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/*
* 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
{
/// 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 (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,
/// Absolute pointer value
DW_EH_PE_absptr = 0x00,
/// 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 (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 |= ((int64_t)-1) << bits;
}
return (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);
uint64_t v;
switch (type)
{
// Read fixed-length types
#define READ(dwarf, type) \
case dwarf:\
v = (uint64_t)(*(type*)(*data));\
*data += sizeof(type);\
break;
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:
v = read_sleb128(data);
break;
case DW_EH_PE_uleb128:
v = read_uleb128(data);
break;
default: abort();
}
return v;
}
/**
* 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 += (uint64_t)start;
break;
case DW_EH_PE_textrel:
v += (uint64_t)_Unwind_GetTextRelBase(c);
break;
case DW_EH_PE_datarel:
v += (uint64_t)_Unwind_GetDataRelBase(c);
break;
case DW_EH_PE_funcrel:
v += (uint64_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 = (uint64_t)(uintptr_t)*(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 = (dw_eh_ptr_t)(uintptr_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 = (uint64_t)(uintptr_t)lsda.region_start;
read_value_with_encoding(context, &data, &v);
lsda.landing_pads = (dw_eh_ptr_t)(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 __arm__
lsda.type_table_encoding = (DW_EH_PE_pcrel | DW_EH_PE_indirect);
#endif
lsda.callsite_encoding = (enum dwarf_data_encoding)(*(data++));
// Action table is immediately after the call site table
lsda.action_table = data;
uintptr_t callsite_size = (uintptr_t)read_uleb128(&data);
lsda.action_table = data + callsite_size;
// Call site table is immediately after the header
lsda.call_site_table = (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 = (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) \
(((uint64_t)a << 56) +\
((uint64_t)b << 48) +\
((uint64_t)c << 40) +\
((uint64_t)d << 32) +\
((uint64_t)e << 24) +\
((uint64_t)f << 16) +\
((uint64_t)g << 8) +\
((uint64_t)h))
#define GENERIC_EXCEPTION_CLASS(e,f,g,h) \
((uint32_t)e << 24) +\
((uint32_t)f << 16) +\
((uint32_t)g << 8) +\
((uint32_t)h)
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