arch/arm/kernel/unwind.c - linux - Git at Google

 /*
  * arch/arm/kernel/unwind.c
  *
  * Copyright (C) 2008 ARM Limited
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  *
  *
  * Stack unwinding support for ARM
  *
  * An ARM EABI version of gcc is required to generate the unwind
  * tables. For information about the structure of the unwind tables,
  * see "Exception Handling ABI for the ARM Architecture" at:
  *
  * http://infocenter.arm.com/help/topic/com.arm.doc.subset.swdev.abi/index.html
  */

 #ifndef __CHECKER__
 #if !defined (__ARM_EABI__)
 #warning Your compiler does not have EABI support.
 #warning    ARM unwind is known to compile only with EABI compilers.
 #warning    Change compiler or disable ARM_UNWIND option.
 #elif (__GNUC__ == 4 && __GNUC_MINOR__ <= 2)
 #warning Your compiler is too buggy; it is known to not compile ARM unwind support.
 #warning    Change compiler or disable ARM_UNWIND option.
 #endif
 #endif /* __CHECKER__ */

 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/list.h>

 #include <asm/stacktrace.h>
 #include <asm/traps.h>
 #include <asm/unwind.h>

 /* Dummy functions to avoid linker complaints */
 void __aeabi_unwind_cpp_pr0(void)
 {
 };
 EXPORT_SYMBOL(__aeabi_unwind_cpp_pr0);

 void __aeabi_unwind_cpp_pr1(void)
 {
 };
 EXPORT_SYMBOL(__aeabi_unwind_cpp_pr1);

 void __aeabi_unwind_cpp_pr2(void)
 {
 };
 EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);

 struct unwind_ctrl_block {
 	unsigned long vrs[16];		/* virtual register set */
 	unsigned long *insn;		/* pointer to the current instructions word */
 	int entries;			/* number of entries left to interpret */
 	int byte;			/* current byte number in the instructions word */
 };

 enum regs {
 #ifdef CONFIG_THUMB2_KERNEL
 	FP = 7,
 #else
 	FP = 11,
 #endif
 	SP = 13,
 	LR = 14,
 	PC = 15
 };

 extern struct unwind_idx __start_unwind_idx[];
 extern struct unwind_idx __stop_unwind_idx[];

 static DEFINE_SPINLOCK(unwind_lock);
 static LIST_HEAD(unwind_tables);

 /* Convert a prel31 symbol to an absolute address */
 #define prel31_to_addr(ptr)				\
 ({							\
 	/* sign-extend to 32 bits */			\
 	long offset = (((long)*(ptr)) << 1) >> 1;	\
 	(unsigned long)(ptr) + offset;			\
 })

 /*
  * Binary search in the unwind index. The entries entries are
  * guaranteed to be sorted in ascending order by the linker.
  */
 static struct unwind_idx *search_index(unsigned long addr,
 				       struct unwind_idx *first,
 				       struct unwind_idx *last)
 {
 	pr_debug("%s(%08lx, %p, %p)\n", __func__, addr, first, last);

 	if (addr < first->addr) {
 		pr_warning("unwind: Unknown symbol address %08lx\n", addr);
 		return NULL;
 	} else if (addr >= last->addr)
 		return last;

 	while (first < last - 1) {
 		struct unwind_idx *mid = first + ((last - first + 1) >> 1);

 		if (addr < mid->addr)
 			last = mid;
 		else
 			first = mid;
 	}

 	return first;
 }

 static struct unwind_idx *unwind_find_idx(unsigned long addr)
 {
 	struct unwind_idx *idx = NULL;
 	unsigned long flags;

 	pr_debug("%s(%08lx)\n", __func__, addr);

 	if (core_kernel_text(addr))
 		/* main unwind table */
 		idx = search_index(addr, __start_unwind_idx,
 				   __stop_unwind_idx - 1);
 	else {
 		/* module unwind tables */
 		struct unwind_table *table;

 		spin_lock_irqsave(&unwind_lock, flags);
 		list_for_each_entry(table, &unwind_tables, list) {
 			if (addr >= table->begin_addr &&
 			    addr < table->end_addr) {
 				idx = search_index(addr, table->start,
 						   table->stop - 1);
 				break;
 			}
 		}
 		spin_unlock_irqrestore(&unwind_lock, flags);
 	}

 	pr_debug("%s: idx = %p\n", __func__, idx);
 	return idx;
 }

 static unsigned long unwind_get_byte(struct unwind_ctrl_block *ctrl)
 {
 	unsigned long ret;

 	if (ctrl->entries <= 0) {
 		pr_warning("unwind: Corrupt unwind table\n");
 		return 0;
 	}

 	ret = (*ctrl->insn >> (ctrl->byte * 8)) & 0xff;

 	if (ctrl->byte == 0) {
 		ctrl->insn++;
 		ctrl->entries--;
 		ctrl->byte = 3;
 	} else
 		ctrl->byte--;

 	return ret;
 }

 /*
  * Execute the current unwind instruction.
  */
 static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
 {
 	unsigned long insn = unwind_get_byte(ctrl);

 	pr_debug("%s: insn = %08lx\n", __func__, insn);

 	if ((insn & 0xc0) == 0x00)
 		ctrl->vrs[SP] += ((insn & 0x3f) << 2) + 4;
 	else if ((insn & 0xc0) == 0x40)
 		ctrl->vrs[SP] -= ((insn & 0x3f) << 2) + 4;
 	else if ((insn & 0xf0) == 0x80) {
 		unsigned long mask;
 		unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
 		int load_sp, reg = 4;

 		insn = (insn << 8) | unwind_get_byte(ctrl);
 		mask = insn & 0x0fff;
 		if (mask == 0) {
 			pr_warning("unwind: 'Refuse to unwind' instruction %04lx\n",
 				   insn);
 			return -URC_FAILURE;
 		}

 		/* pop R4-R15 according to mask */
 		load_sp = mask & (1 << (13 - 4));
 		while (mask) {
 			if (mask & 1)
 				ctrl->vrs[reg] = *vsp++;
 			mask >>= 1;
 			reg++;
 		}
 		if (!load_sp)
 			ctrl->vrs[SP] = (unsigned long)vsp;
 	} else if ((insn & 0xf0) == 0x90 &&
 		   (insn & 0x0d) != 0x0d)
 		ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
 	else if ((insn & 0xf0) == 0xa0) {
 		unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
 		int reg;

 		/* pop R4-R[4+bbb] */
 		for (reg = 4; reg <= 4 + (insn & 7); reg++)
 			ctrl->vrs[reg] = *vsp++;
 		if (insn & 0x80)
 			ctrl->vrs[14] = *vsp++;
 		ctrl->vrs[SP] = (unsigned long)vsp;
 	} else if (insn == 0xb0) {
 		if (ctrl->vrs[PC] == 0)
 			ctrl->vrs[PC] = ctrl->vrs[LR];
 		/* no further processing */
 		ctrl->entries = 0;
 	} else if (insn == 0xb1) {
 		unsigned long mask = unwind_get_byte(ctrl);
 		unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
 		int reg = 0;

 		if (mask == 0 || mask & 0xf0) {
 			pr_warning("unwind: Spare encoding %04lx\n",
 			       (insn << 8) | mask);
 			return -URC_FAILURE;
 		}

 		/* pop R0-R3 according to mask */
 		while (mask) {
 			if (mask & 1)
 				ctrl->vrs[reg] = *vsp++;
 			mask >>= 1;
 			reg++;
 		}
 		ctrl->vrs[SP] = (unsigned long)vsp;
 	} else if (insn == 0xb2) {
 		unsigned long uleb128 = unwind_get_byte(ctrl);

 		ctrl->vrs[SP] += 0x204 + (uleb128 << 2);
 	} else {
 		pr_warning("unwind: Unhandled instruction %02lx\n", insn);
 		return -URC_FAILURE;
 	}

 	pr_debug("%s: fp = %08lx sp = %08lx lr = %08lx pc = %08lx\n", __func__,
 		 ctrl->vrs[FP], ctrl->vrs[SP], ctrl->vrs[LR], ctrl->vrs[PC]);

 	return URC_OK;
 }

 /*
  * Unwind a single frame starting with *sp for the symbol at *pc. It
  * updates the *pc and *sp with the new values.
  */
 int unwind_frame(struct stackframe *frame)
 {
 	unsigned long high, low;
 	struct unwind_idx *idx;
 	struct unwind_ctrl_block ctrl;

 	/* only go to a higher address on the stack */
 	low = frame->sp;
 	high = ALIGN(low, THREAD_SIZE) + THREAD_SIZE;

 	pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
 		 frame->pc, frame->lr, frame->sp);

 	if (!kernel_text_address(frame->pc))
 		return -URC_FAILURE;

 	idx = unwind_find_idx(frame->pc);
 	if (!idx) {
 		pr_warning("unwind: Index not found %08lx\n", frame->pc);
 		return -URC_FAILURE;
 	}

 	ctrl.vrs[FP] = frame->fp;
 	ctrl.vrs[SP] = frame->sp;
 	ctrl.vrs[LR] = frame->lr;
 	ctrl.vrs[PC] = 0;

 	if (idx->insn == 1)
 		/* can't unwind */
 		return -URC_FAILURE;
 	else if ((idx->insn & 0x80000000) == 0)
 		/* prel31 to the unwind table */
 		ctrl.insn = (unsigned long *)prel31_to_addr(&idx->insn);
 	else if ((idx->insn & 0xff000000) == 0x80000000)
 		/* only personality routine 0 supported in the index */
 		ctrl.insn = &idx->insn;
 	else {
 		pr_warning("unwind: Unsupported personality routine %08lx in the index at %p\n",
 			   idx->insn, idx);
 		return -URC_FAILURE;
 	}

 	/* check the personality routine */
 	if ((*ctrl.insn & 0xff000000) == 0x80000000) {
 		ctrl.byte = 2;
 		ctrl.entries = 1;
 	} else if ((*ctrl.insn & 0xff000000) == 0x81000000) {
 		ctrl.byte = 1;
 		ctrl.entries = 1 + ((*ctrl.insn & 0x00ff0000) >> 16);
 	} else {
 		pr_warning("unwind: Unsupported personality routine %08lx at %p\n",
 			   *ctrl.insn, ctrl.insn);
 		return -URC_FAILURE;
 	}

 	while (ctrl.entries > 0) {
 		int urc = unwind_exec_insn(&ctrl);
 		if (urc < 0)
 			return urc;
 		if (ctrl.vrs[SP] < low || ctrl.vrs[SP] >= high)
 			return -URC_FAILURE;
 	}

 	if (ctrl.vrs[PC] == 0)
 		ctrl.vrs[PC] = ctrl.vrs[LR];

 	/* check for infinite loop */
 	if (frame->pc == ctrl.vrs[PC])
 		return -URC_FAILURE;

 	frame->fp = ctrl.vrs[FP];
 	frame->sp = ctrl.vrs[SP];
 	frame->lr = ctrl.vrs[LR];
 	frame->pc = ctrl.vrs[PC];

 	return URC_OK;
 }

 void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 {
 	struct stackframe frame;
 	register unsigned long current_sp asm ("sp");

 	pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);

 	if (!tsk)
 		tsk = current;

 	if (regs) {
 		frame.fp = regs->ARM_fp;
 		frame.sp = regs->ARM_sp;
 		frame.lr = regs->ARM_lr;
 		/* PC might be corrupted, use LR in that case. */
 		frame.pc = kernel_text_address(regs->ARM_pc)
 			 ? regs->ARM_pc : regs->ARM_lr;
 	} else if (tsk == current) {
 		frame.fp = (unsigned long)__builtin_frame_address(0);
 		frame.sp = current_sp;
 		frame.lr = (unsigned long)__builtin_return_address(0);
 		frame.pc = (unsigned long)unwind_backtrace;
 	} else {
 		/* task blocked in __switch_to */
 		frame.fp = thread_saved_fp(tsk);
 		frame.sp = thread_saved_sp(tsk);
 		/*
 		 * The function calling __switch_to cannot be a leaf function
 		 * so LR is recovered from the stack.
 		 */
 		frame.lr = 0;
 		frame.pc = thread_saved_pc(tsk);
 	}

 	while (1) {
 		int urc;
 		unsigned long where = frame.pc;

 		urc = unwind_frame(&frame);
 		if (urc < 0)
 			break;
 		dump_backtrace_entry(where, frame.pc, frame.sp - 4);
 	}
 }

 struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
 				      unsigned long text_addr,
 				      unsigned long text_size)
 {
 	unsigned long flags;
 	struct unwind_idx *idx;
 	struct unwind_table *tab = kmalloc(sizeof(*tab), GFP_KERNEL);

 	pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
 		 text_addr, text_size);

 	if (!tab)
 		return tab;

 	tab->start = (struct unwind_idx *)start;
 	tab->stop = (struct unwind_idx *)(start + size);
 	tab->begin_addr = text_addr;
 	tab->end_addr = text_addr + text_size;

 	/* Convert the symbol addresses to absolute values */
 	for (idx = tab->start; idx < tab->stop; idx++)
 		idx->addr = prel31_to_addr(&idx->addr);

 	spin_lock_irqsave(&unwind_lock, flags);
 	list_add_tail(&tab->list, &unwind_tables);
 	spin_unlock_irqrestore(&unwind_lock, flags);

 	return tab;
 }

 void unwind_table_del(struct unwind_table *tab)
 {
 	unsigned long flags;

 	if (!tab)
 		return;

 	spin_lock_irqsave(&unwind_lock, flags);
 	list_del(&tab->list);
 	spin_unlock_irqrestore(&unwind_lock, flags);

 	kfree(tab);
 }

 int __init unwind_init(void)
 {
 	struct unwind_idx *idx;

 	/* Convert the symbol addresses to absolute values */
 	for (idx = __start_unwind_idx; idx < __stop_unwind_idx; idx++)
 		idx->addr = prel31_to_addr(&idx->addr);

 	pr_debug("unwind: ARM stack unwinding initialised\n");

 	return 0;
 }
	/*
	* arch/arm/kernel/unwind.c
	*
	* Copyright (C) 2008 ARM Limited
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License version 2 as
	* published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
	*
	*
	* Stack unwinding support for ARM
	*
	* An ARM EABI version of gcc is required to generate the unwind
	* tables. For information about the structure of the unwind tables,
	* see "Exception Handling ABI for the ARM Architecture" at:
	*
	* http://infocenter.arm.com/help/topic/com.arm.doc.subset.swdev.abi/index.html
	*/

	#ifndef __CHECKER__
	#if !defined (__ARM_EABI__)
	#warning Your compiler does not have EABI support.
	#warning ARM unwind is known to compile only with EABI compilers.
	#warning Change compiler or disable ARM_UNWIND option.
	#elif (__GNUC__ == 4 && __GNUC_MINOR__ <= 2)
	#warning Your compiler is too buggy; it is known to not compile ARM unwind support.
	#warning Change compiler or disable ARM_UNWIND option.
	#endif
	#endif /* __CHECKER__ */

	#include <linux/kernel.h>
	#include <linux/init.h>
	#include <linux/module.h>
	#include <linux/sched.h>
	#include <linux/slab.h>
	#include <linux/spinlock.h>
	#include <linux/list.h>

	#include <asm/stacktrace.h>
	#include <asm/traps.h>
	#include <asm/unwind.h>

	/* Dummy functions to avoid linker complaints */
	void __aeabi_unwind_cpp_pr0(void)
	{
	};
	EXPORT_SYMBOL(__aeabi_unwind_cpp_pr0);

	void __aeabi_unwind_cpp_pr1(void)
	{
	};
	EXPORT_SYMBOL(__aeabi_unwind_cpp_pr1);

	void __aeabi_unwind_cpp_pr2(void)
	{
	};
	EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);

	struct unwind_ctrl_block {
	unsigned long vrs[16]; /* virtual register set */
	unsigned long insn; / pointer to the current instructions word */
	int entries; /* number of entries left to interpret */
	int byte; /* current byte number in the instructions word */
	};

	enum regs {
	#ifdef CONFIG_THUMB2_KERNEL
	FP = 7,
	#else
	FP = 11,
	#endif
	SP = 13,
	LR = 14,
	PC = 15
	};

	extern struct unwind_idx __start_unwind_idx[];
	extern struct unwind_idx __stop_unwind_idx[];

	static DEFINE_SPINLOCK(unwind_lock);
	static LIST_HEAD(unwind_tables);

	/* Convert a prel31 symbol to an absolute address */
	#define prel31_to_addr(ptr) \
	({ \
	/* sign-extend to 32 bits */ \
	long offset = (((long)*(ptr)) << 1) >> 1; \
	(unsigned long)(ptr) + offset; \
	})

	/*
	* Binary search in the unwind index. The entries entries are
	* guaranteed to be sorted in ascending order by the linker.
	*/
	static struct unwind_idx *search_index(unsigned long addr,
	struct unwind_idx *first,
	struct unwind_idx *last)
	{
	pr_debug("%s(%08lx, %p, %p)\n", __func__, addr, first, last);

	if (addr < first->addr) {
	pr_warning("unwind: Unknown symbol address %08lx\n", addr);
	return NULL;
	} else if (addr >= last->addr)
	return last;

	while (first < last - 1) {
	struct unwind_idx *mid = first + ((last - first + 1) >> 1);

	if (addr < mid->addr)
	last = mid;
	else
	first = mid;
	}

	return first;
	}

	static struct unwind_idx *unwind_find_idx(unsigned long addr)
	{
	struct unwind_idx *idx = NULL;
	unsigned long flags;

	pr_debug("%s(%08lx)\n", __func__, addr);

	if (core_kernel_text(addr))
	/* main unwind table */
	idx = search_index(addr, __start_unwind_idx,
	__stop_unwind_idx - 1);
	else {
	/* module unwind tables */
	struct unwind_table *table;

	spin_lock_irqsave(&unwind_lock, flags);
	list_for_each_entry(table, &unwind_tables, list) {
	if (addr >= table->begin_addr &&
	addr < table->end_addr) {
	idx = search_index(addr, table->start,
	table->stop - 1);
	break;
	}
	}
	spin_unlock_irqrestore(&unwind_lock, flags);
	}

	pr_debug("%s: idx = %p\n", __func__, idx);
	return idx;
	}

	static unsigned long unwind_get_byte(struct unwind_ctrl_block *ctrl)
	{
	unsigned long ret;

	if (ctrl->entries <= 0) {
	pr_warning("unwind: Corrupt unwind table\n");
	return 0;
	}

	ret = (ctrl->insn >> (ctrl->byte 8)) & 0xff;

	if (ctrl->byte == 0) {
	ctrl->insn++;
	ctrl->entries--;
	ctrl->byte = 3;
	} else
	ctrl->byte--;

	return ret;
	}

	/*
	* Execute the current unwind instruction.
	*/
	static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
	{
	unsigned long insn = unwind_get_byte(ctrl);

	pr_debug("%s: insn = %08lx\n", __func__, insn);

	if ((insn & 0xc0) == 0x00)
	ctrl->vrs[SP] += ((insn & 0x3f) << 2) + 4;
	else if ((insn & 0xc0) == 0x40)
	ctrl->vrs[SP] -= ((insn & 0x3f) << 2) + 4;
	else if ((insn & 0xf0) == 0x80) {
	unsigned long mask;
	unsigned long vsp = (unsigned long )ctrl->vrs[SP];
	int load_sp, reg = 4;

	insn = (insn << 8) \| unwind_get_byte(ctrl);
	mask = insn & 0x0fff;
	if (mask == 0) {
	pr_warning("unwind: 'Refuse to unwind' instruction %04lx\n",
	insn);
	return -URC_FAILURE;
	}

	/* pop R4-R15 according to mask */
	load_sp = mask & (1 << (13 - 4));
	while (mask) {
	if (mask & 1)
	ctrl->vrs[reg] = *vsp++;
	mask >>= 1;
	reg++;
	}
	if (!load_sp)
	ctrl->vrs[SP] = (unsigned long)vsp;
	} else if ((insn & 0xf0) == 0x90 &&
	(insn & 0x0d) != 0x0d)
	ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
	else if ((insn & 0xf0) == 0xa0) {
	unsigned long vsp = (unsigned long )ctrl->vrs[SP];
	int reg;

	/* pop R4-R[4+bbb] */
	for (reg = 4; reg <= 4 + (insn & 7); reg++)
	ctrl->vrs[reg] = *vsp++;
	if (insn & 0x80)
	ctrl->vrs[14] = *vsp++;
	ctrl->vrs[SP] = (unsigned long)vsp;
	} else if (insn == 0xb0) {
	if (ctrl->vrs[PC] == 0)
	ctrl->vrs[PC] = ctrl->vrs[LR];
	/* no further processing */
	ctrl->entries = 0;
	} else if (insn == 0xb1) {
	unsigned long mask = unwind_get_byte(ctrl);
	unsigned long vsp = (unsigned long )ctrl->vrs[SP];
	int reg = 0;

	if (mask == 0 \|\| mask & 0xf0) {
	pr_warning("unwind: Spare encoding %04lx\n",
	(insn << 8) \| mask);
	return -URC_FAILURE;
	}

	/* pop R0-R3 according to mask */
	while (mask) {
	if (mask & 1)
	ctrl->vrs[reg] = *vsp++;
	mask >>= 1;
	reg++;
	}
	ctrl->vrs[SP] = (unsigned long)vsp;
	} else if (insn == 0xb2) {
	unsigned long uleb128 = unwind_get_byte(ctrl);

	ctrl->vrs[SP] += 0x204 + (uleb128 << 2);
	} else {
	pr_warning("unwind: Unhandled instruction %02lx\n", insn);
	return -URC_FAILURE;
	}

	pr_debug("%s: fp = %08lx sp = %08lx lr = %08lx pc = %08lx\n", __func__,
	ctrl->vrs[FP], ctrl->vrs[SP], ctrl->vrs[LR], ctrl->vrs[PC]);

	return URC_OK;
	}

	/*
	* Unwind a single frame starting with sp for the symbol at pc. It
	* updates the pc and sp with the new values.
	*/
	int unwind_frame(struct stackframe *frame)
	{
	unsigned long high, low;
	struct unwind_idx *idx;
	struct unwind_ctrl_block ctrl;

	/* only go to a higher address on the stack */
	low = frame->sp;
	high = ALIGN(low, THREAD_SIZE) + THREAD_SIZE;

	pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
	frame->pc, frame->lr, frame->sp);

	if (!kernel_text_address(frame->pc))
	return -URC_FAILURE;

	idx = unwind_find_idx(frame->pc);
	if (!idx) {
	pr_warning("unwind: Index not found %08lx\n", frame->pc);
	return -URC_FAILURE;
	}

	ctrl.vrs[FP] = frame->fp;
	ctrl.vrs[SP] = frame->sp;
	ctrl.vrs[LR] = frame->lr;
	ctrl.vrs[PC] = 0;

	if (idx->insn == 1)
	/* can't unwind */
	return -URC_FAILURE;
	else if ((idx->insn & 0x80000000) == 0)
	/* prel31 to the unwind table */
	ctrl.insn = (unsigned long *)prel31_to_addr(&idx->insn);
	else if ((idx->insn & 0xff000000) == 0x80000000)
	/* only personality routine 0 supported in the index */
	ctrl.insn = &idx->insn;
	else {
	pr_warning("unwind: Unsupported personality routine %08lx in the index at %p\n",
	idx->insn, idx);
	return -URC_FAILURE;
	}

	/* check the personality routine */
	if ((*ctrl.insn & 0xff000000) == 0x80000000) {
	ctrl.byte = 2;
	ctrl.entries = 1;
	} else if ((*ctrl.insn & 0xff000000) == 0x81000000) {
	ctrl.byte = 1;
	ctrl.entries = 1 + ((*ctrl.insn & 0x00ff0000) >> 16);
	} else {
	pr_warning("unwind: Unsupported personality routine %08lx at %p\n",
	*ctrl.insn, ctrl.insn);
	return -URC_FAILURE;
	}

	while (ctrl.entries > 0) {
	int urc = unwind_exec_insn(&ctrl);
	if (urc < 0)
	return urc;
	if (ctrl.vrs[SP] < low \|\| ctrl.vrs[SP] >= high)
	return -URC_FAILURE;
	}

	if (ctrl.vrs[PC] == 0)
	ctrl.vrs[PC] = ctrl.vrs[LR];

	/* check for infinite loop */
	if (frame->pc == ctrl.vrs[PC])
	return -URC_FAILURE;

	frame->fp = ctrl.vrs[FP];
	frame->sp = ctrl.vrs[SP];
	frame->lr = ctrl.vrs[LR];
	frame->pc = ctrl.vrs[PC];

	return URC_OK;
	}

	void unwind_backtrace(struct pt_regs regs, struct task_struct tsk)
	{
	struct stackframe frame;
	register unsigned long current_sp asm ("sp");

	pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);

	if (!tsk)
	tsk = current;

	if (regs) {
	frame.fp = regs->ARM_fp;
	frame.sp = regs->ARM_sp;
	frame.lr = regs->ARM_lr;
	/* PC might be corrupted, use LR in that case. */
	frame.pc = kernel_text_address(regs->ARM_pc)
	? regs->ARM_pc : regs->ARM_lr;
	} else if (tsk == current) {
	frame.fp = (unsigned long)__builtin_frame_address(0);
	frame.sp = current_sp;
	frame.lr = (unsigned long)__builtin_return_address(0);
	frame.pc = (unsigned long)unwind_backtrace;
	} else {
	/* task blocked in __switch_to */
	frame.fp = thread_saved_fp(tsk);
	frame.sp = thread_saved_sp(tsk);
	/*
	* The function calling __switch_to cannot be a leaf function
	* so LR is recovered from the stack.
	*/
	frame.lr = 0;
	frame.pc = thread_saved_pc(tsk);
	}

	while (1) {
	int urc;
	unsigned long where = frame.pc;

	urc = unwind_frame(&frame);
	if (urc < 0)
	break;
	dump_backtrace_entry(where, frame.pc, frame.sp - 4);
	}
	}

	struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
	unsigned long text_addr,
	unsigned long text_size)
	{
	unsigned long flags;
	struct unwind_idx *idx;
	struct unwind_table tab = kmalloc(sizeof(tab), GFP_KERNEL);

	pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
	text_addr, text_size);

	if (!tab)
	return tab;

	tab->start = (struct unwind_idx *)start;
	tab->stop = (struct unwind_idx *)(start + size);
	tab->begin_addr = text_addr;
	tab->end_addr = text_addr + text_size;

	/* Convert the symbol addresses to absolute values */
	for (idx = tab->start; idx < tab->stop; idx++)
	idx->addr = prel31_to_addr(&idx->addr);

	spin_lock_irqsave(&unwind_lock, flags);
	list_add_tail(&tab->list, &unwind_tables);
	spin_unlock_irqrestore(&unwind_lock, flags);

	return tab;
	}

	void unwind_table_del(struct unwind_table *tab)
	{
	unsigned long flags;

	if (!tab)
	return;

	spin_lock_irqsave(&unwind_lock, flags);
	list_del(&tab->list);
	spin_unlock_irqrestore(&unwind_lock, flags);

	kfree(tab);
	}

	int __init unwind_init(void)
	{
	struct unwind_idx *idx;

	/* Convert the symbol addresses to absolute values */
	for (idx = __start_unwind_idx; idx < __stop_unwind_idx; idx++)
	idx->addr = prel31_to_addr(&idx->addr);

	pr_debug("unwind: ARM stack unwinding initialised\n");

	return 0;
	}