(call cc-disable-warning, attribute-alias)
40 -ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
41 -KBUILD_CFLAGS += $(call cc-option,-ffunction-sections,)
42 -KBUILD_CFLAGS += $(call cc-option,-fdata-sections,)
45 ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
46 KBUILD_CFLAGS += $(call cc-option,-Oz,-Os)
47 KBUILD_CFLAGS += $(call cc-disable-warning,maybe-uninitialized,) $(EXTRA_OPTIMIZATION)
48 --- a/arch/arm/Kconfig
49 +++ b/arch/arm/Kconfig
50 @@ -81,6 +81,7 @@ config ARM
52 select HAVE_VIRT_CPU_ACCOUNTING_GEN
53 select IRQ_FORCED_THREADING
54 + select LD_DEAD_CODE_DATA_ELIMINATION
55 select MODULES_USE_ELF_REL
57 select OF_EARLY_FLATTREE if OF
58 --- a/arch/arm/boot/compressed/Makefile
59 +++ b/arch/arm/boot/compressed/Makefile
60 @@ -102,6 +102,7 @@ ifeq ($(CONFIG_FUNCTION_TRACER),y)
61 ORIG_CFLAGS := $(KBUILD_CFLAGS)
62 KBUILD_CFLAGS = $(subst -pg, , $(ORIG_CFLAGS))
64 +KBUILD_CFLAGS_KERNEL := $(patsubst -f%-sections,,$(KBUILD_CFLAGS_KERNEL))
66 # -fstack-protector-strong triggers protection checks in this code,
67 # but it is being used too early to link to meaningful stack_chk logic.
68 --- a/arch/arm/kernel/vmlinux.lds.S
69 +++ b/arch/arm/kernel/vmlinux.lds.S
73 VMLINUX_SYMBOL(__proc_info_begin) = .; \
74 - *(.proc.info.init) \
75 + KEEP(*(.proc.info.init)) \
76 VMLINUX_SYMBOL(__proc_info_end) = .;
78 #define HYPERVISOR_TEXT \
82 VMLINUX_SYMBOL(__idmap_text_start) = .; \
84 + KEEP(*(.idmap.text)) \
85 VMLINUX_SYMBOL(__idmap_text_end) = .; \
86 . = ALIGN(PAGE_SIZE); \
87 VMLINUX_SYMBOL(__hyp_idmap_text_start) = .; \
88 - *(.hyp.idmap.text) \
89 + KEEP(*(.hyp.idmap.text)) \
90 VMLINUX_SYMBOL(__hyp_idmap_text_end) = .;
92 #ifdef CONFIG_HOTPLUG_CPU
93 @@ -105,7 +105,7 @@ SECTIONS
94 _stext = .; /* Text and read-only data */
96 __exception_text_start = .;
98 + KEEP(*(.exception.text))
99 __exception_text_end = .;
102 @@ -134,7 +134,7 @@ SECTIONS
103 __ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {
104 __start___ex_table = .;
107 + KEEP(*(__ex_table))
109 __stop___ex_table = .;
111 @@ -146,12 +146,12 @@ SECTIONS
114 __start_unwind_idx = .;
116 + KEEP(*(.ARM.exidx*))
117 __stop_unwind_idx = .;
120 __start_unwind_tab = .;
122 + KEEP(*(.ARM.extab*))
123 __stop_unwind_tab = .;
126 @@ -171,14 +171,14 @@ SECTIONS
129 .vectors 0xffff0000 : AT(__vectors_start) {
133 . = __vectors_start + SIZEOF(.vectors);
137 .stubs ADDR(.vectors) + 0x1000 : AT(__stubs_start) {
141 . = __stubs_start + SIZEOF(.stubs);
143 @@ -194,24 +194,24 @@ SECTIONS
146 __arch_info_begin = .;
148 + KEEP(*(.arch.info.init))
152 __tagtable_begin = .;
154 + KEEP(*(.taglist.init))
157 #ifdef CONFIG_SMP_ON_UP
161 + KEEP(*(.alt.smp.init))
166 __pv_table_begin = .;
172 --- a/arch/mips/Kconfig
173 +++ b/arch/mips/Kconfig
174 @@ -55,6 +55,7 @@ config MIPS
175 select CLONE_BACKWARDS
176 select HAVE_DEBUG_STACKOVERFLOW
177 select HAVE_CC_STACKPROTECTOR
178 + select LD_DEAD_CODE_DATA_ELIMINATION
179 select CPU_PM if CPU_IDLE
180 select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
181 select ARCH_BINFMT_ELF_STATE
182 --- a/arch/mips/kernel/vmlinux.lds.S
183 +++ b/arch/mips/kernel/vmlinux.lds.S
184 @@ -71,7 +71,7 @@ SECTIONS
185 /* Exception table for data bus errors */
187 __start___dbe_table = .;
189 + KEEP(*(__dbe_table))
190 __stop___dbe_table = .;
193 @@ -121,7 +121,7 @@ SECTIONS
195 .mips.machines.init : AT(ADDR(.mips.machines.init) - LOAD_OFFSET) {
196 __mips_machines_start = .;
197 - *(.mips.machines.init)
198 + KEEP(*(.mips.machines.init))
199 __mips_machines_end = .;
202 --- a/include/asm-generic/vmlinux.lds.h
203 +++ b/include/asm-generic/vmlinux.lds.h
205 #ifdef CONFIG_FTRACE_MCOUNT_RECORD
206 #define MCOUNT_REC() . = ALIGN(8); \
207 VMLINUX_SYMBOL(__start_mcount_loc) = .; \
209 + KEEP(*(__mcount_loc)) \
210 VMLINUX_SYMBOL(__stop_mcount_loc) = .;
215 #ifdef CONFIG_TRACE_BRANCH_PROFILING
216 #define LIKELY_PROFILE() VMLINUX_SYMBOL(__start_annotated_branch_profile) = .; \
217 - *(_ftrace_annotated_branch) \
218 + KEEP(*(_ftrace_annotated_branch)) \
219 VMLINUX_SYMBOL(__stop_annotated_branch_profile) = .;
221 #define LIKELY_PROFILE()
224 #ifdef CONFIG_PROFILE_ALL_BRANCHES
225 #define BRANCH_PROFILE() VMLINUX_SYMBOL(__start_branch_profile) = .; \
226 - *(_ftrace_branch) \
227 + KEEP(*(_ftrace_branch)) \
228 VMLINUX_SYMBOL(__stop_branch_profile) = .;
230 #define BRANCH_PROFILE()
232 #ifdef CONFIG_KPROBES
233 #define KPROBE_BLACKLIST() . = ALIGN(8); \
234 VMLINUX_SYMBOL(__start_kprobe_blacklist) = .; \
235 - *(_kprobe_blacklist) \
236 + KEEP(*(_kprobe_blacklist)) \
237 VMLINUX_SYMBOL(__stop_kprobe_blacklist) = .;
239 #define KPROBE_BLACKLIST()
240 @@ -139,10 +139,10 @@
241 #ifdef CONFIG_EVENT_TRACING
242 #define FTRACE_EVENTS() . = ALIGN(8); \
243 VMLINUX_SYMBOL(__start_ftrace_events) = .; \
244 - *(_ftrace_events) \
245 + KEEP(*(_ftrace_events)) \
246 VMLINUX_SYMBOL(__stop_ftrace_events) = .; \
247 VMLINUX_SYMBOL(__start_ftrace_enum_maps) = .; \
248 - *(_ftrace_enum_map) \
249 + KEEP(*(_ftrace_enum_map)) \
250 VMLINUX_SYMBOL(__stop_ftrace_enum_maps) = .;
252 #define FTRACE_EVENTS()
254 #ifdef CONFIG_FTRACE_SYSCALLS
255 #define TRACE_SYSCALLS() . = ALIGN(8); \
256 VMLINUX_SYMBOL(__start_syscalls_metadata) = .; \
257 - *(__syscalls_metadata) \
258 + KEEP(*(__syscalls_metadata)) \
259 VMLINUX_SYMBOL(__stop_syscalls_metadata) = .;
261 #define TRACE_SYSCALLS()
263 #ifdef CONFIG_SERIAL_EARLYCON
264 #define EARLYCON_TABLE() . = ALIGN(8); \
265 VMLINUX_SYMBOL(__earlycon_table) = .; \
266 - *(__earlycon_table) \
267 + KEEP(*(__earlycon_table)) \
268 VMLINUX_SYMBOL(__earlycon_table_end) = .;
270 #define EARLYCON_TABLE()
272 #define _OF_TABLE_1(name) \
274 VMLINUX_SYMBOL(__##name##_of_table) = .; \
275 - *(__##name##_of_table) \
276 - *(__##name##_of_table_end)
277 + KEEP(*(__##name##_of_table)) \
278 + KEEP(*(__##name##_of_table_end))
280 #define CLKSRC_OF_TABLES() OF_TABLE(CONFIG_CLKSRC_OF, clksrc)
281 #define IRQCHIP_OF_MATCH_TABLE() OF_TABLE(CONFIG_IRQCHIP, irqchip)
283 #define KERNEL_DTB() \
285 VMLINUX_SYMBOL(__dtb_start) = .; \
286 - *(.dtb.init.rodata) \
287 + KEEP(*(.dtb.init.rodata)) \
288 VMLINUX_SYMBOL(__dtb_end) = .;
291 @@ -227,16 +227,17 @@
292 /* implement dynamic printk debug */ \
294 VMLINUX_SYMBOL(__start___jump_table) = .; \
296 + KEEP(*(__jump_table)) \
297 VMLINUX_SYMBOL(__stop___jump_table) = .; \
299 VMLINUX_SYMBOL(__start___verbose) = .; \
301 + KEEP(*(__verbose)) \
302 VMLINUX_SYMBOL(__stop___verbose) = .; \
308 + *(.data.[a-zA-Z_]*)
311 * Data section helpers
312 @@ -304,35 +305,35 @@
314 .pci_fixup : AT(ADDR(.pci_fixup) - LOAD_OFFSET) { \
315 VMLINUX_SYMBOL(__start_pci_fixups_early) = .; \
316 - *(.pci_fixup_early) \
317 + KEEP(*(.pci_fixup_early)) \
318 VMLINUX_SYMBOL(__end_pci_fixups_early) = .; \
319 VMLINUX_SYMBOL(__start_pci_fixups_header) = .; \
320 - *(.pci_fixup_header) \
321 + KEEP(*(.pci_fixup_header)) \
322 VMLINUX_SYMBOL(__end_pci_fixups_header) = .; \
323 VMLINUX_SYMBOL(__start_pci_fixups_final) = .; \
324 - *(.pci_fixup_final) \
325 + KEEP(*(.pci_fixup_final)) \
326 VMLINUX_SYMBOL(__end_pci_fixups_final) = .; \
327 VMLINUX_SYMBOL(__start_pci_fixups_enable) = .; \
328 - *(.pci_fixup_enable) \
329 + KEEP(*(.pci_fixup_enable)) \
330 VMLINUX_SYMBOL(__end_pci_fixups_enable) = .; \
331 VMLINUX_SYMBOL(__start_pci_fixups_resume) = .; \
332 - *(.pci_fixup_resume) \
333 + KEEP(*(.pci_fixup_resume)) \
334 VMLINUX_SYMBOL(__end_pci_fixups_resume) = .; \
335 VMLINUX_SYMBOL(__start_pci_fixups_resume_early) = .; \
336 - *(.pci_fixup_resume_early) \
337 + KEEP(*(.pci_fixup_resume_early)) \
338 VMLINUX_SYMBOL(__end_pci_fixups_resume_early) = .; \
339 VMLINUX_SYMBOL(__start_pci_fixups_suspend) = .; \
340 - *(.pci_fixup_suspend) \
341 + KEEP(*(.pci_fixup_suspend)) \
342 VMLINUX_SYMBOL(__end_pci_fixups_suspend) = .; \
343 VMLINUX_SYMBOL(__start_pci_fixups_suspend_late) = .; \
344 - *(.pci_fixup_suspend_late) \
345 + KEEP(*(.pci_fixup_suspend_late)) \
346 VMLINUX_SYMBOL(__end_pci_fixups_suspend_late) = .; \
349 /* Built-in firmware blobs */ \
350 .builtin_fw : AT(ADDR(.builtin_fw) - LOAD_OFFSET) { \
351 VMLINUX_SYMBOL(__start_builtin_fw) = .; \
353 + KEEP(*(.builtin_fw)) \
354 VMLINUX_SYMBOL(__end_builtin_fw) = .; \
359 /* Kernel symbol table: strings */ \
360 __ksymtab_strings : AT(ADDR(__ksymtab_strings) - LOAD_OFFSET) { \
361 - KEEP(*(__ksymtab_strings)) \
362 + *(__ksymtab_strings) \
365 /* __*init sections */ \
366 @@ -423,14 +424,14 @@
367 /* Built-in module parameters. */ \
368 __param : AT(ADDR(__param) - LOAD_OFFSET) { \
369 VMLINUX_SYMBOL(__start___param) = .; \
372 VMLINUX_SYMBOL(__stop___param) = .; \
375 /* Built-in module versions. */ \
376 __modver : AT(ADDR(__modver) - LOAD_OFFSET) { \
377 VMLINUX_SYMBOL(__start___modver) = .; \
379 + KEEP(*(__modver)) \
380 VMLINUX_SYMBOL(__stop___modver) = .; \
381 . = ALIGN((align)); \
382 VMLINUX_SYMBOL(__end_rodata) = .; \
386 VMLINUX_SYMBOL(__entry_text_start) = .; \
388 + KEEP(*(.entry.text)) \
389 VMLINUX_SYMBOL(__entry_text_end) = .;
391 #if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
394 __ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) { \
395 VMLINUX_SYMBOL(__start___ex_table) = .; \
397 + KEEP(*(__ex_table)) \
398 VMLINUX_SYMBOL(__stop___ex_table) = .; \
402 #ifdef CONFIG_CONSTRUCTORS
403 #define KERNEL_CTORS() . = ALIGN(8); \
404 VMLINUX_SYMBOL(__ctors_start) = .; \
407 *(SORT(.init_array.*)) \
409 + KEEP(*(.init_array)) \
410 VMLINUX_SYMBOL(__ctors_end) = .;
412 #define KERNEL_CTORS()
414 #define SBSS(sbss_align) \
415 . = ALIGN(sbss_align); \
416 .sbss : AT(ADDR(.sbss) - LOAD_OFFSET) { \
424 __bug_table : AT(ADDR(__bug_table) - LOAD_OFFSET) { \
425 VMLINUX_SYMBOL(__start___bug_table) = .; \
427 + KEEP(*(__bug_table)) \
428 VMLINUX_SYMBOL(__stop___bug_table) = .; \
433 .tracedata : AT(ADDR(.tracedata) - LOAD_OFFSET) { \
434 VMLINUX_SYMBOL(__tracedata_start) = .; \
436 + KEEP(*(.tracedata)) \
437 VMLINUX_SYMBOL(__tracedata_end) = .; \
441 #define INIT_SETUP(initsetup_align) \
442 . = ALIGN(initsetup_align); \
443 VMLINUX_SYMBOL(__setup_start) = .; \
445 + KEEP(*(.init.setup)) \
446 VMLINUX_SYMBOL(__setup_end) = .;
448 #define INIT_CALLS_LEVEL(level) \