text: /* 
   * Copyright 2010-2011 PathScale, Inc. All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are met:
   *
   * 1. Redistributions of source code must retain the above copyright notice,
   *    this list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form must reproduce the above copyright notice,
   *    this list of conditions and the following disclaimer in the documentation
   *    and/or other materials provided with the distribution.
   * 
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS
   * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
   * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
   * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
   * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
   * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  /**
   * dwarf_eh.h - Defines some helper functions for parsing DWARF exception
   * handling tables.
   *
   * This file contains various helper functions that are independent of the
   * language-specific code.  It can be used in any personality function for the
   * Itanium ABI.
   */
  #include <assert.h>
  
  // TODO: Factor out Itanium / ARM differences.  We probably want an itanium.h
  // and arm.h that can be included by this file depending on the target ABI.
  
  // _GNU_SOURCE must be defined for unwind.h to expose some of the functions
  // that we want.  If it isn't, then we define it and undefine it to make sure
  // that it doesn't impact the rest of the program.
  #ifndef _GNU_SOURCE
  #	define _GNU_SOURCE 1
  #	include "unwind.h"
  #	undef _GNU_SOURCE
  #else
  #	include "unwind.h"
  #endif
  
  #include <stdint.h>
  
  /// Type used for pointers into DWARF data
  typedef unsigned char *dw_eh_ptr_t;
  
  // Flag indicating a signed quantity
  #define DW_EH_PE_signed 0x08
  /// DWARF data encoding types.  
  enum dwarf_data_encoding
  {
  	/// Absolute pointer value
  	DW_EH_PE_absptr   = 0x00,
  	/// Unsigned, little-endian, base 128-encoded (variable length).
  	DW_EH_PE_uleb128 = 0x01,
  	/// Unsigned 16-bit integer.
  	DW_EH_PE_udata2  = 0x02,
  	/// Unsigned 32-bit integer.
  	DW_EH_PE_udata4  = 0x03,
  	/// Unsigned 64-bit integer.
  	DW_EH_PE_udata8  = 0x04,
  	/// Signed, little-endian, base 128-encoded (variable length)
  	DW_EH_PE_sleb128 = DW_EH_PE_uleb128 | DW_EH_PE_signed,
  	/// Signed 16-bit integer.
  	DW_EH_PE_sdata2  = DW_EH_PE_udata2 | DW_EH_PE_signed,
  	/// Signed 32-bit integer.
  	DW_EH_PE_sdata4  = DW_EH_PE_udata4 | DW_EH_PE_signed,
  	/// Signed 32-bit integer.
  	DW_EH_PE_sdata8  = DW_EH_PE_udata8 | DW_EH_PE_signed
  };
  
  /**
   * Returns the encoding for a DWARF EH table entry.  The encoding is stored in
   * the low four of an octet.  The high four bits store the addressing mode.
   */
  static inline enum dwarf_data_encoding get_encoding(unsigned char x)
  {
  	return static_cast<enum dwarf_data_encoding>(x & 0xf);
  }
  
  /**
   * DWARF addressing mode constants.  When reading a pointer value from a DWARF
   * exception table, you must know how it is stored and what the addressing mode
   * is.  The low four bits tell you the encoding, allowing you to decode a
   * number.  The high four bits tell you the addressing mode, allowing you to
   * turn that number into an address in memory.
   */
  enum dwarf_data_relative
  {
  	/// Value is omitted
  	DW_EH_PE_omit     = 0xff,
  	/// Value relative to program counter
  	DW_EH_PE_pcrel    = 0x10,
  	/// Value relative to the text segment
  	DW_EH_PE_textrel  = 0x20,
  	/// Value relative to the data segment
  	DW_EH_PE_datarel  = 0x30,
  	/// Value relative to the start of the function
  	DW_EH_PE_funcrel  = 0x40,
  	/// Aligned pointer (Not supported yet - are they actually used?)
  	DW_EH_PE_aligned  = 0x50,
  	/// Pointer points to address of real value
  	DW_EH_PE_indirect = 0x80
  };
  /**
   * Returns the addressing mode component of this encoding.
   */
  static inline enum dwarf_data_relative get_base(unsigned char x)
  {
  	return static_cast<enum dwarf_data_relative>(x & 0x70);
  }
  /**
   * Returns whether an encoding represents an indirect address.
   */
  static int is_indirect(unsigned char x)
  {
  	return ((x & DW_EH_PE_indirect) == DW_EH_PE_indirect);
  }
  
  /**
   * Returns the size of a fixed-size encoding.  This function will abort if
   * called with a value that is not a fixed-size encoding.
   */
  static inline int dwarf_size_of_fixed_size_field(unsigned char type)
  {
  	switch (get_encoding(type))
  	{
  		default: abort();
  		case DW_EH_PE_sdata2: 
  		case DW_EH_PE_udata2: return 2;
  		case DW_EH_PE_sdata4:
  		case DW_EH_PE_udata4: return 4;
  		case DW_EH_PE_sdata8:
  		case DW_EH_PE_udata8: return 8;
  		case DW_EH_PE_absptr: return sizeof(void*);
  	}
  }
  
  /** 
   * Read an unsigned, little-endian, base-128, DWARF value.  Updates *data to
   * point to the end of the value.  Stores the number of bits read in the value
   * pointed to by b, allowing you to determine the value of the highest bit, and
   * therefore the sign of a signed value.
   *
   * This function is not intended to be called directly.  Use read_sleb128() or
   * read_uleb128() for reading signed and unsigned versions, respectively.
   */
  static uint64_t read_leb128(dw_eh_ptr_t *data, int *b)
  {
  	uint64_t uleb = 0;
  	unsigned int bit = 0;
  	unsigned char digit = 0;
  	// We have to read at least one octet, and keep reading until we get to one
  	// with the high bit unset
  	do
  	{
  		// This check is a bit too strict - we should also check the highest
  		// bit of the digit.
  		assert(bit < sizeof(uint64_t) * 8);
  		// Get the base 128 digit 
  		digit = (**data) & 0x7f;
  		// Add it to the current value
  		uleb += digit << bit;
  		// Increase the shift value
  		bit += 7;
  		// Proceed to the next octet
  		(*data)++;
  		// Terminate when we reach a value that does not have the high bit set
  		// (i.e. which was not modified when we mask it with 0x7f)
  	} while ((*(*data - 1)) != digit);
  	*b = bit;
  
  	return uleb;
  }
  
  /**
   * Reads an unsigned little-endian base-128 value starting at the address
   * pointed to by *data.  Updates *data to point to the next byte after the end
   * of the variable-length value.
   */
  static int64_t read_uleb128(dw_eh_ptr_t *data)
  {
  	int b;
  	return read_leb128(data, &b);
  }
  
  /**
   * Reads a signed little-endian base-128 value starting at the address pointed
   * to by *data.  Updates *data to point to the next byte after the end of the
   * variable-length value.
   */
  static int64_t read_sleb128(dw_eh_ptr_t *data)
  {
  	int bits;
  	// Read as if it's signed
  	uint64_t uleb = read_leb128(data, &bits);
  	// If the most significant bit read is 1, then we need to sign extend it
  	if ((uleb >> (bits-1)) == 1)
  	{
  		// Sign extend by setting all bits in front of it to 1
  		uleb |= static_cast<int64_t>(-1) << bits;
  	}
  	return static_cast<int64_t>(uleb);
  }
  /**
   * Reads a value using the specified encoding from the address pointed to by
   * *data.  Updates the value of *data to point to the next byte after the end
   * of the data.
   */
  static uint64_t read_value(char encoding, dw_eh_ptr_t *data)
  {
  	enum dwarf_data_encoding type = get_encoding(encoding);
  	switch (type)
  	{
  		// Read fixed-length types
  #define READ(dwarf, type) \
  		case dwarf:\
  		{\
  			type t;\
  			memcpy(&t, *data, sizeof t);\
  			*data += sizeof t;\
  			return static_cast<uint64_t>(t);\
  		}
  		READ(DW_EH_PE_udata2, uint16_t)
  		READ(DW_EH_PE_udata4, uint32_t)
  		READ(DW_EH_PE_udata8, uint64_t)
  		READ(DW_EH_PE_sdata2, int16_t)
  		READ(DW_EH_PE_sdata4, int32_t)
  		READ(DW_EH_PE_sdata8, int64_t)
  		READ(DW_EH_PE_absptr, intptr_t)
  #undef READ
  		// Read variable-length types
  		case DW_EH_PE_sleb128:
  			return read_sleb128(data);
  		case DW_EH_PE_uleb128:
  			return read_uleb128(data);
  		default: abort();
  	}
  }
  
  /**
   * Resolves an indirect value.  This expects an unwind context, an encoding, a
   * decoded value, and the start of the region as arguments.  The returned value
   * is a pointer to the address identified by the encoded value.
   *
   * If the encoding does not specify an indirect value, then this returns v.
   */
  static uint64_t resolve_indirect_value(_Unwind_Context *c,
                                         unsigned char encoding,
                                         int64_t v,
                                         dw_eh_ptr_t start)
  {
  	switch (get_base(encoding))
  	{
  		case DW_EH_PE_pcrel:
  			v += reinterpret_cast<uint64_t>(start);
  			break;
  		case DW_EH_PE_textrel:
  			v += static_cast<uint64_t>(static_cast<uintptr_t>(_Unwind_GetTextRelBase(c)));
  			break;
  		case DW_EH_PE_datarel:
  			v += static_cast<uint64_t>(static_cast<uintptr_t>(_Unwind_GetDataRelBase(c)));
  			break;
  		case DW_EH_PE_funcrel:
  			v += static_cast<uint64_t>(static_cast<uintptr_t>(_Unwind_GetRegionStart(c)));
  		default:
  			break;
  	}
  	// If this is an indirect value, then it is really the address of the real
  	// value
  	// TODO: Check whether this should really always be a pointer - it seems to
  	// be a GCC extensions, so not properly documented...
  	if (is_indirect(encoding))
  	{
  		v = static_cast<uint64_t>(reinterpret_cast<uintptr_t>(*reinterpret_cast<void**>(v)));
  	}
  	return v;
  }
  
  
  /**
   * Reads an encoding and a value, updating *data to point to the next byte.  
   */
  static inline void read_value_with_encoding(_Unwind_Context *context,
                                              dw_eh_ptr_t *data,
                                              uint64_t *out)
  {
  	dw_eh_ptr_t start = *data;
  	unsigned char encoding = *((*data)++);
  	// If this value is omitted, skip it and don't touch the output value
  	if (encoding == DW_EH_PE_omit) { return; }
  
  	*out = read_value(encoding, data);
  	*out = resolve_indirect_value(context, encoding, *out, start);
  }
  
  /**
   * Structure storing a decoded language-specific data area.  Use parse_lsda()
   * to generate an instance of this structure from the address returned by the
   * generic unwind library.  
   *
   * You should not need to inspect the fields of this structure directly if you
   * are just using this header.  The structure stores the locations of the
   * various tables used for unwinding exceptions and is used by the functions
   * for reading values from these tables.
   */
  struct dwarf_eh_lsda
  {
  	/// The start of the region.  This is a cache of the value returned by
  	/// _Unwind_GetRegionStart().
  	dw_eh_ptr_t region_start;
  	/// The start of the landing pads table.
  	dw_eh_ptr_t landing_pads;
  	/// The start of the type table.
  	dw_eh_ptr_t type_table;
  	/// The encoding used for entries in the type tables.
  	unsigned char type_table_encoding;
  	/// The location of the call-site table.
  	dw_eh_ptr_t call_site_table;
  	/// The location of the action table.
  	dw_eh_ptr_t action_table;
  	/// The encoding used for entries in the call-site table.
  	unsigned char callsite_encoding;
  };
  
  /**
   * Parse the header on the language-specific data area and return a structure
   * containing the addresses and encodings of the various tables.
   */
  static inline struct dwarf_eh_lsda parse_lsda(_Unwind_Context *context,
                                                unsigned char *data)
  {
  	struct dwarf_eh_lsda lsda;
  
  	lsda.region_start = reinterpret_cast<dw_eh_ptr_t>(_Unwind_GetRegionStart(context));
  
  	// If the landing pads are relative to anything other than the start of
  	// this region, find out where.  This is @LPStart in the spec, although the
  	// encoding that GCC uses does not quite match the spec.
  	uint64_t v = static_cast<uint64_t>(reinterpret_cast<uintptr_t>(lsda.region_start));
  	read_value_with_encoding(context, &data, &v);
  	lsda.landing_pads = reinterpret_cast<dw_eh_ptr_t>(static_cast<uintptr_t>(v));
  
  	// If there is a type table, find out where it is.  This is @TTBase in the
  	// spec.  Note: we find whether there is a type table pointer by checking
  	// whether the leading byte is DW_EH_PE_omit (0xff), which is not what the
  	// spec says, but does seem to be how G++ indicates this.
  	lsda.type_table = 0;
  	lsda.type_table_encoding = *data++;
  	if (lsda.type_table_encoding != DW_EH_PE_omit)
  	{
  		v = read_uleb128(&data);
  		dw_eh_ptr_t type_table = data;
  		type_table += v;
  		lsda.type_table = type_table;
  		//lsda.type_table = (uintptr_t*)(data + v);
  	}
  #if defined(__arm__) && !defined(__ARM_DWARF_EH__)
  	lsda.type_table_encoding = (DW_EH_PE_pcrel | DW_EH_PE_indirect);
  #endif
  
  	lsda.callsite_encoding = static_cast<enum dwarf_data_encoding>(*(data++));
  
  	// Action table is immediately after the call site table
  	lsda.action_table = data;
  	uintptr_t callsite_size = static_cast<uintptr_t>(read_uleb128(&data));
  	lsda.action_table = data + callsite_size;
  	// Call site table is immediately after the header
  	lsda.call_site_table = static_cast<dw_eh_ptr_t>(data);
  
  
  	return lsda;
  }
  
  /**
   * Structure representing an action to be performed while unwinding.  This
   * contains the address that should be unwound to and the action record that
   * provoked this action.
   */
  struct dwarf_eh_action
  {
  	/** 
  	 * The address that this action directs should be the new program counter
  	 * value after unwinding.
  	 */
  	dw_eh_ptr_t landing_pad;
  	/// The address of the action record.
  	dw_eh_ptr_t action_record;
  };
  
  /**
   * Look up the landing pad that corresponds to the current invoke.
   * Returns true if record exists.  The context is provided by the generic
   * unwind library and the lsda should be the result of a call to parse_lsda().
   *
   * The action record is returned via the result parameter.  
   */
  static bool dwarf_eh_find_callsite(struct _Unwind_Context *context,
                                     struct dwarf_eh_lsda *lsda,
                                     struct dwarf_eh_action *result)
  {
  	result->action_record = 0;
  	result->landing_pad = 0;
  	// The current instruction pointer offset within the region
  	uint64_t ip = _Unwind_GetIP(context) - _Unwind_GetRegionStart(context);
  	unsigned char *callsite_table = static_cast<unsigned char*>(lsda->call_site_table);
  
  	while (callsite_table <= lsda->action_table)
  	{
  		// Once again, the layout deviates from the spec.
  		uint64_t call_site_start, call_site_size, landing_pad, action;
  		call_site_start = read_value(lsda->callsite_encoding, &callsite_table);
  		call_site_size = read_value(lsda->callsite_encoding, &callsite_table);
  
  		// Call site entries are sorted, so if we find a call site that's after
  		// the current instruction pointer then there is no action associated
  		// with this call and we should unwind straight through this frame
  		// without doing anything.
  		if (call_site_start > ip) { break; }
  
  		// Read the address of the landing pad and the action from the call
  		// site table.
  		landing_pad = read_value(lsda->callsite_encoding, &callsite_table);
  		action = read_uleb128(&callsite_table);
  
  		// We should not include the call_site_start (beginning of the region)
  		// address in the ip range. For each call site:
  		//
  		// address1: call proc
  		// address2: next instruction
  		//
  		// The call stack contains address2 and not address1, address1 can be
  		// at the end of another EH region.
  		if (call_site_start < ip && ip <= call_site_start + call_site_size)
  		{
  			if (action)
  			{
  				// Action records are 1-biased so both no-record and zeroth
  				// record can be stored.
  				result->action_record = lsda->action_table + action - 1;
  			}
  			// No landing pad means keep unwinding.
  			if (landing_pad)
  			{
  				// Landing pad is the offset from the value in the header
  				result->landing_pad = lsda->landing_pads + landing_pad;
  			}
  			return true;
  		}
  	}
  	return false;
  }
  
  /// Defines an exception class from 8 bytes (endian independent)
  #define EXCEPTION_CLASS(a,b,c,d,e,f,g,h) \
  	((static_cast<uint64_t>(a) << 56) +\
  	 (static_cast<uint64_t>(b) << 48) +\
  	 (static_cast<uint64_t>(c) << 40) +\
  	 (static_cast<uint64_t>(d) << 32) +\
  	 (static_cast<uint64_t>(e) << 24) +\
  	 (static_cast<uint64_t>(f) << 16) +\
  	 (static_cast<uint64_t>(g) << 8) +\
  	 (static_cast<uint64_t>(h)))
  
  #define GENERIC_EXCEPTION_CLASS(e,f,g,h) \
  	 (static_cast<uint32_t>(e) << 24) +\
  	 (static_cast<uint32_t>(f) << 16) +\
  	 (static_cast<uint32_t>(g) << 8) +\
  	 (static_cast<uint32_t>(h))
  