text: /*
   * Copyright (C) 2009 Matt Fleming <matt@console-pimps.org>
   *
   * 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.
   *
   * This is an implementation of a DWARF unwinder. Its main purpose is
   * for generating stacktrace information. Based on the DWARF 3
   * specification from http://www.dwarfstd.org.
   *
   * TODO:
   *	- DWARF64 doesn't work.
   *	- Registers with DWARF_VAL_OFFSET rules aren't handled properly.
   */
  
  /* #define DEBUG */
  #include <linux/kernel.h>
  #include <linux/io.h>
  #include <linux/list.h>
  #include <linux/mempool.h>
  #include <linux/mm.h>
  #include <linux/elf.h>
  #include <linux/ftrace.h>
  #include <linux/slab.h>
  #include <asm/dwarf.h>
  #include <asm/unwinder.h>
  #include <asm/sections.h>
  #include <asm/unaligned.h>
  #include <asm/stacktrace.h>
  
  /* Reserve enough memory for two stack frames */
  #define DWARF_FRAME_MIN_REQ	2
  /* ... with 4 registers per frame. */
  #define DWARF_REG_MIN_REQ	(DWARF_FRAME_MIN_REQ * 4)
  
  static struct kmem_cache *dwarf_frame_cachep;
  static mempool_t *dwarf_frame_pool;
  
  static struct kmem_cache *dwarf_reg_cachep;
  static mempool_t *dwarf_reg_pool;
  
  static struct rb_root cie_root;
  static DEFINE_SPINLOCK(dwarf_cie_lock);
  
  static struct rb_root fde_root;
  static DEFINE_SPINLOCK(dwarf_fde_lock);
  
  static struct dwarf_cie *cached_cie;
  
  /**
   *	dwarf_frame_alloc_reg - allocate memory for a DWARF register
   *	@frame: the DWARF frame whose list of registers we insert on
   *	@reg_num: the register number
   *
   *	Allocate space for, and initialise, a dwarf reg from
   *	dwarf_reg_pool and insert it onto the (unsorted) linked-list of
   *	dwarf registers for @frame.
   *
   *	Return the initialised DWARF reg.
   */
  static struct dwarf_reg *dwarf_frame_alloc_reg(struct dwarf_frame *frame,
  					       unsigned int reg_num)
  {
  	struct dwarf_reg *reg;
  
  	reg = mempool_alloc(dwarf_reg_pool, GFP_ATOMIC);
  	if (!reg) {
  		printk(KERN_WARNING "Unable to allocate a DWARF register\n");
  		/*
  		 * Let's just bomb hard here, we have no way to
  		 * gracefully recover.
  		 */
  		UNWINDER_BUG();
  	}
  
  	reg->number = reg_num;
  	reg->addr = 0;
  	reg->flags = 0;
  
  	list_add(&reg->link, &frame->reg_list);
  
  	return reg;
  }
  
  static void dwarf_frame_free_regs(struct dwarf_frame *frame)
  {
  	struct dwarf_reg *reg, *n;
  
  	list_for_each_entry_safe(reg, n, &frame->reg_list, link) {
  		list_del(&reg->link);
  		mempool_free(reg, dwarf_reg_pool);
  	}
  }
  
  /**
   *	dwarf_frame_reg - return a DWARF register
   *	@frame: the DWARF frame to search in for @reg_num
   *	@reg_num: the register number to search for
   *
   *	Lookup and return the dwarf reg @reg_num for this frame. Return
   *	NULL if @reg_num is an register invalid number.
   */
  static struct dwarf_reg *dwarf_frame_reg(struct dwarf_frame *frame,
  					 unsigned int reg_num)
  {
  	struct dwarf_reg *reg;
  
  	list_for_each_entry(reg, &frame->reg_list, link) {
  		if (reg->number == reg_num)
  			return reg;
  	}
  
  	return NULL;
  }
  
  /**
   *	dwarf_read_addr - read dwarf data
   *	@src: source address of data
   *	@dst: destination address to store the data to
   *
   *	Read 'n' bytes from @src, where 'n' is the size of an address on
   *	the native machine. We return the number of bytes read, which
   *	should always be 'n'. We also have to be careful when reading
   *	from @src and writing to @dst, because they can be arbitrarily
   *	aligned. Return 'n' - the number of bytes read.
   */
  static inline int dwarf_read_addr(unsigned long *src, unsigned long *dst)
  {
  	u32 val = get_unaligned(src);
  	put_unaligned(val, dst);
  	return sizeof(unsigned long *);
  }
  
  /**
   *	dwarf_read_uleb128 - read unsigned LEB128 data
   *	@addr: the address where the ULEB128 data is stored
   *	@ret: address to store the result
   *
   *	Decode an unsigned LEB128 encoded datum. The algorithm is taken
   *	from Appendix C of the DWARF 3 spec. For information on the
   *	encodings refer to section "7.6 - Variable Length Data". Return
   *	the number of bytes read.
   */
  static inline unsigned long dwarf_read_uleb128(char *addr, unsigned int *ret)
  {
  	unsigned int result;
  	unsigned char byte;
  	int shift, count;
  
  	result = 0;
  	shift = 0;
  	count = 0;
  
  	while (1) {
  		byte = __raw_readb(addr);
  		addr++;
  		count++;
  
  		result |= (byte & 0x7f) << shift;
  		shift += 7;
  
  		if (!(byte & 0x80))
  			break;
  	}
  
  	*ret = result;
  
  	return count;
  }
  
  /**
   *	dwarf_read_leb128 - read signed LEB128 data
   *	@addr: the address of the LEB128 encoded data
   *	@ret: address to store the result
   *
   *	Decode signed LEB128 data. The algorithm is taken from Appendix
   *	C of the DWARF 3 spec. Return the number of bytes read.
   */
  static inline unsigned long dwarf_read_leb128(char *addr, int *ret)
  {
  	unsigned char byte;
  	int result, shift;
  	int num_bits;
  	int count;
  
  	result = 0;
  	shift = 0;
  	count = 0;
  
  	while (1) {
  		byte = __raw_readb(addr);
  		addr++;
  		result |= (byte & 0x7f) << shift;
  		shift += 7;
  		count++;
  
  		if (!(byte & 0x80))
  			break;
  	}
  
  	/* The number of bits in a signed integer. */
  	num_bits = 8 * sizeof(result);
  
  	if ((shift < num_bits) && (byte & 0x40))
  		result |= (-1 << shift);
  
  	*ret = result;
  
  	return count;
  }
  
  /**
   *	dwarf_read_encoded_value - return the decoded value at @addr
   *	@addr: the address of the encoded value
   *	@val: where to write the decoded value
   *	@encoding: the encoding with which we can decode @addr
   *
   *	GCC emits encoded address in the .eh_frame FDE entries. Decode
   *	the value at @addr using @encoding. The decoded value is written
   *	to @val and the number of bytes read is returned.
   */
  static int dwarf_read_encoded_value(char *addr, unsigned long *val,
  				    char encoding)
  {
  	unsigned long decoded_addr = 0;
  	int count = 0;
  
  	switch (encoding & 0x70) {
  	case DW_EH_PE_absptr:
  		break;
  	case DW_EH_PE_pcrel:
  		decoded_addr = (unsigned long)addr;
  		break;
  	default:
  		pr_debug("encoding=0x%x\n", (encoding & 0x70));
  		UNWINDER_BUG();
  	}
  
  	if ((encoding & 0x07) == 0x00)
  		encoding |= DW_EH_PE_udata4;
  
  	switch (encoding & 0x0f) {
  	case DW_EH_PE_sdata4:
  	case DW_EH_PE_udata4:
  		count += 4;
  		decoded_addr += get_unaligned((u32 *)addr);
  		__raw_writel(decoded_addr, val);
  		break;
  	default:
  		pr_debug("encoding=0x%x\n", encoding);
  		UNWINDER_BUG();
  	}
  
  	return count;
  }
  
  /**
   *	dwarf_entry_len - return the length of an FDE or CIE
   *	@addr: the address of the entry
   *	@len: the length of the entry
   *
   *	Read the initial_length field of the entry and store the size of
   *	the entry in @len. We return the number of bytes read. Return a
   *	count of 0 on error.
   */
  static inline int dwarf_entry_len(char *addr, unsigned long *len)
  {
  	u32 initial_len;
  	int count;
  
  	initial_len = get_unaligned((u32 *)addr);
  	count = 4;
  
  	/*
  	 * An initial length field value in the range DW_LEN_EXT_LO -
  	 * DW_LEN_EXT_HI indicates an extension, and should not be
  	 * interpreted as a length. The only extension that we currently
  	 * understand is the use of DWARF64 addresses.
  	 */
  	if (initial_len >= DW_EXT_LO && initial_len <= DW_EXT_HI) {
  		/*
  		 * The 64-bit length field immediately follows the
  		 * compulsory 32-bit length field.
  		 */
  		if (initial_len == DW_EXT_DWARF64) {
  			*len = get_unaligned((u64 *)addr + 4);
  			count = 12;
  		} else {
  			printk(KERN_WARNING "Unknown DWARF extension\n");
  			count = 0;
  		}
  	} else
  		*len = initial_len;
  
  	return count;
  }
  
  /**
   *	dwarf_lookup_cie - locate the cie
   *	@cie_ptr: pointer to help with lookup
   */
  static struct dwarf_cie *dwarf_lookup_cie(unsigned long cie_ptr)
  {
  	struct rb_node **rb_node = &cie_root.rb_node;
  	struct dwarf_cie *cie = NULL;
  	unsigned long flags;
  
  	spin_lock_irqsave(&dwarf_cie_lock, flags);
  
  	/*
  	 * We've cached the last CIE we looked up because chances are
  	 * that the FDE wants this CIE.
  	 */
  	if (cached_cie && cached_cie->cie_pointer == cie_ptr) {
  		cie = cached_cie;
  		goto out;
  	}
  
  	while (*rb_node) {
  		struct dwarf_cie *cie_tmp;
  
  		cie_tmp = rb_entry(*rb_node, struct dwarf_cie, node);
  		BUG_ON(!cie_tmp);
  
  		if (cie_ptr == cie_tmp->cie_pointer) {
  			cie = cie_tmp;
  			cached_cie = cie_tmp;
  			goto out;
  		} else {
  			if (cie_ptr < cie_tmp->cie_pointer)
  				rb_node = &(*rb_node)->rb_left;
  			else
  				rb_node = &(*rb_node)->rb_right;
  		}
  	}
  
  out:
  	spin_unlock_irqrestore(&dwarf_cie_lock, flags);
  	return cie;
  }
  
  /**
   *	dwarf_lookup_fde - locate the FDE that covers pc
   *	@pc: the program counter
   */
  struct dwarf_fde *dwarf_lookup_fde(unsigned long pc)
  {
  	struct rb_node **rb_node = &fde_root.rb_node;
  	struct dwarf_fde *fde = NULL;
  	unsigned long flags;
  
  	spin_lock_irqsave(&dwarf_fde_lock, flags);
  
  	while (*rb_node) {
  		struct dwarf_fde *fde_tmp;
  		unsigned long tmp_start, tmp_end;
  
  		fde_tmp = rb_entry(*rb_node, struct dwarf_fde, node);
  		BUG_ON(!fde_tmp);
  
  		tmp_start = fde_tmp->initial_location;
  		tmp_end = fde_tmp->initial_location + fde_tmp->address_range;
  
  		if (pc < tmp_start) {
  			rb_node = &(*rb_node)->rb_left;
  		} else {
  			if (pc < tmp_end) {
  				fde = fde_tmp;
  				goto out;
  			} else
  				rb_node = &(*rb_node)->rb_right;
  		}
  	}
  
  out:
  	spin_unlock_irqrestore(&dwarf_fde_lock, flags);
  
  	return fde;
  }
  
  /**
   *	dwarf_cfa_execute_insns - execute instructions to calculate a CFA
   *	@insn_start: address of the first instruction
   *	@insn_end: address of the last instruction
   *	@cie: the CIE for this function
   *	@fde: the FDE for this function
   *	@frame: the instructions calculate the CFA for this frame
   *	@pc: the program counter of the address we're interested in
   *
   *	Execute the Call Frame instruction sequence starting at
   *	@insn_start and ending at @insn_end. The instructions describe
   *	how to calculate the Canonical Frame Address of a stackframe.
   *	Store the results in @frame.
   */
  static int dwarf_cfa_execute_insns(unsigned char *insn_start,
  				   unsigned char *insn_end,
  				   struct dwarf_cie *cie,
  				   struct dwarf_fde *fde,
  				   struct dwarf_frame *frame,
  				   unsigned long pc)
  {
  	unsigned char insn;
  	unsigned char *current_insn;
  	unsigned int count, delta, reg, expr_len, offset;
  	struct dwarf_reg *regp;
  
  	current_insn = insn_start;
  
  	while (current_insn < insn_end && frame->pc <= pc) {
  		insn = __raw_readb(current_insn++);
  
  		/*
  		 * Firstly, handle the opcodes that embed their operands
  		 * in the instructions.
  		 */
  		switch (DW_CFA_opcode(insn)) {
  		case DW_CFA_advance_loc:
  			delta = DW_CFA_operand(insn);
  			delta *= cie->code_alignment_factor;
  			frame->pc += delta;
  			continue;
  			/* NOTREACHED */
  		case DW_CFA_offset:
  			reg = DW_CFA_operand(insn);
  			count = dwarf_read_uleb128(current_insn, &offset);
  			current_insn += count;
  			offset *= cie->data_alignment_factor;
  			regp = dwarf_frame_alloc_reg(frame, reg);
  			regp->addr = offset;
  			regp->flags |= DWARF_REG_OFFSET;
  			continue;
  			/* NOTREACHED */
  		case DW_CFA_restore:
  			reg = DW_CFA_operand(insn);
  			continue;
  			/* NOTREACHED */
  		}
  
  		/*
  		 * Secondly, handle the opcodes that don't embed their
  		 * operands in the instruction.
  		 */
  		switch (insn) {
  		case DW_CFA_nop:
  			continue;
  		case DW_CFA_advance_loc1:
  			delta = *current_insn++;
  			frame->pc += delta * cie->code_alignment_factor;
  			break;
  		case DW_CFA_advance_loc2:
  			delta = get_unaligned((u16 *)current_insn);
  			current_insn += 2;
  			frame->pc += delta * cie->code_alignment_factor;
  			break;
  		case DW_CFA_advance_loc4:
  			delta = get_unaligned((u32 *)current_insn);
  			current_insn += 4;
  			frame->pc += delta * cie->code_alignment_factor;
  			break;
  		case DW_CFA_offset_extended:
  			count = dwarf_read_uleb128(current_insn, &reg);
  			current_insn += count;
  			count = dwarf_read_uleb128(current_insn, &offset);
  			current_insn += count;
  			offset *= cie->data_alignment_factor;
  			break;
  		case DW_CFA_restore_extended:
  			count = dwarf_read_uleb128(current_insn, &reg);
  			current_insn += count;
  			break;
  		case DW_CFA_undefined:
  			count = dwarf_read_uleb128(current_insn, &reg);
  			current_insn += count;
  			regp = dwarf_frame_alloc_reg(frame, reg);
  			regp->flags |= DWARF_UNDEFINED;
  			break;
  		case DW_CFA_def_cfa:
  			count = dwarf_read_uleb128(current_insn,
  						   &frame->cfa_register);
  			current_insn += count;
  			count = dwarf_read_uleb128(current_insn,
  						   &frame->cfa_offset);
  			current_insn += count;
  
  			frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
  			break;
  		case DW_CFA_def_cfa_register:
  			count = dwarf_read_uleb128(current_insn,
  						   &frame->cfa_register);
  			current_insn += count;
  			frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
  			break;
  		case DW_CFA_def_cfa_offset:
  			count = dwarf_read_uleb128(current_insn, &offset);
  			current_insn += count;
  			frame->cfa_offset = offset;
  			break;
  		case DW_CFA_def_cfa_expression:
  			count = dwarf_read_uleb128(current_insn, &expr_len);
  			current_insn += count;
  
  			frame->cfa_expr = current_insn;
  			frame->cfa_expr_len = expr_len;
  			current_insn += expr_len;
  
  			frame->flags |= DWARF_FRAME_CFA_REG_EXP;
  			break;
  		case DW_CFA_offset_extended_sf:
  			count = dwarf_read_uleb128(current_insn, &reg);
  			current_insn += count;
  			count = dwarf_read_leb128(current_insn, &offset);
  			current_insn += count;
  			offset *= cie->data_alignment_factor;
  			regp = dwarf_frame_alloc_reg(frame, reg);
  			regp->flags |= DWARF_REG_OFFSET;
  			regp->addr = offset;
  			break;
  		case DW_CFA_val_offset:
  			count = dwarf_read_uleb128(current_insn, &reg);
  			current_insn += count;
  			count = dwarf_read_leb128(current_insn, &offset);
  			offset *= cie->data_alignment_factor;
  			regp = dwarf_frame_alloc_reg(frame, reg);
  			regp->flags |= DWARF_VAL_OFFSET;
  			regp->addr = offset;
  			break;
  		case DW_CFA_GNU_args_size:
  			count = dwarf_read_uleb128(current_insn, &offset);
  			current_insn += count;
  			break;
  		case DW_CFA_GNU_negative_offset_extended:
  			count = dwarf_read_uleb128(current_insn, &reg);
  			current_insn += count;
  			count = dwarf_read_uleb128(current_insn, &offset);
  			offset *= cie->data_alignment_factor;
  
  			regp = dwarf_frame_alloc_reg(frame, reg);
  			regp->flags |= DWARF_REG_OFFSET;
  			regp->addr = -offset;
  			break;
  		default:
  			pr_debug("unhandled DWARF instruction 0x%x\n", insn);
  			UNWINDER_BUG();
  			break;
  		}
  	}
  
  	return 0;
  }
  
  /**
   *	dwarf_free_frame - free the memory allocated for @frame
   *	@frame: the frame to free
   */
  void dwarf_free_frame(struct dwarf_frame *frame)
  {
  	dwarf_frame_free_regs(frame);
  	mempool_free(frame, dwarf_frame_pool);
  }
  
  extern void ret_from_irq(void);
  
  /**
   *	dwarf_unwind_stack - unwind the stack
   *
   *	@pc: address of the function to unwind
   *	@prev: struct dwarf_frame of the previous stackframe on the callstack
   *
   *	Return a struct dwarf_frame representing the most recent frame
   *	on the callstack. Each of the lower (older) stack frames are
   *	linked via the "prev" member.
   */
  struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
  				       struct dwarf_frame *prev)
  {
  	struct dwarf_frame *frame;
  	struct dwarf_cie *cie;
  	struct dwarf_fde *fde;
  	struct dwarf_reg *reg;
  	unsigned long addr;
  
  	/*
  	 * If we're starting at the top of the stack we need get the
  	 * contents of a physical register to get the CFA in order to
  	 * begin the virtual unwinding of the stack.
  	 *
  	 * NOTE: the return address is guaranteed to be setup by the
  	 * time this function makes its first function call.
  	 */
  	if (!pc || !prev)
  		pc = (unsigned long)current_text_addr();
  
  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
  	/*
  	 * If our stack has been patched by the function graph tracer
  	 * then we might see the address of return_to_handler() where we
  	 * expected to find the real return address.
  	 */
  	if (pc == (unsigned long)&return_to_handler) {
  		int index = current->curr_ret_stack;
  
  		/*
  		 * We currently have no way of tracking how many
  		 * return_to_handler()'s we've seen. If there is more
  		 * than one patched return address on our stack,
  		 * complain loudly.
  		 */
  		WARN_ON(index > 0);
  
  		pc = current->ret_stack[index].ret;
  	}
  #endif
  
  	frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC);
  	if (!frame) {
  		printk(KERN_ERR "Unable to allocate a dwarf frame\n");
  		UNWINDER_BUG();
  	}
  
  	INIT_LIST_HEAD(&frame->reg_list);
  	frame->flags = 0;
  	frame->prev = prev;
  	frame->return_addr = 0;
  
  	fde = dwarf_lookup_fde(pc);
  	if (!fde) {
  		/*
  		 * This is our normal exit path. There are two reasons
  		 * why we might exit here,
  		 *
  		 *	a) pc has no asscociated DWARF frame info and so
  		 *	we don't know how to unwind this frame. This is
  		 *	usually the case when we're trying to unwind a
  		 *	frame that was called from some assembly code
  		 *	that has no DWARF info, e.g. syscalls.
  		 *
  		 *	b) the DEBUG info for pc is bogus. There's
  		 *	really no way to distinguish this case from the
  		 *	case above, which sucks because we could print a
  		 *	warning here.
  		 */
  		goto bail;
  	}
  
  	cie = dwarf_lookup_cie(fde->cie_pointer);
  
  	frame->pc = fde->initial_location;
  
  	/* CIE initial instructions */
  	dwarf_cfa_execute_insns(cie->initial_instructions,
  				cie->instructions_end, cie, fde,
  				frame, pc);
  
  	/* FDE instructions */
  	dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
  				fde, frame, pc);
  
  	/* Calculate the CFA */
  	switch (frame->flags) {
  	case DWARF_FRAME_CFA_REG_OFFSET:
  		if (prev) {
  			reg = dwarf_frame_reg(prev, frame->cfa_register);
  			UNWINDER_BUG_ON(!reg);
  			UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
  
  			addr = prev->cfa + reg->addr;
  			frame->cfa = __raw_readl(addr);
  
  		} else {
  			/*
  			 * Again, we're starting from the top of the
  			 * stack. We need to physically read
  			 * the contents of a register in order to get
  			 * the Canonical Frame Address for this
  			 * function.
  			 */
  			frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
  		}
  
  		frame->cfa += frame->cfa_offset;
  		break;
  	default:
  		UNWINDER_BUG();
  	}
  
  	reg = dwarf_frame_reg(frame, DWARF_ARCH_RA_REG);
  
  	/*
  	 * If we haven't seen the return address register or the return
  	 * address column is undefined then we must assume that this is
  	 * the end of the callstack.
  	 */
  	if (!reg || reg->flags == DWARF_UNDEFINED)
  		goto bail;
  
  	UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
  
  	addr = frame->cfa + reg->addr;
  	frame->return_addr = __raw_readl(addr);
  
  	/*
  	 * Ah, the joys of unwinding through interrupts.
  	 *
  	 * Interrupts are tricky - the DWARF info needs to be _really_
  	 * accurate and unfortunately I'm seeing a lot of bogus DWARF
  	 * info. For example, I've seen interrupts occur in epilogues
  	 * just after the frame pointer (r14) had been restored. The
  	 * problem was that the DWARF info claimed that the CFA could be
  	 * reached by using the value of the frame pointer before it was
  	 * restored.
  	 *
  	 * So until the compiler can be trusted to produce reliable
  	 * DWARF info when it really matters, let's stop unwinding once
  	 * we've calculated the function that was interrupted.
  	 */
  	if (prev && prev->pc == (unsigned long)ret_from_irq)
  		frame->return_addr = 0;
  
  	return frame;
  
  bail:
  	dwarf_free_frame(frame);
  	return NULL;
  }
  
  static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
  			   unsigned char *end, struct module *mod)
  {
  	struct rb_node **rb_node = &cie_root.rb_node;
  	struct rb_node *parent = *rb_node;
  	struct dwarf_cie *cie;
  	unsigned long flags;
  	int count;
  
  	cie = kzalloc(sizeof(*cie), GFP_KERNEL);
  	if (!cie)
  		return -ENOMEM;
  
  	cie->length = len;
  
  	/*
  	 * Record the offset into the .eh_frame section
  	 * for this CIE. It allows this CIE to be
  	 * quickly and easily looked up from the
  	 * corresponding FDE.
  	 */
  	cie->cie_pointer = (unsigned long)entry;
  
  	cie->version = *(char *)p++;
  	UNWINDER_BUG_ON(cie->version != 1);
  
  	cie->augmentation = p;
  	p += strlen(cie->augmentation) + 1;
  
  	count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
  	p += count;
  
  	count = dwarf_read_leb128(p, &cie->data_alignment_factor);
  	p += count;
  
  	/*
  	 * Which column in the rule table contains the
  	 * return address?
  	 */
  	if (cie->version == 1) {
  		cie->return_address_reg = __raw_readb(p);
  		p++;
  	} else {
  		count = dwarf_read_uleb128(p, &cie->return_address_reg);
  		p += count;
  	}
  
  	if (cie->augmentation[0] == 'z') {
  		unsigned int length, count;
  		cie->flags |= DWARF_CIE_Z_AUGMENTATION;
  
  		count = dwarf_read_uleb128(p, &length);
  		p += count;
  
  		UNWINDER_BUG_ON((unsigned char *)p > end);
  
  		cie->initial_instructions = p + length;
  		cie->augmentation++;
  	}
  
  	while (*cie->augmentation) {
  		/*
  		 * "L" indicates a byte showing how the
  		 * LSDA pointer is encoded. Skip it.
  		 */
  		if (*cie->augmentation == 'L') {
  			p++;
  			cie->augmentation++;
  		} else if (*cie->augmentation == 'R') {
  			/*
  			 * "R" indicates a byte showing
  			 * how FDE addresses are
  			 * encoded.
  			 */
  			cie->encoding = *(char *)p++;
  			cie->augmentation++;
  		} else if (*cie->augmentation == 'P') {
  			/*
  			 * "R" indicates a personality
  			 * routine in the CIE
  			 * augmentation.
  			 */
  			UNWINDER_BUG();
  		} else if (*cie->augmentation == 'S') {
  			UNWINDER_BUG();
  		} else {
  			/*
  			 * Unknown augmentation. Assume
  			 * 'z' augmentation.
  			 */
  			p = cie->initial_instructions;
  			UNWINDER_BUG_ON(!p);
  			break;
  		}
  	}
  
  	cie->initial_instructions = p;
  	cie->instructions_end = end;
  
  	/* Add to list */
  	spin_lock_irqsave(&dwarf_cie_lock, flags);
  
  	while (*rb_node) {
  		struct dwarf_cie *cie_tmp;
  
  		cie_tmp = rb_entry(*rb_node, struct dwarf_cie, node);
  
  		parent = *rb_node;
  
  		if (cie->cie_pointer < cie_tmp->cie_pointer)
  			rb_node = &parent->rb_left;
  		else if (cie->cie_pointer >= cie_tmp->cie_pointer)
  			rb_node = &parent->rb_right;
  		else
  			WARN_ON(1);
  	}
  
  	rb_link_node(&cie->node, parent, rb_node);
  	rb_insert_color(&cie->node, &cie_root);
  
  	if (mod != NULL)
  		list_add_tail(&cie->link, &mod->arch.cie_list);
  
  	spin_unlock_irqrestore(&dwarf_cie_lock, flags);
  
  	return 0;
  }
  
  static int dwarf_parse_fde(void *entry, u32 entry_type,
  			   void *start, unsigned long len,
  			   unsigned char *end, struct module *mod)
  {
  	struct rb_node **rb_node = &fde_root.rb_node;
  	struct rb_node *parent = *rb_node;
  	struct dwarf_fde *fde;
  	struct dwarf_cie *cie;
  	unsigned long flags;
  	int count;
  	void *p = start;
  
  	fde = kzalloc(sizeof(*fde), GFP_KERNEL);
  	if (!fde)
  		return -ENOMEM;
  
  	fde->length = len;
  
  	/*
  	 * In a .eh_frame section the CIE pointer is the
  	 * delta between the address within the FDE
  	 */
  	fde->cie_pointer = (unsigned long)(p - entry_type - 4);
  
  	cie = dwarf_lookup_cie(fde->cie_pointer);
  	fde->cie = cie;
  
  	if (cie->encoding)
  		count = dwarf_read_encoded_value(p, &fde->initial_location,
  						 cie->encoding);
  	else
  		count = dwarf_read_addr(p, &fde->initial_location);
  
  	p += count;
  
  	if (cie->encoding)
  		count = dwarf_read_encoded_value(p, &fde->address_range,
  						 cie->encoding & 0x0f);
  	else
  		count = dwarf_read_addr(p, &fde->address_range);
  
  	p += count;
  
  	if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
  		unsigned int length;
  		count = dwarf_read_uleb128(p, &length);
  		p += count + length;
  	}
  
  	/* Call frame instructions. */
  	fde->instructions = p;
  	fde->end = end;
  
  	/* Add to list. */
  	spin_lock_irqsave(&dwarf_fde_lock, flags);
  
  	while (*rb_node) {
  		struct dwarf_fde *fde_tmp;
  		unsigned long tmp_start, tmp_end;
  		unsigned long start, end;
  
  		fde_tmp = rb_entry(*rb_node, struct dwarf_fde, node);
  
  		start = fde->initial_location;
  		end = fde->initial_location + fde->address_range;
  
  		tmp_start = fde_tmp->initial_location;
  		tmp_end = fde_tmp->initial_location + fde_tmp->address_range;
  
  		parent = *rb_node;
  
  		if (start < tmp_start)
  			rb_node = &parent->rb_left;
  		else if (start >= tmp_end)
  			rb_node = &parent->rb_right;
  		else
  			WARN_ON(1);
  	}
  
  	rb_link_node(&fde->node, parent, rb_node);
  	rb_insert_color(&fde->node, &fde_root);
  
  	if (mod != NULL)
  		list_add_tail(&fde->link, &mod->arch.fde_list);
  
  	spin_unlock_irqrestore(&dwarf_fde_lock, flags);
  
  	return 0;
  }
  
  static void dwarf_unwinder_dump(struct task_struct *task,
  				struct pt_regs *regs,
  				unsigned long *sp,
  				const struct stacktrace_ops *ops,
  				void *data)
  {
  	struct dwarf_frame *frame, *_frame;
  	unsigned long return_addr;
  
  	_frame = NULL;
  	return_addr = 0;
  
  	while (1) {
  		frame = dwarf_unwind_stack(return_addr, _frame);
  
  		if (_frame)
  			dwarf_free_frame(_frame);
  
  		_frame = frame;
  
  		if (!frame || !frame->return_addr)
  			break;
  
  		return_addr = frame->return_addr;
  		ops->address(data, return_addr, 1);
  	}
  
  	if (frame)
  		dwarf_free_frame(frame);
  }
  
  static struct unwinder dwarf_unwinder = {
  	.name = "dwarf-unwinder",
  	.dump = dwarf_unwinder_dump,
  	.rating = 150,
  };
  
  static void dwarf_unwinder_cleanup(void)
  {
  	struct rb_node **fde_rb_node = &fde_root.rb_node;
  	struct rb_node **cie_rb_node = &cie_root.rb_node;
  
  	/*
  	 * Deallocate all the memory allocated for the DWARF unwinder.
  	 * Traverse all the FDE/CIE lists and remove and free all the
  	 * memory associated with those data structures.
  	 */
  	while (*fde_rb_node) {
  		struct dwarf_fde *fde;
  
  		fde = rb_entry(*fde_rb_node, struct dwarf_fde, node);
  		rb_erase(*fde_rb_node, &fde_root);
  		kfree(fde);
  	}
  
  	while (*cie_rb_node) {
  		struct dwarf_cie *cie;
  
  		cie = rb_entry(*cie_rb_node, struct dwarf_cie, node);
  		rb_erase(*cie_rb_node, &cie_root);
  		kfree(cie);
  	}
  
  	kmem_cache_destroy(dwarf_reg_cachep);
  	kmem_cache_destroy(dwarf_frame_cachep);
  }
  
  /**
   *	dwarf_parse_section - parse DWARF section
   *	@eh_frame_start: start address of the .eh_frame section
   *	@eh_frame_end: end address of the .eh_frame section
   *	@mod: the kernel module containing the .eh_frame section
   *
   *	Parse the information in a .eh_frame section.
   */
  static int dwarf_parse_section(char *eh_frame_start, char *eh_frame_end,
  			       struct module *mod)
  {
  	u32 entry_type;
  	void *p, *entry;
  	int count, err = 0;
  	unsigned long len = 0;
  	unsigned int c_entries, f_entries;
  	unsigned char *end;
  
  	c_entries = 0;
  	f_entries = 0;
  	entry = eh_frame_start;
  
  	while ((char *)entry < eh_frame_end) {
  		p = entry;
  
  		count = dwarf_entry_len(p, &len);
  		if (count == 0) {
  			/*
  			 * We read a bogus length field value. There is
  			 * nothing we can do here apart from disabling
  			 * the DWARF unwinder. We can't even skip this
  			 * entry and move to the next one because 'len'
  			 * tells us where our next entry is.
  			 */
  			err = -EINVAL;
  			goto out;
  		} else
  			p += count;
  
  		/* initial length does not include itself */
  		end = p + len;
  
  		entry_type = get_unaligned((u32 *)p);
  		p += 4;
  
  		if (entry_type == DW_EH_FRAME_CIE) {
  			err = dwarf_parse_cie(entry, p, len, end, mod);
  			if (err < 0)
  				goto out;
  			else
  				c_entries++;
  		} else {
  			err = dwarf_parse_fde(entry, entry_type, p, len,
  					      end, mod);
  			if (err < 0)
  				goto out;
  			else
  				f_entries++;
  		}
  
  		entry = (char *)entry + len + 4;
  	}
  
  	printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
  	       c_entries, f_entries);
  
  	return 0;
  
  out:
  	return err;
  }
  
  #ifdef CONFIG_MODULES
  int module_dwarf_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
  			  struct module *me)
  {
  	unsigned int i, err;
  	unsigned long start, end;
  	char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
  
  	start = end = 0;
  
  	for (i = 1; i < hdr->e_shnum; i++) {
  		/* Alloc bit cleared means "ignore it." */
  		if ((sechdrs[i].sh_flags & SHF_ALLOC)
  		    && !strcmp(secstrings+sechdrs[i].sh_name, ".eh_frame")) {
  			start = sechdrs[i].sh_addr;
  			end = start + sechdrs[i].sh_size;
  			break;
  		}
  	}
  
  	/* Did we find the .eh_frame section? */
  	if (i != hdr->e_shnum) {
  		INIT_LIST_HEAD(&me->arch.cie_list);
  		INIT_LIST_HEAD(&me->arch.fde_list);
  		err = dwarf_parse_section((char *)start, (char *)end, me);
  		if (err) {
  			printk(KERN_WARNING "%s: failed to parse DWARF info\n",
  			       me->name);
  			return err;
  		}
  	}
  
  	return 0;
  }
  
  /**
   *	module_dwarf_cleanup - remove FDE/CIEs associated with @mod
   *	@mod: the module that is being unloaded
   *
   *	Remove any FDEs and CIEs from the global lists that came from
   *	@mod's .eh_frame section because @mod is being unloaded.
   */
  void module_dwarf_cleanup(struct module *mod)
  {
  	struct dwarf_fde *fde, *ftmp;
  	struct dwarf_cie *cie, *ctmp;
  	unsigned long flags;
  
  	spin_lock_irqsave(&dwarf_cie_lock, flags);
  
  	list_for_each_entry_safe(cie, ctmp, &mod->arch.cie_list, link) {
  		list_del(&cie->link);
  		rb_erase(&cie->node, &cie_root);
  		kfree(cie);
  	}
  
  	spin_unlock_irqrestore(&dwarf_cie_lock, flags);
  
  	spin_lock_irqsave(&dwarf_fde_lock, flags);
  
  	list_for_each_entry_safe(fde, ftmp, &mod->arch.fde_list, link) {
  		list_del(&fde->link);
  		rb_erase(&fde->node, &fde_root);
  		kfree(fde);
  	}
  
  	spin_unlock_irqrestore(&dwarf_fde_lock, flags);
  }
  #endif /* CONFIG_MODULES */
  
  /**
   *	dwarf_unwinder_init - initialise the dwarf unwinder
   *
   *	Build the data structures describing the .dwarf_frame section to
   *	make it easier to lookup CIE and FDE entries. Because the
   *	.eh_frame section is packed as tightly as possible it is not
   *	easy to lookup the FDE for a given PC, so we build a list of FDE
   *	and CIE entries that make it easier.
   */
  static int __init dwarf_unwinder_init(void)
  {
  	int err;
  
  	dwarf_frame_cachep = kmem_cache_create("dwarf_frames",
  			sizeof(struct dwarf_frame), 0,
  			SLAB_PANIC | SLAB_HWCACHE_ALIGN | SLAB_NOTRACK, NULL);
  
  	dwarf_reg_cachep = kmem_cache_create("dwarf_regs",
  			sizeof(struct dwarf_reg), 0,
  			SLAB_PANIC | SLAB_HWCACHE_ALIGN | SLAB_NOTRACK, NULL);
  
  	dwarf_frame_pool = mempool_create(DWARF_FRAME_MIN_REQ,
  					  mempool_alloc_slab,
  					  mempool_free_slab,
  					  dwarf_frame_cachep);
  
  	dwarf_reg_pool = mempool_create(DWARF_REG_MIN_REQ,
  					 mempool_alloc_slab,
  					 mempool_free_slab,
  					 dwarf_reg_cachep);
  
  	err = dwarf_parse_section(__start_eh_frame, __stop_eh_frame, NULL);
  	if (err)
  		goto out;
  
  	err = unwinder_register(&dwarf_unwinder);
  	if (err)
  		goto out;
  
  	return 0;
  
  out:
  	printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
  	dwarf_unwinder_cleanup();
  	return -EINVAL;
  }
  early_initcall(dwarf_unwinder_init);
  