diff options
| -rw-r--r-- | Makefile | 9 | ||||
| -rw-r--r-- | arch/Kconfig | 13 | ||||
| -rw-r--r-- | include/asm-generic/vmlinux.lds.h | 52 | ||||
| -rw-r--r-- | include/linux/compiler.h | 23 | ||||
| -rw-r--r-- | include/linux/export.h | 30 | ||||
| -rw-r--r-- | include/linux/init.h | 38 | ||||
| -rw-r--r-- | init/Makefile | 2 |
7 files changed, 104 insertions, 63 deletions
@@ -622,6 +622,11 @@ include arch/$(SRCARCH)/Makefile KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,) KBUILD_CFLAGS += $(call cc-disable-warning,maybe-uninitialized,) +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 else @@ -809,6 +814,10 @@ LDFLAGS_BUILD_ID = $(patsubst -Wl$(comma)%,%,\ KBUILD_LDFLAGS_MODULE += $(LDFLAGS_BUILD_ID) LDFLAGS_vmlinux += $(LDFLAGS_BUILD_ID) +ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION +LDFLAGS_vmlinux += $(call ld-option, --gc-sections,) +endif + ifeq ($(CONFIG_STRIP_ASM_SYMS),y) LDFLAGS_vmlinux += $(call ld-option, -X,) endif diff --git a/arch/Kconfig b/arch/Kconfig index 6842154813e5..3f948c422d9d 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -467,6 +467,19 @@ config THIN_ARCHIVES Select this if the architecture wants to use thin archives instead of ld -r to create the built-in.o files. +config LD_DEAD_CODE_DATA_ELIMINATION + bool + help + Select this if the architecture wants to do dead code and + data elimination with the linker by compiling with + -ffunction-sections -fdata-sections and linking with + --gc-sections. + + This requires that the arch annotates or otherwise protects + its external entry points from being discarded. Linker scripts + must also merge .text.*, .data.*, and .bss.* correctly into + output sections. + config HAVE_CONTEXT_TRACKING bool help diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 24563970ff7b..ad9d8f94dc7a 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -196,9 +196,14 @@ *(.dtb.init.rodata) \ VMLINUX_SYMBOL(__dtb_end) = .; -/* .data section */ +/* + * .data section + * -fdata-sections generates .data.identifier which needs to be pulled in + * with .data, but don't want to pull in .data..stuff which has its own + * requirements. Same for bss. + */ #define DATA_DATA \ - *(.data) \ + *(.data .data.[0-9a-zA-Z_]*) \ *(.ref.data) \ *(.data..shared_aligned) /* percpu related */ \ MEM_KEEP(init.data) \ @@ -320,76 +325,76 @@ /* Kernel symbol table: Normal symbols */ \ __ksymtab : AT(ADDR(__ksymtab) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___ksymtab) = .; \ - *(SORT(___ksymtab+*)) \ + KEEP(*(SORT(___ksymtab+*))) \ VMLINUX_SYMBOL(__stop___ksymtab) = .; \ } \ \ /* Kernel symbol table: GPL-only symbols */ \ __ksymtab_gpl : AT(ADDR(__ksymtab_gpl) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___ksymtab_gpl) = .; \ - *(SORT(___ksymtab_gpl+*)) \ + KEEP(*(SORT(___ksymtab_gpl+*))) \ VMLINUX_SYMBOL(__stop___ksymtab_gpl) = .; \ } \ \ /* Kernel symbol table: Normal unused symbols */ \ __ksymtab_unused : AT(ADDR(__ksymtab_unused) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___ksymtab_unused) = .; \ - *(SORT(___ksymtab_unused+*)) \ + KEEP(*(SORT(___ksymtab_unused+*))) \ VMLINUX_SYMBOL(__stop___ksymtab_unused) = .; \ } \ \ /* Kernel symbol table: GPL-only unused symbols */ \ __ksymtab_unused_gpl : AT(ADDR(__ksymtab_unused_gpl) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___ksymtab_unused_gpl) = .; \ - *(SORT(___ksymtab_unused_gpl+*)) \ + KEEP(*(SORT(___ksymtab_unused_gpl+*))) \ VMLINUX_SYMBOL(__stop___ksymtab_unused_gpl) = .; \ } \ \ /* Kernel symbol table: GPL-future-only symbols */ \ __ksymtab_gpl_future : AT(ADDR(__ksymtab_gpl_future) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___ksymtab_gpl_future) = .; \ - *(SORT(___ksymtab_gpl_future+*)) \ + KEEP(*(SORT(___ksymtab_gpl_future+*))) \ VMLINUX_SYMBOL(__stop___ksymtab_gpl_future) = .; \ } \ \ /* Kernel symbol table: Normal symbols */ \ __kcrctab : AT(ADDR(__kcrctab) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___kcrctab) = .; \ - *(SORT(___kcrctab+*)) \ + KEEP(*(SORT(___kcrctab+*))) \ VMLINUX_SYMBOL(__stop___kcrctab) = .; \ } \ \ /* Kernel symbol table: GPL-only symbols */ \ __kcrctab_gpl : AT(ADDR(__kcrctab_gpl) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___kcrctab_gpl) = .; \ - *(SORT(___kcrctab_gpl+*)) \ + KEEP(*(SORT(___kcrctab_gpl+*))) \ VMLINUX_SYMBOL(__stop___kcrctab_gpl) = .; \ } \ \ /* Kernel symbol table: Normal unused symbols */ \ __kcrctab_unused : AT(ADDR(__kcrctab_unused) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___kcrctab_unused) = .; \ - *(SORT(___kcrctab_unused+*)) \ + KEEP(*(SORT(___kcrctab_unused+*))) \ VMLINUX_SYMBOL(__stop___kcrctab_unused) = .; \ } \ \ /* Kernel symbol table: GPL-only unused symbols */ \ __kcrctab_unused_gpl : AT(ADDR(__kcrctab_unused_gpl) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___kcrctab_unused_gpl) = .; \ - *(SORT(___kcrctab_unused_gpl+*)) \ + KEEP(*(SORT(___kcrctab_unused_gpl+*))) \ VMLINUX_SYMBOL(__stop___kcrctab_unused_gpl) = .; \ } \ \ /* Kernel symbol table: GPL-future-only symbols */ \ __kcrctab_gpl_future : AT(ADDR(__kcrctab_gpl_future) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___kcrctab_gpl_future) = .; \ - *(SORT(___kcrctab_gpl_future+*)) \ + KEEP(*(SORT(___kcrctab_gpl_future+*))) \ VMLINUX_SYMBOL(__stop___kcrctab_gpl_future) = .; \ } \ \ /* Kernel symbol table: strings */ \ __ksymtab_strings : AT(ADDR(__ksymtab_strings) - LOAD_OFFSET) { \ - *(__ksymtab_strings) \ + KEEP(*(__ksymtab_strings)) \ } \ \ /* __*init sections */ \ @@ -424,7 +429,7 @@ #define SECURITY_INIT \ .security_initcall.init : AT(ADDR(.security_initcall.init) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__security_initcall_start) = .; \ - *(.security_initcall.init) \ + KEEP(*(.security_initcall.init)) \ VMLINUX_SYMBOL(__security_initcall_end) = .; \ } @@ -432,7 +437,7 @@ * during second ld run in second ld pass when generating System.map */ #define TEXT_TEXT \ ALIGN_FUNCTION(); \ - *(.text.hot .text .text.fixup .text.unlikely) \ + *(.text.hot .text .text.fixup .text.unlikely .text.*) \ *(.ref.text) \ MEM_KEEP(init.text) \ MEM_KEEP(exit.text) \ @@ -527,6 +532,7 @@ /* init and exit section handling */ #define INIT_DATA \ + KEEP(*(SORT(___kentry+*))) \ *(.init.data) \ MEM_DISCARD(init.data) \ KERNEL_CTORS() \ @@ -593,7 +599,7 @@ BSS_FIRST_SECTIONS \ *(.bss..page_aligned) \ *(.dynbss) \ - *(.bss) \ + *(.bss .bss.[0-9a-zA-Z_]*) \ *(COMMON) \ } @@ -676,12 +682,12 @@ #define INIT_CALLS_LEVEL(level) \ VMLINUX_SYMBOL(__initcall##level##_start) = .; \ - *(.initcall##level##.init) \ - *(.initcall##level##s.init) \ + KEEP(*(.initcall##level##.init)) \ + KEEP(*(.initcall##level##s.init)) \ #define INIT_CALLS \ VMLINUX_SYMBOL(__initcall_start) = .; \ - *(.initcallearly.init) \ + KEEP(*(.initcallearly.init)) \ INIT_CALLS_LEVEL(0) \ INIT_CALLS_LEVEL(1) \ INIT_CALLS_LEVEL(2) \ @@ -695,21 +701,21 @@ #define CON_INITCALL \ VMLINUX_SYMBOL(__con_initcall_start) = .; \ - *(.con_initcall.init) \ + KEEP(*(.con_initcall.init)) \ VMLINUX_SYMBOL(__con_initcall_end) = .; #define SECURITY_INITCALL \ VMLINUX_SYMBOL(__security_initcall_start) = .; \ - *(.security_initcall.init) \ + KEEP(*(.security_initcall.init)) \ VMLINUX_SYMBOL(__security_initcall_end) = .; #ifdef CONFIG_BLK_DEV_INITRD #define INIT_RAM_FS \ . = ALIGN(4); \ VMLINUX_SYMBOL(__initramfs_start) = .; \ - *(.init.ramfs) \ + KEEP(*(.init.ramfs)) \ . = ALIGN(8); \ - *(.init.ramfs.info) + KEEP(*(.init.ramfs.info)) #else #define INIT_RAM_FS #endif diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 1bb954842725..86130cded110 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -182,6 +182,29 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); # define unreachable() do { } while (1) #endif +/* + * KENTRY - kernel entry point + * This can be used to annotate symbols (functions or data) that are used + * without their linker symbol being referenced explicitly. For example, + * interrupt vector handlers, or functions in the kernel image that are found + * programatically. + * + * Not required for symbols exported with EXPORT_SYMBOL, or initcalls. Those + * are handled in their own way (with KEEP() in linker scripts). + * + * KENTRY can be avoided if the symbols in question are marked as KEEP() in the + * linker script. For example an architecture could KEEP() its entire + * boot/exception vector code rather than annotate each function and data. + */ +#ifndef KENTRY +# define KENTRY(sym) \ + extern typeof(sym) sym; \ + static const unsigned long __kentry_##sym \ + __used \ + __attribute__((section("___kentry" "+" #sym ), used)) \ + = (unsigned long)&sym; +#endif + #ifndef RELOC_HIDE # define RELOC_HIDE(ptr, off) \ ({ unsigned long __ptr; \ diff --git a/include/linux/export.h b/include/linux/export.h index c565f87f005e..337cb90f3668 100644 --- a/include/linux/export.h +++ b/include/linux/export.h @@ -1,5 +1,6 @@ #ifndef _LINUX_EXPORT_H #define _LINUX_EXPORT_H + /* * Export symbols from the kernel to modules. Forked from module.h * to reduce the amount of pointless cruft we feed to gcc when only @@ -42,27 +43,26 @@ extern struct module __this_module; #ifdef CONFIG_MODVERSIONS /* Mark the CRC weak since genksyms apparently decides not to * generate a checksums for some symbols */ -#define __CRC_SYMBOL(sym, sec) \ - extern __visible void *__crc_##sym __attribute__((weak)); \ - static const unsigned long __kcrctab_##sym \ - __used \ - __attribute__((section("___kcrctab" sec "+" #sym), unused)) \ +#define __CRC_SYMBOL(sym, sec) \ + extern __visible void *__crc_##sym __attribute__((weak)); \ + static const unsigned long __kcrctab_##sym \ + __used \ + __attribute__((section("___kcrctab" sec "+" #sym), used)) \ = (unsigned long) &__crc_##sym; #else #define __CRC_SYMBOL(sym, sec) #endif /* For every exported symbol, place a struct in the __ksymtab section */ -#define ___EXPORT_SYMBOL(sym, sec) \ - extern typeof(sym) sym; \ - __CRC_SYMBOL(sym, sec) \ - static const char __kstrtab_##sym[] \ - __attribute__((section("__ksymtab_strings"), aligned(1))) \ - = VMLINUX_SYMBOL_STR(sym); \ - extern const struct kernel_symbol __ksymtab_##sym; \ - __visible const struct kernel_symbol __ksymtab_##sym \ - __used \ - __attribute__((section("___ksymtab" sec "+" #sym), unused)) \ +#define ___EXPORT_SYMBOL(sym, sec) \ + extern typeof(sym) sym; \ + __CRC_SYMBOL(sym, sec) \ + static const char __kstrtab_##sym[] \ + __attribute__((section("__ksymtab_strings"), aligned(1))) \ + = VMLINUX_SYMBOL_STR(sym); \ + static const struct kernel_symbol __ksymtab_##sym \ + __used \ + __attribute__((section("___ksymtab" sec "+" #sym), used)) \ = { (unsigned long)&sym, __kstrtab_##sym } #if defined(__KSYM_DEPS__) diff --git a/include/linux/init.h b/include/linux/init.h index 6935d02474aa..e571fec4bb28 100644 --- a/include/linux/init.h +++ b/include/linux/init.h @@ -150,24 +150,8 @@ extern bool initcall_debug; #ifndef __ASSEMBLY__ -#ifdef CONFIG_LTO -/* Work around a LTO gcc problem: when there is no reference to a variable - * in a module it will be moved to the end of the program. This causes - * reordering of initcalls which the kernel does not like. - * Add a dummy reference function to avoid this. The function is - * deleted by the linker. - */ -#define LTO_REFERENCE_INITCALL(x) \ - ; /* yes this is needed */ \ - static __used __exit void *reference_##x(void) \ - { \ - return &x; \ - } -#else -#define LTO_REFERENCE_INITCALL(x) -#endif - -/* initcalls are now grouped by functionality into separate +/* + * initcalls are now grouped by functionality into separate * subsections. Ordering inside the subsections is determined * by link order. * For backwards compatibility, initcall() puts the call in @@ -175,12 +159,16 @@ extern bool initcall_debug; * * The `id' arg to __define_initcall() is needed so that multiple initcalls * can point at the same handler without causing duplicate-symbol build errors. + * + * Initcalls are run by placing pointers in initcall sections that the + * kernel iterates at runtime. The linker can do dead code / data elimination + * and remove that completely, so the initcall sections have to be marked + * as KEEP() in the linker script. */ #define __define_initcall(fn, id) \ static initcall_t __initcall_##fn##id __used \ - __attribute__((__section__(".initcall" #id ".init"))) = fn; \ - LTO_REFERENCE_INITCALL(__initcall_##fn##id) + __attribute__((__section__(".initcall" #id ".init"))) = fn; /* * Early initcalls run before initializing SMP. @@ -216,15 +204,15 @@ extern bool initcall_debug; #define __initcall(fn) device_initcall(fn) -#define __exitcall(fn) \ +#define __exitcall(fn) \ static exitcall_t __exitcall_##fn __exit_call = fn -#define console_initcall(fn) \ - static initcall_t __initcall_##fn \ +#define console_initcall(fn) \ + static initcall_t __initcall_##fn \ __used __section(.con_initcall.init) = fn -#define security_initcall(fn) \ - static initcall_t __initcall_##fn \ +#define security_initcall(fn) \ + static initcall_t __initcall_##fn \ __used __section(.security_initcall.init) = fn struct obs_kernel_param { diff --git a/init/Makefile b/init/Makefile index 7bc47ee31c36..c4fb45525d08 100644 --- a/init/Makefile +++ b/init/Makefile @@ -2,6 +2,8 @@ # Makefile for the linux kernel. # +ccflags-y := -fno-function-sections -fno-data-sections + obj-y := main.o version.o mounts.o ifneq ($(CONFIG_BLK_DEV_INITRD),y) obj-y += noinitramfs.o |