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-rw-r--r--Makefile9
-rw-r--r--arch/Kconfig13
-rw-r--r--include/asm-generic/vmlinux.lds.h52
-rw-r--r--include/linux/compiler.h23
-rw-r--r--include/linux/export.h30
-rw-r--r--include/linux/init.h38
-rw-r--r--init/Makefile2
7 files changed, 104 insertions, 63 deletions
diff --git a/Makefile b/Makefile
index 70de1448c571..6d40f3a3a8cc 100644
--- a/Makefile
+++ b/Makefile
@@ -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
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-01 12:25:07 +0000