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// -*- mode: C++ -*-
// 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
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#ifndef COMMON_DWARF_BYTEREADER_H__
#define COMMON_DWARF_BYTEREADER_H__
#include <stdint.h>
#include <string>
#include "common/dwarf/types.h"
#include "common/dwarf/dwarf2enums.h"
namespace dwarf2reader {
// We can't use the obvious name of LITTLE_ENDIAN and BIG_ENDIAN
// because it conflicts with a macro
enum Endianness {
ENDIANNESS_BIG,
ENDIANNESS_LITTLE
};
// A ByteReader knows how to read single- and multi-byte values of
// various endiannesses, sizes, and encodings, as used in DWARF
// debugging information and Linux C++ exception handling data.
class ByteReader {
public:
// Construct a ByteReader capable of reading one-, two-, four-, and
// eight-byte values according to ENDIANNESS, absolute machine-sized
// addresses, DWARF-style "initial length" values, signed and
// unsigned LEB128 numbers, and Linux C++ exception handling data's
// encoded pointers.
explicit ByteReader(enum Endianness endianness);
virtual ~ByteReader();
// Read a single byte from BUFFER and return it as an unsigned 8 bit
// number.
uint8 ReadOneByte(const uint8_t *buffer) const;
// Read two bytes from BUFFER and return them as an unsigned 16 bit
// number, using this ByteReader's endianness.
uint16 ReadTwoBytes(const uint8_t *buffer) const;
// Read four bytes from BUFFER and return them as an unsigned 32 bit
// number, using this ByteReader's endianness. This function returns
// a uint64 so that it is compatible with ReadAddress and
// ReadOffset. The number it returns will never be outside the range
// of an unsigned 32 bit integer.
uint64 ReadFourBytes(const uint8_t *buffer) const;
// Read eight bytes from BUFFER and return them as an unsigned 64
// bit number, using this ByteReader's endianness.
uint64 ReadEightBytes(const uint8_t *buffer) const;
// Read an unsigned LEB128 (Little Endian Base 128) number from
// BUFFER and return it as an unsigned 64 bit integer. Set LEN to
// the number of bytes read.
//
// The unsigned LEB128 representation of an integer N is a variable
// number of bytes:
//
// - If N is between 0 and 0x7f, then its unsigned LEB128
// representation is a single byte whose value is N.
//
// - Otherwise, its unsigned LEB128 representation is (N & 0x7f) |
// 0x80, followed by the unsigned LEB128 representation of N /
// 128, rounded towards negative infinity.
//
// In other words, we break VALUE into groups of seven bits, put
// them in little-endian order, and then write them as eight-bit
// bytes with the high bit on all but the last.
uint64 ReadUnsignedLEB128(const uint8_t *buffer, size_t *len) const;
// Read a signed LEB128 number from BUFFER and return it as an
// signed 64 bit integer. Set LEN to the number of bytes read.
//
// The signed LEB128 representation of an integer N is a variable
// number of bytes:
//
// - If N is between -0x40 and 0x3f, then its signed LEB128
// representation is a single byte whose value is N in two's
// complement.
//
// - Otherwise, its signed LEB128 representation is (N & 0x7f) |
// 0x80, followed by the signed LEB128 representation of N / 128,
// rounded towards negative infinity.
//
// In other words, we break VALUE into groups of seven bits, put
// them in little-endian order, and then write them as eight-bit
// bytes with the high bit on all but the last.
int64 ReadSignedLEB128(const uint8_t *buffer, size_t *len) const;
// Indicate that addresses on this architecture are SIZE bytes long. SIZE
// must be either 4 or 8. (DWARF allows addresses to be any number of
// bytes in length from 1 to 255, but we only support 32- and 64-bit
// addresses at the moment.) You must call this before using the
// ReadAddress member function.
//
// For data in a .debug_info section, or something that .debug_info
// refers to like line number or macro data, the compilation unit
// header's address_size field indicates the address size to use. Call
// frame information doesn't indicate its address size (a shortcoming of
// the spec); you must supply the appropriate size based on the
// architecture of the target machine.
void SetAddressSize(uint8 size);
// Return the current address size, in bytes. This is either 4,
// indicating 32-bit addresses, or 8, indicating 64-bit addresses.
uint8 AddressSize() const { return address_size_; }
// Read an address from BUFFER and return it as an unsigned 64 bit
// integer, respecting this ByteReader's endianness and address size. You
// must call SetAddressSize before calling this function.
uint64 ReadAddress(const uint8_t *buffer) const;
// DWARF actually defines two slightly different formats: 32-bit DWARF
// and 64-bit DWARF. This is *not* related to the size of registers or
// addresses on the target machine; it refers only to the size of section
// offsets and data lengths appearing in the DWARF data. One only needs
// 64-bit DWARF when the debugging data itself is larger than 4GiB.
// 32-bit DWARF can handle x86_64 or PPC64 code just fine, unless the
// debugging data itself is very large.
//
// DWARF information identifies itself as 32-bit or 64-bit DWARF: each
// compilation unit and call frame information entry begins with an
// "initial length" field, which, in addition to giving the length of the
// data, also indicates the size of section offsets and lengths appearing
// in that data. The ReadInitialLength member function, below, reads an
// initial length and sets the ByteReader's offset size as a side effect.
// Thus, in the normal process of reading DWARF data, the appropriate
// offset size is set automatically. So, you should only need to call
// SetOffsetSize if you are using the same ByteReader to jump from the
// midst of one block of DWARF data into another.
// Read a DWARF "initial length" field from START, and return it as
// an unsigned 64 bit integer, respecting this ByteReader's
// endianness. Set *LEN to the length of the initial length in
// bytes, either four or twelve. As a side effect, set this
// ByteReader's offset size to either 4 (if we see a 32-bit DWARF
// initial length) or 8 (if we see a 64-bit DWARF initial length).
//
// A DWARF initial length is either:
//
// - a byte count stored as an unsigned 32-bit value less than
// 0xffffff00, indicating that the data whose length is being
// measured uses the 32-bit DWARF format, or
//
// - The 32-bit value 0xffffffff, followed by a 64-bit byte count,
// indicating that the data whose length is being measured uses
// the 64-bit DWARF format.
uint64 ReadInitialLength(const uint8_t *start, size_t *len);
// Read an offset from BUFFER and return it as an unsigned 64 bit
// integer, respecting the ByteReader's endianness. In 32-bit DWARF, the
// offset is 4 bytes long; in 64-bit DWARF, the offset is eight bytes
// long. You must call ReadInitialLength or SetOffsetSize before calling
// this function; see the comments above for details.
uint64 ReadOffset(const uint8_t *buffer) const;
// Return the current offset size, in bytes.
// A return value of 4 indicates that we are reading 32-bit DWARF.
// A return value of 8 indicates that we are reading 64-bit DWARF.
uint8 OffsetSize() const { return offset_size_; }
// Indicate that section offsets and lengths are SIZE bytes long. SIZE
// must be either 4 (meaning 32-bit DWARF) or 8 (meaning 64-bit DWARF).
// Usually, you should not call this function yourself; instead, let a
// call to ReadInitialLength establish the data's offset size
// automatically.
void SetOffsetSize(uint8 size);
// The Linux C++ ABI uses a variant of DWARF call frame information
// for exception handling. This data is included in the program's
// address space as the ".eh_frame" section, and intepreted at
// runtime to walk the stack, find exception handlers, and run
// cleanup code. The format is mostly the same as DWARF CFI, with
// some adjustments made to provide the additional
// exception-handling data, and to make the data easier to work with
// in memory --- for example, to allow it to be placed in read-only
// memory even when describing position-independent code.
//
// In particular, exception handling data can select a number of
// different encodings for pointers that appear in the data, as
// described by the DwarfPointerEncoding enum. There are actually
// four axes(!) to the encoding:
//
// - The pointer size: pointers can be 2, 4, or 8 bytes long, or use
// the DWARF LEB128 encoding.
//
// - The pointer's signedness: pointers can be signed or unsigned.
//
// - The pointer's base address: the data stored in the exception
// handling data can be the actual address (that is, an absolute
// pointer), or relative to one of a number of different base
// addreses --- including that of the encoded pointer itself, for
// a form of "pc-relative" addressing.
//
// - The pointer may be indirect: it may be the address where the
// true pointer is stored. (This is used to refer to things via
// global offset table entries, program linkage table entries, or
// other tricks used in position-independent code.)
//
// There are also two options that fall outside that matrix
// altogether: the pointer may be omitted, or it may have padding to
// align it on an appropriate address boundary. (That last option
// may seem like it should be just another axis, but it is not.)
// Indicate that the exception handling data is loaded starting at
// SECTION_BASE, and that the start of its buffer in our own memory
// is BUFFER_BASE. This allows us to find the address that a given
// byte in our buffer would have when loaded into the program the
// data describes. We need this to resolve DW_EH_PE_pcrel pointers.
void SetCFIDataBase(uint64 section_base, const uint8_t *buffer_base);
// Indicate that the base address of the program's ".text" section
// is TEXT_BASE. We need this to resolve DW_EH_PE_textrel pointers.
void SetTextBase(uint64 text_base);
// Indicate that the base address for DW_EH_PE_datarel pointers is
// DATA_BASE. The proper value depends on the ABI; it is usually the
// address of the global offset table, held in a designated register in
// position-independent code. You will need to look at the startup code
// for the target system to be sure. I tried; my eyes bled.
void SetDataBase(uint64 data_base);
// Indicate that the base address for the FDE we are processing is
// FUNCTION_BASE. This is the start address of DW_EH_PE_funcrel
// pointers. (This encoding does not seem to be used by the GNU
// toolchain.)
void SetFunctionBase(uint64 function_base);
// Indicate that we are no longer processing any FDE, so any use of
// a DW_EH_PE_funcrel encoding is an error.
void ClearFunctionBase();
// Return true if ENCODING is a valid pointer encoding.
bool ValidEncoding(DwarfPointerEncoding encoding) const;
// Return true if we have all the information we need to read a
// pointer that uses ENCODING. This checks that the appropriate
// SetFooBase function for ENCODING has been called.
bool UsableEncoding(DwarfPointerEncoding encoding) const;
// Read an encoded pointer from BUFFER using ENCODING; return the
// absolute address it represents, and set *LEN to the pointer's
// length in bytes, including any padding for aligned pointers.
//
// This function calls 'abort' if ENCODING is invalid or refers to a
// base address this reader hasn't been given, so you should check
// with ValidEncoding and UsableEncoding first if you would rather
// die in a more helpful way.
uint64 ReadEncodedPointer(const uint8_t *buffer,
DwarfPointerEncoding encoding,
size_t *len) const;
Endianness GetEndianness() const;
private:
// Function pointer type for our address and offset readers.
typedef uint64 (ByteReader::*AddressReader)(const uint8_t *) const;
// Read an offset from BUFFER and return it as an unsigned 64 bit
// integer. DWARF2/3 define offsets as either 4 or 8 bytes,
// generally depending on the amount of DWARF2/3 info present.
// This function pointer gets set by SetOffsetSize.
AddressReader offset_reader_;
// Read an address from BUFFER and return it as an unsigned 64 bit
// integer. DWARF2/3 allow addresses to be any size from 0-255
// bytes currently. Internally we support 4 and 8 byte addresses,
// and will CHECK on anything else.
// This function pointer gets set by SetAddressSize.
AddressReader address_reader_;
Endianness endian_;
uint8 address_size_;
uint8 offset_size_;
// Base addresses for Linux C++ exception handling data's encoded pointers.
bool have_section_base_, have_text_base_, have_data_base_;
bool have_function_base_;
uint64 section_base_, text_base_, data_base_, function_base_;
const uint8_t *buffer_base_;
};
} // namespace dwarf2reader
#endif // COMMON_DWARF_BYTEREADER_H__