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