third_party/tcmalloc/chromium/src/base/elf_mem_image.cc

   1 // Copyright (c) 2008, Google Inc.
   2 // All rights reserved.
   3 //
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   6 // met:
   7 //
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   9 // notice, this list of conditions and the following disclaimer.
  10 //     * Redistributions in binary form must reproduce the above
  11 // copyright notice, this list of conditions and the following disclaimer
  12 // in the documentation and/or other materials provided with the
  13 // distribution.
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  15 // contributors may be used to endorse or promote products derived from
  16 // this software without specific prior written permission.
  17 //
  18 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  19 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  20 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  21 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  22 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  23 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  24 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  25 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  26 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  27 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  28 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  29
  30 // ---
  31 // Author: Paul Pluzhnikov
  32 //
  33 // Allow dynamic symbol lookup in an in-memory Elf image.
  34 //
  35
  36 #include "base/elf_mem_image.h"
  37
  38 #ifdef HAVE_ELF_MEM_IMAGE  // defined in elf_mem_image.h
  39
  40 #include <stddef.h>   // for size_t, ptrdiff_t
  41 #include "base/logging.h"
  42
  43 // From binutils/include/elf/common.h (this doesn't appear to be documented
  44 // anywhere else).
  45 //
  46 //   /* This flag appears in a Versym structure.  It means that the symbol
  47 //      is hidden, and is only visible with an explicit version number.
  48 //      This is a GNU extension.  */
  49 //   #define VERSYM_HIDDEN           0x8000
  50 //
  51 //   /* This is the mask for the rest of the Versym information.  */
  52 //   #define VERSYM_VERSION          0x7fff
  53
  54 #define VERSYM_VERSION 0x7fff
  55
  56 namespace base {
  57
  58 namespace {
  59 template <int N> class ElfClass {
  60  public:
  61   static const int kElfClass = -1;
  62   static int ElfBind(const ElfW(Sym) *) {
  63     CHECK(false); // << "Unexpected word size";
  64     return 0;
  65   }
  66   static int ElfType(const ElfW(Sym) *) {
  67     CHECK(false); // << "Unexpected word size";
  68     return 0;
  69   }
  70 };
  71
  72 template <> class ElfClass<32> {
  73  public:
  74   static const int kElfClass = ELFCLASS32;
  75   static int ElfBind(const ElfW(Sym) *symbol) {
  76     return ELF32_ST_BIND(symbol->st_info);
  77   }
  78   static int ElfType(const ElfW(Sym) *symbol) {
  79     return ELF32_ST_TYPE(symbol->st_info);
  80   }
  81 };
  82
  83 template <> class ElfClass<64> {
  84  public:
  85   static const int kElfClass = ELFCLASS64;
  86   static int ElfBind(const ElfW(Sym) *symbol) {
  87     return ELF64_ST_BIND(symbol->st_info);
  88   }
  89   static int ElfType(const ElfW(Sym) *symbol) {
  90     return ELF64_ST_TYPE(symbol->st_info);
  91   }
  92 };
  93
  94 typedef ElfClass<__WORDSIZE> CurrentElfClass;
  95
  96 // Extract an element from one of the ELF tables, cast it to desired type.
  97 // This is just a simple arithmetic and a glorified cast.
  98 // Callers are responsible for bounds checking.
  99 template <class T>
 100 const T* GetTableElement(const ElfW(Ehdr) *ehdr,
 101                          ElfW(Off) table_offset,
 102                          ElfW(Word) element_size,
 103                          size_t index) {
 104   return reinterpret_cast<const T*>(reinterpret_cast<const char *>(ehdr)
 105                                     + table_offset
 106                                     + index * element_size);
 107 }
 108 }  // namespace
 109
 110 const void *const ElfMemImage::kInvalidBase =
 111     reinterpret_cast<const void *>(~0L);
 112
 113 ElfMemImage::ElfMemImage(const void *base) {
 114   CHECK(base != kInvalidBase);
 115   Init(base);
 116 }
 117
 118 int ElfMemImage::GetNumSymbols() const {
 119   if (!hash_) {
 120     return 0;
 121   }
 122   // See http://www.caldera.com/developers/gabi/latest/ch5.dynamic.html#hash
 123   return hash_[1];
 124 }
 125
 126 const ElfW(Sym) *ElfMemImage::GetDynsym(int index) const {
 127   CHECK_LT(index, GetNumSymbols());
 128   return dynsym_ + index;
 129 }
 130
 131 const ElfW(Versym) *ElfMemImage::GetVersym(int index) const {
 132   CHECK_LT(index, GetNumSymbols());
 133   return versym_ + index;
 134 }
 135
 136 const ElfW(Phdr) *ElfMemImage::GetPhdr(int index) const {
 137   CHECK_LT(index, ehdr_->e_phnum);
 138   return GetTableElement<ElfW(Phdr)>(ehdr_,
 139                                      ehdr_->e_phoff,
 140                                      ehdr_->e_phentsize,
 141                                      index);
 142 }
 143
 144 const char *ElfMemImage::GetDynstr(ElfW(Word) offset) const {
 145   CHECK_LT(offset, strsize_);
 146   return dynstr_ + offset;
 147 }
 148
 149 const void *ElfMemImage::GetSymAddr(const ElfW(Sym) *sym) const {
 150   if (sym->st_shndx == SHN_UNDEF || sym->st_shndx >= SHN_LORESERVE) {
 151     // Symbol corresponds to "special" (e.g. SHN_ABS) section.
 152     return reinterpret_cast<const void *>(sym->st_value);
 153   }
 154   CHECK_LT(link_base_, sym->st_value);
 155   return GetTableElement<char>(ehdr_, 0, 1, sym->st_value) - link_base_;
 156 }
 157
 158 const ElfW(Verdef) *ElfMemImage::GetVerdef(int index) const {
 159   CHECK_LE(index, verdefnum_);
 160   const ElfW(Verdef) *version_definition = verdef_;
 161   while (version_definition->vd_ndx < index && version_definition->vd_next) {
 162     const char *const version_definition_as_char =
 163         reinterpret_cast<const char *>(version_definition);
 164     version_definition =
 165         reinterpret_cast<const ElfW(Verdef) *>(version_definition_as_char +
 166                                                version_definition->vd_next);
 167   }
 168   return version_definition->vd_ndx == index ? version_definition : NULL;
 169 }
 170
 171 const ElfW(Verdaux) *ElfMemImage::GetVerdefAux(
 172     const ElfW(Verdef) *verdef) const {
 173   return reinterpret_cast<const ElfW(Verdaux) *>(verdef+1);
 174 }
 175
 176 const char *ElfMemImage::GetVerstr(ElfW(Word) offset) const {
 177   CHECK_LT(offset, strsize_);
 178   return dynstr_ + offset;
 179 }
 180
 181 void ElfMemImage::Init(const void *base) {
 182   ehdr_      = NULL;
 183   dynsym_    = NULL;
 184   dynstr_    = NULL;
 185   versym_    = NULL;
 186   verdef_    = NULL;
 187   hash_      = NULL;
 188   strsize_   = 0;
 189   verdefnum_ = 0;
 190   link_base_ = ~0L;  // Sentinel: PT_LOAD .p_vaddr can't possibly be this.
 191   if (!base) {
 192     return;
 193   }
 194   const intptr_t base_as_uintptr_t = reinterpret_cast<uintptr_t>(base);
 195   // Fake VDSO has low bit set.
 196   const bool fake_vdso = ((base_as_uintptr_t & 1) != 0);
 197   base = reinterpret_cast<const void *>(base_as_uintptr_t & ~1);
 198   const char *const base_as_char = reinterpret_cast<const char *>(base);
 199   if (base_as_char[EI_MAG0] != ELFMAG0 || base_as_char[EI_MAG1] != ELFMAG1 ||
 200       base_as_char[EI_MAG2] != ELFMAG2 || base_as_char[EI_MAG3] != ELFMAG3) {
 201     RAW_DCHECK(false, "no ELF magic"); // at %p", base);
 202     return;
 203   }
 204   int elf_class = base_as_char[EI_CLASS];
 205   if (elf_class != CurrentElfClass::kElfClass) {
 206     DCHECK_EQ(elf_class, CurrentElfClass::kElfClass);
 207     return;
 208   }
 209   switch (base_as_char[EI_DATA]) {
 210     case ELFDATA2LSB: {
 211       if (__LITTLE_ENDIAN != __BYTE_ORDER) {
 212         DCHECK_EQ(__LITTLE_ENDIAN, __BYTE_ORDER); // << ": wrong byte order";
 213         return;
 214       }
 215       break;
 216     }
 217     case ELFDATA2MSB: {
 218       if (__BIG_ENDIAN != __BYTE_ORDER) {
 219         DCHECK_EQ(__BIG_ENDIAN, __BYTE_ORDER); // << ": wrong byte order";
 220         return;
 221       }
 222       break;
 223     }
 224     default: {
 225       RAW_DCHECK(false, "unexpected data encoding"); // << base_as_char[EI_DATA];
 226       return;
 227     }
 228   }
 229
 230   ehdr_ = reinterpret_cast<const ElfW(Ehdr) *>(base);
 231   const ElfW(Phdr) *dynamic_program_header = NULL;
 232   for (int i = 0; i < ehdr_->e_phnum; ++i) {
 233     const ElfW(Phdr) *const program_header = GetPhdr(i);
 234     switch (program_header->p_type) {
 235       case PT_LOAD:
 236         if (link_base_ == ~0L) {
 237           link_base_ = program_header->p_vaddr;
 238         }
 239         break;
 240       case PT_DYNAMIC:
 241         dynamic_program_header = program_header;
 242         break;
 243     }
 244   }
 245   if (link_base_ == ~0L || !dynamic_program_header) {
 246     RAW_DCHECK(~0L != link_base_, "no PT_LOADs in VDSO");
 247     RAW_DCHECK(dynamic_program_header, "no PT_DYNAMIC in VDSO");
 248     // Mark this image as not present. Can not recur infinitely.
 249     Init(0);
 250     return;
 251   }
 252   ptrdiff_t relocation =
 253       base_as_char - reinterpret_cast<const char *>(link_base_);
 254   ElfW(Dyn) *dynamic_entry =
 255       reinterpret_cast<ElfW(Dyn) *>(dynamic_program_header->p_vaddr +
 256                                     relocation);
 257   for (; dynamic_entry->d_tag != DT_NULL; ++dynamic_entry) {
 258     ElfW(Xword) value = dynamic_entry->d_un.d_val;
 259     if (fake_vdso) {
 260       // A complication: in the real VDSO, dynamic entries are not relocated
 261       // (it wasn't loaded by a dynamic loader). But when testing with a
 262       // "fake" dlopen()ed vdso library, the loader relocates some (but
 263       // not all!) of them before we get here.
 264       if (dynamic_entry->d_tag == DT_VERDEF) {
 265         // The only dynamic entry (of the ones we care about) libc-2.3.6
 266         // loader doesn't relocate.
 267         value += relocation;
 268       }
 269     } else {
 270       // Real VDSO. Everything needs to be relocated.
 271       value += relocation;
 272     }
 273     switch (dynamic_entry->d_tag) {
 274       case DT_HASH:
 275         hash_ = reinterpret_cast<ElfW(Word) *>(value);
 276         break;
 277       case DT_SYMTAB:
 278         dynsym_ = reinterpret_cast<ElfW(Sym) *>(value);
 279         break;
 280       case DT_STRTAB:
 281         dynstr_ = reinterpret_cast<const char *>(value);
 282         break;
 283       case DT_VERSYM:
 284         versym_ = reinterpret_cast<ElfW(Versym) *>(value);
 285         break;
 286       case DT_VERDEF:
 287         verdef_ = reinterpret_cast<ElfW(Verdef) *>(value);
 288         break;
 289       case DT_VERDEFNUM:
 290         verdefnum_ = dynamic_entry->d_un.d_val;
 291         break;
 292       case DT_STRSZ:
 293         strsize_ = dynamic_entry->d_un.d_val;
 294         break;
 295       default:
 296         // Unrecognized entries explicitly ignored.
 297         break;
 298     }
 299   }
 300   if (!hash_ || !dynsym_ || !dynstr_ || !versym_ ||
 301       !verdef_ || !verdefnum_ || !strsize_) {
 302     RAW_DCHECK(hash_, "invalid VDSO (no DT_HASH)");
 303     RAW_DCHECK(dynsym_, "invalid VDSO (no DT_SYMTAB)");
 304     RAW_DCHECK(dynstr_, "invalid VDSO (no DT_STRTAB)");
 305     RAW_DCHECK(versym_, "invalid VDSO (no DT_VERSYM)");
 306     RAW_DCHECK(verdef_, "invalid VDSO (no DT_VERDEF)");
 307     RAW_DCHECK(verdefnum_, "invalid VDSO (no DT_VERDEFNUM)");
 308     RAW_DCHECK(strsize_, "invalid VDSO (no DT_STRSZ)");
 309     // Mark this image as not present. Can not recur infinitely.
 310     Init(0);
 311     return;
 312   }
 313 }
 314
 315 bool ElfMemImage::LookupSymbol(const char *name,
 316                                const char *version,
 317                                int type,
 318                                SymbolInfo *info) const {
 319   for (SymbolIterator it = begin(); it != end(); ++it) {
 320     if (strcmp(it->name, name) == 0 && strcmp(it->version, version) == 0 &&
 321         CurrentElfClass::ElfType(it->symbol) == type) {
 322       if (info) {
 323         *info = *it;
 324       }
 325       return true;
 326     }
 327   }
 328   return false;
 329 }
 330
 331 bool ElfMemImage::LookupSymbolByAddress(const void *address,
 332                                         SymbolInfo *info_out) const {
 333   for (SymbolIterator it = begin(); it != end(); ++it) {
 334     const char *const symbol_start =
 335         reinterpret_cast<const char *>(it->address);
 336     const char *const symbol_end = symbol_start + it->symbol->st_size;
 337     if (symbol_start <= address && address < symbol_end) {
 338       if (info_out) {
 339         // Client wants to know details for that symbol (the usual case).
 340         if (CurrentElfClass::ElfBind(it->symbol) == STB_GLOBAL) {
 341           // Strong symbol; just return it.
 342           *info_out = *it;
 343           return true;
 344         } else {
 345           // Weak or local. Record it, but keep looking for a strong one.
 346           *info_out = *it;
 347         }
 348       } else {
 349         // Client only cares if there is an overlapping symbol.
 350         return true;
 351       }
 352     }
 353   }
 354   return false;
 355 }
 356
 357 ElfMemImage::SymbolIterator::SymbolIterator(const void *const image, int index)
 358     : index_(index), image_(image) {
 359 }
 360
 361 const ElfMemImage::SymbolInfo *ElfMemImage::SymbolIterator::operator->() const {
 362   return &info_;
 363 }
 364
 365 const ElfMemImage::SymbolInfo& ElfMemImage::SymbolIterator::operator*() const {
 366   return info_;
 367 }
 368
 369 bool ElfMemImage::SymbolIterator::operator==(const SymbolIterator &rhs) const {
 370   return this->image_ == rhs.image_ && this->index_ == rhs.index_;
 371 }
 372
 373 bool ElfMemImage::SymbolIterator::operator!=(const SymbolIterator &rhs) const {
 374   return !(*this == rhs);
 375 }
 376
 377 ElfMemImage::SymbolIterator &ElfMemImage::SymbolIterator::operator++() {
 378   this->Update(1);
 379   return *this;
 380 }
 381
 382 ElfMemImage::SymbolIterator ElfMemImage::begin() const {
 383   SymbolIterator it(this, 0);
 384   it.Update(0);
 385   return it;
 386 }
 387
 388 ElfMemImage::SymbolIterator ElfMemImage::end() const {
 389   return SymbolIterator(this, GetNumSymbols());
 390 }
 391
 392 void ElfMemImage::SymbolIterator::Update(int increment) {
 393   const ElfMemImage *image = reinterpret_cast<const ElfMemImage *>(image_);
 394   CHECK(image->IsPresent() || increment == 0);
 395   if (!image->IsPresent()) {
 396     return;
 397   }
 398   index_ += increment;
 399   if (index_ >= image->GetNumSymbols()) {
 400     index_ = image->GetNumSymbols();
 401     return;
 402   }
 403   const ElfW(Sym)    *symbol = image->GetDynsym(index_);
 404   const ElfW(Versym) *version_symbol = image->GetVersym(index_);
 405   CHECK(symbol && version_symbol);
 406   const char *const symbol_name = image->GetDynstr(symbol->st_name);
 407   const ElfW(Versym) version_index = version_symbol[0] & VERSYM_VERSION;
 408   const ElfW(Verdef) *version_definition = NULL;
 409   const char *version_name = "";
 410   if (symbol->st_shndx == SHN_UNDEF) {
 411     // Undefined symbols reference DT_VERNEED, not DT_VERDEF, and
 412     // version_index could well be greater than verdefnum_, so calling
 413     // GetVerdef(version_index) may trigger assertion.
 414   } else {
 415     version_definition = image->GetVerdef(version_index);
 416   }
 417   if (version_definition) {
 418     // I am expecting 1 or 2 auxiliary entries: 1 for the version itself,
 419     // optional 2nd if the version has a parent.
 420     CHECK_LE(1, version_definition->vd_cnt);
 421     CHECK_LE(version_definition->vd_cnt, 2);
 422     const ElfW(Verdaux) *version_aux = image->GetVerdefAux(version_definition);
 423     version_name = image->GetVerstr(version_aux->vda_name);
 424   }
 425   info_.name    = symbol_name;
 426   info_.version = version_name;
 427   info_.address = image->GetSymAddr(symbol);
 428   info_.symbol  = symbol;
 429 }
 430
 431 }  // namespace base
 432
 433 #endif  // HAVE_ELF_MEM_IMAGE