elfcpp/elfcpp_swap.h

   1 // elfcpp_swap.h -- Handle swapping for elfcpp   -*- C++ -*-
   2
   3 // Copyright (C) 2006-2021 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 #endif // defined(HAVE_BYTESWAP_H)
  50
  51 // Provide our own versions of the byteswap functions.
  52 #if !HAVE_DECL_BSWAP_16
  53 static inline uint16_t
  54 bswap_16(uint16_t v)
  55 {
  56   return ((v >> 8) & 0xff) | ((v & 0xff) << 8);
  57 }
  58 #endif // !HAVE_DECL_BSWAP16
  59
  60 #if !HAVE_DECL_BSWAP_32
  61 static inline uint32_t
  62 bswap_32(uint32_t v)
  63 {
  64   return (  ((v & 0xff000000) >> 24)
  65           | ((v & 0x00ff0000) >>  8)
  66           | ((v & 0x0000ff00) <<  8)
  67           | ((v & 0x000000ff) << 24));
  68 }
  69 #endif // !HAVE_DECL_BSWAP32
  70
  71 #if !HAVE_DECL_BSWAP_64
  72 static inline uint64_t
  73 bswap_64(uint64_t v)
  74 {
  75   return (  ((v & 0xff00000000000000ULL) >> 56)
  76           | ((v & 0x00ff000000000000ULL) >> 40)
  77           | ((v & 0x0000ff0000000000ULL) >> 24)
  78           | ((v & 0x000000ff00000000ULL) >>  8)
  79           | ((v & 0x00000000ff000000ULL) <<  8)
  80           | ((v & 0x0000000000ff0000ULL) << 24)
  81           | ((v & 0x000000000000ff00ULL) << 40)
  82           | ((v & 0x00000000000000ffULL) << 56));
  83 }
  84 #endif // !HAVE_DECL_BSWAP64
  85
  86 // gcc 4.3 and later provides __builtin_bswap32 and __builtin_bswap64.
  87
  88 #if defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3))
  89 #undef bswap_32
  90 #define bswap_32 __builtin_bswap32
  91 #undef bswap_64
  92 #define bswap_64 __builtin_bswap64
  93 #endif
  94
  95 namespace elfcpp
  96 {
  97
  98 // Endian simply indicates whether the host is big endian or not.
  99
 100 struct Endian
 101 {
 102  public:
 103   // Used for template specializations.
 104   static const bool host_big_endian =
 105 #ifdef WORDS_BIGENDIAN
 106     true
 107 #else
 108     false
 109 #endif
 110     ;
 111 };
 112
 113 // Valtype_base is a template based on size (8, 16, 32, 64) which
 114 // defines the type Valtype as the unsigned integer, and
 115 // Signed_valtype as the signed integer, of the specified size.
 116
 117 template<int size>
 118 struct Valtype_base;
 119
 120 template<>
 121 struct Valtype_base<8>
 122 {
 123   typedef uint8_t Valtype;
 124   typedef int8_t Signed_valtype;
 125 };
 126
 127 template<>
 128 struct Valtype_base<16>
 129 {
 130   typedef uint16_t Valtype;
 131   typedef int16_t Signed_valtype;
 132 };
 133
 134 template<>
 135 struct Valtype_base<32>
 136 {
 137   typedef uint32_t Valtype;
 138   typedef int32_t Signed_valtype;
 139 };
 140
 141 template<>
 142 struct Valtype_base<64>
 143 {
 144   typedef uint64_t Valtype;
 145   typedef int64_t Signed_valtype;
 146 };
 147
 148 // Convert_endian is a template based on size and on whether the host
 149 // and target have the same endianness.  It defines the type Valtype
 150 // as Valtype_base does, and also defines a function convert_host
 151 // which takes an argument of type Valtype and returns the same value,
 152 // but swapped if the host and target have different endianness.
 153
 154 template<int size, bool same_endian>
 155 struct Convert_endian;
 156
 157 template<int size>
 158 struct Convert_endian<size, true>
 159 {
 160   typedef typename Valtype_base<size>::Valtype Valtype;
 161
 162   static inline Valtype
 163   convert_host(Valtype v)
 164   { return v; }
 165 };
 166
 167 template<>
 168 struct Convert_endian<8, false>
 169 {
 170   typedef Valtype_base<8>::Valtype Valtype;
 171
 172   static inline Valtype
 173   convert_host(Valtype v)
 174   { return v; }
 175 };
 176
 177 template<>
 178 struct Convert_endian<16, false>
 179 {
 180   typedef Valtype_base<16>::Valtype Valtype;
 181
 182   static inline Valtype
 183   convert_host(Valtype v)
 184   { return bswap_16(v); }
 185 };
 186
 187 template<>
 188 struct Convert_endian<32, false>
 189 {
 190   typedef Valtype_base<32>::Valtype Valtype;
 191
 192   static inline Valtype
 193   convert_host(Valtype v)
 194   { return bswap_32(v); }
 195 };
 196
 197 template<>
 198 struct Convert_endian<64, false>
 199 {
 200   typedef Valtype_base<64>::Valtype Valtype;
 201
 202   static inline Valtype
 203   convert_host(Valtype v)
 204   { return bswap_64(v); }
 205 };
 206
 207 // Convert is a template based on size and on whether the target is
 208 // big endian.  It defines Valtype and convert_host like
 209 // Convert_endian.  That is, it is just like Convert_endian except in
 210 // the meaning of the second template parameter.
 211
 212 template<int size, bool big_endian>
 213 struct Convert
 214 {
 215   typedef typename Valtype_base<size>::Valtype Valtype;
 216
 217   static inline Valtype
 218   convert_host(Valtype v)
 219   {
 220     return Convert_endian<size, big_endian == Endian::host_big_endian>
 221       ::convert_host(v);
 222   }
 223 };
 224
 225 // Swap is a template based on size and on whether the target is big
 226 // endian.  It defines the type Valtype and the functions readval and
 227 // writeval.  The functions read and write values of the appropriate
 228 // size out of buffers, swapping them if necessary.  readval and
 229 // writeval are overloaded to take pointers to the appropriate type or
 230 // pointers to unsigned char.
 231
 232 template<int size, bool big_endian>
 233 struct Swap
 234 {
 235   typedef typename Valtype_base<size>::Valtype Valtype;
 236
 237   static inline Valtype
 238   readval(const Valtype* wv)
 239   { return Convert<size, big_endian>::convert_host(*wv); }
 240
 241   static inline void
 242   writeval(Valtype* wv, Valtype v)
 243   { *wv = Convert<size, big_endian>::convert_host(v); }
 244
 245   static inline Valtype
 246   readval(const unsigned char* wv)
 247   { return readval(reinterpret_cast<const Valtype*>(wv)); }
 248
 249   static inline void
 250   writeval(unsigned char* wv, Valtype v)
 251   { writeval(reinterpret_cast<Valtype*>(wv), v); }
 252 };
 253
 254 // We need to specialize the 8-bit version of Swap to avoid
 255 // conflicting overloads, since both versions of readval and writeval
 256 // will have the same type parameters.
 257
 258 template<bool big_endian>
 259 struct Swap<8, big_endian>
 260 {
 261   typedef typename Valtype_base<8>::Valtype Valtype;
 262
 263   static inline Valtype
 264   readval(const Valtype* wv)
 265   { return *wv; }
 266
 267   static inline void
 268   writeval(Valtype* wv, Valtype v)
 269   { *wv = v; }
 270 };
 271
 272 // Swap_unaligned is a template based on size and on whether the
 273 // target is big endian.  It defines the type Valtype and the
 274 // functions readval and writeval.  The functions read and write
 275 // values of the appropriate size out of buffers which may be
 276 // misaligned.
 277
 278 template<int size, bool big_endian>
 279 struct Swap_unaligned;
 280
 281 template<bool big_endian>
 282 struct Swap_unaligned<8, big_endian>
 283 {
 284   typedef typename Valtype_base<8>::Valtype Valtype;
 285
 286   static inline Valtype
 287   readval(const unsigned char* wv)
 288   { return *wv; }
 289
 290   static inline void
 291   writeval(unsigned char* wv, Valtype v)
 292   { *wv = v; }
 293 };
 294
 295 template<>
 296 struct Swap_unaligned<16, false>
 297 {
 298   typedef Valtype_base<16>::Valtype Valtype;
 299
 300   static inline Valtype
 301   readval(const unsigned char* wv)
 302   {
 303     return (wv[1] << 8) | wv[0];
 304   }
 305
 306   static inline void
 307   writeval(unsigned char* wv, Valtype v)
 308   {
 309     wv[1] = v >> 8;
 310     wv[0] = v;
 311   }
 312 };
 313
 314 template<>
 315 struct Swap_unaligned<16, true>
 316 {
 317   typedef Valtype_base<16>::Valtype Valtype;
 318
 319   static inline Valtype
 320   readval(const unsigned char* wv)
 321   {
 322     return (wv[0] << 8) | wv[1];
 323   }
 324
 325   static inline void
 326   writeval(unsigned char* wv, Valtype v)
 327   {
 328     wv[0] = v >> 8;
 329     wv[1] = v;
 330   }
 331 };
 332
 333 template<>
 334 struct Swap_unaligned<32, false>
 335 {
 336   typedef Valtype_base<32>::Valtype Valtype;
 337
 338   static inline Valtype
 339   readval(const unsigned char* wv)
 340   {
 341     return (wv[3] << 24) | (wv[2] << 16) | (wv[1] << 8) | wv[0];
 342   }
 343
 344   static inline void
 345   writeval(unsigned char* wv, Valtype v)
 346   {
 347     wv[3] = v >> 24;
 348     wv[2] = v >> 16;
 349     wv[1] = v >> 8;
 350     wv[0] = v;
 351   }
 352 };
 353
 354 template<>
 355 struct Swap_unaligned<32, true>
 356 {
 357   typedef Valtype_base<32>::Valtype Valtype;
 358
 359   static inline Valtype
 360   readval(const unsigned char* wv)
 361   {
 362     return (wv[0] << 24) | (wv[1] << 16) | (wv[2] << 8) | wv[3];
 363   }
 364
 365   static inline void
 366   writeval(unsigned char* wv, Valtype v)
 367   {
 368     wv[0] = v >> 24;
 369     wv[1] = v >> 16;
 370     wv[2] = v >> 8;
 371     wv[3] = v;
 372   }
 373 };
 374
 375 template<>
 376 struct Swap_unaligned<64, false>
 377 {
 378   typedef Valtype_base<64>::Valtype Valtype;
 379
 380   static inline Valtype
 381   readval(const unsigned char* wv)
 382   {
 383     return ((static_cast<Valtype>(wv[7]) << 56)
 384             | (static_cast<Valtype>(wv[6]) << 48)
 385             | (static_cast<Valtype>(wv[5]) << 40)
 386             | (static_cast<Valtype>(wv[4]) << 32)
 387             | (static_cast<Valtype>(wv[3]) << 24)
 388             | (static_cast<Valtype>(wv[2]) << 16)
 389             | (static_cast<Valtype>(wv[1]) << 8)
 390             | static_cast<Valtype>(wv[0]));
 391   }
 392
 393   static inline void
 394   writeval(unsigned char* wv, Valtype v)
 395   {
 396     wv[7] = v >> 56;
 397     wv[6] = v >> 48;
 398     wv[5] = v >> 40;
 399     wv[4] = v >> 32;
 400     wv[3] = v >> 24;
 401     wv[2] = v >> 16;
 402     wv[1] = v >> 8;
 403     wv[0] = v;
 404   }
 405 };
 406
 407 template<>
 408 struct Swap_unaligned<64, true>
 409 {
 410   typedef Valtype_base<64>::Valtype Valtype;
 411
 412   static inline Valtype
 413   readval(const unsigned char* wv)
 414   {
 415     return ((static_cast<Valtype>(wv[0]) << 56)
 416             | (static_cast<Valtype>(wv[1]) << 48)
 417             | (static_cast<Valtype>(wv[2]) << 40)
 418             | (static_cast<Valtype>(wv[3]) << 32)
 419             | (static_cast<Valtype>(wv[4]) << 24)
 420             | (static_cast<Valtype>(wv[5]) << 16)
 421             | (static_cast<Valtype>(wv[6]) << 8)
 422             | static_cast<Valtype>(wv[7]));
 423   }
 424
 425   static inline void
 426   writeval(unsigned char* wv, Valtype v)
 427   {
 428     wv[0] = v >> 56;
 429     wv[1] = v >> 48;
 430     wv[2] = v >> 40;
 431     wv[3] = v >> 32;
 432     wv[4] = v >> 24;
 433     wv[5] = v >> 16;
 434     wv[6] = v >> 8;
 435     wv[7] = v;
 436   }
 437 };
 438
 439 // Swap_aligned32 is a template based on size and on whether the
 440 // target is big endian.  It defines the type Valtype and the
 441 // functions readval and writeval.  The functions read and write
 442 // values of the appropriate size out of buffers which may not be
 443 // 64-bit aligned, but are 32-bit aligned.
 444
 445 template<int size, bool big_endian>
 446 struct Swap_aligned32
 447 {
 448   typedef typename Valtype_base<size>::Valtype Valtype;
 449
 450   static inline Valtype
 451   readval(const unsigned char* wv)
 452   { return Swap<size, big_endian>::readval(
 453         reinterpret_cast<const Valtype*>(wv)); }
 454
 455   static inline void
 456   writeval(unsigned char* wv, Valtype v)
 457   { Swap<size, big_endian>::writeval(reinterpret_cast<Valtype*>(wv), v); }
 458 };
 459
 460 template<>
 461 struct Swap_aligned32<64, true>
 462 {
 463   typedef Valtype_base<64>::Valtype Valtype;
 464
 465   static inline Valtype
 466   readval(const unsigned char* wv)
 467   {
 468     return ((static_cast<Valtype>(Swap<32, true>::readval(wv)) << 32)
 469             | static_cast<Valtype>(Swap<32, true>::readval(wv + 4)));
 470   }
 471
 472   static inline void
 473   writeval(unsigned char* wv, Valtype v)
 474   {
 475     typedef Valtype_base<32>::Valtype Valtype32;
 476
 477     Swap<32, true>::writeval(wv, static_cast<Valtype32>(v >> 32));
 478     Swap<32, true>::writeval(wv + 4, static_cast<Valtype32>(v));
 479   }
 480 };
 481
 482 template<>
 483 struct Swap_aligned32<64, false>
 484 {
 485   typedef Valtype_base<64>::Valtype Valtype;
 486
 487   static inline Valtype
 488   readval(const unsigned char* wv)
 489   {
 490     return ((static_cast<Valtype>(Swap<32, false>::readval(wv + 4)) << 32)
 491             | static_cast<Valtype>(Swap<32, false>::readval(wv)));
 492   }
 493
 494   static inline void
 495   writeval(unsigned char* wv, Valtype v)
 496   {
 497     typedef Valtype_base<32>::Valtype Valtype32;
 498
 499     Swap<32, false>::writeval(wv + 4, static_cast<Valtype32>(v >> 32));
 500     Swap<32, false>::writeval(wv, static_cast<Valtype32>(v));
 501   }
 502 };
 503
 504 } // End namespace elfcpp.
 505
 506 #endif // !defined(ELFCPP_SWAP_H)