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// Copyright (c) 2010 Google 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:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * 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.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// 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
// OWNER 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.
#include <assert.h>
#include <stdint.h>
#include <stdlib.h>
#include "common/dwarf/bytereader-inl.h"
#include "common/dwarf/bytereader.h"
namespace dwarf2reader {
ByteReader::ByteReader(enum Endianness endian)
:offset_reader_(NULL), address_reader_(NULL), endian_(endian),
address_size_(0), offset_size_(0),
have_section_base_(), have_text_base_(), have_data_base_(),
have_function_base_() { }
ByteReader::~ByteReader() { }
void ByteReader::SetOffsetSize(uint8 size) {
offset_size_ = size;
assert(size == 4 || size == 8);
if (size == 4) {
this->offset_reader_ = &ByteReader::ReadFourBytes;
} else {
this->offset_reader_ = &ByteReader::ReadEightBytes;
}
}
void ByteReader::SetAddressSize(uint8 size) {
address_size_ = size;
assert(size == 4 || size == 8);
if (size == 4) {
this->address_reader_ = &ByteReader::ReadFourBytes;
} else {
this->address_reader_ = &ByteReader::ReadEightBytes;
}
}
uint64 ByteReader::ReadInitialLength(const uint8_t *start, size_t* len) {
const uint64 initial_length = ReadFourBytes(start);
start += 4;
// In DWARF2/3, if the initial length is all 1 bits, then the offset
// size is 8 and we need to read the next 8 bytes for the real length.
if (initial_length == 0xffffffff) {
SetOffsetSize(8);
*len = 12;
return ReadOffset(start);
} else {
SetOffsetSize(4);
*len = 4;
}
return initial_length;
}
bool ByteReader::ValidEncoding(DwarfPointerEncoding encoding) const {
if (encoding == DW_EH_PE_omit) return true;
if (encoding == DW_EH_PE_aligned) return true;
if ((encoding & 0x7) > DW_EH_PE_udata8)
return false;
if ((encoding & 0x70) > DW_EH_PE_funcrel)
return false;
return true;
}
bool ByteReader::UsableEncoding(DwarfPointerEncoding encoding) const {
switch (encoding & 0x70) {
case DW_EH_PE_absptr: return true;
case DW_EH_PE_pcrel: return have_section_base_;
case DW_EH_PE_textrel: return have_text_base_;
case DW_EH_PE_datarel: return have_data_base_;
case DW_EH_PE_funcrel: return have_function_base_;
default: return false;
}
}
uint64 ByteReader::ReadEncodedPointer(const uint8_t *buffer,
DwarfPointerEncoding encoding,
size_t *len) const {
// UsableEncoding doesn't approve of DW_EH_PE_omit, so we shouldn't
// see it here.
assert(encoding != DW_EH_PE_omit);
// The Linux Standards Base 4.0 does not make this clear, but the
// GNU tools (gcc/unwind-pe.h; readelf/dwarf.c; gdb/dwarf2-frame.c)
// agree that aligned pointers are always absolute, machine-sized,
// machine-signed pointers.
if (encoding == DW_EH_PE_aligned) {
assert(have_section_base_);
// We don't need to align BUFFER in *our* address space. Rather, we
// need to find the next position in our buffer that would be aligned
// when the .eh_frame section the buffer contains is loaded into the
// program's memory. So align assuming that buffer_base_ gets loaded at
// address section_base_, where section_base_ itself may or may not be
// aligned.
// First, find the offset to START from the closest prior aligned
// address.
uint64 skew = section_base_ & (AddressSize() - 1);
// Now find the offset from that aligned address to buffer.
uint64 offset = skew + (buffer - buffer_base_);
// Round up to the next boundary.
uint64 aligned = (offset + AddressSize() - 1) & -AddressSize();
// Convert back to a pointer.
const uint8_t *aligned_buffer = buffer_base_ + (aligned - skew);
// Finally, store the length and actually fetch the pointer.
*len = aligned_buffer - buffer + AddressSize();
return ReadAddress(aligned_buffer);
}
// Extract the value first, ignoring whether it's a pointer or an
// offset relative to some base.
uint64 offset;
switch (encoding & 0x0f) {
case DW_EH_PE_absptr:
// DW_EH_PE_absptr is weird, as it is used as a meaningful value for
// both the high and low nybble of encoding bytes. When it appears in
// the high nybble, it means that the pointer is absolute, not an
// offset from some base address. When it appears in the low nybble,
// as here, it means that the pointer is stored as a normal
// machine-sized and machine-signed address. A low nybble of
// DW_EH_PE_absptr does not imply that the pointer is absolute; it is
// correct for us to treat the value as an offset from a base address
// if the upper nybble is not DW_EH_PE_absptr.
offset = ReadAddress(buffer);
*len = AddressSize();
break;
case DW_EH_PE_uleb128:
offset = ReadUnsignedLEB128(buffer, len);
break;
case DW_EH_PE_udata2:
offset = ReadTwoBytes(buffer);
*len = 2;
break;
case DW_EH_PE_udata4:
offset = ReadFourBytes(buffer);
*len = 4;
break;
case DW_EH_PE_udata8:
offset = ReadEightBytes(buffer);
*len = 8;
break;
case DW_EH_PE_sleb128:
offset = ReadSignedLEB128(buffer, len);
break;
case DW_EH_PE_sdata2:
offset = ReadTwoBytes(buffer);
// Sign-extend from 16 bits.
offset = (offset ^ 0x8000) - 0x8000;
*len = 2;
break;
case DW_EH_PE_sdata4:
offset = ReadFourBytes(buffer);
// Sign-extend from 32 bits.
offset = (offset ^ 0x80000000ULL) - 0x80000000ULL;
*len = 4;
break;
case DW_EH_PE_sdata8:
// No need to sign-extend; this is the full width of our type.
offset = ReadEightBytes(buffer);
*len = 8;
break;
default:
abort();
}
// Find the appropriate base address.
uint64 base;
switch (encoding & 0x70) {
case DW_EH_PE_absptr:
base = 0;
break;
case DW_EH_PE_pcrel:
assert(have_section_base_);
base = section_base_ + (buffer - buffer_base_);
break;
case DW_EH_PE_textrel:
assert(have_text_base_);
base = text_base_;
break;
case DW_EH_PE_datarel:
assert(have_data_base_);
base = data_base_;
break;
case DW_EH_PE_funcrel:
assert(have_function_base_);
base = function_base_;
break;
default:
abort();
}
uint64 pointer = base + offset;
// Remove inappropriate upper bits.
if (AddressSize() == 4)
pointer = pointer & 0xffffffff;
else
assert(AddressSize() == sizeof(uint64));
return pointer;
}
Endianness ByteReader::GetEndianness() const {
return endian_;
}
} // namespace dwarf2reader
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