The Tor Browser: mozglue/linker/ElfLoader.h@b8a032363ba2 (annotated)

mozglue/linker/ElfLoader.h@b8a032363ba2 (annotated)

mozglue/linker/ElfLoader.h

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /* 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/RefPtr.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(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();
 }
 /**
  * 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;
 template <> inline RefCounted<LibHandle, AtomicRefCount>::~RefCounted()
 {
   MOZ_ASSERT(refCnt == 0x7fffdead);
 }
 } /* 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::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 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()
   {
     ++directRefCnt;
     mozilla::AtomicRefCounted<LibHandle>::AddRef();
   }
   /**
    * Releases a direct reference, and returns whether there are any direct
    * references left.
    */
   bool ReleaseDirectRef()
   {
     bool ret = false;
     if (directRefCnt) {
       MOZ_ASSERT(directRefCnt <=
                  mozilla::AtomicRefCounted<LibHandle>::refCount());
       if (--directRefCnt)
         ret = true;
       mozilla::AtomicRefCounted<LibHandle>::Release();
     }
     return ret;
   }
   /**
    * 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 whether the handle is a SystemElf or not. (short of a better way
    * to do this without RTTI)
    */
   friend class ElfLoader;
   friend class CustomElf;
   friend class SEGVHandler;
   virtual bool IsSystemElf() const { return false; }
 private:
   MozRefCountType directRefCnt;
   char *path;
   /* Mappable object keeping the result of GetMappable() */
   mutable mozilla::RefPtr<Mappable> mappable;
 };
 /**
  * Specialized RefCounted<LibHandle>::Release. Under normal operation, when
  * refCnt reaches 0, the LibHandle is deleted. Its refCnt 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 refCnt 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 (refCnt > 0x7fff0000)
     MOZ_ASSERT(refCnt > 0x7fffdead);
 #endif
   MOZ_ASSERT(refCnt > 0);
   if (refCnt > 0) {
     if (0 == --refCnt) {
 #ifdef DEBUG
       refCnt = 0x7fffdead;
 #else
       refCnt = 1;
 #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 mozilla::TemporaryRef<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 */ }
 #ifdef __ARM_EABI__
   virtual const void *FindExidx(int *pcount) const;
 #endif
 protected:
   virtual Mappable *GetMappable() const;
   /**
    * Returns whether the handle is a SystemElf or not. (short of a better way
    * to do this without RTTI)
    */
   friend class ElfLoader;
   virtual bool IsSystemElf() const { return true; }
   /**
    * 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() {
     return registeredHandler;
   }
   bool isSignalHandlingBroken() {
     return signalHandlingBroken;
   }
 protected:
   SEGVHandler();
   ~SEGVHandler();
 private:
   static int __wrap_sigaction(int signum, const struct sigaction *act,
                               struct sigaction *oldact);
   /**
    * 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 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.
    */
   mozilla::TemporaryRef<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().
    */
   mozilla::TemporaryRef<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);
 protected:
   /**
    * Registers the given handle. This method is meant to be called by
    * LibHandle subclass creators.
    */
   void Register(LibHandle *handle);
   /**
    * Forget about the given handle. This method is meant to be called by
    * LibHandle subclass destructors.
    */
   void Forget(LibHandle *handle);
   /* Last error. Used for dlerror() */
   friend class SystemElf;
   friend const char *__wrap_dlerror(void);
   friend void *__wrap_dlsym(void *handle, const char *symbol);
   friend int __wrap_dlclose(void *handle);
   const char *lastError;
 private:
   ~ElfLoader();
   /* Bookkeeping */
   typedef std::vector<LibHandle *> LibHandleList;
   LibHandleList handles;
 protected:
   friend class CustomElf;
   /**
    * Show some stats about Mappables in CustomElfs. The when argument is to
    * be used by the caller to give an identifier of the when the stats call
    * is made.
    */
   static void stats(const char *when);
   /* 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;
   };
   /* Helper class used to integrate libraries loaded by this linker in
    * r_debug */
   class DebuggerHelper
   {
   public:
     DebuggerHelper();
     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;
       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 */

The Tor Browser / annotate

mozglue/linker/ElfLoader.h@b8a032363ba2 (annotated)

mozglue/linker/ElfLoader.h