The Tor Browser: comparison toolkit/crashreporter/google-breakpad/src/common/dwarf/bytereader.h

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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
+// "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.
+#ifndef COMMON_DWARF_BYTEREADER_H__
+#define COMMON_DWARF_BYTEREADER_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 char* buffer) const;
+// Read two bytes from BUFFER and return them as an unsigned 16 bit
+// number, using this ByteReader's endianness.
+uint16 ReadTwoBytes(const char* 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 char* buffer) const;
+// Read eight bytes from BUFFER and return them as an unsigned 64
+// bit number, using this ByteReader's endianness.
+uint64 ReadEightBytes(const char* 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 char* 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 char* 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 char* 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 char* 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 char* 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 char *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 char *buffer, DwarfPointerEncoding encoding,
+size_t *len) const;
+private:
+// Function pointer type for our address and offset readers.
+typedef uint64 (ByteReader::*AddressReader)(const char*) 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 char *buffer_base_;
+};
+}  // namespace dwarf2reader
+#endif  // COMMON_DWARF_BYTEREADER_H__

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