libunwindstack/ElfInterface.cpp - android_system_core - Gitiles

 /*
  * Copyright (C) 2017 The Android Open Source Project
  *
  * 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
  *
  *      http://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.
  */

 #include <elf.h>
 #include <stdint.h>

 #include <memory>
 #include <string>

 #include <7zCrc.h>
 #include <Xz.h>
 #include <XzCrc64.h>

 #include <unwindstack/DwarfSection.h>
 #include <unwindstack/ElfInterface.h>
 #include <unwindstack/Log.h>
 #include <unwindstack/Memory.h>
 #include <unwindstack/Regs.h>

 #include "DwarfDebugFrame.h"
 #include "DwarfEhFrame.h"
 #include "Symbols.h"

 namespace unwindstack {

 ElfInterface::~ElfInterface() {
   for (auto symbol : symbols_) {
     delete symbol;
   }
 }

 Memory* ElfInterface::CreateGnuDebugdataMemory() {
   if (gnu_debugdata_offset_ == 0 || gnu_debugdata_size_ == 0) {
     return nullptr;
   }

   // TODO: Only call these initialization functions once.
   CrcGenerateTable();
   Crc64GenerateTable();

   std::vector<uint8_t> src(gnu_debugdata_size_);
   if (!memory_->Read(gnu_debugdata_offset_, src.data(), gnu_debugdata_size_)) {
     gnu_debugdata_offset_ = 0;
     gnu_debugdata_size_ = static_cast<uint64_t>(-1);
     return nullptr;
   }

   ISzAlloc alloc;
   CXzUnpacker state;
   alloc.Alloc = [](void*, size_t size) { return malloc(size); };
   alloc.Free = [](void*, void* ptr) { return free(ptr); };

   XzUnpacker_Construct(&state, &alloc);

   std::unique_ptr<MemoryBuffer> dst(new MemoryBuffer);
   int return_val;
   size_t src_offset = 0;
   size_t dst_offset = 0;
   ECoderStatus status;
   dst->Resize(5 * gnu_debugdata_size_);
   do {
     size_t src_remaining = src.size() - src_offset;
     size_t dst_remaining = dst->Size() - dst_offset;
     if (dst_remaining < 2 * gnu_debugdata_size_) {
       dst->Resize(dst->Size() + 2 * gnu_debugdata_size_);
       dst_remaining += 2 * gnu_debugdata_size_;
     }
     return_val = XzUnpacker_Code(&state, dst->GetPtr(dst_offset), &dst_remaining, &src[src_offset],
                                  &src_remaining, CODER_FINISH_ANY, &status);
     src_offset += src_remaining;
     dst_offset += dst_remaining;
   } while (return_val == SZ_OK && status == CODER_STATUS_NOT_FINISHED);
   XzUnpacker_Free(&state);
   if (return_val != SZ_OK || !XzUnpacker_IsStreamWasFinished(&state)) {
     gnu_debugdata_offset_ = 0;
     gnu_debugdata_size_ = static_cast<uint64_t>(-1);
     return nullptr;
   }

   // Shrink back down to the exact size.
   dst->Resize(dst_offset);

   return dst.release();
 }

 template <typename AddressType>
 void ElfInterface::InitHeadersWithTemplate() {
   if (eh_frame_offset_ != 0) {
     eh_frame_.reset(new DwarfEhFrame<AddressType>(memory_));
     if (!eh_frame_->Init(eh_frame_offset_, eh_frame_size_)) {
       eh_frame_.reset(nullptr);
       eh_frame_offset_ = 0;
       eh_frame_size_ = static_cast<uint64_t>(-1);
     }
   }

   if (debug_frame_offset_ != 0) {
     debug_frame_.reset(new DwarfDebugFrame<AddressType>(memory_));
     if (!debug_frame_->Init(debug_frame_offset_, debug_frame_size_)) {
       debug_frame_.reset(nullptr);
       debug_frame_offset_ = 0;
       debug_frame_size_ = static_cast<uint64_t>(-1);
     }
   }
 }

 template <typename EhdrType, typename PhdrType, typename ShdrType>
 bool ElfInterface::ReadAllHeaders() {
   EhdrType ehdr;
   if (!memory_->Read(0, &ehdr, sizeof(ehdr))) {
     return false;
   }

   if (!ReadProgramHeaders<EhdrType, PhdrType>(ehdr)) {
     return false;
   }

   // We could still potentially unwind without the section header
   // information, so ignore any errors.
   if (!ReadSectionHeaders<EhdrType, ShdrType>(ehdr)) {
     log(0, "Malformed section header found, ignoring...");
   }
   return true;
 }

 template <typename EhdrType, typename PhdrType>
 bool ElfInterface::ReadProgramHeaders(const EhdrType& ehdr) {
   uint64_t offset = ehdr.e_phoff;
   for (size_t i = 0; i < ehdr.e_phnum; i++, offset += ehdr.e_phentsize) {
     PhdrType phdr;
     if (!memory_->ReadField(offset, &phdr, &phdr.p_type, sizeof(phdr.p_type))) {
       return false;
     }

     if (HandleType(offset, phdr.p_type)) {
       continue;
     }

     switch (phdr.p_type) {
     case PT_LOAD:
     {
       // Get the flags first, if this isn't an executable header, ignore it.
       if (!memory_->ReadField(offset, &phdr, &phdr.p_flags, sizeof(phdr.p_flags))) {
         return false;
       }
       if ((phdr.p_flags & PF_X) == 0) {
         continue;
       }

       if (!memory_->ReadField(offset, &phdr, &phdr.p_vaddr, sizeof(phdr.p_vaddr))) {
         return false;
       }
       if (!memory_->ReadField(offset, &phdr, &phdr.p_offset, sizeof(phdr.p_offset))) {
         return false;
       }
       if (!memory_->ReadField(offset, &phdr, &phdr.p_memsz, sizeof(phdr.p_memsz))) {
         return false;
       }
       pt_loads_[phdr.p_offset] = LoadInfo{phdr.p_offset, phdr.p_vaddr,
                                           static_cast<size_t>(phdr.p_memsz)};
       if (phdr.p_offset == 0) {
         load_bias_ = phdr.p_vaddr;
       }
       break;
     }

     case PT_GNU_EH_FRAME:
       if (!memory_->ReadField(offset, &phdr, &phdr.p_offset, sizeof(phdr.p_offset))) {
         return false;
       }
       eh_frame_offset_ = phdr.p_offset;
       if (!memory_->ReadField(offset, &phdr, &phdr.p_memsz, sizeof(phdr.p_memsz))) {
         return false;
       }
       eh_frame_size_ = phdr.p_memsz;
       break;

     case PT_DYNAMIC:
       if (!memory_->ReadField(offset, &phdr, &phdr.p_offset, sizeof(phdr.p_offset))) {
         return false;
       }
       dynamic_offset_ = phdr.p_offset;
       if (!memory_->ReadField(offset, &phdr, &phdr.p_memsz, sizeof(phdr.p_memsz))) {
         return false;
       }
       dynamic_size_ = phdr.p_memsz;
       break;
     }
   }
   return true;
 }

 template <typename EhdrType, typename ShdrType>
 bool ElfInterface::ReadSectionHeaders(const EhdrType& ehdr) {
   uint64_t offset = ehdr.e_shoff;
   uint64_t sec_offset = 0;
   uint64_t sec_size = 0;

   // Get the location of the section header names.
   // If something is malformed in the header table data, we aren't going
   // to terminate, we'll simply ignore this part.
   ShdrType shdr;
   if (ehdr.e_shstrndx < ehdr.e_shnum) {
     uint64_t sh_offset = offset + ehdr.e_shstrndx * ehdr.e_shentsize;
     if (memory_->ReadField(sh_offset, &shdr, &shdr.sh_offset, sizeof(shdr.sh_offset)) &&
         memory_->ReadField(sh_offset, &shdr, &shdr.sh_size, sizeof(shdr.sh_size))) {
       sec_offset = shdr.sh_offset;
       sec_size = shdr.sh_size;
     }
   }

   // Skip the first header, it's always going to be NULL.
   offset += ehdr.e_shentsize;
   for (size_t i = 1; i < ehdr.e_shnum; i++, offset += ehdr.e_shentsize) {
     if (!memory_->ReadField(offset, &shdr, &shdr.sh_type, sizeof(shdr.sh_type))) {
       return false;
     }

     if (shdr.sh_type == SHT_SYMTAB || shdr.sh_type == SHT_DYNSYM) {
       if (!memory_->Read(offset, &shdr, sizeof(shdr))) {
         return false;
       }
       // Need to go get the information about the section that contains
       // the string terminated names.
       ShdrType str_shdr;
       if (shdr.sh_link >= ehdr.e_shnum) {
         return false;
       }
       uint64_t str_offset = ehdr.e_shoff + shdr.sh_link * ehdr.e_shentsize;
       if (!memory_->ReadField(str_offset, &str_shdr, &str_shdr.sh_type, sizeof(str_shdr.sh_type))) {
         return false;
       }
       if (str_shdr.sh_type != SHT_STRTAB) {
         return false;
       }
       if (!memory_->ReadField(str_offset, &str_shdr, &str_shdr.sh_offset,
                               sizeof(str_shdr.sh_offset))) {
         return false;
       }
       if (!memory_->ReadField(str_offset, &str_shdr, &str_shdr.sh_size, sizeof(str_shdr.sh_size))) {
         return false;
       }
       symbols_.push_back(new Symbols(shdr.sh_offset, shdr.sh_size, shdr.sh_entsize,
                                      str_shdr.sh_offset, str_shdr.sh_size));
     } else if (shdr.sh_type == SHT_PROGBITS && sec_size != 0) {
       // Look for the .debug_frame and .gnu_debugdata.
       if (!memory_->ReadField(offset, &shdr, &shdr.sh_name, sizeof(shdr.sh_name))) {
         return false;
       }
       if (shdr.sh_name < sec_size) {
         std::string name;
         if (memory_->ReadString(sec_offset + shdr.sh_name, &name)) {
           uint64_t* offset_ptr = nullptr;
           uint64_t* size_ptr = nullptr;
           if (name == ".debug_frame") {
             offset_ptr = &debug_frame_offset_;
             size_ptr = &debug_frame_size_;
           } else if (name == ".gnu_debugdata") {
             offset_ptr = &gnu_debugdata_offset_;
             size_ptr = &gnu_debugdata_size_;
           }
           if (offset_ptr != nullptr &&
               memory_->ReadField(offset, &shdr, &shdr.sh_offset, sizeof(shdr.sh_offset)) &&
               memory_->ReadField(offset, &shdr, &shdr.sh_size, sizeof(shdr.sh_size))) {
             *offset_ptr = shdr.sh_offset;
             *size_ptr = shdr.sh_size;
           }
         }
       }
     }
   }
   return true;
 }

 template <typename DynType>
 bool ElfInterface::GetSonameWithTemplate(std::string* soname) {
   if (soname_type_ == SONAME_INVALID) {
     return false;
   }
   if (soname_type_ == SONAME_VALID) {
     *soname = soname_;
     return true;
   }

   soname_type_ = SONAME_INVALID;

   uint64_t soname_offset = 0;
   uint64_t strtab_offset = 0;
   uint64_t strtab_size = 0;

   // Find the soname location from the dynamic headers section.
   DynType dyn;
   uint64_t offset = dynamic_offset_;
   uint64_t max_offset = offset + dynamic_size_;
   for (uint64_t offset = dynamic_offset_; offset < max_offset; offset += sizeof(DynType)) {
     if (!memory_->Read(offset, &dyn, sizeof(dyn))) {
       return false;
     }

     if (dyn.d_tag == DT_STRTAB) {
       strtab_offset = dyn.d_un.d_ptr;
     } else if (dyn.d_tag == DT_STRSZ) {
       strtab_size = dyn.d_un.d_val;
     } else if (dyn.d_tag == DT_SONAME) {
       soname_offset = dyn.d_un.d_val;
     } else if (dyn.d_tag == DT_NULL) {
       break;
     }
   }

   soname_offset += strtab_offset;
   if (soname_offset >= strtab_offset + strtab_size) {
     return false;
   }
   if (!memory_->ReadString(soname_offset, &soname_)) {
     return false;
   }
   soname_type_ = SONAME_VALID;
   *soname = soname_;
   return true;
 }

 template <typename SymType>
 bool ElfInterface::GetFunctionNameWithTemplate(uint64_t addr, std::string* name,
                                                uint64_t* func_offset) {
   if (symbols_.empty()) {
     return false;
   }

   for (const auto symbol : symbols_) {
     if (symbol->GetName<SymType>(addr, load_bias_, memory_, name, func_offset)) {
       return true;
     }
   }
   return false;
 }

 bool ElfInterface::Step(uint64_t pc, Regs* regs, Memory* process_memory, bool* finished) {
   // Need to subtract off the load_bias to get the correct pc.
   if (pc < load_bias_) {
     return false;
   }
   pc -= load_bias_;

   // Try the eh_frame first.
   DwarfSection* eh_frame = eh_frame_.get();
   if (eh_frame != nullptr && eh_frame->Step(pc, regs, process_memory, finished)) {
     return true;
   }

   // Try the debug_frame next.
   DwarfSection* debug_frame = debug_frame_.get();
   if (debug_frame != nullptr && debug_frame->Step(pc, regs, process_memory, finished)) {
     return true;
   }
   return false;
 }

 // This is an estimation of the size of the elf file using the location
 // of the section headers and size. This assumes that the section headers
 // are at the end of the elf file. If the elf has a load bias, the size
 // will be too large, but this is acceptable.
 template <typename EhdrType>
 void ElfInterface::GetMaxSizeWithTemplate(Memory* memory, uint64_t* size) {
   EhdrType ehdr;
   if (!memory->Read(0, &ehdr, sizeof(ehdr))) {
     return;
   }
   if (ehdr.e_shnum == 0) {
     return;
   }
   *size = ehdr.e_shoff + ehdr.e_shentsize * ehdr.e_shnum;
 }

 // Instantiate all of the needed template functions.
 template void ElfInterface::InitHeadersWithTemplate<uint32_t>();
 template void ElfInterface::InitHeadersWithTemplate<uint64_t>();

 template bool ElfInterface::ReadAllHeaders<Elf32_Ehdr, Elf32_Phdr, Elf32_Shdr>();
 template bool ElfInterface::ReadAllHeaders<Elf64_Ehdr, Elf64_Phdr, Elf64_Shdr>();

 template bool ElfInterface::ReadProgramHeaders<Elf32_Ehdr, Elf32_Phdr>(const Elf32_Ehdr&);
 template bool ElfInterface::ReadProgramHeaders<Elf64_Ehdr, Elf64_Phdr>(const Elf64_Ehdr&);

 template bool ElfInterface::ReadSectionHeaders<Elf32_Ehdr, Elf32_Shdr>(const Elf32_Ehdr&);
 template bool ElfInterface::ReadSectionHeaders<Elf64_Ehdr, Elf64_Shdr>(const Elf64_Ehdr&);

 template bool ElfInterface::GetSonameWithTemplate<Elf32_Dyn>(std::string*);
 template bool ElfInterface::GetSonameWithTemplate<Elf64_Dyn>(std::string*);

 template bool ElfInterface::GetFunctionNameWithTemplate<Elf32_Sym>(uint64_t, std::string*,
                                                                    uint64_t*);
 template bool ElfInterface::GetFunctionNameWithTemplate<Elf64_Sym>(uint64_t, std::string*,
                                                                    uint64_t*);

 template void ElfInterface::GetMaxSizeWithTemplate<Elf32_Ehdr>(Memory*, uint64_t*);
 template void ElfInterface::GetMaxSizeWithTemplate<Elf64_Ehdr>(Memory*, uint64_t*);

 }  // namespace unwindstack
	/*
	* Copyright (C) 2017 The Android Open Source Project
	*
	* 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
	*
	* http://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.
	*/

	#include <elf.h>
	#include <stdint.h>

	#include <memory>
	#include <string>

	#include <7zCrc.h>
	#include <Xz.h>
	#include <XzCrc64.h>

	#include <unwindstack/DwarfSection.h>
	#include <unwindstack/ElfInterface.h>
	#include <unwindstack/Log.h>
	#include <unwindstack/Memory.h>
	#include <unwindstack/Regs.h>

	#include "DwarfDebugFrame.h"
	#include "DwarfEhFrame.h"
	#include "Symbols.h"

	namespace unwindstack {

	ElfInterface::~ElfInterface() {
	for (auto symbol : symbols_) {
	delete symbol;
	}
	}

	Memory* ElfInterface::CreateGnuDebugdataMemory() {
	if (gnu_debugdata_offset_ == 0 \|\| gnu_debugdata_size_ == 0) {
	return nullptr;
	}

	// TODO: Only call these initialization functions once.
	CrcGenerateTable();
	Crc64GenerateTable();

	std::vector<uint8_t> src(gnu_debugdata_size_);
	if (!memory_->Read(gnu_debugdata_offset_, src.data(), gnu_debugdata_size_)) {
	gnu_debugdata_offset_ = 0;
	gnu_debugdata_size_ = static_cast<uint64_t>(-1);
	return nullptr;
	}

	ISzAlloc alloc;
	CXzUnpacker state;
	alloc.Alloc = [](void*, size_t size) { return malloc(size); };
	alloc.Free = [](void, void ptr) { return free(ptr); };

	XzUnpacker_Construct(&state, &alloc);

	std::unique_ptr<MemoryBuffer> dst(new MemoryBuffer);
	int return_val;
	size_t src_offset = 0;
	size_t dst_offset = 0;
	ECoderStatus status;
	dst->Resize(5 * gnu_debugdata_size_);
	do {
	size_t src_remaining = src.size() - src_offset;
	size_t dst_remaining = dst->Size() - dst_offset;
	if (dst_remaining < 2 * gnu_debugdata_size_) {
	dst->Resize(dst->Size() + 2 * gnu_debugdata_size_);
	dst_remaining += 2 * gnu_debugdata_size_;
	}
	return_val = XzUnpacker_Code(&state, dst->GetPtr(dst_offset), &dst_remaining, &src[src_offset],
	&src_remaining, CODER_FINISH_ANY, &status);
	src_offset += src_remaining;
	dst_offset += dst_remaining;
	} while (return_val == SZ_OK && status == CODER_STATUS_NOT_FINISHED);
	XzUnpacker_Free(&state);
	if (return_val != SZ_OK \|\| !XzUnpacker_IsStreamWasFinished(&state)) {
	gnu_debugdata_offset_ = 0;
	gnu_debugdata_size_ = static_cast<uint64_t>(-1);
	return nullptr;
	}

	// Shrink back down to the exact size.
	dst->Resize(dst_offset);

	return dst.release();
	}

	template <typename AddressType>
	void ElfInterface::InitHeadersWithTemplate() {
	if (eh_frame_offset_ != 0) {
	eh_frame_.reset(new DwarfEhFrame<AddressType>(memory_));
	if (!eh_frame_->Init(eh_frame_offset_, eh_frame_size_)) {
	eh_frame_.reset(nullptr);
	eh_frame_offset_ = 0;
	eh_frame_size_ = static_cast<uint64_t>(-1);
	}
	}

	if (debug_frame_offset_ != 0) {
	debug_frame_.reset(new DwarfDebugFrame<AddressType>(memory_));
	if (!debug_frame_->Init(debug_frame_offset_, debug_frame_size_)) {
	debug_frame_.reset(nullptr);
	debug_frame_offset_ = 0;
	debug_frame_size_ = static_cast<uint64_t>(-1);
	}
	}
	}

	template <typename EhdrType, typename PhdrType, typename ShdrType>
	bool ElfInterface::ReadAllHeaders() {
	EhdrType ehdr;
	if (!memory_->Read(0, &ehdr, sizeof(ehdr))) {
	return false;
	}

	if (!ReadProgramHeaders<EhdrType, PhdrType>(ehdr)) {
	return false;
	}

	// We could still potentially unwind without the section header
	// information, so ignore any errors.
	if (!ReadSectionHeaders<EhdrType, ShdrType>(ehdr)) {
	log(0, "Malformed section header found, ignoring...");
	}
	return true;
	}

	template <typename EhdrType, typename PhdrType>
	bool ElfInterface::ReadProgramHeaders(const EhdrType& ehdr) {
	uint64_t offset = ehdr.e_phoff;
	for (size_t i = 0; i < ehdr.e_phnum; i++, offset += ehdr.e_phentsize) {
	PhdrType phdr;
	if (!memory_->ReadField(offset, &phdr, &phdr.p_type, sizeof(phdr.p_type))) {
	return false;
	}

	if (HandleType(offset, phdr.p_type)) {
	continue;
	}

	switch (phdr.p_type) {
	case PT_LOAD:
	{
	// Get the flags first, if this isn't an executable header, ignore it.
	if (!memory_->ReadField(offset, &phdr, &phdr.p_flags, sizeof(phdr.p_flags))) {
	return false;
	}
	if ((phdr.p_flags & PF_X) == 0) {
	continue;
	}

	if (!memory_->ReadField(offset, &phdr, &phdr.p_vaddr, sizeof(phdr.p_vaddr))) {
	return false;
	}
	if (!memory_->ReadField(offset, &phdr, &phdr.p_offset, sizeof(phdr.p_offset))) {
	return false;
	}
	if (!memory_->ReadField(offset, &phdr, &phdr.p_memsz, sizeof(phdr.p_memsz))) {
	return false;
	}
	pt_loads_[phdr.p_offset] = LoadInfo{phdr.p_offset, phdr.p_vaddr,
	static_cast<size_t>(phdr.p_memsz)};
	if (phdr.p_offset == 0) {
	load_bias_ = phdr.p_vaddr;
	}
	break;
	}

	case PT_GNU_EH_FRAME:
	if (!memory_->ReadField(offset, &phdr, &phdr.p_offset, sizeof(phdr.p_offset))) {
	return false;
	}
	eh_frame_offset_ = phdr.p_offset;
	if (!memory_->ReadField(offset, &phdr, &phdr.p_memsz, sizeof(phdr.p_memsz))) {
	return false;
	}
	eh_frame_size_ = phdr.p_memsz;
	break;

	case PT_DYNAMIC:
	if (!memory_->ReadField(offset, &phdr, &phdr.p_offset, sizeof(phdr.p_offset))) {
	return false;
	}
	dynamic_offset_ = phdr.p_offset;
	if (!memory_->ReadField(offset, &phdr, &phdr.p_memsz, sizeof(phdr.p_memsz))) {
	return false;
	}
	dynamic_size_ = phdr.p_memsz;
	break;
	}
	}
	return true;
	}

	template <typename EhdrType, typename ShdrType>
	bool ElfInterface::ReadSectionHeaders(const EhdrType& ehdr) {
	uint64_t offset = ehdr.e_shoff;
	uint64_t sec_offset = 0;
	uint64_t sec_size = 0;

	// Get the location of the section header names.
	// If something is malformed in the header table data, we aren't going
	// to terminate, we'll simply ignore this part.
	ShdrType shdr;
	if (ehdr.e_shstrndx < ehdr.e_shnum) {
	uint64_t sh_offset = offset + ehdr.e_shstrndx * ehdr.e_shentsize;
	if (memory_->ReadField(sh_offset, &shdr, &shdr.sh_offset, sizeof(shdr.sh_offset)) &&
	memory_->ReadField(sh_offset, &shdr, &shdr.sh_size, sizeof(shdr.sh_size))) {
	sec_offset = shdr.sh_offset;
	sec_size = shdr.sh_size;
	}
	}

	// Skip the first header, it's always going to be NULL.
	offset += ehdr.e_shentsize;
	for (size_t i = 1; i < ehdr.e_shnum; i++, offset += ehdr.e_shentsize) {
	if (!memory_->ReadField(offset, &shdr, &shdr.sh_type, sizeof(shdr.sh_type))) {
	return false;
	}

	if (shdr.sh_type == SHT_SYMTAB \|\| shdr.sh_type == SHT_DYNSYM) {
	if (!memory_->Read(offset, &shdr, sizeof(shdr))) {
	return false;
	}
	// Need to go get the information about the section that contains
	// the string terminated names.
	ShdrType str_shdr;
	if (shdr.sh_link >= ehdr.e_shnum) {
	return false;
	}
	uint64_t str_offset = ehdr.e_shoff + shdr.sh_link * ehdr.e_shentsize;
	if (!memory_->ReadField(str_offset, &str_shdr, &str_shdr.sh_type, sizeof(str_shdr.sh_type))) {
	return false;
	}
	if (str_shdr.sh_type != SHT_STRTAB) {
	return false;
	}
	if (!memory_->ReadField(str_offset, &str_shdr, &str_shdr.sh_offset,
	sizeof(str_shdr.sh_offset))) {
	return false;
	}
	if (!memory_->ReadField(str_offset, &str_shdr, &str_shdr.sh_size, sizeof(str_shdr.sh_size))) {
	return false;
	}
	symbols_.push_back(new Symbols(shdr.sh_offset, shdr.sh_size, shdr.sh_entsize,
	str_shdr.sh_offset, str_shdr.sh_size));
	} else if (shdr.sh_type == SHT_PROGBITS && sec_size != 0) {
	// Look for the .debug_frame and .gnu_debugdata.
	if (!memory_->ReadField(offset, &shdr, &shdr.sh_name, sizeof(shdr.sh_name))) {
	return false;
	}
	if (shdr.sh_name < sec_size) {
	std::string name;
	if (memory_->ReadString(sec_offset + shdr.sh_name, &name)) {
	uint64_t* offset_ptr = nullptr;
	uint64_t* size_ptr = nullptr;
	if (name == ".debug_frame") {
	offset_ptr = &debug_frame_offset_;
	size_ptr = &debug_frame_size_;
	} else if (name == ".gnu_debugdata") {
	offset_ptr = &gnu_debugdata_offset_;
	size_ptr = &gnu_debugdata_size_;
	}
	if (offset_ptr != nullptr &&
	memory_->ReadField(offset, &shdr, &shdr.sh_offset, sizeof(shdr.sh_offset)) &&
	memory_->ReadField(offset, &shdr, &shdr.sh_size, sizeof(shdr.sh_size))) {
	*offset_ptr = shdr.sh_offset;
	*size_ptr = shdr.sh_size;
	}
	}
	}
	}
	}
	return true;
	}

	template <typename DynType>
	bool ElfInterface::GetSonameWithTemplate(std::string* soname) {
	if (soname_type_ == SONAME_INVALID) {
	return false;
	}
	if (soname_type_ == SONAME_VALID) {
	*soname = soname_;
	return true;
	}

	soname_type_ = SONAME_INVALID;

	uint64_t soname_offset = 0;
	uint64_t strtab_offset = 0;
	uint64_t strtab_size = 0;

	// Find the soname location from the dynamic headers section.
	DynType dyn;
	uint64_t offset = dynamic_offset_;
	uint64_t max_offset = offset + dynamic_size_;
	for (uint64_t offset = dynamic_offset_; offset < max_offset; offset += sizeof(DynType)) {
	if (!memory_->Read(offset, &dyn, sizeof(dyn))) {
	return false;
	}

	if (dyn.d_tag == DT_STRTAB) {
	strtab_offset = dyn.d_un.d_ptr;
	} else if (dyn.d_tag == DT_STRSZ) {
	strtab_size = dyn.d_un.d_val;
	} else if (dyn.d_tag == DT_SONAME) {
	soname_offset = dyn.d_un.d_val;
	} else if (dyn.d_tag == DT_NULL) {
	break;
	}
	}

	soname_offset += strtab_offset;
	if (soname_offset >= strtab_offset + strtab_size) {
	return false;
	}
	if (!memory_->ReadString(soname_offset, &soname_)) {
	return false;
	}
	soname_type_ = SONAME_VALID;
	*soname = soname_;
	return true;
	}

	template <typename SymType>
	bool ElfInterface::GetFunctionNameWithTemplate(uint64_t addr, std::string* name,
	uint64_t* func_offset) {
	if (symbols_.empty()) {
	return false;
	}

	for (const auto symbol : symbols_) {
	if (symbol->GetName<SymType>(addr, load_bias_, memory_, name, func_offset)) {
	return true;
	}
	}
	return false;
	}

	bool ElfInterface::Step(uint64_t pc, Regs* regs, Memory* process_memory, bool* finished) {
	// Need to subtract off the load_bias to get the correct pc.
	if (pc < load_bias_) {
	return false;
	}
	pc -= load_bias_;

	// Try the eh_frame first.
	DwarfSection* eh_frame = eh_frame_.get();
	if (eh_frame != nullptr && eh_frame->Step(pc, regs, process_memory, finished)) {
	return true;
	}

	// Try the debug_frame next.
	DwarfSection* debug_frame = debug_frame_.get();
	if (debug_frame != nullptr && debug_frame->Step(pc, regs, process_memory, finished)) {
	return true;
	}
	return false;
	}

	// This is an estimation of the size of the elf file using the location
	// of the section headers and size. This assumes that the section headers
	// are at the end of the elf file. If the elf has a load bias, the size
	// will be too large, but this is acceptable.
	template <typename EhdrType>
	void ElfInterface::GetMaxSizeWithTemplate(Memory* memory, uint64_t* size) {
	EhdrType ehdr;
	if (!memory->Read(0, &ehdr, sizeof(ehdr))) {
	return;
	}
	if (ehdr.e_shnum == 0) {
	return;
	}
	size = ehdr.e_shoff + ehdr.e_shentsize ehdr.e_shnum;
	}

	// Instantiate all of the needed template functions.
	template void ElfInterface::InitHeadersWithTemplate<uint32_t>();
	template void ElfInterface::InitHeadersWithTemplate<uint64_t>();

	template bool ElfInterface::ReadAllHeaders<Elf32_Ehdr, Elf32_Phdr, Elf32_Shdr>();
	template bool ElfInterface::ReadAllHeaders<Elf64_Ehdr, Elf64_Phdr, Elf64_Shdr>();

	template bool ElfInterface::ReadProgramHeaders<Elf32_Ehdr, Elf32_Phdr>(const Elf32_Ehdr&);
	template bool ElfInterface::ReadProgramHeaders<Elf64_Ehdr, Elf64_Phdr>(const Elf64_Ehdr&);

	template bool ElfInterface::ReadSectionHeaders<Elf32_Ehdr, Elf32_Shdr>(const Elf32_Ehdr&);
	template bool ElfInterface::ReadSectionHeaders<Elf64_Ehdr, Elf64_Shdr>(const Elf64_Ehdr&);

	template bool ElfInterface::GetSonameWithTemplate<Elf32_Dyn>(std::string*);
	template bool ElfInterface::GetSonameWithTemplate<Elf64_Dyn>(std::string*);

	template bool ElfInterface::GetFunctionNameWithTemplate<Elf32_Sym>(uint64_t, std::string*,
	uint64_t*);
	template bool ElfInterface::GetFunctionNameWithTemplate<Elf64_Sym>(uint64_t, std::string*,
	uint64_t*);

	template void ElfInterface::GetMaxSizeWithTemplate<Elf32_Ehdr>(Memory, uint64_t);
	template void ElfInterface::GetMaxSizeWithTemplate<Elf64_Ehdr>(Memory, uint64_t);

	} // namespace unwindstack