1 // -*- mode: C++ -*- 2 3 // Copyright (c) 2010 Google Inc. All Rights Reserved. 4 // 5 // Redistribution and use in source and binary forms, with or without 6 // modification, are permitted provided that the following conditions are 7 // met: 8 // 9 // * Redistributions of source code must retain the above copyright 10 // notice, this list of conditions and the following disclaimer. 11 // * Redistributions in binary form must reproduce the above 12 // copyright notice, this list of conditions and the following disclaimer 13 // in the documentation and/or other materials provided with the 14 // distribution. 15 // * Neither the name of Google Inc. nor the names of its 16 // contributors may be used to endorse or promote products derived from 17 // this software without specific prior written permission. 18 // 19 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 20 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 21 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 22 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 23 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 24 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 25 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 26 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 27 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 28 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 29 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30 31 #ifndef COMMON_DWARF_BYTEREADER_H__ 32 #define COMMON_DWARF_BYTEREADER_H__ 33 34 #include <string> 35 #include "common/dwarf/types.h" 36 #include "common/dwarf/dwarf2enums.h" 37 38 namespace dwarf2reader { 39 40 // We can't use the obvious name of LITTLE_ENDIAN and BIG_ENDIAN 41 // because it conflicts with a macro 42 enum Endianness { 43 ENDIANNESS_BIG, 44 ENDIANNESS_LITTLE 45 }; 46 47 // A ByteReader knows how to read single- and multi-byte values of 48 // various endiannesses, sizes, and encodings, as used in DWARF 49 // debugging information and Linux C++ exception handling data. 50 class ByteReader { 51 public: 52 // Construct a ByteReader capable of reading one-, two-, four-, and 53 // eight-byte values according to ENDIANNESS, absolute machine-sized 54 // addresses, DWARF-style "initial length" values, signed and 55 // unsigned LEB128 numbers, and Linux C++ exception handling data's 56 // encoded pointers. 57 explicit ByteReader(enum Endianness endianness); 58 virtual ~ByteReader(); 59 60 // Read a single byte from BUFFER and return it as an unsigned 8 bit 61 // number. 62 uint8 ReadOneByte(const char* buffer) const; 63 64 // Read two bytes from BUFFER and return them as an unsigned 16 bit 65 // number, using this ByteReader's endianness. 66 uint16 ReadTwoBytes(const char* buffer) const; 67 68 // Read four bytes from BUFFER and return them as an unsigned 32 bit 69 // number, using this ByteReader's endianness. This function returns 70 // a uint64 so that it is compatible with ReadAddress and 71 // ReadOffset. The number it returns will never be outside the range 72 // of an unsigned 32 bit integer. 73 uint64 ReadFourBytes(const char* buffer) const; 74 75 // Read eight bytes from BUFFER and return them as an unsigned 64 76 // bit number, using this ByteReader's endianness. 77 uint64 ReadEightBytes(const char* buffer) const; 78 79 // Read an unsigned LEB128 (Little Endian Base 128) number from 80 // BUFFER and return it as an unsigned 64 bit integer. Set LEN to 81 // the number of bytes read. 82 // 83 // The unsigned LEB128 representation of an integer N is a variable 84 // number of bytes: 85 // 86 // - If N is between 0 and 0x7f, then its unsigned LEB128 87 // representation is a single byte whose value is N. 88 // 89 // - Otherwise, its unsigned LEB128 representation is (N & 0x7f) | 90 // 0x80, followed by the unsigned LEB128 representation of N / 91 // 128, rounded towards negative infinity. 92 // 93 // In other words, we break VALUE into groups of seven bits, put 94 // them in little-endian order, and then write them as eight-bit 95 // bytes with the high bit on all but the last. 96 uint64 ReadUnsignedLEB128(const char* buffer, size_t* len) const; 97 98 // Read a signed LEB128 number from BUFFER and return it as an 99 // signed 64 bit integer. Set LEN to the number of bytes read. 100 // 101 // The signed LEB128 representation of an integer N is a variable 102 // number of bytes: 103 // 104 // - If N is between -0x40 and 0x3f, then its signed LEB128 105 // representation is a single byte whose value is N in two's 106 // complement. 107 // 108 // - Otherwise, its signed LEB128 representation is (N & 0x7f) | 109 // 0x80, followed by the signed LEB128 representation of N / 128, 110 // rounded towards negative infinity. 111 // 112 // In other words, we break VALUE into groups of seven bits, put 113 // them in little-endian order, and then write them as eight-bit 114 // bytes with the high bit on all but the last. 115 int64 ReadSignedLEB128(const char* buffer, size_t* len) const; 116 117 // Indicate that addresses on this architecture are SIZE bytes long. SIZE 118 // must be either 4 or 8. (DWARF allows addresses to be any number of 119 // bytes in length from 1 to 255, but we only support 32- and 64-bit 120 // addresses at the moment.) You must call this before using the 121 // ReadAddress member function. 122 // 123 // For data in a .debug_info section, or something that .debug_info 124 // refers to like line number or macro data, the compilation unit 125 // header's address_size field indicates the address size to use. Call 126 // frame information doesn't indicate its address size (a shortcoming of 127 // the spec); you must supply the appropriate size based on the 128 // architecture of the target machine. 129 void SetAddressSize(uint8 size); 130 131 // Return the current address size, in bytes. This is either 4, 132 // indicating 32-bit addresses, or 8, indicating 64-bit addresses. AddressSize()133 uint8 AddressSize() const { return address_size_; } 134 135 // Read an address from BUFFER and return it as an unsigned 64 bit 136 // integer, respecting this ByteReader's endianness and address size. You 137 // must call SetAddressSize before calling this function. 138 uint64 ReadAddress(const char* buffer) const; 139 140 // DWARF actually defines two slightly different formats: 32-bit DWARF 141 // and 64-bit DWARF. This is *not* related to the size of registers or 142 // addresses on the target machine; it refers only to the size of section 143 // offsets and data lengths appearing in the DWARF data. One only needs 144 // 64-bit DWARF when the debugging data itself is larger than 4GiB. 145 // 32-bit DWARF can handle x86_64 or PPC64 code just fine, unless the 146 // debugging data itself is very large. 147 // 148 // DWARF information identifies itself as 32-bit or 64-bit DWARF: each 149 // compilation unit and call frame information entry begins with an 150 // "initial length" field, which, in addition to giving the length of the 151 // data, also indicates the size of section offsets and lengths appearing 152 // in that data. The ReadInitialLength member function, below, reads an 153 // initial length and sets the ByteReader's offset size as a side effect. 154 // Thus, in the normal process of reading DWARF data, the appropriate 155 // offset size is set automatically. So, you should only need to call 156 // SetOffsetSize if you are using the same ByteReader to jump from the 157 // midst of one block of DWARF data into another. 158 159 // Read a DWARF "initial length" field from START, and return it as 160 // an unsigned 64 bit integer, respecting this ByteReader's 161 // endianness. Set *LEN to the length of the initial length in 162 // bytes, either four or twelve. As a side effect, set this 163 // ByteReader's offset size to either 4 (if we see a 32-bit DWARF 164 // initial length) or 8 (if we see a 64-bit DWARF initial length). 165 // 166 // A DWARF initial length is either: 167 // 168 // - a byte count stored as an unsigned 32-bit value less than 169 // 0xffffff00, indicating that the data whose length is being 170 // measured uses the 32-bit DWARF format, or 171 // 172 // - The 32-bit value 0xffffffff, followed by a 64-bit byte count, 173 // indicating that the data whose length is being measured uses 174 // the 64-bit DWARF format. 175 uint64 ReadInitialLength(const char* start, size_t* len); 176 177 // Read an offset from BUFFER and return it as an unsigned 64 bit 178 // integer, respecting the ByteReader's endianness. In 32-bit DWARF, the 179 // offset is 4 bytes long; in 64-bit DWARF, the offset is eight bytes 180 // long. You must call ReadInitialLength or SetOffsetSize before calling 181 // this function; see the comments above for details. 182 uint64 ReadOffset(const char* buffer) const; 183 184 // Return the current offset size, in bytes. 185 // A return value of 4 indicates that we are reading 32-bit DWARF. 186 // A return value of 8 indicates that we are reading 64-bit DWARF. OffsetSize()187 uint8 OffsetSize() const { return offset_size_; } 188 189 // Indicate that section offsets and lengths are SIZE bytes long. SIZE 190 // must be either 4 (meaning 32-bit DWARF) or 8 (meaning 64-bit DWARF). 191 // Usually, you should not call this function yourself; instead, let a 192 // call to ReadInitialLength establish the data's offset size 193 // automatically. 194 void SetOffsetSize(uint8 size); 195 196 // The Linux C++ ABI uses a variant of DWARF call frame information 197 // for exception handling. This data is included in the program's 198 // address space as the ".eh_frame" section, and intepreted at 199 // runtime to walk the stack, find exception handlers, and run 200 // cleanup code. The format is mostly the same as DWARF CFI, with 201 // some adjustments made to provide the additional 202 // exception-handling data, and to make the data easier to work with 203 // in memory --- for example, to allow it to be placed in read-only 204 // memory even when describing position-independent code. 205 // 206 // In particular, exception handling data can select a number of 207 // different encodings for pointers that appear in the data, as 208 // described by the DwarfPointerEncoding enum. There are actually 209 // four axes(!) to the encoding: 210 // 211 // - The pointer size: pointers can be 2, 4, or 8 bytes long, or use 212 // the DWARF LEB128 encoding. 213 // 214 // - The pointer's signedness: pointers can be signed or unsigned. 215 // 216 // - The pointer's base address: the data stored in the exception 217 // handling data can be the actual address (that is, an absolute 218 // pointer), or relative to one of a number of different base 219 // addreses --- including that of the encoded pointer itself, for 220 // a form of "pc-relative" addressing. 221 // 222 // - The pointer may be indirect: it may be the address where the 223 // true pointer is stored. (This is used to refer to things via 224 // global offset table entries, program linkage table entries, or 225 // other tricks used in position-independent code.) 226 // 227 // There are also two options that fall outside that matrix 228 // altogether: the pointer may be omitted, or it may have padding to 229 // align it on an appropriate address boundary. (That last option 230 // may seem like it should be just another axis, but it is not.) 231 232 // Indicate that the exception handling data is loaded starting at 233 // SECTION_BASE, and that the start of its buffer in our own memory 234 // is BUFFER_BASE. This allows us to find the address that a given 235 // byte in our buffer would have when loaded into the program the 236 // data describes. We need this to resolve DW_EH_PE_pcrel pointers. 237 void SetCFIDataBase(uint64 section_base, const char *buffer_base); 238 239 // Indicate that the base address of the program's ".text" section 240 // is TEXT_BASE. We need this to resolve DW_EH_PE_textrel pointers. 241 void SetTextBase(uint64 text_base); 242 243 // Indicate that the base address for DW_EH_PE_datarel pointers is 244 // DATA_BASE. The proper value depends on the ABI; it is usually the 245 // address of the global offset table, held in a designated register in 246 // position-independent code. You will need to look at the startup code 247 // for the target system to be sure. I tried; my eyes bled. 248 void SetDataBase(uint64 data_base); 249 250 // Indicate that the base address for the FDE we are processing is 251 // FUNCTION_BASE. This is the start address of DW_EH_PE_funcrel 252 // pointers. (This encoding does not seem to be used by the GNU 253 // toolchain.) 254 void SetFunctionBase(uint64 function_base); 255 256 // Indicate that we are no longer processing any FDE, so any use of 257 // a DW_EH_PE_funcrel encoding is an error. 258 void ClearFunctionBase(); 259 260 // Return true if ENCODING is a valid pointer encoding. 261 bool ValidEncoding(DwarfPointerEncoding encoding) const; 262 263 // Return true if we have all the information we need to read a 264 // pointer that uses ENCODING. This checks that the appropriate 265 // SetFooBase function for ENCODING has been called. 266 bool UsableEncoding(DwarfPointerEncoding encoding) const; 267 268 // Read an encoded pointer from BUFFER using ENCODING; return the 269 // absolute address it represents, and set *LEN to the pointer's 270 // length in bytes, including any padding for aligned pointers. 271 // 272 // This function calls 'abort' if ENCODING is invalid or refers to a 273 // base address this reader hasn't been given, so you should check 274 // with ValidEncoding and UsableEncoding first if you would rather 275 // die in a more helpful way. 276 uint64 ReadEncodedPointer(const char *buffer, DwarfPointerEncoding encoding, 277 size_t *len) const; 278 279 private: 280 281 // Function pointer type for our address and offset readers. 282 typedef uint64 (ByteReader::*AddressReader)(const char*) const; 283 284 // Read an offset from BUFFER and return it as an unsigned 64 bit 285 // integer. DWARF2/3 define offsets as either 4 or 8 bytes, 286 // generally depending on the amount of DWARF2/3 info present. 287 // This function pointer gets set by SetOffsetSize. 288 AddressReader offset_reader_; 289 290 // Read an address from BUFFER and return it as an unsigned 64 bit 291 // integer. DWARF2/3 allow addresses to be any size from 0-255 292 // bytes currently. Internally we support 4 and 8 byte addresses, 293 // and will CHECK on anything else. 294 // This function pointer gets set by SetAddressSize. 295 AddressReader address_reader_; 296 297 Endianness endian_; 298 uint8 address_size_; 299 uint8 offset_size_; 300 301 // Base addresses for Linux C++ exception handling data's encoded pointers. 302 bool have_section_base_, have_text_base_, have_data_base_; 303 bool have_function_base_; 304 uint64 section_base_, text_base_, data_base_, function_base_; 305 const char *buffer_base_; 306 }; 307 308 } // namespace dwarf2reader 309 310 #endif // COMMON_DWARF_BYTEREADER_H__ 311