diff --git a/mozglue/linker/CustomElf.cpp b/mozglue/linker/CustomElf.cpp
index bcd26b0fef52..158d9f9d7409 100644
--- a/mozglue/linker/CustomElf.cpp
+++ b/mozglue/linker/CustomElf.cpp
@@ -746,3 +746,13 @@ CustomElf::CallFini()
   if (fini)
     CallFunction(fini);
 }
+
+Mappable *
+CustomElf::GetMappable() const
+{
+  if (!mappable)
+    return NULL;
+  if (mappable->GetKind() == Mappable::MAPPABLE_EXTRACT_FILE)
+    return mappable;
+  return ElfLoader::GetMappableFromPath(GetPath());
+}
diff --git a/mozglue/linker/CustomElf.h b/mozglue/linker/CustomElf.h
index 74f789b27c3f..4a29727af1ea 100644
--- a/mozglue/linker/CustomElf.h
+++ b/mozglue/linker/CustomElf.h
@@ -39,6 +39,10 @@ public:
   virtual void *GetSymbolPtr(const char *symbol) const;
   virtual bool Contains(void *addr) const;
 
+protected:
+  virtual Mappable *GetMappable() const;
+
+public:
   /**
    * Shows some stats about the Mappable instance. The when argument is to be
    * used by the caller to give an identifier of the when the stats call is
diff --git a/mozglue/linker/ElfLoader.cpp b/mozglue/linker/ElfLoader.cpp
index 61f5df90181b..aad2829ea7e1 100644
--- a/mozglue/linker/ElfLoader.cpp
+++ b/mozglue/linker/ElfLoader.cpp
@@ -2,6 +2,7 @@
  * 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/. */
 
+#include <string>
 #include <cstring>
 #include <cstdlib>
 #include <cstdio>
@@ -130,6 +131,34 @@ __wrap_dl_iterate_phdr(dl_phdr_cb callback, void *data)
   return 0;
 }
 
+/**
+ * faulty.lib public API
+ */
+
+MFBT_API size_t
+__dl_get_mappable_length(void *handle) {
+  if (!handle)
+    return 0;
+  return reinterpret_cast<LibHandle *>(handle)->GetMappableLength();
+}
+
+MFBT_API void *
+__dl_mmap(void *handle, void *addr, size_t length, off_t offset)
+{
+  if (!handle)
+    return NULL;
+  return reinterpret_cast<LibHandle *>(handle)->MappableMMap(addr, length,
+                                                             offset);
+}
+
+MFBT_API void
+__dl_munmap(void *handle, void *addr, size_t length)
+{
+  if (!handle)
+    return;
+  return reinterpret_cast<LibHandle *>(handle)->MappableMUnmap(addr, length);
+}
+
 namespace {
 
 /**
@@ -152,6 +181,8 @@ LeafName(const char *path)
 LibHandle::~LibHandle()
 {
   free(path);
+  if (mappable->GetKind() != Mappable::MAPPABLE_EXTRACT_FILE)
+    delete mappable;
 }
 
 const char *
@@ -160,6 +191,33 @@ LibHandle::GetName() const
   return path ? LeafName(path) : NULL;
 }
 
+size_t
+LibHandle::GetMappableLength() const
+{
+  MOZ_ASSERT(mappable != NULL, "GetMappableLength needs to be called first,"
+                               " and only once");
+  mappable = GetMappable();
+  if (!mappable)
+    return 0;
+  return mappable->GetLength();
+}
+
+void *
+LibHandle::MappableMMap(void *addr, size_t length, off_t offset) const
+{
+  MOZ_ASSERT(mappable == NULL, "MappableMMap must be called after"
+                               " GetMappableLength");
+  return mappable->mmap(addr, length, PROT_READ, MAP_PRIVATE, offset);
+}
+
+void
+LibHandle::MappableMUnmap(void *addr, size_t length) const
+{
+  MOZ_ASSERT(mappable == NULL, "MappableMUnmap must be called after"
+                               " MappableMMap and GetMappableLength");
+  mappable->munmap(addr, length);
+}
+
 /**
  * SystemElf
  */
@@ -203,6 +261,26 @@ SystemElf::GetSymbolPtr(const char *symbol) const
   return sym;
 }
 
+Mappable *
+SystemElf::GetMappable() const
+{
+  const char *path = GetPath();
+  if (!path)
+    return NULL;
+#ifdef ANDROID
+  /* On Android, if we don't have the full path, try in /system/lib */
+  const char *name = LeafName(path);
+  std::string systemPath;
+  if (name == path) {
+    systemPath = "/system/lib/";
+    systemPath += path;
+    path = systemPath.c_str();
+  }
+#endif
+
+  return MappableFile::Create(path);
+}
+
 /**
  * ElfLoader
  */
@@ -253,38 +331,7 @@ ElfLoader::Load(const char *path, int flags, LibHandle *parent)
     path = abs_path;
   }
 
-  /* Create a mappable object for the given 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. */
-  Mappable *mappable = NULL;
-  RefPtr<Zip> zip;
-  const char *subpath;
-  if ((subpath = strchr(path, '!'))) {
-    char *zip_path = strndup(path, subpath - path);
-    while (*(++subpath) == '/') { }
-    zip = ZipCollection::GetZip(zip_path);
-    Zip::Stream s;
-    if (zip && zip->GetStream(subpath, &s)) {
-      /* When the MOZ_LINKER_EXTRACT environment variable is set to "1",
-       * compressed libraries are going to be (temporarily) extracted as
-       * files, in the directory pointed by the MOZ_LINKER_CACHE
-       * environment variable. */
-      const char *extract = getenv("MOZ_LINKER_EXTRACT");
-      if (extract && !strncmp(extract, "1", 2 /* Including '\0' */))
-        mappable = MappableExtractFile::Create(name, zip, &s);
-      if (!mappable) {
-        if (s.GetType() == Zip::Stream::DEFLATE) {
-          mappable = MappableDeflate::Create(name, zip, &s);
-        } else if (s.GetType() == Zip::Stream::STORE) {
-          mappable = MappableSeekableZStream::Create(name, zip, &s);
-        }
-      }
-    }
-  }
-  /* If we couldn't load above, try with a MappableFile */
-  if (!mappable && !zip)
-    mappable = MappableFile::Create(path);
+  Mappable *mappable = GetMappableFromPath(path);
 
   /* Try loading with the custom linker if we have a Mappable */
   if (mappable)
@@ -318,6 +365,42 @@ ElfLoader::GetHandleByPtr(void *addr)
   return NULL;
 }
 
+Mappable *
+ElfLoader::GetMappableFromPath(const char *path)
+{
+  const char *name = LeafName(path);
+  Mappable *mappable = NULL;
+  RefPtr<Zip> zip;
+  const char *subpath;
+  if ((subpath = strchr(path, '!'))) {
+    char *zip_path = strndup(path, subpath - path);
+    while (*(++subpath) == '/') { }
+    zip = ZipCollection::GetZip(zip_path);
+    Zip::Stream s;
+    if (zip && zip->GetStream(subpath, &s)) {
+      /* When the MOZ_LINKER_EXTRACT environment variable is set to "1",
+       * compressed libraries are going to be (temporarily) extracted as
+       * files, in the directory pointed by the MOZ_LINKER_CACHE
+       * environment variable. */
+      const char *extract = getenv("MOZ_LINKER_EXTRACT");
+      if (extract && !strncmp(extract, "1", 2 /* Including '\0' */))
+        mappable = MappableExtractFile::Create(name, zip, &s);
+      if (!mappable) {
+        if (s.GetType() == Zip::Stream::DEFLATE) {
+          mappable = MappableDeflate::Create(name, zip, &s);
+        } else if (s.GetType() == Zip::Stream::STORE) {
+          mappable = MappableSeekableZStream::Create(name, zip, &s);
+        }
+      }
+    }
+  }
+  /* If we couldn't load above, try with a MappableFile */
+  if (!mappable && !zip)
+    mappable = MappableFile::Create(path);
+
+  return mappable;
+}
+
 void
 ElfLoader::Register(LibHandle *handle)
 {
diff --git a/mozglue/linker/ElfLoader.h b/mozglue/linker/ElfLoader.h
index 528718d781af..90e742baeeda 100644
--- a/mozglue/linker/ElfLoader.h
+++ b/mozglue/linker/ElfLoader.h
@@ -44,6 +44,19 @@ extern "C" {
 
   typedef int (*dl_phdr_cb)(struct dl_phdr_info *, size_t, void *);
   int __wrap_dl_iterate_phdr(dl_phdr_cb callback, void *data);
+
+/**
+ * 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);
+
 }
 
 /**
@@ -65,6 +78,9 @@ template <> inline RefCounted<LibHandle>::~RefCounted()
 
 } /* namespace mozilla */
 
+/* Forward declaration */
+class Mappable;
+
 /**
  * Abstract class for loaded libraries. Libraries may be loaded through the
  * system linker or this linker, both cases will be derived from this class.
@@ -77,7 +93,7 @@ public:
    * of the leaf name.
    */
   LibHandle(const char *path)
-  : directRefCnt(0), path(path ? strdup(path) : NULL) { }
+  : directRefCnt(0), path(path ? strdup(path) : NULL), mappable(NULL) { }
 
   /**
    * Destructor.
@@ -147,7 +163,30 @@ public:
     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;
+
 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)
@@ -160,6 +199,9 @@ protected:
 private:
   int directRefCnt;
   char *path;
+
+  /* Mappable object keeping the result of GetMappable() */
+  mutable Mappable *mappable;
 };
 
 /**
@@ -212,6 +254,8 @@ public:
   virtual bool Contains(void *addr) const { return false; /* UNIMPLEMENTED */ }
 
 protected:
+  virtual Mappable *GetMappable() const;
+
   /**
    * Returns whether the handle is a SystemElf or not. (short of a better way
    * to do this without RTTI)
@@ -314,6 +358,14 @@ public:
    */
   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
diff --git a/mozglue/linker/Makefile.in b/mozglue/linker/Makefile.in
index e057acc500de..7d305e3a803a 100644
--- a/mozglue/linker/Makefile.in
+++ b/mozglue/linker/Makefile.in
@@ -33,6 +33,8 @@ CPPSRCS += \
   SeekableZStream.cpp \
   $(NULL)
 
+DEFINES += -DIMPL_MFBT
+
 include $(topsrcdir)/config/rules.mk
 
 ifeq (arm,$(TARGET_CPU))
diff --git a/mozglue/linker/Mappable.cpp b/mozglue/linker/Mappable.cpp
index 6497c4e06a5c..338c735537ac 100644
--- a/mozglue/linker/Mappable.cpp
+++ b/mozglue/linker/Mappable.cpp
@@ -65,6 +65,13 @@ MappableFile::finalize()
   fd = -1;
 }
 
+size_t
+MappableFile::GetLength() const
+{
+  struct stat st;
+  return fstat(fd, &st) ? 0 : st.st_size;
+}
+
 Mappable *
 MappableExtractFile::Create(const char *name, Zip *zip, Zip::Stream *stream)
 {
@@ -342,6 +349,12 @@ MappableDeflate::finalize()
   zip = NULL;
 }
 
+size_t
+MappableDeflate::GetLength() const
+{
+  return buffer->GetLength();
+}
+
 Mappable *
 MappableSeekableZStream::Create(const char *name, Zip *zip,
                                 Zip::Stream *stream)
@@ -543,3 +556,9 @@ MappableSeekableZStream::stats(const char *when, const char *name) const
     }
   }
 }
+
+size_t
+MappableSeekableZStream::GetLength() const
+{
+  return buffer->GetLength();
+}
diff --git a/mozglue/linker/Mappable.h b/mozglue/linker/Mappable.h
index d776d1b45d9c..dea213d22cbe 100644
--- a/mozglue/linker/Mappable.h
+++ b/mozglue/linker/Mappable.h
@@ -30,6 +30,15 @@ public:
   virtual void *mmap(const void *addr, size_t length, int prot, int flags,
                      off_t offset) = 0;
 
+  enum Kind {
+    MAPPABLE_FILE,
+    MAPPABLE_EXTRACT_FILE,
+    MAPPABLE_DEFLATE,
+    MAPPABLE_SEEKABLE_ZSTREAM
+  };
+
+  virtual Kind GetKind() const = 0;
+
 private:
   virtual void munmap(void *addr, size_t length) {
     ::munmap(addr, length);
@@ -37,6 +46,7 @@ private:
   /* Limit use of Mappable::munmap to classes that keep track of the address
    * and size of the mapping. This allows to ignore ::munmap return value. */
   friend class Mappable1stPagePtr;
+  friend class LibHandle;
 
 public:
   /**
@@ -60,6 +70,12 @@ public:
    * the stats call is made.
    */
   virtual void stats(const char *when, const char *name) const { }
+
+  /**
+   * Returns the maximum length that can be mapped from this Mappable for
+   * offset = 0.
+   */
+  virtual size_t GetLength() const = 0;
 };
 
 /**
@@ -78,7 +94,9 @@ public:
   /* Inherited from Mappable */
   virtual void *mmap(const void *addr, size_t length, int prot, int flags, off_t offset);
   virtual void finalize();
+  virtual size_t GetLength() const;
 
+  virtual Kind GetKind() const { return MAPPABLE_FILE; };
 protected:
   MappableFile(int fd): fd(fd) { }
 
@@ -102,6 +120,7 @@ public:
    */
   static Mappable *Create(const char *name, Zip *zip, Zip::Stream *stream);
 
+  virtual Kind GetKind() const { return MAPPABLE_EXTRACT_FILE; };
 private:
   MappableExtractFile(int fd, char *path)
   : MappableFile(fd), path(path), pid(getpid()) { }
@@ -150,7 +169,9 @@ public:
   /* Inherited from Mappable */
   virtual void *mmap(const void *addr, size_t length, int prot, int flags, off_t offset);
   virtual void finalize();
+  virtual size_t GetLength() const;
 
+  virtual Kind GetKind() const { return MAPPABLE_DEFLATE; };
 private:
   MappableDeflate(_MappableBuffer *buf, Zip *zip, Zip::Stream *stream);
 
@@ -188,7 +209,9 @@ public:
   virtual void finalize();
   virtual bool ensure(const void *addr);
   virtual void stats(const char *when, const char *name) const;
+  virtual size_t GetLength() const;
 
+  virtual Kind GetKind() const { return MAPPABLE_SEEKABLE_ZSTREAM; };
 private:
   MappableSeekableZStream(Zip *zip);