246 lines
7.8 KiB
C++
246 lines
7.8 KiB
C++
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// Copyright (c) 2010 Google 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
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#include <assert.h>
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#include <stdlib.h>
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#include "common/dwarf/bytereader-inl.h"
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#include "common/dwarf/bytereader.h"
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namespace dwarf2reader {
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ByteReader::ByteReader(enum Endianness endian)
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:offset_reader_(NULL), address_reader_(NULL), endian_(endian),
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address_size_(0), offset_size_(0),
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have_section_base_(), have_text_base_(), have_data_base_(),
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have_function_base_() { }
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ByteReader::~ByteReader() { }
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void ByteReader::SetOffsetSize(uint8 size) {
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offset_size_ = size;
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assert(size == 4 || size == 8);
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if (size == 4) {
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this->offset_reader_ = &ByteReader::ReadFourBytes;
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} else {
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this->offset_reader_ = &ByteReader::ReadEightBytes;
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}
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}
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void ByteReader::SetAddressSize(uint8 size) {
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address_size_ = size;
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assert(size == 4 || size == 8);
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if (size == 4) {
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this->address_reader_ = &ByteReader::ReadFourBytes;
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} else {
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this->address_reader_ = &ByteReader::ReadEightBytes;
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}
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}
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uint64 ByteReader::ReadInitialLength(const char* start, size_t* len) {
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const uint64 initial_length = ReadFourBytes(start);
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start += 4;
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// In DWARF2/3, if the initial length is all 1 bits, then the offset
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// size is 8 and we need to read the next 8 bytes for the real length.
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if (initial_length == 0xffffffff) {
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SetOffsetSize(8);
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*len = 12;
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return ReadOffset(start);
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} else {
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SetOffsetSize(4);
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*len = 4;
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}
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return initial_length;
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}
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bool ByteReader::ValidEncoding(DwarfPointerEncoding encoding) const {
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if (encoding == DW_EH_PE_omit) return true;
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if (encoding == DW_EH_PE_aligned) return true;
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if ((encoding & 0x7) > DW_EH_PE_udata8)
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return false;
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if ((encoding & 0x70) > DW_EH_PE_funcrel)
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return false;
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return true;
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}
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bool ByteReader::UsableEncoding(DwarfPointerEncoding encoding) const {
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switch (encoding & 0x70) {
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case DW_EH_PE_absptr: return true;
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case DW_EH_PE_pcrel: return have_section_base_;
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case DW_EH_PE_textrel: return have_text_base_;
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case DW_EH_PE_datarel: return have_data_base_;
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case DW_EH_PE_funcrel: return have_function_base_;
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default: return false;
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}
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}
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uint64 ByteReader::ReadEncodedPointer(const char *buffer,
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DwarfPointerEncoding encoding,
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size_t *len) const {
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// UsableEncoding doesn't approve of DW_EH_PE_omit, so we shouldn't
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// see it here.
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assert(encoding != DW_EH_PE_omit);
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// The Linux Standards Base 4.0 does not make this clear, but the
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// GNU tools (gcc/unwind-pe.h; readelf/dwarf.c; gdb/dwarf2-frame.c)
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// agree that aligned pointers are always absolute, machine-sized,
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// machine-signed pointers.
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if (encoding == DW_EH_PE_aligned) {
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assert(have_section_base_);
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// We don't need to align BUFFER in *our* address space. Rather, we
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// need to find the next position in our buffer that would be aligned
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// when the .eh_frame section the buffer contains is loaded into the
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// program's memory. So align assuming that buffer_base_ gets loaded at
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// address section_base_, where section_base_ itself may or may not be
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// aligned.
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// First, find the offset to START from the closest prior aligned
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// address.
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uint64 skew = section_base_ & (AddressSize() - 1);
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// Now find the offset from that aligned address to buffer.
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uint64 offset = skew + (buffer - buffer_base_);
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// Round up to the next boundary.
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uint64 aligned = (offset + AddressSize() - 1) & -AddressSize();
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// Convert back to a pointer.
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const char *aligned_buffer = buffer_base_ + (aligned - skew);
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// Finally, store the length and actually fetch the pointer.
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*len = aligned_buffer - buffer + AddressSize();
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return ReadAddress(aligned_buffer);
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}
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// Extract the value first, ignoring whether it's a pointer or an
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// offset relative to some base.
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uint64 offset;
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switch (encoding & 0x0f) {
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case DW_EH_PE_absptr:
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// DW_EH_PE_absptr is weird, as it is used as a meaningful value for
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// both the high and low nybble of encoding bytes. When it appears in
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// the high nybble, it means that the pointer is absolute, not an
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// offset from some base address. When it appears in the low nybble,
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// as here, it means that the pointer is stored as a normal
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// machine-sized and machine-signed address. A low nybble of
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// DW_EH_PE_absptr does not imply that the pointer is absolute; it is
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// correct for us to treat the value as an offset from a base address
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// if the upper nybble is not DW_EH_PE_absptr.
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offset = ReadAddress(buffer);
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*len = AddressSize();
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break;
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case DW_EH_PE_uleb128:
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offset = ReadUnsignedLEB128(buffer, len);
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break;
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case DW_EH_PE_udata2:
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offset = ReadTwoBytes(buffer);
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*len = 2;
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break;
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case DW_EH_PE_udata4:
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offset = ReadFourBytes(buffer);
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*len = 4;
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break;
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case DW_EH_PE_udata8:
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offset = ReadEightBytes(buffer);
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*len = 8;
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break;
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case DW_EH_PE_sleb128:
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offset = ReadSignedLEB128(buffer, len);
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break;
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case DW_EH_PE_sdata2:
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offset = ReadTwoBytes(buffer);
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// Sign-extend from 16 bits.
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offset = (offset ^ 0x8000) - 0x8000;
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*len = 2;
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break;
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case DW_EH_PE_sdata4:
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offset = ReadFourBytes(buffer);
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// Sign-extend from 32 bits.
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offset = (offset ^ 0x80000000ULL) - 0x80000000ULL;
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*len = 4;
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break;
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case DW_EH_PE_sdata8:
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// No need to sign-extend; this is the full width of our type.
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offset = ReadEightBytes(buffer);
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*len = 8;
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break;
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default:
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abort();
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}
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// Find the appropriate base address.
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uint64 base;
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switch (encoding & 0x70) {
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case DW_EH_PE_absptr:
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base = 0;
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break;
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case DW_EH_PE_pcrel:
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assert(have_section_base_);
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base = section_base_ + (buffer - buffer_base_);
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break;
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case DW_EH_PE_textrel:
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assert(have_text_base_);
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base = text_base_;
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break;
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case DW_EH_PE_datarel:
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assert(have_data_base_);
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base = data_base_;
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break;
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case DW_EH_PE_funcrel:
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assert(have_function_base_);
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base = function_base_;
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break;
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default:
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abort();
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}
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uint64 pointer = base + offset;
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// Remove inappropriate upper bits.
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if (AddressSize() == 4)
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pointer = pointer & 0xffffffff;
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else
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assert(AddressSize() == sizeof(uint64));
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return pointer;
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}
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} // namespace dwarf2reader
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