1 files changed, 634 insertions, 0 deletions
diff --git a/mozglue/linker/ElfLoader.h b/mozglue/linker/ElfLoader.h
new file mode 100644
index 0000000000..059c092f6d
--- /dev/null
+++ b/mozglue/linker/ElfLoader.h
@@ -0,0 +1,634 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef ElfLoader_h
+#define ElfLoader_h
+
+#include <vector>
+#include <dlfcn.h>
+#include <signal.h>
+#include "mozilla/Atomics.h"
+#include "mozilla/RefCounted.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/UniquePtr.h"
+#include "Zip.h"
+#include "Elfxx.h"
+#include "Mappable.h"
+
+/**
+ * dlfcn.h replacement functions
+ */
+extern "C" {
+void* __wrap_dlopen(const char* path, int flags);
+const char* __wrap_dlerror(void);
+void* __wrap_dlsym(void* handle, const char* symbol);
+int __wrap_dlclose(void* handle);
+
+#ifndef HAVE_DLADDR
+typedef struct {
+  const char* dli_fname;
+  void* dli_fbase;
+  const char* dli_sname;
+  void* dli_saddr;
+} Dl_info;
+#endif
+int __wrap_dladdr(const void* addr, Dl_info* info);
+
+struct dl_phdr_info {
+  Elf::Addr dlpi_addr;
+  const char* dlpi_name;
+  const Elf::Phdr* dlpi_phdr;
+  Elf::Half dlpi_phnum;
+};
+
+typedef int (*dl_phdr_cb)(struct dl_phdr_info*, size_t, void*);
+int __wrap_dl_iterate_phdr(dl_phdr_cb callback, void* data);
+
+#ifdef __ARM_EABI__
+const void* __wrap___gnu_Unwind_Find_exidx(void* pc, int* pcount);
+#endif
+
+/**
+ * faulty.lib public API
+ */
+MFBT_API size_t __dl_get_mappable_length(void* handle);
+
+MFBT_API void* __dl_mmap(void* handle, void* addr, size_t length, off_t offset);
+
+MFBT_API void __dl_munmap(void* handle, void* addr, size_t length);
+
+MFBT_API bool IsSignalHandlingBroken();
+}
+
+/* Forward declarations for use in LibHandle */
+class BaseElf;
+class CustomElf;
+class SystemElf;
+
+/**
+ * Specialize RefCounted template for LibHandle. We may get references to
+ * LibHandles during the execution of their destructor, so we need
+ * RefCounted<LibHandle>::Release to support some reentrancy. See further
+ * below.
+ */
+class LibHandle;
+
+namespace mozilla {
+namespace detail {
+
+template <>
+inline void RefCounted<LibHandle, AtomicRefCount>::Release() const;
+
+#ifdef DEBUG
+template <>
+inline RefCounted<LibHandle, AtomicRefCount>::~RefCounted() {
+  MOZ_ASSERT(mRefCnt == 0x7fffdead);
+}
+#endif
+
+} /* namespace detail */
+} /* namespace mozilla */
+
+/**
+ * Abstract class for loaded libraries. Libraries may be loaded through the
+ * system linker or this linker, both cases will be derived from this class.
+ */
+class LibHandle : public mozilla::external::AtomicRefCounted<LibHandle> {
+ public:
+  MOZ_DECLARE_REFCOUNTED_TYPENAME(LibHandle)
+  /**
+   * Constructor. Takes the path of the loaded library and will store a copy
+   * of the leaf name.
+   */
+  LibHandle(const char* path)
+      : directRefCnt(0),
+        path(path ? strdup(path) : nullptr),
+        mappable(nullptr) {}
+
+  /**
+   * Destructor.
+   */
+  virtual ~LibHandle();
+
+  /**
+   * Returns the pointer to the address to which the given symbol resolves
+   * inside the library. It is not supposed to resolve the symbol in other
+   * libraries, although in practice, it will for system libraries.
+   */
+  virtual void* GetSymbolPtr(const char* symbol) const = 0;
+
+  /**
+   * Returns whether the given address is part of the virtual address space
+   * covered by the loaded library.
+   */
+  virtual bool Contains(void* addr) const = 0;
+
+  /**
+   * Returns the base address of the loaded library.
+   */
+  virtual void* GetBase() const = 0;
+
+  /**
+   * Returns the file name of the library without the containing directory.
+   */
+  const char* GetName() const;
+
+  /**
+   * Returns the full path of the library, when available. Otherwise, returns
+   * the file name.
+   */
+  const char* GetPath() const { return path; }
+
+  /**
+   * Library handles can be referenced from other library handles or
+   * externally (when dlopen()ing using this linker). We need to be
+   * able to distinguish between the two kind of referencing for better
+   * bookkeeping.
+   */
+  void AddDirectRef() {
+    mozilla::external::AtomicRefCounted<LibHandle>::AddRef();
+    ++directRefCnt;
+  }
+
+  /**
+   * Releases a direct reference, and returns whether there are any direct
+   * references left.
+   */
+  bool ReleaseDirectRef() {
+    const MozRefCountType count = --directRefCnt;
+    MOZ_ASSERT(count + 1 > 0);
+    MOZ_ASSERT(count + 1 <=
+               mozilla::external::AtomicRefCounted<LibHandle>::refCount());
+    mozilla::external::AtomicRefCounted<LibHandle>::Release();
+    return !!count;
+  }
+
+  /**
+   * Returns the number of direct references
+   */
+  MozRefCountType DirectRefCount() { return directRefCnt; }
+
+  /**
+   * Returns the complete size of the file or stream behind the library
+   * handle.
+   */
+  size_t GetMappableLength() const;
+
+  /**
+   * Returns a memory mapping of the file or stream behind the library
+   * handle.
+   */
+  void* MappableMMap(void* addr, size_t length, off_t offset) const;
+
+  /**
+   * Unmaps a memory mapping of the file or stream behind the library
+   * handle.
+   */
+  void MappableMUnmap(void* addr, size_t length) const;
+
+#ifdef __ARM_EABI__
+  /**
+   * Find the address and entry count of the ARM.exidx section
+   * associated with the library
+   */
+  virtual const void* FindExidx(int* pcount) const = 0;
+#endif
+
+ protected:
+  /**
+   * Returns a mappable object for use by MappableMMap and related functions.
+   */
+  virtual Mappable* GetMappable() const = 0;
+
+  /**
+   * Returns the instance, casted as the wanted type. Returns nullptr if
+   * that's not the actual type. (short of a better way to do this without
+   * RTTI)
+   */
+  friend class ElfLoader;
+  friend class CustomElf;
+  friend class SEGVHandler;
+  friend int __wrap_dl_iterate_phdr(dl_phdr_cb callback, void* data);
+  virtual BaseElf* AsBaseElf() { return nullptr; }
+  virtual SystemElf* AsSystemElf() { return nullptr; }
+
+ private:
+  mozilla::Atomic<MozRefCountType> directRefCnt;
+  char* path;
+
+  /* Mappable object keeping the result of GetMappable() */
+  mutable RefPtr<Mappable> mappable;
+};
+
+/**
+ * Specialized RefCounted<LibHandle>::Release. Under normal operation, when
+ * mRefCnt reaches 0, the LibHandle is deleted. Its mRefCnt is however
+ * increased to 1 on normal builds, and 0x7fffdead on debug builds so that the
+ * LibHandle can still be referenced while the destructor is executing. The
+ * mRefCnt is allowed to grow > 0x7fffdead, but not to decrease under that
+ * value, which would mean too many Releases from within the destructor.
+ */
+namespace mozilla {
+namespace detail {
+
+template <>
+inline void RefCounted<LibHandle, AtomicRefCount>::Release() const {
+#ifdef DEBUG
+  if (mRefCnt > 0x7fff0000) MOZ_ASSERT(mRefCnt > 0x7fffdead);
+#endif
+  MOZ_ASSERT(mRefCnt > 0);
+  if (mRefCnt > 0) {
+    if (0 == --mRefCnt) {
+#ifdef DEBUG
+      mRefCnt = 0x7fffdead;
+#else
+      ++mRefCnt;
+#endif
+      delete static_cast<const LibHandle*>(this);
+    }
+  }
+}
+
+} /* namespace detail */
+} /* namespace mozilla */
+
+/**
+ * Class handling libraries loaded by the system linker
+ */
+class SystemElf : public LibHandle {
+ public:
+  /**
+   * Returns a new SystemElf for the given path. The given flags are passed
+   * to dlopen().
+   */
+  static already_AddRefed<LibHandle> Load(const char* path, int flags);
+
+  /**
+   * Inherited from LibHandle
+   */
+  virtual ~SystemElf();
+  virtual void* GetSymbolPtr(const char* symbol) const;
+  virtual bool Contains(void* addr) const { return false; /* UNIMPLEMENTED */ }
+  virtual void* GetBase() const { return nullptr; /* UNIMPLEMENTED */ }
+
+#ifdef __ARM_EABI__
+  virtual const void* FindExidx(int* pcount) const;
+#endif
+
+ protected:
+  virtual Mappable* GetMappable() const;
+
+  /**
+   * Returns the instance, casted as SystemElf. (short of a better way to do
+   * this without RTTI)
+   */
+  friend class ElfLoader;
+  virtual SystemElf* AsSystemElf() { return this; }
+
+  /**
+   * Remove the reference to the system linker handle. This avoids dlclose()
+   * being called when the instance is destroyed.
+   */
+  void Forget() { dlhandle = nullptr; }
+
+ private:
+  /**
+   * Private constructor
+   */
+  SystemElf(const char* path, void* handle)
+      : LibHandle(path), dlhandle(handle) {}
+
+  /* Handle as returned by system dlopen() */
+  void* dlhandle;
+};
+
+/**
+ * The ElfLoader registers its own SIGSEGV handler to handle segmentation
+ * faults within the address space of the loaded libraries. It however
+ * allows a handler to be set for faults in other places, and redispatches
+ * to the handler set through signal() or sigaction().
+ */
+class SEGVHandler {
+ public:
+  bool hasRegisteredHandler() {
+    if (!initialized) FinishInitialization();
+    return registeredHandler;
+  }
+
+  bool isSignalHandlingBroken() { return signalHandlingBroken; }
+
+  static int __wrap_sigaction(int signum, const struct sigaction* act,
+                              struct sigaction* oldact);
+
+ protected:
+  SEGVHandler();
+  ~SEGVHandler();
+
+ private:
+  /**
+   * The constructor doesn't do all initialization, and the tail is done
+   * at a later time.
+   */
+  void FinishInitialization();
+
+  /**
+   * SIGSEGV handler registered with __wrap_signal or __wrap_sigaction.
+   */
+  struct sigaction action;
+
+  /**
+   * ElfLoader SIGSEGV handler.
+   */
+  static void handler(int signum, siginfo_t* info, void* context);
+
+  /**
+   * Temporary test handler.
+   */
+  static void test_handler(int signum, siginfo_t* info, void* context);
+
+  /**
+   * Size of the alternative stack. The printf family requires more than 8KB
+   * of stack, and our signal handler may print a few things.
+   */
+  static const size_t stackSize = 12 * 1024;
+
+  /**
+   * Alternative stack information used before initialization.
+   */
+  stack_t oldStack;
+
+  /**
+   * Pointer to an alternative stack for signals. Only set if oldStack is
+   * not set or not big enough.
+   */
+  MappedPtr stackPtr;
+
+  bool initialized;
+  bool registeredHandler;
+  bool signalHandlingBroken;
+  bool signalHandlingSlow;
+};
+
+/**
+ * Elf Loader class in charge of loading and bookkeeping libraries.
+ */
+class ElfLoader : public SEGVHandler {
+ public:
+  /**
+   * The Elf Loader instance
+   */
+  static ElfLoader Singleton;
+
+  /**
+   * Loads the given library with the given flags. Equivalent to dlopen()
+   * The extra "parent" argument optionally gives the handle of the library
+   * requesting the given library to be loaded. The loader may look in the
+   * directory containing that parent library for the library to load.
+   */
+  already_AddRefed<LibHandle> Load(const char* path, int flags,
+                                   LibHandle* parent = nullptr);
+
+  /**
+   * Returns the handle of the library containing the given address in
+   * its virtual address space, i.e. the library handle for which
+   * LibHandle::Contains returns true. Its purpose is to allow to
+   * implement dladdr().
+   */
+  already_AddRefed<LibHandle> GetHandleByPtr(void* addr);
+
+  /**
+   * Returns a Mappable object for the path. Paths in the form
+   *   /foo/bar/baz/archive!/directory/lib.so
+   * try to load the directory/lib.so in /foo/bar/baz/archive, provided
+   * that file is a Zip archive.
+   */
+  static Mappable* GetMappableFromPath(const char* path);
+
+  void ExpectShutdown(bool val) { expect_shutdown = val; }
+  bool IsShutdownExpected() { return expect_shutdown; }
+
+ private:
+  bool expect_shutdown;
+
+ protected:
+  /**
+   * Registers the given handle. This method is meant to be called by
+   * LibHandle subclass creators.
+   */
+  void Register(LibHandle* handle);
+  void Register(CustomElf* handle);
+
+  /**
+   * Forget about the given handle. This method is meant to be called by
+   * LibHandle subclass destructors.
+   */
+  void Forget(LibHandle* handle);
+  void Forget(CustomElf* handle);
+
+  friend class SystemElf;
+  friend const char* __wrap_dlerror(void);
+  friend void* __wrap_dlsym(void* handle, const char* symbol);
+  friend int __wrap_dlclose(void* handle);
+  /* __wrap_dlerror() returns this custom last error if non-null or the system
+   * dlerror() value if this is null. Must refer to a string constant. */
+  mozilla::Atomic<const char*, mozilla::Relaxed> lastError;
+
+ private:
+  ElfLoader() : expect_shutdown(true), lastError(nullptr) {
+    pthread_mutex_init(&handlesMutex, nullptr);
+  }
+
+  ~ElfLoader();
+
+  /* Initialization code that can't run during static initialization. */
+  void Init();
+
+  /* System loader handle for the library/program containing our code. This
+   * is used to resolve wrapped functions. */
+  RefPtr<LibHandle> self_elf;
+
+#if defined(ANDROID)
+  /* System loader handle for the libc. This is used to resolve weak symbols
+   * that some libcs contain that the Android linker won't dlsym(). Normally,
+   * we wouldn't treat non-Android differently, but glibc uses versioned
+   * symbols which this linker doesn't support. */
+  RefPtr<LibHandle> libc;
+
+  /* And for libm. */
+  RefPtr<LibHandle> libm;
+#endif
+
+  /* Bookkeeping */
+  typedef std::vector<LibHandle*> LibHandleList;
+  LibHandleList handles;
+
+  pthread_mutex_t handlesMutex;
+
+ protected:
+  friend class CustomElf;
+  friend class LoadedElf;
+
+  /* Definition of static destructors as to be used for C++ ABI compatibility */
+  typedef void (*Destructor)(void* object);
+
+  /**
+   * C++ ABI makes static initializers register destructors through a specific
+   * atexit interface. On glibc/linux systems, the dso_handle is a pointer
+   * within a given library. On bionic/android systems, it is an undefined
+   * symbol. Making sense of the value is not really important, and all that
+   * is really important is that it is different for each loaded library, so
+   * that they can be discriminated when shutting down. For convenience, on
+   * systems where the dso handle is a symbol, that symbol is resolved to
+   * point at corresponding CustomElf.
+   *
+   * Destructors are registered with __*_atexit with an associated object to
+   * be passed as argument when it is called.
+   *
+   * When __cxa_finalize is called, destructors registered for the given
+   * DSO handle are called in the reverse order they were registered.
+   */
+#ifdef __ARM_EABI__
+  static int __wrap_aeabi_atexit(void* that, Destructor destructor,
+                                 void* dso_handle);
+#else
+  static int __wrap_cxa_atexit(Destructor destructor, void* that,
+                               void* dso_handle);
+#endif
+
+  static void __wrap_cxa_finalize(void* dso_handle);
+
+  /**
+   * Registered destructor. Keeps track of the destructor function pointer,
+   * associated object to call it with, and DSO handle.
+   */
+  class DestructorCaller {
+   public:
+    DestructorCaller(Destructor destructor, void* object, void* dso_handle)
+        : destructor(destructor), object(object), dso_handle(dso_handle) {}
+
+    /**
+     * Call the destructor function with the associated object.
+     * Call only once, see CustomElf::~CustomElf.
+     */
+    void Call();
+
+    /**
+     * Returns whether the destructor is associated to the given DSO handle
+     */
+    bool IsForHandle(void* handle) const { return handle == dso_handle; }
+
+   private:
+    Destructor destructor;
+    void* object;
+    void* dso_handle;
+  };
+
+ private:
+  /* Keep track of all registered destructors */
+  std::vector<DestructorCaller> destructors;
+
+  /* Forward declaration, see further below */
+  class DebuggerHelper;
+
+ public:
+  /* Loaded object descriptor for the debugger interface below*/
+  struct link_map {
+    /* Base address of the loaded object. */
+    const void* l_addr;
+    /* File name */
+    const char* l_name;
+    /* Address of the PT_DYNAMIC segment. */
+    const void* l_ld;
+
+   private:
+    friend class ElfLoader::DebuggerHelper;
+    /* Double linked list of loaded objects. */
+    link_map *l_next, *l_prev;
+  };
+
+ private:
+  /* Data structure used by the linker to give details about shared objects it
+   * loaded to debuggers. This is normally defined in link.h, but Android
+   * headers lack this file. */
+  struct r_debug {
+    /* Version number of the protocol. */
+    int r_version;
+
+    /* Head of the linked list of loaded objects. */
+    link_map* r_map;
+
+    /* Function to be called when updates to the linked list of loaded objects
+     * are going to occur. The function is to be called before and after
+     * changes. */
+    void (*r_brk)(void);
+
+    /* Indicates to the debugger what state the linked list of loaded objects
+     * is in when the function above is called. */
+    enum {
+      RT_CONSISTENT, /* Changes are complete */
+      RT_ADD,        /* Beginning to add a new object */
+      RT_DELETE      /* Beginning to remove an object */
+    } r_state;
+  };
+
+  /* Memory representation of ELF Auxiliary Vectors */
+  struct AuxVector {
+    Elf::Addr type;
+    Elf::Addr value;
+  };
+
+  /* Helper class used to integrate libraries loaded by this linker in
+   * r_debug */
+  class DebuggerHelper {
+   public:
+    DebuggerHelper();
+
+    void Init(AuxVector* auvx);
+
+    explicit operator bool() { return dbg; }
+
+    /* Make the debugger aware of a new loaded object */
+    void Add(link_map* map);
+
+    /* Make the debugger aware of the unloading of an object */
+    void Remove(link_map* map);
+
+    /* Iterates over all link_maps */
+    class iterator {
+     public:
+      const link_map* operator->() const { return item; }
+
+      const link_map& operator++() {
+        item = item->l_next;
+        return *item;
+      }
+
+      bool operator<(const iterator& other) const {
+        if (other.item == nullptr) return item ? true : false;
+        MOZ_CRASH(
+            "DebuggerHelper::iterator::operator< called with something else "
+            "than DebuggerHelper::end()");
+      }
+
+     protected:
+      friend class DebuggerHelper;
+      explicit iterator(const link_map* item) : item(item) {}
+
+     private:
+      const link_map* item;
+    };
+
+    iterator begin() const { return iterator(dbg ? dbg->r_map : nullptr); }
+
+    iterator end() const { return iterator(nullptr); }
+
+   private:
+    r_debug* dbg;
+    link_map* firstAdded;
+  };
+  friend int __wrap_dl_iterate_phdr(dl_phdr_cb callback, void* data);
+  DebuggerHelper dbg;
+};
+
+#endif /* ElfLoader_h */