elfcpp/elfcpp_swap.h

   1 // elfcpp_swap.h -- Handle swapping for elfcpp   -*- C++ -*-
   2
   3 // Copyright (C) 2006-2020 Free Software Foundation, Inc.
   4 // Written by Ian Lance Taylor <iant@google.com>.
   5
   6 // This file is part of elfcpp.
   7
   8 // This program is free software; you can redistribute it and/or
   9 // modify it under the terms of the GNU Library General Public License
  10 // as published by the Free Software Foundation; either version 2, or
  11 // (at your option) any later version.
  12
  13 // In addition to the permissions in the GNU Library General Public
  14 // License, the Free Software Foundation gives you unlimited
  15 // permission to link the compiled version of this file into
  16 // combinations with other programs, and to distribute those
  17 // combinations without any restriction coming from the use of this
  18 // file.  (The Library Public License restrictions do apply in other
  19 // respects; for example, they cover modification of the file, and
  20 /// distribution when not linked into a combined executable.)
  21
  22 // This program is distributed in the hope that it will be useful, but
  23 // WITHOUT ANY WARRANTY; without even the implied warranty of
  24 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  25 // Library General Public License for more details.
  26
  27 // You should have received a copy of the GNU Library General Public
  28 // License along with this program; if not, write to the Free Software
  29 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA
  30 // 02110-1301, USA.
  31
  32 // This header file defines basic template classes to efficiently swap
  33 // numbers between host form and target form.  When the host and
  34 // target have the same endianness, these turn into no-ops.
  35
  36 #ifndef ELFCPP_SWAP_H
  37 #define ELFCPP_SWAP_H
  38
  39 #include <stdint.h>
  40
  41 // We need an autoconf-generated config.h file for endianness and
  42 // swapping.  We check two macros: WORDS_BIGENDIAN and
  43 // HAVE_BYTESWAP_H.
  44
  45 #include "config.h"
  46
  47 #ifdef HAVE_BYTESWAP_H
  48 #include <byteswap.h>
  49 #else
  50 // Provide our own versions of the byteswap functions.
  51 inline uint16_t
  52 bswap_16(uint16_t v)
  53 {
  54   return ((v >> 8) & 0xff) | ((v & 0xff) << 8);
  55 }
  56
  57 inline uint32_t
  58 bswap_32(uint32_t v)
  59 {
  60   return (  ((v & 0xff000000) >> 24)
  61           | ((v & 0x00ff0000) >>  8)
  62           | ((v & 0x0000ff00) <<  8)
  63           | ((v & 0x000000ff) << 24));
  64 }
  65
  66 inline uint64_t
  67 bswap_64(uint64_t v)
  68 {
  69   return (  ((v & 0xff00000000000000ULL) >> 56)
  70           | ((v & 0x00ff000000000000ULL) >> 40)
  71           | ((v & 0x0000ff0000000000ULL) >> 24)
  72           | ((v & 0x000000ff00000000ULL) >>  8)
  73           | ((v & 0x00000000ff000000ULL) <<  8)
  74           | ((v & 0x0000000000ff0000ULL) << 24)
  75           | ((v & 0x000000000000ff00ULL) << 40)
  76           | ((v & 0x00000000000000ffULL) << 56));
  77 }
  78 #endif // !defined(HAVE_BYTESWAP_H)
  79
  80 // gcc 4.3 and later provides __builtin_bswap32 and __builtin_bswap64.
  81
  82 #if defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3))
  83 #undef bswap_32
  84 #define bswap_32 __builtin_bswap32
  85 #undef bswap_64
  86 #define bswap_64 __builtin_bswap64
  87 #endif
  88
  89 namespace elfcpp
  90 {
  91
  92 // Endian simply indicates whether the host is big endian or not.
  93
  94 struct Endian
  95 {
  96  public:
  97   // Used for template specializations.
  98   static const bool host_big_endian =
  99 #ifdef WORDS_BIGENDIAN
 100     true
 101 #else
 102     false
 103 #endif
 104     ;
 105 };
 106
 107 // Valtype_base is a template based on size (8, 16, 32, 64) which
 108 // defines the type Valtype as the unsigned integer, and
 109 // Signed_valtype as the signed integer, of the specified size.
 110
 111 template<int size>
 112 struct Valtype_base;
 113
 114 template<>
 115 struct Valtype_base<8>
 116 {
 117   typedef uint8_t Valtype;
 118   typedef int8_t Signed_valtype;
 119 };
 120
 121 template<>
 122 struct Valtype_base<16>
 123 {
 124   typedef uint16_t Valtype;
 125   typedef int16_t Signed_valtype;
 126 };
 127
 128 template<>
 129 struct Valtype_base<32>
 130 {
 131   typedef uint32_t Valtype;
 132   typedef int32_t Signed_valtype;
 133 };
 134
 135 template<>
 136 struct Valtype_base<64>
 137 {
 138   typedef uint64_t Valtype;
 139   typedef int64_t Signed_valtype;
 140 };
 141
 142 // Convert_endian is a template based on size and on whether the host
 143 // and target have the same endianness.  It defines the type Valtype
 144 // as Valtype_base does, and also defines a function convert_host
 145 // which takes an argument of type Valtype and returns the same value,
 146 // but swapped if the host and target have different endianness.
 147
 148 template<int size, bool same_endian>
 149 struct Convert_endian;
 150
 151 template<int size>
 152 struct Convert_endian<size, true>
 153 {
 154   typedef typename Valtype_base<size>::Valtype Valtype;
 155
 156   static inline Valtype
 157   convert_host(Valtype v)
 158   { return v; }
 159 };
 160
 161 template<>
 162 struct Convert_endian<8, false>
 163 {
 164   typedef Valtype_base<8>::Valtype Valtype;
 165
 166   static inline Valtype
 167   convert_host(Valtype v)
 168   { return v; }
 169 };
 170
 171 template<>
 172 struct Convert_endian<16, false>
 173 {
 174   typedef Valtype_base<16>::Valtype Valtype;
 175
 176   static inline Valtype
 177   convert_host(Valtype v)
 178   { return bswap_16(v); }
 179 };
 180
 181 template<>
 182 struct Convert_endian<32, false>
 183 {
 184   typedef Valtype_base<32>::Valtype Valtype;
 185
 186   static inline Valtype
 187   convert_host(Valtype v)
 188   { return bswap_32(v); }
 189 };
 190
 191 template<>
 192 struct Convert_endian<64, false>
 193 {
 194   typedef Valtype_base<64>::Valtype Valtype;
 195
 196   static inline Valtype
 197   convert_host(Valtype v)
 198   { return bswap_64(v); }
 199 };
 200
 201 // Convert is a template based on size and on whether the target is
 202 // big endian.  It defines Valtype and convert_host like
 203 // Convert_endian.  That is, it is just like Convert_endian except in
 204 // the meaning of the second template parameter.
 205
 206 template<int size, bool big_endian>
 207 struct Convert
 208 {
 209   typedef typename Valtype_base<size>::Valtype Valtype;
 210
 211   static inline Valtype
 212   convert_host(Valtype v)
 213   {
 214     return Convert_endian<size, big_endian == Endian::host_big_endian>
 215       ::convert_host(v);
 216   }
 217 };
 218
 219 // Swap is a template based on size and on whether the target is big
 220 // endian.  It defines the type Valtype and the functions readval and
 221 // writeval.  The functions read and write values of the appropriate
 222 // size out of buffers, swapping them if necessary.  readval and
 223 // writeval are overloaded to take pointers to the appropriate type or
 224 // pointers to unsigned char.
 225
 226 template<int size, bool big_endian>
 227 struct Swap
 228 {
 229   typedef typename Valtype_base<size>::Valtype Valtype;
 230
 231   static inline Valtype
 232   readval(const Valtype* wv)
 233   { return Convert<size, big_endian>::convert_host(*wv); }
 234
 235   static inline void
 236   writeval(Valtype* wv, Valtype v)
 237   { *wv = Convert<size, big_endian>::convert_host(v); }
 238
 239   static inline Valtype
 240   readval(const unsigned char* wv)
 241   { return readval(reinterpret_cast<const Valtype*>(wv)); }
 242
 243   static inline void
 244   writeval(unsigned char* wv, Valtype v)
 245   { writeval(reinterpret_cast<Valtype*>(wv), v); }
 246 };
 247
 248 // We need to specialize the 8-bit version of Swap to avoid
 249 // conflicting overloads, since both versions of readval and writeval
 250 // will have the same type parameters.
 251
 252 template<bool big_endian>
 253 struct Swap<8, big_endian>
 254 {
 255   typedef typename Valtype_base<8>::Valtype Valtype;
 256
 257   static inline Valtype
 258   readval(const Valtype* wv)
 259   { return *wv; }
 260
 261   static inline void
 262   writeval(Valtype* wv, Valtype v)
 263   { *wv = v; }
 264 };
 265
 266 // Swap_unaligned is a template based on size and on whether the
 267 // target is big endian.  It defines the type Valtype and the
 268 // functions readval and writeval.  The functions read and write
 269 // values of the appropriate size out of buffers which may be
 270 // misaligned.
 271
 272 template<int size, bool big_endian>
 273 struct Swap_unaligned;
 274
 275 template<bool big_endian>
 276 struct Swap_unaligned<8, big_endian>
 277 {
 278   typedef typename Valtype_base<8>::Valtype Valtype;
 279
 280   static inline Valtype
 281   readval(const unsigned char* wv)
 282   { return *wv; }
 283
 284   static inline void
 285   writeval(unsigned char* wv, Valtype v)
 286   { *wv = v; }
 287 };
 288
 289 template<>
 290 struct Swap_unaligned<16, false>
 291 {
 292   typedef Valtype_base<16>::Valtype Valtype;
 293
 294   static inline Valtype
 295   readval(const unsigned char* wv)
 296   {
 297     return (wv[1] << 8) | wv[0];
 298   }
 299
 300   static inline void
 301   writeval(unsigned char* wv, Valtype v)
 302   {
 303     wv[1] = v >> 8;
 304     wv[0] = v;
 305   }
 306 };
 307
 308 template<>
 309 struct Swap_unaligned<16, true>
 310 {
 311   typedef Valtype_base<16>::Valtype Valtype;
 312
 313   static inline Valtype
 314   readval(const unsigned char* wv)
 315   {
 316     return (wv[0] << 8) | wv[1];
 317   }
 318
 319   static inline void
 320   writeval(unsigned char* wv, Valtype v)
 321   {
 322     wv[0] = v >> 8;
 323     wv[1] = v;
 324   }
 325 };
 326
 327 template<>
 328 struct Swap_unaligned<32, false>
 329 {
 330   typedef Valtype_base<32>::Valtype Valtype;
 331
 332   static inline Valtype
 333   readval(const unsigned char* wv)
 334   {
 335     return (wv[3] << 24) | (wv[2] << 16) | (wv[1] << 8) | wv[0];
 336   }
 337
 338   static inline void
 339   writeval(unsigned char* wv, Valtype v)
 340   {
 341     wv[3] = v >> 24;
 342     wv[2] = v >> 16;
 343     wv[1] = v >> 8;
 344     wv[0] = v;
 345   }
 346 };
 347
 348 template<>
 349 struct Swap_unaligned<32, true>
 350 {
 351   typedef Valtype_base<32>::Valtype Valtype;
 352
 353   static inline Valtype
 354   readval(const unsigned char* wv)
 355   {
 356     return (wv[0] << 24) | (wv[1] << 16) | (wv[2] << 8) | wv[3];
 357   }
 358
 359   static inline void
 360   writeval(unsigned char* wv, Valtype v)
 361   {
 362     wv[0] = v >> 24;
 363     wv[1] = v >> 16;
 364     wv[2] = v >> 8;
 365     wv[3] = v;
 366   }
 367 };
 368
 369 template<>
 370 struct Swap_unaligned<64, false>
 371 {
 372   typedef Valtype_base<64>::Valtype Valtype;
 373
 374   static inline Valtype
 375   readval(const unsigned char* wv)
 376   {
 377     return ((static_cast<Valtype>(wv[7]) << 56)
 378             | (static_cast<Valtype>(wv[6]) << 48)
 379             | (static_cast<Valtype>(wv[5]) << 40)
 380             | (static_cast<Valtype>(wv[4]) << 32)
 381             | (static_cast<Valtype>(wv[3]) << 24)
 382             | (static_cast<Valtype>(wv[2]) << 16)
 383             | (static_cast<Valtype>(wv[1]) << 8)
 384             | static_cast<Valtype>(wv[0]));
 385   }
 386
 387   static inline void
 388   writeval(unsigned char* wv, Valtype v)
 389   {
 390     wv[7] = v >> 56;
 391     wv[6] = v >> 48;
 392     wv[5] = v >> 40;
 393     wv[4] = v >> 32;
 394     wv[3] = v >> 24;
 395     wv[2] = v >> 16;
 396     wv[1] = v >> 8;
 397     wv[0] = v;
 398   }
 399 };
 400
 401 template<>
 402 struct Swap_unaligned<64, true>
 403 {
 404   typedef Valtype_base<64>::Valtype Valtype;
 405
 406   static inline Valtype
 407   readval(const unsigned char* wv)
 408   {
 409     return ((static_cast<Valtype>(wv[0]) << 56)
 410             | (static_cast<Valtype>(wv[1]) << 48)
 411             | (static_cast<Valtype>(wv[2]) << 40)
 412             | (static_cast<Valtype>(wv[3]) << 32)
 413             | (static_cast<Valtype>(wv[4]) << 24)
 414             | (static_cast<Valtype>(wv[5]) << 16)
 415             | (static_cast<Valtype>(wv[6]) << 8)
 416             | static_cast<Valtype>(wv[7]));
 417   }
 418
 419   static inline void
 420   writeval(unsigned char* wv, Valtype v)
 421   {
 422     wv[0] = v >> 56;
 423     wv[1] = v >> 48;
 424     wv[2] = v >> 40;
 425     wv[3] = v >> 32;
 426     wv[4] = v >> 24;
 427     wv[5] = v >> 16;
 428     wv[6] = v >> 8;
 429     wv[7] = v;
 430   }
 431 };
 432
 433 // Swap_aligned32 is a template based on size and on whether the
 434 // target is big endian.  It defines the type Valtype and the
 435 // functions readval and writeval.  The functions read and write
 436 // values of the appropriate size out of buffers which may not be
 437 // 64-bit aligned, but are 32-bit aligned.
 438
 439 template<int size, bool big_endian>
 440 struct Swap_aligned32
 441 {
 442   typedef typename Valtype_base<size>::Valtype Valtype;
 443
 444   static inline Valtype
 445   readval(const unsigned char* wv)
 446   { return Swap<size, big_endian>::readval(
 447         reinterpret_cast<const Valtype*>(wv)); }
 448
 449   static inline void
 450   writeval(unsigned char* wv, Valtype v)
 451   { Swap<size, big_endian>::writeval(reinterpret_cast<Valtype*>(wv), v); }
 452 };
 453
 454 template<>
 455 struct Swap_aligned32<64, true>
 456 {
 457   typedef Valtype_base<64>::Valtype Valtype;
 458
 459   static inline Valtype
 460   readval(const unsigned char* wv)
 461   {
 462     return ((static_cast<Valtype>(Swap<32, true>::readval(wv)) << 32)
 463             | static_cast<Valtype>(Swap<32, true>::readval(wv + 4)));
 464   }
 465
 466   static inline void
 467   writeval(unsigned char* wv, Valtype v)
 468   {
 469     typedef Valtype_base<32>::Valtype Valtype32;
 470
 471     Swap<32, true>::writeval(wv, static_cast<Valtype32>(v >> 32));
 472     Swap<32, true>::writeval(wv + 4, static_cast<Valtype32>(v));
 473   }
 474 };
 475
 476 template<>
 477 struct Swap_aligned32<64, false>
 478 {
 479   typedef Valtype_base<64>::Valtype Valtype;
 480
 481   static inline Valtype
 482   readval(const unsigned char* wv)
 483   {
 484     return ((static_cast<Valtype>(Swap<32, false>::readval(wv + 4)) << 32)
 485             | static_cast<Valtype>(Swap<32, false>::readval(wv)));
 486   }
 487
 488   static inline void
 489   writeval(unsigned char* wv, Valtype v)
 490   {
 491     typedef Valtype_base<32>::Valtype Valtype32;
 492
 493     Swap<32, false>::writeval(wv + 4, static_cast<Valtype32>(v >> 32));
 494     Swap<32, false>::writeval(wv, static_cast<Valtype32>(v));
 495   }
 496 };
 497
 498 } // End namespace elfcpp.
 499
 500 #endif // !defined(ELFCPP_SWAP_H)