arch/mips/kernel/relocate.c - linux/torvalds/linux - Git at Google

 /*
  * This file is subject to the terms and conditions of the GNU General Public
  * License.  See the file "COPYING" in the main directory of this archive
  * for more details.
  *
  * Support for Kernel relocation at boot time
  *
  * Copyright (C) 2015, Imagination Technologies Ltd.
  * Authors: Matt Redfearn (matt.redfearn@mips.com)
  */
 #include <asm/bootinfo.h>
 #include <asm/cacheflush.h>
 #include <asm/fw/fw.h>
 #include <asm/sections.h>
 #include <asm/setup.h>
 #include <asm/timex.h>
 #include <linux/elf.h>
 #include <linux/kernel.h>
 #include <linux/libfdt.h>
 #include <linux/of_fdt.h>
 #include <linux/sched/task.h>
 #include <linux/start_kernel.h>
 #include <linux/string.h>
 #include <linux/printk.h>

 #define RELOCATED(x) ((void *)((long)x + offset))

 extern u32 _relocation_start[];	/* End kernel image / start relocation table */
 extern u32 _relocation_end[];	/* End relocation table */

 extern long __start___ex_table;	/* Start exception table */
 extern long __stop___ex_table;	/* End exception table */

 extern void __weak plat_fdt_relocated(void *new_location);

 /*
  * This function may be defined for a platform to perform any post-relocation
  * fixup necessary.
  * Return non-zero to abort relocation
  */
 int __weak plat_post_relocation(long offset)
 {
 	return 0;
 }

 static inline u32 __init get_synci_step(void)
 {
 	u32 res;

 	__asm__("rdhwr  %0, $1" : "=r" (res));

 	return res;
 }

 static void __init sync_icache(void *kbase, unsigned long kernel_length)
 {
 	void *kend = kbase + kernel_length;
 	u32 step = get_synci_step();

 	do {
 		__asm__ __volatile__(
 			"synci  0(%0)"
 			: /* no output */
 			: "r" (kbase));

 		kbase += step;
 	} while (kbase < kend);

 	/* Completion barrier */
 	__sync();
 }

 static int __init apply_r_mips_64_rel(u32 *loc_orig, u32 *loc_new, long offset)
 {
 	*(u64 *)loc_new += offset;

 	return 0;
 }

 static int __init apply_r_mips_32_rel(u32 *loc_orig, u32 *loc_new, long offset)
 {
 	*loc_new += offset;

 	return 0;
 }

 static int __init apply_r_mips_26_rel(u32 *loc_orig, u32 *loc_new, long offset)
 {
 	unsigned long target_addr = (*loc_orig) & 0x03ffffff;

 	if (offset % 4) {
 		pr_err("Dangerous R_MIPS_26 REL relocation\n");
 		return -ENOEXEC;
 	}

 	/* Original target address */
 	target_addr <<= 2;
 	target_addr += (unsigned long)loc_orig & ~0x03ffffff;

 	/* Get the new target address */
 	target_addr += offset;

 	if ((target_addr & 0xf0000000) != ((unsigned long)loc_new & 0xf0000000)) {
 		pr_err("R_MIPS_26 REL relocation overflow\n");
 		return -ENOEXEC;
 	}

 	target_addr -= (unsigned long)loc_new & ~0x03ffffff;
 	target_addr >>= 2;

 	*loc_new = (*loc_new & ~0x03ffffff) | (target_addr & 0x03ffffff);

 	return 0;
 }


 static int __init apply_r_mips_hi16_rel(u32 *loc_orig, u32 *loc_new, long offset)
 {
 	unsigned long insn = *loc_orig;
 	unsigned long target = (insn & 0xffff) << 16; /* high 16bits of target */

 	target += offset;

 	*loc_new = (insn & ~0xffff) | ((target >> 16) & 0xffff);
 	return 0;
 }

 static int (*reloc_handlers_rel[]) (u32 *, u32 *, long) __initdata = {
 	[R_MIPS_64]		= apply_r_mips_64_rel,
 	[R_MIPS_32]		= apply_r_mips_32_rel,
 	[R_MIPS_26]		= apply_r_mips_26_rel,
 	[R_MIPS_HI16]		= apply_r_mips_hi16_rel,
 };

 int __init do_relocations(void *kbase_old, void *kbase_new, long offset)
 {
 	u32 *r;
 	u32 *loc_orig;
 	u32 *loc_new;
 	int type;
 	int res;

 	for (r = _relocation_start; r < _relocation_end; r++) {
 		/* Sentinel for last relocation */
 		if (*r == 0)
 			break;

 		type = (*r >> 24) & 0xff;
 		loc_orig = kbase_old + ((*r & 0x00ffffff) << 2);
 		loc_new = RELOCATED(loc_orig);

 		if (reloc_handlers_rel[type] == NULL) {
 			/* Unsupported relocation */
 			pr_err("Unhandled relocation type %d at 0x%pK\n",
 			       type, loc_orig);
 			return -ENOEXEC;
 		}

 		res = reloc_handlers_rel[type](loc_orig, loc_new, offset);
 		if (res)
 			return res;
 	}

 	return 0;
 }

 /*
  * The exception table is filled in by the relocs tool after vmlinux is linked.
  * It must be relocated separately since there will not be any relocation
  * information for it filled in by the linker.
  */
 static int __init relocate_exception_table(long offset)
 {
 	unsigned long *etable_start, *etable_end, *e;

 	etable_start = RELOCATED(&__start___ex_table);
 	etable_end = RELOCATED(&__stop___ex_table);

 	for (e = etable_start; e < etable_end; e++)
 		*e += offset;

 	return 0;
 }

 #ifdef CONFIG_RANDOMIZE_BASE

 static inline __init unsigned long rotate_xor(unsigned long hash,
 					      const void *area, size_t size)
 {
 	size_t i;
 	unsigned long *ptr = (unsigned long *)area;

 	for (i = 0; i < size / sizeof(hash); i++) {
 		/* Rotate by odd number of bits and XOR. */
 		hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
 		hash ^= ptr[i];
 	}

 	return hash;
 }

 static inline __init unsigned long get_random_boot(void)
 {
 	unsigned long entropy = random_get_entropy();
 	unsigned long hash = 0;

 	/* Attempt to create a simple but unpredictable starting entropy. */
 	hash = rotate_xor(hash, linux_banner, strlen(linux_banner));

 	/* Add in any runtime entropy we can get */
 	hash = rotate_xor(hash, &entropy, sizeof(entropy));

 #if defined(CONFIG_USE_OF)
 	/* Get any additional entropy passed in device tree */
 	if (initial_boot_params) {
 		int node, len;
 		u64 *prop;

 		node = fdt_path_offset(initial_boot_params, "/chosen");
 		if (node >= 0) {
 			prop = fdt_getprop_w(initial_boot_params, node,
 					     "kaslr-seed", &len);
 			if (prop && (len == sizeof(u64)))
 				hash = rotate_xor(hash, prop, sizeof(*prop));
 		}
 	}
 #endif /* CONFIG_USE_OF */

 	return hash;
 }

 static inline __init bool kaslr_disabled(void)
 {
 	char *str;

 #if defined(CONFIG_CMDLINE_BOOL)
 	const char *builtin_cmdline = CONFIG_CMDLINE;

 	str = strstr(builtin_cmdline, "nokaslr");
 	if (str == builtin_cmdline ||
 	    (str > builtin_cmdline && *(str - 1) == ' '))
 		return true;
 #endif
 	str = strstr(arcs_cmdline, "nokaslr");
 	if (str == arcs_cmdline || (str > arcs_cmdline && *(str - 1) == ' '))
 		return true;

 	return false;
 }

 static inline void __init *determine_relocation_address(void)
 {
 	/* Choose a new address for the kernel */
 	unsigned long kernel_length;
 	void *dest = &_text;
 	unsigned long offset;

 	if (kaslr_disabled())
 		return dest;

 	kernel_length = (long)_end - (long)(&_text);

 	offset = get_random_boot() << 16;
 	offset &= (CONFIG_RANDOMIZE_BASE_MAX_OFFSET - 1);
 	if (offset < kernel_length)
 		offset += ALIGN(kernel_length, 0xffff);

 	return RELOCATED(dest);
 }

 #else

 static inline void __init *determine_relocation_address(void)
 {
 	/*
 	 * Choose a new address for the kernel
 	 * For now we'll hard code the destination
 	 */
 	return (void *)0xffffffff81000000;
 }

 #endif

 static inline int __init relocation_addr_valid(void *loc_new)
 {
 	if ((unsigned long)loc_new & 0x0000ffff) {
 		/* Inappropriately aligned new location */
 		return 0;
 	}
 	if ((unsigned long)loc_new < (unsigned long)&_end) {
 		/* New location overlaps original kernel */
 		return 0;
 	}
 	return 1;
 }

 void *__init relocate_kernel(void)
 {
 	void *loc_new;
 	unsigned long kernel_length;
 	unsigned long bss_length;
 	long offset = 0;
 	int res = 1;
 	/* Default to original kernel entry point */
 	void *kernel_entry = start_kernel;
 	void *fdt = NULL;

 	/* Get the command line */
 	fw_init_cmdline();
 #if defined(CONFIG_USE_OF)
 	/* Deal with the device tree */
 	fdt = plat_get_fdt();
 	early_init_dt_scan(fdt);
 	if (boot_command_line[0]) {
 		/* Boot command line was passed in device tree */
 		strlcpy(arcs_cmdline, boot_command_line, COMMAND_LINE_SIZE);
 	}
 #endif /* CONFIG_USE_OF */

 	kernel_length = (long)(&_relocation_start) - (long)(&_text);
 	bss_length = (long)&__bss_stop - (long)&__bss_start;

 	loc_new = determine_relocation_address();

 	/* Sanity check relocation address */
 	if (relocation_addr_valid(loc_new))
 		offset = (unsigned long)loc_new - (unsigned long)(&_text);

 	/* Reset the command line now so we don't end up with a duplicate */
 	arcs_cmdline[0] = '\0';

 	if (offset) {
 		void (*fdt_relocated_)(void *) = NULL;
 #if defined(CONFIG_USE_OF)
 		unsigned long fdt_phys = virt_to_phys(fdt);

 		/*
 		 * If built-in dtb is used then it will have been relocated
 		 * during kernel _text relocation. If appended DTB is used
 		 * then it will not be relocated, but it should remain
 		 * intact in the original location. If dtb is loaded by
 		 * the bootloader then it may need to be moved if it crosses
 		 * the target memory area
 		 */

 		if (fdt_phys >= virt_to_phys(RELOCATED(&_text)) &&
 			fdt_phys <= virt_to_phys(RELOCATED(&_end))) {
 			void *fdt_relocated =
 				RELOCATED(ALIGN((long)&_end, PAGE_SIZE));
 			memcpy(fdt_relocated, fdt, fdt_totalsize(fdt));
 			fdt = fdt_relocated;
 			fdt_relocated_ = RELOCATED(&plat_fdt_relocated);
 		}
 #endif /* CONFIG_USE_OF */

 		/* Copy the kernel to it's new location */
 		memcpy(loc_new, &_text, kernel_length);

 		/* Perform relocations on the new kernel */
 		res = do_relocations(&_text, loc_new, offset);
 		if (res < 0)
 			goto out;

 		/* Sync the caches ready for execution of new kernel */
 		sync_icache(loc_new, kernel_length);

 		res = relocate_exception_table(offset);
 		if (res < 0)
 			goto out;

 		/*
 		 * The original .bss has already been cleared, and
 		 * some variables such as command line parameters
 		 * stored to it so make a copy in the new location.
 		 */
 		memcpy(RELOCATED(&__bss_start), &__bss_start, bss_length);

 		/*
 		 * If fdt was stored outside of the kernel image and
 		 * had to be moved then update platform's state data
 		 * with the new fdt location
 		 */
 		if (fdt_relocated_)
 			fdt_relocated_(fdt);

 		/*
 		 * Last chance for the platform to abort relocation.
 		 * This may also be used by the platform to perform any
 		 * initialisation required now that the new kernel is
 		 * resident in memory and ready to be executed.
 		 */
 		if (plat_post_relocation(offset))
 			goto out;

 		/* The current thread is now within the relocated image */
 		__current_thread_info = RELOCATED(&init_thread_union);

 		/* Return the new kernel's entry point */
 		kernel_entry = RELOCATED(start_kernel);
 	}
 out:
 	return kernel_entry;
 }

 /*
  * Show relocation information on panic.
  */
 void show_kernel_relocation(const char *level)
 {
 	unsigned long offset;

 	offset = __pa_symbol(_text) - __pa_symbol(VMLINUX_LOAD_ADDRESS);

 	if (IS_ENABLED(CONFIG_RELOCATABLE) && offset > 0) {
 		printk(level);
 		pr_cont("Kernel relocated by 0x%pK\n", (void *)offset);
 		pr_cont(" .text @ 0x%pK\n", _text);
 		pr_cont(" .data @ 0x%pK\n", _sdata);
 		pr_cont(" .bss  @ 0x%pK\n", __bss_start);
 	}
 }

 static int kernel_location_notifier_fn(struct notifier_block *self,
 				       unsigned long v, void *p)
 {
 	show_kernel_relocation(KERN_EMERG);
 	return NOTIFY_DONE;
 }

 static struct notifier_block kernel_location_notifier = {
 	.notifier_call = kernel_location_notifier_fn
 };

 static int __init register_kernel_offset_dumper(void)
 {
 	atomic_notifier_chain_register(&panic_notifier_list,
 				       &kernel_location_notifier);
 	return 0;
 }
 __initcall(register_kernel_offset_dumper);
	/*
	* This file is subject to the terms and conditions of the GNU General Public
	* License. See the file "COPYING" in the main directory of this archive
	* for more details.
	*
	* Support for Kernel relocation at boot time
	*
	* Copyright (C) 2015, Imagination Technologies Ltd.
	* Authors: Matt Redfearn (matt.redfearn@mips.com)
	*/
	#include <asm/bootinfo.h>
	#include <asm/cacheflush.h>
	#include <asm/fw/fw.h>
	#include <asm/sections.h>
	#include <asm/setup.h>
	#include <asm/timex.h>
	#include <linux/elf.h>
	#include <linux/kernel.h>
	#include <linux/libfdt.h>
	#include <linux/of_fdt.h>
	#include <linux/sched/task.h>
	#include <linux/start_kernel.h>
	#include <linux/string.h>
	#include <linux/printk.h>

	#define RELOCATED(x) ((void *)((long)x + offset))

	extern u32 _relocation_start[]; /* End kernel image / start relocation table */
	extern u32 _relocation_end[]; /* End relocation table */

	extern long __start___ex_table; /* Start exception table */
	extern long __stop___ex_table; /* End exception table */

	extern void __weak plat_fdt_relocated(void *new_location);

	/*
	* This function may be defined for a platform to perform any post-relocation
	* fixup necessary.
	* Return non-zero to abort relocation
	*/
	int __weak plat_post_relocation(long offset)
	{
	return 0;
	}

	static inline u32 __init get_synci_step(void)
	{
	u32 res;

	__asm__("rdhwr %0, $1" : "=r" (res));

	return res;
	}

	static void __init sync_icache(void *kbase, unsigned long kernel_length)
	{
	void *kend = kbase + kernel_length;
	u32 step = get_synci_step();

	do {
	__asm__ __volatile__(
	"synci 0(%0)"
	: /* no output */
	: "r" (kbase));

	kbase += step;
	} while (kbase < kend);

	/* Completion barrier */
	__sync();
	}

	static int __init apply_r_mips_64_rel(u32 loc_orig, u32 loc_new, long offset)
	{
	(u64 )loc_new += offset;

	return 0;
	}

	static int __init apply_r_mips_32_rel(u32 loc_orig, u32 loc_new, long offset)
	{
	*loc_new += offset;

	return 0;
	}

	static int __init apply_r_mips_26_rel(u32 loc_orig, u32 loc_new, long offset)
	{
	unsigned long target_addr = (*loc_orig) & 0x03ffffff;

	if (offset % 4) {
	pr_err("Dangerous R_MIPS_26 REL relocation\n");
	return -ENOEXEC;
	}

	/* Original target address */
	target_addr <<= 2;
	target_addr += (unsigned long)loc_orig & ~0x03ffffff;

	/* Get the new target address */
	target_addr += offset;

	if ((target_addr & 0xf0000000) != ((unsigned long)loc_new & 0xf0000000)) {
	pr_err("R_MIPS_26 REL relocation overflow\n");
	return -ENOEXEC;
	}

	target_addr -= (unsigned long)loc_new & ~0x03ffffff;
	target_addr >>= 2;

	loc_new = (loc_new & ~0x03ffffff) \| (target_addr & 0x03ffffff);

	return 0;
	}


	static int __init apply_r_mips_hi16_rel(u32 loc_orig, u32 loc_new, long offset)
	{
	unsigned long insn = *loc_orig;
	unsigned long target = (insn & 0xffff) << 16; /* high 16bits of target */

	target += offset;

	*loc_new = (insn & ~0xffff) \| ((target >> 16) & 0xffff);
	return 0;
	}

	static int (reloc_handlers_rel[]) (u32 , u32 *, long) __initdata = {
	[R_MIPS_64] = apply_r_mips_64_rel,
	[R_MIPS_32] = apply_r_mips_32_rel,
	[R_MIPS_26] = apply_r_mips_26_rel,
	[R_MIPS_HI16] = apply_r_mips_hi16_rel,
	};

	int __init do_relocations(void kbase_old, void kbase_new, long offset)
	{
	u32 *r;
	u32 *loc_orig;
	u32 *loc_new;
	int type;
	int res;

	for (r = _relocation_start; r < _relocation_end; r++) {
	/* Sentinel for last relocation */
	if (*r == 0)
	break;

	type = (*r >> 24) & 0xff;
	loc_orig = kbase_old + ((*r & 0x00ffffff) << 2);
	loc_new = RELOCATED(loc_orig);

	if (reloc_handlers_rel[type] == NULL) {
	/* Unsupported relocation */
	pr_err("Unhandled relocation type %d at 0x%pK\n",
	type, loc_orig);
	return -ENOEXEC;
	}

	res = reloc_handlers_rel[type](loc_orig, loc_new, offset);
	if (res)
	return res;
	}

	return 0;
	}

	/*
	* The exception table is filled in by the relocs tool after vmlinux is linked.
	* It must be relocated separately since there will not be any relocation
	* information for it filled in by the linker.
	*/
	static int __init relocate_exception_table(long offset)
	{
	unsigned long etable_start, etable_end, *e;

	etable_start = RELOCATED(&__start___ex_table);
	etable_end = RELOCATED(&__stop___ex_table);

	for (e = etable_start; e < etable_end; e++)
	*e += offset;

	return 0;
	}

	#ifdef CONFIG_RANDOMIZE_BASE

	static inline __init unsigned long rotate_xor(unsigned long hash,
	const void *area, size_t size)
	{
	size_t i;
	unsigned long ptr = (unsigned long )area;

	for (i = 0; i < size / sizeof(hash); i++) {
	/* Rotate by odd number of bits and XOR. */
	hash = (hash << ((sizeof(hash) * 8) - 7)) \| (hash >> 7);
	hash ^= ptr[i];
	}

	return hash;
	}

	static inline __init unsigned long get_random_boot(void)
	{
	unsigned long entropy = random_get_entropy();
	unsigned long hash = 0;

	/* Attempt to create a simple but unpredictable starting entropy. */
	hash = rotate_xor(hash, linux_banner, strlen(linux_banner));

	/* Add in any runtime entropy we can get */
	hash = rotate_xor(hash, &entropy, sizeof(entropy));

	#if defined(CONFIG_USE_OF)
	/* Get any additional entropy passed in device tree */
	if (initial_boot_params) {
	int node, len;
	u64 *prop;

	node = fdt_path_offset(initial_boot_params, "/chosen");
	if (node >= 0) {
	prop = fdt_getprop_w(initial_boot_params, node,
	"kaslr-seed", &len);
	if (prop && (len == sizeof(u64)))
	hash = rotate_xor(hash, prop, sizeof(*prop));
	}
	}
	#endif /* CONFIG_USE_OF */

	return hash;
	}

	static inline __init bool kaslr_disabled(void)
	{
	char *str;

	#if defined(CONFIG_CMDLINE_BOOL)
	const char *builtin_cmdline = CONFIG_CMDLINE;

	str = strstr(builtin_cmdline, "nokaslr");
	if (str == builtin_cmdline \|\|
	(str > builtin_cmdline && *(str - 1) == ' '))
	return true;
	#endif
	str = strstr(arcs_cmdline, "nokaslr");
	if (str == arcs_cmdline \|\| (str > arcs_cmdline && *(str - 1) == ' '))
	return true;

	return false;
	}

	static inline void __init *determine_relocation_address(void)
	{
	/* Choose a new address for the kernel */
	unsigned long kernel_length;
	void *dest = &_text;
	unsigned long offset;

	if (kaslr_disabled())
	return dest;

	kernel_length = (long)_end - (long)(&_text);

	offset = get_random_boot() << 16;
	offset &= (CONFIG_RANDOMIZE_BASE_MAX_OFFSET - 1);
	if (offset < kernel_length)
	offset += ALIGN(kernel_length, 0xffff);

	return RELOCATED(dest);
	}

	#else

	static inline void __init *determine_relocation_address(void)
	{
	/*
	* Choose a new address for the kernel
	* For now we'll hard code the destination
	*/
	return (void *)0xffffffff81000000;
	}

	#endif

	static inline int __init relocation_addr_valid(void *loc_new)
	{
	if ((unsigned long)loc_new & 0x0000ffff) {
	/* Inappropriately aligned new location */
	return 0;
	}
	if ((unsigned long)loc_new < (unsigned long)&_end) {
	/* New location overlaps original kernel */
	return 0;
	}
	return 1;
	}

	void *__init relocate_kernel(void)
	{
	void *loc_new;
	unsigned long kernel_length;
	unsigned long bss_length;
	long offset = 0;
	int res = 1;
	/* Default to original kernel entry point */
	void *kernel_entry = start_kernel;
	void *fdt = NULL;

	/* Get the command line */
	fw_init_cmdline();
	#if defined(CONFIG_USE_OF)
	/* Deal with the device tree */
	fdt = plat_get_fdt();
	early_init_dt_scan(fdt);
	if (boot_command_line[0]) {
	/* Boot command line was passed in device tree */
	strlcpy(arcs_cmdline, boot_command_line, COMMAND_LINE_SIZE);
	}
	#endif /* CONFIG_USE_OF */

	kernel_length = (long)(&_relocation_start) - (long)(&_text);
	bss_length = (long)&__bss_stop - (long)&__bss_start;

	loc_new = determine_relocation_address();

	/* Sanity check relocation address */
	if (relocation_addr_valid(loc_new))
	offset = (unsigned long)loc_new - (unsigned long)(&_text);

	/* Reset the command line now so we don't end up with a duplicate */
	arcs_cmdline[0] = '\0';

	if (offset) {
	void (fdt_relocated_)(void ) = NULL;
	#if defined(CONFIG_USE_OF)
	unsigned long fdt_phys = virt_to_phys(fdt);

	/*
	* If built-in dtb is used then it will have been relocated
	* during kernel _text relocation. If appended DTB is used
	* then it will not be relocated, but it should remain
	* intact in the original location. If dtb is loaded by
	* the bootloader then it may need to be moved if it crosses
	* the target memory area
	*/

	if (fdt_phys >= virt_to_phys(RELOCATED(&_text)) &&
	fdt_phys <= virt_to_phys(RELOCATED(&_end))) {
	void *fdt_relocated =
	RELOCATED(ALIGN((long)&_end, PAGE_SIZE));
	memcpy(fdt_relocated, fdt, fdt_totalsize(fdt));
	fdt = fdt_relocated;
	fdt_relocated_ = RELOCATED(&plat_fdt_relocated);
	}
	#endif /* CONFIG_USE_OF */

	/* Copy the kernel to it's new location */
	memcpy(loc_new, &_text, kernel_length);

	/* Perform relocations on the new kernel */
	res = do_relocations(&_text, loc_new, offset);
	if (res < 0)
	goto out;

	/* Sync the caches ready for execution of new kernel */
	sync_icache(loc_new, kernel_length);

	res = relocate_exception_table(offset);
	if (res < 0)
	goto out;

	/*
	* The original .bss has already been cleared, and
	* some variables such as command line parameters
	* stored to it so make a copy in the new location.
	*/
	memcpy(RELOCATED(&__bss_start), &__bss_start, bss_length);

	/*
	* If fdt was stored outside of the kernel image and
	* had to be moved then update platform's state data
	* with the new fdt location
	*/
	if (fdt_relocated_)
	fdt_relocated_(fdt);

	/*
	* Last chance for the platform to abort relocation.
	* This may also be used by the platform to perform any
	* initialisation required now that the new kernel is
	* resident in memory and ready to be executed.
	*/
	if (plat_post_relocation(offset))
	goto out;

	/* The current thread is now within the relocated image */
	__current_thread_info = RELOCATED(&init_thread_union);

	/* Return the new kernel's entry point */
	kernel_entry = RELOCATED(start_kernel);
	}
	out:
	return kernel_entry;
	}

	/*
	* Show relocation information on panic.
	*/
	void show_kernel_relocation(const char *level)
	{
	unsigned long offset;

	offset = __pa_symbol(_text) - __pa_symbol(VMLINUX_LOAD_ADDRESS);

	if (IS_ENABLED(CONFIG_RELOCATABLE) && offset > 0) {
	printk(level);
	pr_cont("Kernel relocated by 0x%pK\n", (void *)offset);
	pr_cont(" .text @ 0x%pK\n", _text);
	pr_cont(" .data @ 0x%pK\n", _sdata);
	pr_cont(" .bss @ 0x%pK\n", __bss_start);
	}
	}

	static int kernel_location_notifier_fn(struct notifier_block *self,
	unsigned long v, void *p)
	{
	show_kernel_relocation(KERN_EMERG);
	return NOTIFY_DONE;
	}

	static struct notifier_block kernel_location_notifier = {
	.notifier_call = kernel_location_notifier_fn
	};

	static int __init register_kernel_offset_dumper(void)
	{
	atomic_notifier_chain_register(&panic_notifier_list,
	&kernel_location_notifier);
	return 0;
	}
	__initcall(register_kernel_offset_dumper);