absl/debugging/internal/elf_mem_image.cc - third_party/github/abseil/abseil-cpp - Git at Google

 // Copyright 2017 The Abseil Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //      https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 // Allow dynamic symbol lookup in an in-memory Elf image.
 //

 #include "absl/debugging/internal/elf_mem_image.h"

 #ifdef ABSL_HAVE_ELF_MEM_IMAGE  // defined in elf_mem_image.h

 #include <string.h>

 #include <cassert>
 #include <cstddef>
 #include <cstdint>

 #include "absl/base/config.h"
 #include "absl/base/internal/raw_logging.h"

 // From binutils/include/elf/common.h (this doesn't appear to be documented
 // anywhere else).
 //
 //   /* This flag appears in a Versym structure.  It means that the symbol
 //      is hidden, and is only visible with an explicit version number.
 //      This is a GNU extension.  */
 //   #define VERSYM_HIDDEN           0x8000
 //
 //   /* This is the mask for the rest of the Versym information.  */
 //   #define VERSYM_VERSION          0x7fff

 #define VERSYM_VERSION 0x7fff

 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace debugging_internal {

 namespace {

 #if __SIZEOF_POINTER__ == 4
 const int kElfClass = ELFCLASS32;
 int ElfBind(const ElfW(Sym) *symbol) { return ELF32_ST_BIND(symbol->st_info); }
 int ElfType(const ElfW(Sym) *symbol) { return ELF32_ST_TYPE(symbol->st_info); }
 #elif __SIZEOF_POINTER__ == 8
 const int kElfClass = ELFCLASS64;
 int ElfBind(const ElfW(Sym) *symbol) { return ELF64_ST_BIND(symbol->st_info); }
 int ElfType(const ElfW(Sym) *symbol) { return ELF64_ST_TYPE(symbol->st_info); }
 #else
 const int kElfClass = -1;
 int ElfBind(const ElfW(Sym) *) {
   ABSL_RAW_LOG(FATAL, "Unexpected word size");
   return 0;
 }
 int ElfType(const ElfW(Sym) *) {
   ABSL_RAW_LOG(FATAL, "Unexpected word size");
   return 0;
 }
 #endif

 // Extract an element from one of the ELF tables, cast it to desired type.
 // This is just a simple arithmetic and a glorified cast.
 // Callers are responsible for bounds checking.
 template <typename T>
 const T *GetTableElement(const ElfW(Ehdr) * ehdr, ElfW(Off) table_offset,
                          ElfW(Word) element_size, size_t index) {
   return reinterpret_cast<const T*>(reinterpret_cast<const char *>(ehdr)
                                     + table_offset
                                     + index * element_size);
 }

 }  // namespace

 // The value of this variable doesn't matter; it's used only for its
 // unique address.
 const int ElfMemImage::kInvalidBaseSentinel = 0;

 ElfMemImage::ElfMemImage(const void *base) {
   ABSL_RAW_CHECK(base != kInvalidBase, "bad pointer");
   Init(base);
 }

 uint32_t ElfMemImage::GetNumSymbols() const { return num_syms_; }

 const ElfW(Sym) * ElfMemImage::GetDynsym(uint32_t index) const {
   ABSL_RAW_CHECK(index < GetNumSymbols(), "index out of range");
   return dynsym_ + index;
 }

 const ElfW(Versym) *ElfMemImage::GetVersym(uint32_t index) const {
   ABSL_RAW_CHECK(index < GetNumSymbols(), "index out of range");
   return versym_ + index;
 }

 const ElfW(Phdr) *ElfMemImage::GetPhdr(int index) const {
   ABSL_RAW_CHECK(index >= 0 && index < ehdr_->e_phnum, "index out of range");
   return GetTableElement<ElfW(Phdr)>(ehdr_, ehdr_->e_phoff, ehdr_->e_phentsize,
                                      static_cast<size_t>(index));
 }

 const char *ElfMemImage::GetDynstr(ElfW(Word) offset) const {
   ABSL_RAW_CHECK(offset < strsize_, "offset out of range");
   return dynstr_ + offset;
 }

 const void *ElfMemImage::GetSymAddr(const ElfW(Sym) *sym) const {
   if (sym->st_shndx == SHN_UNDEF || sym->st_shndx >= SHN_LORESERVE) {
     // Symbol corresponds to "special" (e.g. SHN_ABS) section.
     return reinterpret_cast<const void *>(sym->st_value);
   }
   ABSL_RAW_CHECK(link_base_ < sym->st_value, "symbol out of range");
   return GetTableElement<char>(ehdr_, 0, 1, sym->st_value - link_base_);
 }

 const ElfW(Verdef) *ElfMemImage::GetVerdef(int index) const {
   ABSL_RAW_CHECK(0 <= index && static_cast<size_t>(index) <= verdefnum_,
                  "index out of range");
   const ElfW(Verdef) *version_definition = verdef_;
   while (version_definition->vd_ndx < index && version_definition->vd_next) {
     const char *const version_definition_as_char =
         reinterpret_cast<const char *>(version_definition);
     version_definition =
         reinterpret_cast<const ElfW(Verdef) *>(version_definition_as_char +
                                                version_definition->vd_next);
   }
   return version_definition->vd_ndx == index ? version_definition : nullptr;
 }

 const ElfW(Verdaux) *ElfMemImage::GetVerdefAux(
     const ElfW(Verdef) *verdef) const {
   return reinterpret_cast<const ElfW(Verdaux) *>(verdef+1);
 }

 const char *ElfMemImage::GetVerstr(ElfW(Word) offset) const {
   ABSL_RAW_CHECK(offset < strsize_, "offset out of range");
   return dynstr_ + offset;
 }

 void ElfMemImage::Init(const void *base) {
   ehdr_      = nullptr;
   dynsym_    = nullptr;
   dynstr_    = nullptr;
   versym_    = nullptr;
   verdef_    = nullptr;
   num_syms_ = 0;
   strsize_   = 0;
   verdefnum_ = 0;
   // Sentinel: PT_LOAD .p_vaddr can't possibly be this.
   link_base_ = ~ElfW(Addr){0};  // NOLINT(readability/braces)
   if (!base) {
     return;
   }
   const char *const base_as_char = reinterpret_cast<const char *>(base);
   if (base_as_char[EI_MAG0] != ELFMAG0 || base_as_char[EI_MAG1] != ELFMAG1 ||
       base_as_char[EI_MAG2] != ELFMAG2 || base_as_char[EI_MAG3] != ELFMAG3) {
     assert(false);
     return;
   }
   int elf_class = base_as_char[EI_CLASS];
   if (elf_class != kElfClass) {
     assert(false);
     return;
   }
   switch (base_as_char[EI_DATA]) {
     case ELFDATA2LSB: {
 #ifndef ABSL_IS_LITTLE_ENDIAN
       assert(false);
       return;
 #endif
       break;
     }
     case ELFDATA2MSB: {
 #ifndef ABSL_IS_BIG_ENDIAN
       assert(false);
       return;
 #endif
       break;
     }
     default: {
       assert(false);
       return;
     }
   }

   ehdr_ = reinterpret_cast<const ElfW(Ehdr) *>(base);
   const ElfW(Phdr) *dynamic_program_header = nullptr;
   for (int i = 0; i < ehdr_->e_phnum; ++i) {
     const ElfW(Phdr) *const program_header = GetPhdr(i);
     switch (program_header->p_type) {
       case PT_LOAD:
         if (!~link_base_) {
           link_base_ = program_header->p_vaddr;
         }
         break;
       case PT_DYNAMIC:
         dynamic_program_header = program_header;
         break;
     }
   }
   if (!~link_base_ || !dynamic_program_header) {
     assert(false);
     // Mark this image as not present. Can not recur infinitely.
     Init(nullptr);
     return;
   }
   ptrdiff_t relocation =
       base_as_char - reinterpret_cast<const char *>(link_base_);
   ElfW(Dyn)* dynamic_entry = reinterpret_cast<ElfW(Dyn)*>(
       static_cast<intptr_t>(dynamic_program_header->p_vaddr) + relocation);
   uint32_t *sysv_hash = nullptr;
   uint32_t *gnu_hash = nullptr;
   for (; dynamic_entry->d_tag != DT_NULL; ++dynamic_entry) {
     const auto value =
         static_cast<intptr_t>(dynamic_entry->d_un.d_val) + relocation;
     switch (dynamic_entry->d_tag) {
       case DT_HASH:
         sysv_hash = reinterpret_cast<uint32_t *>(value);
         break;
       case DT_GNU_HASH:
         gnu_hash = reinterpret_cast<uint32_t *>(value);
         break;
       case DT_SYMTAB:
         dynsym_ = reinterpret_cast<ElfW(Sym) *>(value);
         break;
       case DT_STRTAB:
         dynstr_ = reinterpret_cast<const char *>(value);
         break;
       case DT_VERSYM:
         versym_ = reinterpret_cast<ElfW(Versym) *>(value);
         break;
       case DT_VERDEF:
         verdef_ = reinterpret_cast<ElfW(Verdef) *>(value);
         break;
       case DT_VERDEFNUM:
         verdefnum_ = static_cast<size_t>(dynamic_entry->d_un.d_val);
         break;
       case DT_STRSZ:
         strsize_ = static_cast<size_t>(dynamic_entry->d_un.d_val);
         break;
       default:
         // Unrecognized entries explicitly ignored.
         break;
     }
   }
   if ((!sysv_hash && !gnu_hash) || !dynsym_ || !dynstr_ || !versym_ ||
       !verdef_ || !verdefnum_ || !strsize_) {
     assert(false);  // invalid VDSO
     // Mark this image as not present. Can not recur infinitely.
     Init(nullptr);
     return;
   }
   if (sysv_hash) {
     num_syms_ = sysv_hash[1];
   } else {
     assert(gnu_hash);
     // Compute the number of symbols for DT_GNU_HASH, which is specified by
     // https://sourceware.org/gnu-gabi/program-loading-and-dynamic-linking.txt
     uint32_t nbuckets = gnu_hash[0];
     // The buckets array is located after the header (4 uint32) and the bloom
     // filter (size_t array of gnu_hash[2] elements).
     uint32_t *buckets = gnu_hash + 4 + sizeof(size_t) / 4 * gnu_hash[2];
     // Find the chain of the last non-empty bucket.
     uint32_t idx = 0;
     for (uint32_t i = nbuckets; i > 0;) {
       idx = buckets[--i];
       if (idx != 0) break;
     }
     if (idx != 0) {
       // Find the last element of the chain, which has an odd value.
       // Add one to get the number of symbols.
       uint32_t *chain = buckets + nbuckets - gnu_hash[1];
       while (chain[idx++] % 2 == 0) {
       }
     }
     num_syms_ = idx;
   }
 }

 bool ElfMemImage::LookupSymbol(const char *name,
                                const char *version,
                                int type,
                                SymbolInfo *info_out) const {
   for (const SymbolInfo& info : *this) {
     if (strcmp(info.name, name) == 0 && strcmp(info.version, version) == 0 &&
         ElfType(info.symbol) == type) {
       if (info_out) {
         *info_out = info;
       }
       return true;
     }
   }
   return false;
 }

 bool ElfMemImage::LookupSymbolByAddress(const void *address,
                                         SymbolInfo *info_out) const {
   for (const SymbolInfo& info : *this) {
     const char *const symbol_start =
         reinterpret_cast<const char *>(info.address);
     const char *const symbol_end = symbol_start + info.symbol->st_size;
     if (symbol_start <= address && address < symbol_end) {
       if (info_out) {
         // Client wants to know details for that symbol (the usual case).
         if (ElfBind(info.symbol) == STB_GLOBAL) {
           // Strong symbol; just return it.
           *info_out = info;
           return true;
         } else {
           // Weak or local. Record it, but keep looking for a strong one.
           *info_out = info;
         }
       } else {
         // Client only cares if there is an overlapping symbol.
         return true;
       }
     }
   }
   return false;
 }

 ElfMemImage::SymbolIterator::SymbolIterator(const void *const image,
                                             uint32_t index)
     : index_(index), image_(image) {}

 const ElfMemImage::SymbolInfo *ElfMemImage::SymbolIterator::operator->() const {
   return &info_;
 }

 const ElfMemImage::SymbolInfo& ElfMemImage::SymbolIterator::operator*() const {
   return info_;
 }

 bool ElfMemImage::SymbolIterator::operator==(const SymbolIterator &rhs) const {
   return this->image_ == rhs.image_ && this->index_ == rhs.index_;
 }

 bool ElfMemImage::SymbolIterator::operator!=(const SymbolIterator &rhs) const {
   return !(*this == rhs);
 }

 ElfMemImage::SymbolIterator &ElfMemImage::SymbolIterator::operator++() {
   this->Update(1);
   return *this;
 }

 ElfMemImage::SymbolIterator ElfMemImage::begin() const {
   SymbolIterator it(this, 0);
   it.Update(0);
   return it;
 }

 ElfMemImage::SymbolIterator ElfMemImage::end() const {
   return SymbolIterator(this, GetNumSymbols());
 }

 void ElfMemImage::SymbolIterator::Update(uint32_t increment) {
   const ElfMemImage *image = reinterpret_cast<const ElfMemImage *>(image_);
   ABSL_RAW_CHECK(image->IsPresent() || increment == 0, "");
   if (!image->IsPresent()) {
     return;
   }
   index_ += increment;
   if (index_ >= image->GetNumSymbols()) {
     index_ = image->GetNumSymbols();
     return;
   }
   const ElfW(Sym)    *symbol = image->GetDynsym(index_);
   const ElfW(Versym) *version_symbol = image->GetVersym(index_);
   ABSL_RAW_CHECK(symbol && version_symbol, "");
   const char *const symbol_name = image->GetDynstr(symbol->st_name);
 #if defined(__NetBSD__)
   const int version_index = version_symbol->vs_vers & VERSYM_VERSION;
 #else
   const ElfW(Versym) version_index = version_symbol[0] & VERSYM_VERSION;
 #endif
   const ElfW(Verdef) *version_definition = nullptr;
   const char *version_name = "";
   if (symbol->st_shndx == SHN_UNDEF) {
     // Undefined symbols reference DT_VERNEED, not DT_VERDEF, and
     // version_index could well be greater than verdefnum_, so calling
     // GetVerdef(version_index) may trigger assertion.
   } else {
     version_definition = image->GetVerdef(version_index);
   }
   if (version_definition) {
     // I am expecting 1 or 2 auxiliary entries: 1 for the version itself,
     // optional 2nd if the version has a parent.
     ABSL_RAW_CHECK(
         version_definition->vd_cnt == 1 || version_definition->vd_cnt == 2,
         "wrong number of entries");
     const ElfW(Verdaux) *version_aux = image->GetVerdefAux(version_definition);
     version_name = image->GetVerstr(version_aux->vda_name);
   }
   info_.name    = symbol_name;
   info_.version = version_name;
   info_.address = image->GetSymAddr(symbol);
   info_.symbol  = symbol;
 }

 }  // namespace debugging_internal
 ABSL_NAMESPACE_END
 }  // namespace absl

 #endif  // ABSL_HAVE_ELF_MEM_IMAGE
	// Copyright 2017 The Abseil Authors.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// https://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	// Allow dynamic symbol lookup in an in-memory Elf image.
	//

	#include "absl/debugging/internal/elf_mem_image.h"

	#ifdef ABSL_HAVE_ELF_MEM_IMAGE // defined in elf_mem_image.h

	#include <string.h>

	#include <cassert>
	#include <cstddef>
	#include <cstdint>

	#include "absl/base/config.h"
	#include "absl/base/internal/raw_logging.h"

	// From binutils/include/elf/common.h (this doesn't appear to be documented
	// anywhere else).
	//
	// /* This flag appears in a Versym structure. It means that the symbol
	// is hidden, and is only visible with an explicit version number.
	// This is a GNU extension. */
	// #define VERSYM_HIDDEN 0x8000
	//
	// /* This is the mask for the rest of the Versym information. */
	// #define VERSYM_VERSION 0x7fff

	#define VERSYM_VERSION 0x7fff

	namespace absl {
	ABSL_NAMESPACE_BEGIN
	namespace debugging_internal {

	namespace {

	#if __SIZEOF_POINTER__ == 4
	const int kElfClass = ELFCLASS32;
	int ElfBind(const ElfW(Sym) *symbol) { return ELF32_ST_BIND(symbol->st_info); }
	int ElfType(const ElfW(Sym) *symbol) { return ELF32_ST_TYPE(symbol->st_info); }
	#elif __SIZEOF_POINTER__ == 8
	const int kElfClass = ELFCLASS64;
	int ElfBind(const ElfW(Sym) *symbol) { return ELF64_ST_BIND(symbol->st_info); }
	int ElfType(const ElfW(Sym) *symbol) { return ELF64_ST_TYPE(symbol->st_info); }
	#else
	const int kElfClass = -1;
	int ElfBind(const ElfW(Sym) *) {
	ABSL_RAW_LOG(FATAL, "Unexpected word size");
	return 0;
	}
	int ElfType(const ElfW(Sym) *) {
	ABSL_RAW_LOG(FATAL, "Unexpected word size");
	return 0;
	}
	#endif

	// Extract an element from one of the ELF tables, cast it to desired type.
	// This is just a simple arithmetic and a glorified cast.
	// Callers are responsible for bounds checking.
	template <typename T>
	const T GetTableElement(const ElfW(Ehdr) ehdr, ElfW(Off) table_offset,
	ElfW(Word) element_size, size_t index) {
	return reinterpret_cast<const T>(reinterpret_cast<const char >(ehdr)
	+ table_offset
	+ index * element_size);
	}

	} // namespace

	// The value of this variable doesn't matter; it's used only for its
	// unique address.
	const int ElfMemImage::kInvalidBaseSentinel = 0;

	ElfMemImage::ElfMemImage(const void *base) {
	ABSL_RAW_CHECK(base != kInvalidBase, "bad pointer");
	Init(base);
	}

	uint32_t ElfMemImage::GetNumSymbols() const { return num_syms_; }

	const ElfW(Sym) * ElfMemImage::GetDynsym(uint32_t index) const {
	ABSL_RAW_CHECK(index < GetNumSymbols(), "index out of range");
	return dynsym_ + index;
	}

	const ElfW(Versym) *ElfMemImage::GetVersym(uint32_t index) const {
	ABSL_RAW_CHECK(index < GetNumSymbols(), "index out of range");
	return versym_ + index;
	}

	const ElfW(Phdr) *ElfMemImage::GetPhdr(int index) const {
	ABSL_RAW_CHECK(index >= 0 && index < ehdr_->e_phnum, "index out of range");
	return GetTableElement<ElfW(Phdr)>(ehdr_, ehdr_->e_phoff, ehdr_->e_phentsize,
	static_cast<size_t>(index));
	}

	const char *ElfMemImage::GetDynstr(ElfW(Word) offset) const {
	ABSL_RAW_CHECK(offset < strsize_, "offset out of range");
	return dynstr_ + offset;
	}

	const void ElfMemImage::GetSymAddr(const ElfW(Sym) sym) const {
	if (sym->st_shndx == SHN_UNDEF \|\| sym->st_shndx >= SHN_LORESERVE) {
	// Symbol corresponds to "special" (e.g. SHN_ABS) section.
	return reinterpret_cast<const void *>(sym->st_value);
	}
	ABSL_RAW_CHECK(link_base_ < sym->st_value, "symbol out of range");
	return GetTableElement<char>(ehdr_, 0, 1, sym->st_value - link_base_);
	}

	const ElfW(Verdef) *ElfMemImage::GetVerdef(int index) const {
	ABSL_RAW_CHECK(0 <= index && static_cast<size_t>(index) <= verdefnum_,
	"index out of range");
	const ElfW(Verdef) *version_definition = verdef_;
	while (version_definition->vd_ndx < index && version_definition->vd_next) {
	const char *const version_definition_as_char =
	reinterpret_cast<const char *>(version_definition);
	version_definition =
	reinterpret_cast<const ElfW(Verdef) *>(version_definition_as_char +
	version_definition->vd_next);
	}
	return version_definition->vd_ndx == index ? version_definition : nullptr;
	}

	const ElfW(Verdaux) *ElfMemImage::GetVerdefAux(
	const ElfW(Verdef) *verdef) const {
	return reinterpret_cast<const ElfW(Verdaux) *>(verdef+1);
	}

	const char *ElfMemImage::GetVerstr(ElfW(Word) offset) const {
	ABSL_RAW_CHECK(offset < strsize_, "offset out of range");
	return dynstr_ + offset;
	}

	void ElfMemImage::Init(const void *base) {
	ehdr_ = nullptr;
	dynsym_ = nullptr;
	dynstr_ = nullptr;
	versym_ = nullptr;
	verdef_ = nullptr;
	num_syms_ = 0;
	strsize_ = 0;
	verdefnum_ = 0;
	// Sentinel: PT_LOAD .p_vaddr can't possibly be this.
	link_base_ = ~ElfW(Addr){0}; // NOLINT(readability/braces)
	if (!base) {
	return;
	}
	const char const base_as_char = reinterpret_cast<const char >(base);
	if (base_as_char[EI_MAG0] != ELFMAG0 \|\| base_as_char[EI_MAG1] != ELFMAG1 \|\|
	base_as_char[EI_MAG2] != ELFMAG2 \|\| base_as_char[EI_MAG3] != ELFMAG3) {
	assert(false);
	return;
	}
	int elf_class = base_as_char[EI_CLASS];
	if (elf_class != kElfClass) {
	assert(false);
	return;
	}
	switch (base_as_char[EI_DATA]) {
	case ELFDATA2LSB: {
	#ifndef ABSL_IS_LITTLE_ENDIAN
	assert(false);
	return;
	#endif
	break;
	}
	case ELFDATA2MSB: {
	#ifndef ABSL_IS_BIG_ENDIAN
	assert(false);
	return;
	#endif
	break;
	}
	default: {
	assert(false);
	return;
	}
	}

	ehdr_ = reinterpret_cast<const ElfW(Ehdr) *>(base);
	const ElfW(Phdr) *dynamic_program_header = nullptr;
	for (int i = 0; i < ehdr_->e_phnum; ++i) {
	const ElfW(Phdr) *const program_header = GetPhdr(i);
	switch (program_header->p_type) {
	case PT_LOAD:
	if (!~link_base_) {
	link_base_ = program_header->p_vaddr;
	}
	break;
	case PT_DYNAMIC:
	dynamic_program_header = program_header;
	break;
	}
	}
	if (!~link_base_ \|\| !dynamic_program_header) {
	assert(false);
	// Mark this image as not present. Can not recur infinitely.
	Init(nullptr);
	return;
	}
	ptrdiff_t relocation =
	base_as_char - reinterpret_cast<const char *>(link_base_);
	ElfW(Dyn)* dynamic_entry = reinterpret_cast<ElfW(Dyn)*>(
	static_cast<intptr_t>(dynamic_program_header->p_vaddr) + relocation);
	uint32_t *sysv_hash = nullptr;
	uint32_t *gnu_hash = nullptr;
	for (; dynamic_entry->d_tag != DT_NULL; ++dynamic_entry) {
	const auto value =
	static_cast<intptr_t>(dynamic_entry->d_un.d_val) + relocation;
	switch (dynamic_entry->d_tag) {
	case DT_HASH:
	sysv_hash = reinterpret_cast<uint32_t *>(value);
	break;
	case DT_GNU_HASH:
	gnu_hash = reinterpret_cast<uint32_t *>(value);
	break;
	case DT_SYMTAB:
	dynsym_ = reinterpret_cast<ElfW(Sym) *>(value);
	break;
	case DT_STRTAB:
	dynstr_ = reinterpret_cast<const char *>(value);
	break;
	case DT_VERSYM:
	versym_ = reinterpret_cast<ElfW(Versym) *>(value);
	break;
	case DT_VERDEF:
	verdef_ = reinterpret_cast<ElfW(Verdef) *>(value);
	break;
	case DT_VERDEFNUM:
	verdefnum_ = static_cast<size_t>(dynamic_entry->d_un.d_val);
	break;
	case DT_STRSZ:
	strsize_ = static_cast<size_t>(dynamic_entry->d_un.d_val);
	break;
	default:
	// Unrecognized entries explicitly ignored.
	break;
	}
	}
	if ((!sysv_hash && !gnu_hash) \|\| !dynsym_ \|\| !dynstr_ \|\| !versym_ \|\|
	!verdef_ \|\| !verdefnum_ \|\| !strsize_) {
	assert(false); // invalid VDSO
	// Mark this image as not present. Can not recur infinitely.
	Init(nullptr);
	return;
	}
	if (sysv_hash) {
	num_syms_ = sysv_hash[1];
	} else {
	assert(gnu_hash);
	// Compute the number of symbols for DT_GNU_HASH, which is specified by
	// https://sourceware.org/gnu-gabi/program-loading-and-dynamic-linking.txt
	uint32_t nbuckets = gnu_hash[0];
	// The buckets array is located after the header (4 uint32) and the bloom
	// filter (size_t array of gnu_hash[2] elements).
	uint32_t buckets = gnu_hash + 4 + sizeof(size_t) / 4 gnu_hash[2];
	// Find the chain of the last non-empty bucket.
	uint32_t idx = 0;
	for (uint32_t i = nbuckets; i > 0;) {
	idx = buckets[--i];
	if (idx != 0) break;
	}
	if (idx != 0) {
	// Find the last element of the chain, which has an odd value.
	// Add one to get the number of symbols.
	uint32_t *chain = buckets + nbuckets - gnu_hash[1];
	while (chain[idx++] % 2 == 0) {
	}
	}
	num_syms_ = idx;
	}
	}

	bool ElfMemImage::LookupSymbol(const char *name,
	const char *version,
	int type,
	SymbolInfo *info_out) const {
	for (const SymbolInfo& info : *this) {
	if (strcmp(info.name, name) == 0 && strcmp(info.version, version) == 0 &&
	ElfType(info.symbol) == type) {
	if (info_out) {
	*info_out = info;
	}
	return true;
	}
	}
	return false;
	}

	bool ElfMemImage::LookupSymbolByAddress(const void *address,
	SymbolInfo *info_out) const {
	for (const SymbolInfo& info : *this) {
	const char *const symbol_start =
	reinterpret_cast<const char *>(info.address);
	const char *const symbol_end = symbol_start + info.symbol->st_size;
	if (symbol_start <= address && address < symbol_end) {
	if (info_out) {
	// Client wants to know details for that symbol (the usual case).
	if (ElfBind(info.symbol) == STB_GLOBAL) {
	// Strong symbol; just return it.
	*info_out = info;
	return true;
	} else {
	// Weak or local. Record it, but keep looking for a strong one.
	*info_out = info;
	}
	} else {
	// Client only cares if there is an overlapping symbol.
	return true;
	}
	}
	}
	return false;
	}

	ElfMemImage::SymbolIterator::SymbolIterator(const void *const image,
	uint32_t index)
	: index_(index), image_(image) {}

	const ElfMemImage::SymbolInfo *ElfMemImage::SymbolIterator::operator->() const {
	return &info_;
	}

	const ElfMemImage::SymbolInfo& ElfMemImage::SymbolIterator::operator*() const {
	return info_;
	}

	bool ElfMemImage::SymbolIterator::operator==(const SymbolIterator &rhs) const {
	return this->image_ == rhs.image_ && this->index_ == rhs.index_;
	}

	bool ElfMemImage::SymbolIterator::operator!=(const SymbolIterator &rhs) const {
	return !(*this == rhs);
	}

	ElfMemImage::SymbolIterator &ElfMemImage::SymbolIterator::operator++() {
	this->Update(1);
	return *this;
	}

	ElfMemImage::SymbolIterator ElfMemImage::begin() const {
	SymbolIterator it(this, 0);
	it.Update(0);
	return it;
	}

	ElfMemImage::SymbolIterator ElfMemImage::end() const {
	return SymbolIterator(this, GetNumSymbols());
	}

	void ElfMemImage::SymbolIterator::Update(uint32_t increment) {
	const ElfMemImage image = reinterpret_cast<const ElfMemImage >(image_);
	ABSL_RAW_CHECK(image->IsPresent() \|\| increment == 0, "");
	if (!image->IsPresent()) {
	return;
	}
	index_ += increment;
	if (index_ >= image->GetNumSymbols()) {
	index_ = image->GetNumSymbols();
	return;
	}
	const ElfW(Sym) *symbol = image->GetDynsym(index_);
	const ElfW(Versym) *version_symbol = image->GetVersym(index_);
	ABSL_RAW_CHECK(symbol && version_symbol, "");
	const char *const symbol_name = image->GetDynstr(symbol->st_name);
	#if defined(__NetBSD__)
	const int version_index = version_symbol->vs_vers & VERSYM_VERSION;
	#else
	const ElfW(Versym) version_index = version_symbol[0] & VERSYM_VERSION;
	#endif
	const ElfW(Verdef) *version_definition = nullptr;
	const char *version_name = "";
	if (symbol->st_shndx == SHN_UNDEF) {
	// Undefined symbols reference DT_VERNEED, not DT_VERDEF, and
	// version_index could well be greater than verdefnum_, so calling
	// GetVerdef(version_index) may trigger assertion.
	} else {
	version_definition = image->GetVerdef(version_index);
	}
	if (version_definition) {
	// I am expecting 1 or 2 auxiliary entries: 1 for the version itself,
	// optional 2nd if the version has a parent.
	ABSL_RAW_CHECK(
	version_definition->vd_cnt == 1 \|\| version_definition->vd_cnt == 2,
	"wrong number of entries");
	const ElfW(Verdaux) *version_aux = image->GetVerdefAux(version_definition);
	version_name = image->GetVerstr(version_aux->vda_name);
	}
	info_.name = symbol_name;
	info_.version = version_name;
	info_.address = image->GetSymAddr(symbol);
	info_.symbol = symbol;
	}

	} // namespace debugging_internal
	ABSL_NAMESPACE_END
	} // namespace absl

	#endif // ABSL_HAVE_ELF_MEM_IMAGE