Index: lib/sanitizer_common/sanitizer_common.h
===================================================================
--- lib/sanitizer_common/sanitizer_common.h
+++ lib/sanitizer_common/sanitizer_common.h
@@ -83,6 +83,18 @@
                           uptr *tls_addr, uptr *tls_size);
 
 // Memory management
+// This class relies on zero-initialization.
+class ReservedAddressRange {
+ public:
+  uptr Init(uptr size, const char *name = nullptr, uptr fixed_addr = (uptr)0);
+  uptr Map(uptr offset, uptr size, bool tolerate_enomem = false);
+  void *base() { return base_; }
+ private:
+  uptr os_cookie_;
+  void* base_;
+  uptr size_;
+};
+
 void *MmapOrDie(uptr size, const char *mem_type, bool raw_report = false);
 INLINE void *MmapOrDieQuietly(uptr size, const char *mem_type) {
   return MmapOrDie(size, mem_type, /*raw_report*/ true);
Index: lib/sanitizer_common/sanitizer_fuchsia.cc
===================================================================
--- lib/sanitizer_common/sanitizer_fuchsia.cc
+++ lib/sanitizer_common/sanitizer_fuchsia.cc
@@ -237,6 +237,19 @@
   return DoAnonymousMmapOrDie(size, mem_type, false, false);
 }
 
+uptr ReservedAddressRange::Init(uptr init_size, const char* name = nullptr,
+                                uptr fixed_addr = uptr(0)) {
+  return reinterpret_cast<uptr>(MmapNoAccess(init_size));
+}
+
+// Uses fixed_addr for now.
+// Will use offset instead once we've implemented this function for real.
+uptr ReservedAddressRange::Map(uptr fixed_addr, uptr map_size,
+                               bool tolerate_enomem = true) {
+  return reinterpret_cast<uptr>(MmapFixedOrDie(fixed_addr, size,
+                                               tolerate_enomem));
+}
+
 // MmapNoAccess and MmapFixedOrDie are used only by sanitizer_allocator.
 // Instead of doing exactly what they say, we make MmapNoAccess actually
 // just allocate a VMAR to reserve the address space.  Then MmapFixedOrDie
Index: lib/sanitizer_common/sanitizer_posix.cc
===================================================================
--- lib/sanitizer_common/sanitizer_posix.cc
+++ lib/sanitizer_common/sanitizer_posix.cc
@@ -141,6 +141,16 @@
   return MmapFixedImpl(fixed_addr, size, false /*tolerate_enomem*/);
 }
 
+// Uses fixed_addr for now.
+// Will use offset instead once we've implemented this function for real.
+uptr ReservedAddressRange::Map(uptr fixed_addr, uptr size,
+                               bool tolerate_enomem) {
+  if (tolerate_enomem) {
+    return reinterpret_cast<uptr>(MmapFixedOrDieOnFatalError(fixed_addr, size));
+  }
+  return reinterpret_cast<uptr>(MmapFixedOrDie(fixed_addr, size));
+}
+
 void *MmapFixedOrDieOnFatalError(uptr fixed_addr, uptr size) {
   return MmapFixedImpl(fixed_addr, size, true /*tolerate_enomem*/);
 }
Index: lib/sanitizer_common/sanitizer_posix_libcdep.cc
===================================================================
--- lib/sanitizer_common/sanitizer_posix_libcdep.cc
+++ lib/sanitizer_common/sanitizer_posix_libcdep.cc
@@ -337,6 +337,13 @@
   return (void *)p;
 }
 
+uptr ReservedAddressRange::Init(uptr size, const char *name, uptr fixed_addr) {
+  if (fixed_addr) {
+    return reinterpret_cast<uptr>(MmapFixedNoAccess(fixed_addr, size, name));
+  }
+  return reinterpret_cast<uptr>(MmapNoAccess(size));
+}
+
 void *MmapFixedNoAccess(uptr fixed_addr, uptr size, const char *name) {
   int fd = name ? GetNamedMappingFd(name, size) : -1;
   unsigned flags = MAP_PRIVATE | MAP_FIXED | MAP_NORESERVE;
Index: lib/sanitizer_common/sanitizer_win.cc
===================================================================
--- lib/sanitizer_common/sanitizer_win.cc
+++ lib/sanitizer_common/sanitizer_win.cc
@@ -236,6 +236,16 @@
   return p;
 }
 
+// Uses fixed_addr for now.
+// Will use offset instead once we've implemented this function for real.
+uptr ReservedAddressRange::Map(uptr fixed_addr, uptr size,
+                               bool tolerate_enomem) {
+  if (tolerate_enomem) {
+    return reinterpret_cast<uptr>(MmapFixedOrDieOnFatalError(fixed_addr, size));
+  }
+  return reinterpret_cast<uptr>(MmapFixedOrDie(uptr fixed_addr, uptr size));
+}
+
 void *MmapFixedOrDieOnFatalError(uptr fixed_addr, uptr size) {
   void *p = VirtualAlloc((LPVOID)fixed_addr, size,
       MEM_COMMIT, PAGE_READWRITE);
@@ -253,6 +263,13 @@
   return MmapOrDie(size, mem_type);
 }
 
+uptr ReservedAddressRange::Init(uptr size, const char *name, uptr fixed_addr) {
+  if (fixed_addr) {
+    return reinterpret_cast<uptr>(MmapFixedNoAccess(fixed_addr, size, name));
+  }
+  return reinterpret_cast<uptr>(MmapNoAccess(size));
+}
+
 void *MmapFixedNoAccess(uptr fixed_addr, uptr size, const char *name) {
   (void)name; // unsupported
   void *res = VirtualAlloc((LPVOID)fixed_addr, size,