Android: Add chrome-specific dynamic linker.

third_party/crazy_linker/crazy_linker/src/crazy_linker_shared_library.cpp

Index: third_party/crazy_linker/crazy_linker/src/crazy_linker_shared_library.cpp
diff --git a/third_party/crazy_linker/crazy_linker/src/crazy_linker_shared_library.cpp b/third_party/crazy_linker/crazy_linker/src/crazy_linker_shared_library.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..f685c43f1898daeaaf02b7ffefc4b9ca390879eb
--- /dev/null
+++ b/third_party/crazy_linker/crazy_linker/src/crazy_linker_shared_library.cpp
@@ -0,0 +1,714 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "crazy_linker_shared_library.h"
+
+#include <dlfcn.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <elf.h>
+#include <sys/exec_elf.h>
+
+#include "crazy_linker_ashmem.h"
+#include "crazy_linker_debug.h"
+#include "crazy_linker_elf_loader.h"
+#include "crazy_linker_elf_relocator.h"
+#include "crazy_linker_library_list.h"
+#include "crazy_linker_library_view.h"
+#include "crazy_linker_globals.h"
+#include "crazy_linker_thread.h"
+#include "crazy_linker_util.h"
+#include "crazy_linker_wrappers.h"
+#include "linker_phdr.h"
+
+#ifndef DF_SYMBOLIC
+#define DF_SYMBOLIC 2
+#endif
+
+#ifndef DF_TEXTREL
+#define DF_TEXTREL 4
+#endif
+
+#ifndef DT_INIT_ARRAY
+#define DT_INIT_ARRAY 25
+#endif
+
+#ifndef DT_INIT_ARRAYSZ
+#define DT_INIT_ARRAYSZ 27
+#endif
+
+#ifndef DT_FINI_ARRAY
+#define DT_FINI_ARRAY 26
+#endif
+
+#ifndef DT_FINI_ARRAYSZ
+#define DT_FINI_ARRAYSZ 28
+#endif
+
+#ifndef DT_FLAGS
+#define DT_FLAGS 30
+#endif
+
+#ifndef DT_PREINIT_ARRAY
+#define DT_PREINIT_ARRAY 32
+#endif
+
+#ifndef DT_PREINIT_ARRAYSZ
+#define DT_PREINIT_ARRAYSZ 33
+#endif
+
+namespace crazy {
+
+namespace {
+
+typedef SharedLibrary::linker_function_t linker_function_t;
+
+// Compute the ELF hash of a given symbol.
+unsigned ElfHash(const char* name) {
+  const uint8_t* ptr = reinterpret_cast<const uint8_t*>(name);
+  unsigned h = 0;
+  while(*ptr) {
+      h = (h << 4) + *ptr++;
+      unsigned g = h & 0xf0000000;
+      h ^= g;
+      h ^= g >> 24;
+  }
+  return h;
+}
+
+ELF::Sym* LookupSymbolForAddress(SharedLibrary* lib, void* address) {
+  ELF::Addr elf_addr = reinterpret_cast<ELF::Addr>(address) - lib->base;
+
+  for (size_t n = 0; n < lib->nchain; ++n) {
+    ELF::Sym* sym = &lib->symtab[n];
+    if (sym->st_shndx != SHN_UNDEF &&
+        elf_addr >= sym->st_value &&
+        elf_addr < sym->st_value + sym->st_size) {
+      return sym;
+    }
+  }
+  return NULL;
+}
+
+// Call a constructor of destructor function pointer. Ignores

[Nico, 2013/09/08 21:24:57]

s/of/or/

[digit1, 2013/09/10 09:23:30]

Done.

+// NULL and -1 values intentionally. They correspond to markers
+// in the tables, or deleted values.
+// |func_type| corresponds to the type of the function, and is only
+// used for debugging (examples are "DT_INIT", "DT_INIT_ARRAY", etc...).
+void CallFunction(linker_function_t func,
+                  const char* func_type) {
+  uintptr_t func_address = reinterpret_cast<uintptr_t>(func);
+
+  LOG("%s: %p %s\n", __FUNCTION__, func, func_type);
+  if (func_address != 0 && func_address != uintptr_t(-1))
+    func();
+}
+
+// Parse the dynamic section of |lib| and populate various important
+// fields from it. On success, returns true. On failure, returns false,
+// and sets |error| message.
+bool ParseLibraryDynamicTable(SharedLibrary* lib, Error* error) {
+  const ELF::Phdr* phdr = lib->phdr;
+  size_t phdr_count = lib->phnum;
+  ELF::Addr base = lib->base;
+
+  phdr_table_get_dynamic_section(phdr, phdr_count, base,
+                                 &lib->dynamic,
+                                 &lib->dynamic_count,
+                                 &lib->dynamic_flags);
+  if (!lib->dynamic) {
+    *error = "No PT_DYNAMIC section!";
+    return false;
+  }
+
+#ifdef __arm__
+  (void) phdr_table_get_arm_exidx(phdr, phdr_count, base,
+                                  &lib->ARM_exidx, &lib->ARM_exidx_count);
+#endif
+
+  for (ELF::Dyn* dyn = lib->dynamic; dyn->d_tag != DT_NULL; ++dyn) {
+    ELF::Addr dyn_value = dyn->d_un.d_val;
+    uintptr_t dyn_addr = base + dyn->d_un.d_ptr;
+    switch (dyn->d_tag) {
+      case DT_HASH:
+        LOG("  DT_HASH addr=%p\n", dyn_addr);
+        {
+          uintptr_t* data = reinterpret_cast<uintptr_t*>(dyn_addr);
+          lib->nbucket = data[0];
+          lib->nchain = data[1];
+          lib->bucket = data + 2;
+          lib->chain = data + 2 + lib->nbucket;
+        }
+        break;
+      case DT_STRTAB:
+        LOG("  DT_STRTAB addr=%p\n", dyn_addr);
+        lib->strtab = reinterpret_cast<const char*>(dyn_addr);
+        break;
+      case DT_SYMTAB:
+        LOG("  DT_SYMTAB addr=%p\n", dyn_addr);
+        lib->symtab = reinterpret_cast<ELF::Sym*>(dyn_addr);
+        break;
+      case DT_DEBUG:
+        // TODO(digit): Move this to a different location.
+        if (lib->dynamic_flags & PF_W) {
+          dyn->d_un.d_val = reinterpret_cast<uintptr_t>(
+              Globals::GetRDebug()->GetAddress());
+        }
+        break;
+      case DT_INIT:
+        LOG("  DT_INIT addr=%p\n", dyn_addr);
+        lib->init_func = reinterpret_cast<linker_function_t>(dyn_addr);
+        break;
+      case DT_FINI:
+        LOG("  DT_FINI addr=%p\n", dyn_addr);
+        lib->fini_func = reinterpret_cast<linker_function_t>(dyn_addr);
+        break;
+      case DT_INIT_ARRAY:
+        LOG("  DT_INIT_ARRAY addr=%p\n", dyn_addr);
+        lib->init_array = reinterpret_cast<linker_function_t*>(dyn_addr);
+        break;
+      case DT_INIT_ARRAYSZ:
+        lib->init_array_count = dyn_value / sizeof(ELF::Addr);
+        LOG("  DT_INIT_ARRAYSZ value=%p count=%p\n", dyn_value, lib->init_array_count);
+        break;
+      case DT_FINI_ARRAY:
+        LOG("  DT_FINI_ARRAY addr=%p\n", dyn_addr);
+        lib->fini_array = reinterpret_cast<linker_function_t*>(dyn_addr);
+        break;
+      case DT_FINI_ARRAYSZ:
+        lib->fini_array_count = dyn_value / sizeof(ELF::Addr);
+        LOG("  DT_FINI_ARRAYSZ value=%p count=%p\n", dyn_value, lib->fini_array_count);
+        break;
+      case DT_PREINIT_ARRAY:
+        LOG("  DT_PREINIT_ARRAY addr=%p\n", dyn_addr);
+        lib->preinit_array = reinterpret_cast<linker_function_t*>(dyn_addr);
+        break;
+      case DT_PREINIT_ARRAYSZ:
+        lib->preinit_array_count = dyn_value / sizeof(ELF::Addr);
+        LOG("  DT_PREINIT_ARRAYSZ value=%p count=%p\n", dyn_value, lib->preinit_array_count);
+        break;
+      case DT_SYMBOLIC:
+        LOG("  DT_SYMBOLIC\n");
+        lib->has_DT_SYMBOLIC = true;
+        break;
+      case DT_FLAGS:
+        if (dyn_value & DF_SYMBOLIC)
+          lib->has_DT_SYMBOLIC = true;
+        break;
+#if defined(__mips__)
+      case DT_MIPS_RLD_MAP:
+        // TODO(digit): Move this to different location.
+        dyn->d_un.d_ptr =
+            reinterpret_cast<ELF::Addr>(Globals::GetRDebug()->GetAddress());
+        break;
+#endif
+      default:
+        ;
+    }
+  }
+
+  // Perform a few sanity checks.
+  if (!lib->nbucket) {
+    *error = "Missing DT_HASH entry (built with --hash-style=gnu?)";
+    return false;
+  }
+  if (!lib->strtab) {
+    *error = "Missing DT_STRTAB entry";
+    return false;
+  }
+  if (!lib->symtab) {
+    *error = "Missing DT_SYMTAB entry";
+    return false;
+  }
+  return true;
+}
+
+bool LoadLibrary(SharedLibrary* lib,
+                 const char* full_path,
+                 size_t load_address,
+                 size_t file_offset,
+                 Error* error) {
+  // First, record the path.
+  LOG("%s: full path '%s'\n", __FUNCTION__, full_path);
+
+  size_t full_path_len = strlen(full_path);
+  if (full_path_len >= sizeof(lib->full_path)) {
+    error->Format("Path too long: %s", full_path);
+    return false;
+  }
+
+  strlcpy(lib->full_path, full_path, sizeof(lib->full_path));
+  lib->base_name = GetBaseNamePtr(lib->full_path);
+
+  // Load the ELF binary in memory.
+  LOG("%s: Loading ELF segments for %s\n", __FUNCTION__, lib->base_name);
+
+  {
+    ElfLoader loader;
+    if (!loader.LoadAt(lib->full_path,
+                       file_offset,
+                       load_address,
+                       error)) {
+      return false;
+    }
+
+    lib->base = loader.load_start();
+    lib->size = loader.load_size();
+    lib->load_bias = loader.load_bias();
+    lib->phnum = loader.phdr_count();
+    lib->phdr = loader.loaded_phdr();
+  }
+
+  // Parse the dynamic table to extract useful information.
+  LOG("%s: Parsing dynamic table of %s\n", __FUNCTION__, lib->base_name);
+  if (!ParseLibraryDynamicTable(lib, error))
+    return false;
+
+  LOG("%s: Load complete for %s\n", __FUNCTION__, lib->base_name);
+  return true;
+}
+
+// An instance of ElfRelocator::SymbolResolver that can be used
+// to resolve symbols in a shared library being loaded by
+// LibraryList::LoadLibrary.
+class SharedLibraryResolver: public ElfRelocator::SymbolResolver {
+public:
+  SharedLibraryResolver(SharedLibrary* lib,
+                        LibraryList* lib_list,
+                        Vector<LibraryView*>* dependencies)
+    : lib_(lib),
+      lib_list_(lib_list),
+      dependencies_(dependencies) {}
+
+  virtual void* Lookup(const char* symbol_name) {
+    // TODO(digit): Add the ability to lookup inside the main executable.
+
+    // First, look inside the current library.
+    ELF::Sym* entry = lib_->LookupSymbolEntry(symbol_name);
+    if (entry)
+      return reinterpret_cast<void*>(lib_->load_bias + entry->st_value);
+
+    // Special case: redirect the dynamic linker symbols to our wrappers.
+    // This ensures that loaded libraries can call dlopen() / dlsym()
+    // and transparently use the crazy linker to perform their duty.
+    void* address = WrapLinkerSymbol(symbol_name);
+    if (address)
+      return address;
+
+    // Then look inside the dependencies.
+    for (size_t n = 0; n < dependencies_->GetCount(); ++n) {
+      LibraryView* wrap = (*dependencies_)[n];
+      //LOG("%s: Looking into dependency %p (%s)\n", __FUNCTION__, wrap, wrap->GetName());
+      if (wrap->IsSystem()) {
+        address = ::dlsym(wrap->GetSystem(), symbol_name);
+        if (address)
+          return address;
+      }
+      if (wrap->IsCrazy()) {
+        SharedLibrary* dep = wrap->GetCrazy();
+        entry = dep->LookupSymbolEntry(symbol_name);
+        if (entry)
+          return reinterpret_cast<void*>(dep->load_bias + entry->st_value);
+      }
+    }
+
+    // Nothing found here.
+    return NULL;
+  }
+
+private:
+  SharedLibrary* lib_;
+  LibraryList* lib_list_;
+  Vector<LibraryView*>* dependencies_;
+};
+
+bool RelocateLibrary(SharedLibrary* lib,
+                     LibraryList* lib_list,
+                     Vector<LibraryView*>* dependencies,
+                     Error* error) {
+  // Apply relocations.
+  LOG("%s: Applying relocations to %s\n", __FUNCTION__, lib->base_name);
+
+  ElfRelocator relocator;
+
+  if (!relocator.Init(lib->phdr,
+                      lib->phnum,
+                      lib->load_bias,
+                      lib->dynamic,
+                      lib->dynamic_count,
+                      error)) {
+    return false;
+  }
+
+  SharedLibraryResolver resolver(lib, lib_list, dependencies);
+  if (!relocator.Apply(&resolver, lib->strtab, lib->symtab, error))
+    return false;
+
+  LOG("%s: Relocations applied for %s\n", __FUNCTION__, lib->base_name);
+  return true;
+}
+
+// Helper class for a memory mapping. This is _not_ scoped.
+class Mapping {
+public:
+  enum Protection {
+    CAN_READ = PROT_READ,
+    CAN_WRITE = PROT_WRITE,
+    CAN_READ_WRITE = PROT_READ|PROT_WRITE
+  };
+  Mapping() : map_(NULL), size_(0) {}
+  ~Mapping() {}
+
+  // Return current mapping address.
+  void* Get() { return map_; }
+
+  // Allocate a new mapping.
+  // |address| is either NULL or a fixed memory address.
+  // |size| is the page-aligned size, must be > 0.
+  // |prot| are the desired protection bit flags.
+  // |fd| is -1 (for anonymous mappings), or a valid file descriptor.
+  // on failure, return false and sets |error| message.
+  bool Allocate(void* address,
+                size_t size,
+                Protection prot,
+                int fd,
+                Error* error) {
+    int flags = (fd >= 0) ? MAP_SHARED : MAP_ANONYMOUS;
+    if (address)
+      flags |= MAP_FIXED;
+
+    size_ = size;
+    map_ = ::mmap(address, size_, static_cast<int>(prot), flags, fd, 0);
+    if (map_ == MAP_FAILED) {
+      error->Format("Cannot map %d bytes (addr=%p, fd=%d): %s",
+                    size, address, fd, strerror(errno));
+      map_ = NULL;
+      return false;
+    }
+
+    return true;
+  }
+
+  // Change the protection flags of the mapping.
+  bool SetProtection(Protection prot, Error* error) {
+    if (map_) {
+      if (::mprotect(map_, size_, static_cast<int>(prot)) < 0) {
+        char* p = reinterpret_cast<char*>(map_);
+        error->Format("Cannot change protection for %p-%p: %s",
+                      p, p + size_, strerror(errno));
+        return false;
+      }
+    }
+    return true;
+  }
+
+  // Deallocate an existing mapping, if any.
+  void Deallocate() {
+    if (map_) {
+      ::munmap(map_, size_);
+      map_ = NULL;
+    }
+  }
+
+protected:
+  void* map_;
+  size_t size_;
+};
+
+// Helper class for a memory mapping that is automatically
+// unmapped on scope exit, unless its Release() method is called.
+class ScopedMapping : public Mapping {
+public:
+  void* Release() {
+    void* ret = map_;
+    map_ = NULL;
+    return ret;
+  }
+
+  ~ScopedMapping() {
+    Deallocate();
+  }
+};
+
+// Copy all the pages from |addr| and |addr + size| into an ashmem
+// region identified by |fd|.
+bool CopyPagesToFd(void* addr, size_t size, int fd, Error* error) {
+
+  // Create temporary mapping of the ashmem region.
+  // And copy current pages there.
+  ScopedMapping fd_map;
+
+  if (!fd_map.Allocate(NULL,
+                      size,
+                      ScopedMapping::CAN_READ_WRITE,
+                      fd,
+                      error)) {
+    return false;
+  }
+
+  // Copy current pages there.
+  ::memcpy(fd_map.Get(), addr, size);
+  return true;
+}
+
+// Swap pages between |addr| and |addr + size| with the bytes
+// from the ashmem region identified by |fd|, starting from
+// a given |offset|. On failure return false and set |error| message.
+bool SwapPagesFromFd(void* addr,
+                     size_t size,
+                     int fd,
+                     size_t offset,
+                     Error* error) {
+  // Unmap current pages.
+  if (::munmap(addr, size) < 0) {
+    error->Format("%s: Could not unmap %p-%p: %s",
+                  __FUNCTION__, addr, (char*)addr + size,
+                  strerror(errno));
+    return false;
+  }
+
+  // Remap the fd pages at the same location now.
+  void* new_map = ::mmap(addr, size, PROT_READ, MAP_FIXED|MAP_SHARED, fd,
+                         static_cast<off_t>(offset));
+  if (new_map == MAP_FAILED) {
+    char* p = reinterpret_cast<char*>(addr);
+    error->Format("%s: Could not map %p-%p: %s",
+                  __FUNCTION__, p, p + size, strerror(errno));
+    return false;
+  }
+
+#ifdef __arm__
+  __clear_cache(addr, (char*)addr + size);
+#endif
+
+  // Done.
+  return true;
+}
+
+bool PageEquals(const char* p1, const char* p2) {
+  // TODO(digit): For some reason, using memcmp() here crashes on Android 4.3.

[Nico, 2013/09/08 21:24:57]

Weird.

[digit1, 2013/09/10 09:23:30]

Indeed :-(

+  for (size_t n = 0; n < PAGE_SIZE; ++n) {
+    if (p1[n] != p2[n])
+      return false;
+  }
+  return true;
+}
+
+// Conditionally swap pages between |address| and |address + size| with
+// the ones from the ashmem region identified by |fd|. This only swaps
+// pages that have exactly the same content. On failure, return false
+// and set |error| message.
+bool SwapSimilarPagesFromFd(void* addr, size_t size, int fd, Error* error) {
+  // Create temporary mapping of the ashmem region.
+  ScopedMapping fd_map;
+
+  LOG("%s: Entering addr=%p size=%p fd=%d\n", __FUNCTION__,
+      addr, (void*)size, fd);
+
+  if (!fd_map.Allocate(NULL, size, ScopedMapping::CAN_READ, fd, error))
+    return false;
+
+  LOG("%s: mapping allocate at %p\n", __FUNCTION__, fd_map.Get());
+
+  char* cur_page = reinterpret_cast<char*>(addr);
+  char* fd_page = reinterpret_cast<char*>(fd_map.Get());
+  size_t p = 0;
+  size_t similar_size = 0;
+
+  do {
+    // Skip over dissimilar pages.
+    LOG("%s: test pos=%d\n", __FUNCTION__, (int)p);
+    while (p < size && !PageEquals(cur_page + p, fd_page + p)) {
+      LOG("%s: Skipped over page at %p\n", __FUNCTION__, cur_page + p);
+      p += PAGE_SIZE;
+    }
+
+    // Count similar pages.
+    size_t p2 = p;
+    while (p2 < size && PageEquals(cur_page + p2, fd_page + p2)) {
+      LOG("%s: Found similar page at %p\n", __FUNCTION__, cur_page + p2);
+      p2 += PAGE_SIZE;
+    }
+
+    if (p2 > p) {
+      // Swap pages between |pos| and |pos2|.
+      LOG("%s: Swap pages at %p-%p\n", __FUNCTION__,
+          cur_page + p, cur_page + p2);
+      if (!SwapPagesFromFd(cur_page + p, p2 - p, fd, p, error))
+        return false;
+
+      similar_size += (p2 - p);
+    }
+
+    p = p2;
+  } while (p < size);
+
+  LOG("%s: Swapped %d pages over %d (%d %%, %d KB)\n",
+      __FUNCTION__,
+      similar_size / PAGE_SIZE,
+      size / PAGE_SIZE,
+      similar_size * 100 / size,
+      similar_size / 4096);
+
+  return true;
+}
+
+}  // namespace
+
+SharedLibrary::SharedLibrary() {
+  // Ensure all fields are empty.
+  memset(this, 0, sizeof(*this));
+  this->relro_fd = -1;
+}
+
+SharedLibrary::~SharedLibrary() {
+  // Ensure the library is unmapped on destruction.
+  if (this->base)
+    munmap(reinterpret_cast<void*>(this->base), this->size);
+  // Ensure the relro ashmem file descriptor is closed.
+  if (this->relro_fd >= 0)
+    close(this->relro_fd);
+}
+
+bool SharedLibrary::Load(const char* full_path,
+                         size_t load_address,
+                         size_t file_offset,
+                         Error* error) {
+  return LoadLibrary(this, full_path, load_address, file_offset, error);
+}
+
+bool SharedLibrary::Relocate(LibraryList* lib_list,
+                             Vector<LibraryView*>* dependencies,
+                             Error* error) {
+  return RelocateLibrary(this, lib_list, dependencies, error);
+}
+
+ELF::Sym* SharedLibrary::LookupSymbolEntry(const char* symbol_name) {
+  unsigned hash = ElfHash(symbol_name);
+  ELF::Sym* symbols = this->symtab;
+  const char* strings = this->strtab;
+
+  for (unsigned n = this->bucket[hash % this->nbucket];
+       n != 0;
+       n = this->chain[n]) {
+    ELF::Sym* symbol = &symbols[n];
+    // Check that the symbol has the appropriate name.
+    if (strcmp(strings + symbol->st_name, symbol_name))
+      continue;
+    // Ignore undefined symbols.
+    if (symbol->st_shndx == SHN_UNDEF)
+      continue;
+    // Ignore anything that isn't a global or weak definition.
+    switch (ELF_ST_BIND(symbol->st_info)) {
+      case STB_GLOBAL:
+      case STB_WEAK:
+        return symbol;
+      default:
+        ;
+    }
+  }
+  return NULL;
+}
+
+void* SharedLibrary::FindAddressForSymbol(const char* symbol_name) {
+  ELF::Sym* entry = LookupSymbolEntry(symbol_name);
+  if (!entry)
+    return NULL;
+
+  return reinterpret_cast<void*>(this->load_bias + entry->st_value);
+}
+
+ELF::Sym* SharedLibrary::FindSymbolForAddress(void* address) {
+  return LookupSymbolForAddress(this, address);
+}
+
+bool SharedLibrary::EnableSharedRelro(Error* error) {
+  if (this->relro_fd != -1)
+    return true;
+
+  ELF::Addr relro_start, relro_size;
+  if (phdr_table_get_relro_info(this->phdr, this->phnum, this->load_bias,
+                                &relro_start, &relro_size) < 0) {
+    // No RELRO section to share.
+    return true;
+  }
+
+  if (relro_size == 0) {
+    // Probably means there is no real RELRO section.
+    return true;
+  }
+
+  // Allocate new ashmem region.
+  this->relro_start = relro_start;
+  this->relro_size = relro_size;
+  AshmemRegion ashmem;
+  String relro_name("RELRO:");
+  relro_name += this->base_name;
+  if (!ashmem.Allocate(relro_size, relro_name.c_str())) {
+    error->Format("Could not allocate ashmem region: %s", strerror(errno));
+    return false;
+  }
+
+  void* relro_addr = reinterpret_cast<void*>(relro_start);
+  if (!CopyPagesToFd(relro_addr, relro_size, ashmem.Get(), error) ||
+      !SwapPagesFromFd(relro_addr, relro_size, ashmem.Get(), 0, error))
+    return false;
+
+  this->relro_fd = ashmem.Release();
+  return true;
+}
+
+bool SharedLibrary::UseSharedRelro(size_t relro_start,
+                               size_t relro_size,

[Nico, 2013/09/08 21:24:57]

(nit: indent)

[digit1, 2013/09/10 09:23:30]

Done.

+                               int relro_fd,
+                               Error* error) {
+  if (relro_fd < 0 || relro_size == 0) {
+    // Nothing to do here.
+    return true;
+  }
+
+  LOG("%s: relro_start=%p relro_size=%p relro_fd=%d\n",
+      __FUNCTION__, (void*)relro_start, (void*)relro_size, relro_fd);
+
+  // Sanity checks.
+  if (this->relro_fd != -1) {
+    *error = "Library already using shared RELRO section";
+    return false;
+  }
+
+  ELF::Addr lib_relro_start, lib_relro_size;
+  if (phdr_table_get_relro_info(this->phdr, this->phnum, this->load_bias,
+                                &lib_relro_start, &lib_relro_size) < 0) {
+    *error = "No RELRO section in library";
+    return false;
+  }
+
+  if (lib_relro_start != relro_start || lib_relro_size != relro_size) {
+    error->Format("RELRO mismatch addr=%p size=%p (wanted addr=%p size=%p)",
+                  lib_relro_start, lib_relro_size, relro_start, relro_size);
+    return false;
+  }
+
+  void* relro_addr = reinterpret_cast<void*>(relro_start);
+  if (!SwapSimilarPagesFromFd(relro_addr, relro_size, relro_fd, error))
+    return false;
+
+  this->relro_fd = relro_fd;
+  return true;
+}
+
+void SharedLibrary::CallConstructors() {
+  CallFunction(this->init_func, "DT_INIT");
+  for (size_t n = 0; n < this->init_array_count; ++n)
+    CallFunction(this->init_array[n], "DT_INIT_ARRAY");
+}
+
+void SharedLibrary::CallDestructors() {
+  for (size_t n = this->fini_array_count; n > 0; --n) {
+    CallFunction(this->fini_array[n - 1], "DT_FINI_ARRAY");
+  }
+  CallFunction(this->fini_func, "DT_FINI");
+}
+
+}  // namespace crazy