Index: lib/asan/asan_allocator.h
===================================================================
--- lib/asan/asan_allocator.h
+++ lib/asan/asan_allocator.h
@@ -125,8 +125,13 @@
 const uptr kAllocatorSpace =  0x10000000000ULL;
 const uptr kAllocatorSize  =  0x10000000000ULL;  // 3T.
 # else
+#  if SANITIZER_WINDOWS
+const uptr kAllocatorSpace = ~(uptr)0;
+const uptr kAllocatorSize  =  0x8000000000ULL;  // 500G
+#  else
 const uptr kAllocatorSpace = 0x600000000000ULL;
 const uptr kAllocatorSize  =  0x40000000000ULL;  // 4T.
+#  endif
 # endif
 typedef DefaultSizeClassMap SizeClassMap;
 struct AP64 {  // Allocator64 parameters. Deliberately using a short name.
Index: lib/asan/asan_interface_internal.h
===================================================================
--- lib/asan/asan_interface_internal.h
+++ lib/asan/asan_interface_internal.h
@@ -29,6 +29,10 @@
   // before any instrumented code is executed and before any call to malloc.
   SANITIZER_INTERFACE_ATTRIBUTE void __asan_init();
 
+  // This function should be called by a loaded instrumented module.
+  SANITIZER_INTERFACE_ATTRIBUTE void __asan_init_from_dll(
+      int *detect_stack_use_after_return, uptr *shadow_memory_dynamic_address);
+
   // This function exists purely to get a linker/loader error when using
   // incompatible versions of instrumentation and runtime library. Please note
   // that __asan_version_mismatch_check is a macro that is replaced with
@@ -170,6 +174,9 @@
   SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE
   /* OPTIONAL */ const char* __asan_default_options();
 
+  SANITIZER_INTERFACE_ATTRIBUTE
+  extern uptr __asan_shadow_memory_dynamic_address;
+
   // Global flag, copy of ASAN_OPTIONS=detect_stack_use_after_return
   SANITIZER_INTERFACE_ATTRIBUTE
   extern int __asan_option_detect_stack_use_after_return;
Index: lib/asan/asan_mapping.h
===================================================================
--- lib/asan/asan_mapping.h
+++ lib/asan/asan_mapping.h
@@ -140,7 +140,6 @@
 static const u64 kFreeBSD_ShadowOffset32 = 1ULL << 30;  // 0x40000000
 static const u64 kFreeBSD_ShadowOffset64 = 1ULL << 46;  // 0x400000000000
 static const u64 kWindowsShadowOffset32 = 3ULL << 28;  // 0x30000000
-static const u64 kWindowsShadowOffset64 = 1ULL << 45;  // 32TB
 
 #define SHADOW_SCALE kDefaultShadowScale
 
@@ -183,7 +182,7 @@
 #  elif defined(__mips64)
 #   define SHADOW_OFFSET kMIPS64_ShadowOffset64
 #  elif SANITIZER_WINDOWS64
-#   define SHADOW_OFFSET kWindowsShadowOffset64
+#   define SHADOW_OFFSET __asan_shadow_memory_dynamic_address
 #  else
 #   define SHADOW_OFFSET kDefaultShort64bitShadowOffset
 #  endif
Index: lib/asan/asan_rtl.cc
===================================================================
--- lib/asan/asan_rtl.cc
+++ lib/asan/asan_rtl.cc
@@ -32,6 +32,7 @@
 #include "ubsan/ubsan_init.h"
 #include "ubsan/ubsan_platform.h"
 
+uptr __asan_shadow_memory_dynamic_address;  // Global interface symbol.
 int __asan_option_detect_stack_use_after_return;  // Global interface symbol.
 uptr *__asan_test_only_reported_buggy_pointer;  // Used only for testing asan.
 
@@ -460,7 +461,20 @@
 
   ReplaceSystemMalloc();
 
+  __asan_shadow_memory_dynamic_address = 0;
   uptr shadow_start = kLowShadowBeg;
+  if (shadow_start == 0) {
+    uptr granularity = GetMmapGranularity();
+    uptr alignment = 8 * granularity;
+    uptr left_padding = granularity;
+    uptr space_size = kHighShadowEnd + left_padding;
+
+    shadow_start = FindAvailableMemoryRange(space_size, alignment, granularity);
+    CHECK_NE((uptr)0, shadow_start);
+    CHECK(IsAligned(shadow_start, alignment));
+  }
+  __asan_shadow_memory_dynamic_address = shadow_start;
+
   if (kLowShadowBeg)
     shadow_start -= GetMmapGranularity();
   bool full_shadow_is_available =
@@ -472,12 +486,6 @@
     kMidMemBeg = kLowMemEnd < 0x3000000000ULL ? 0x3000000000ULL : 0;
     kMidMemEnd = kLowMemEnd < 0x3000000000ULL ? 0x4fffffffffULL : 0;
   }
-#elif SANITIZER_WINDOWS64
-  // Disable the "mid mem" shadow layout.
-  if (!full_shadow_is_available) {
-    kMidMemBeg = 0;
-    kMidMemEnd = 0;
-  }
 #endif
 
   if (Verbosity()) PrintAddressSpaceLayout();
@@ -650,6 +658,15 @@
   AsanInitInternal();
 }
 
+// Called by a loaded DLL to initialize itself.
+void __asan_init_from_dll(
+    int *detect_stack_use_after_return,
+    uptr *shadow_memory_dynamic_address) {
+  __asan_init();
+  *detect_stack_use_after_return = __asan_option_detect_stack_use_after_return;
+  *shadow_memory_dynamic_address = __asan_shadow_memory_dynamic_address;
+}
+
 void __asan_version_mismatch_check() {
   // Do nothing.
 }
Index: lib/asan/asan_win_dll_thunk.cc
===================================================================
--- lib/asan/asan_win_dll_thunk.cc
+++ lib/asan/asan_win_dll_thunk.cc
@@ -197,23 +197,21 @@
 // ----------------- ASan own interface functions --------------------
 // Don't use the INTERFACE_FUNCTION machinery for this function as we actually
 // want to call it in the __asan_init interceptor.
-WRAP_W_V(__asan_should_detect_stack_use_after_return)
-
 extern "C" {
   int __asan_option_detect_stack_use_after_return;
+  uptr __asan_shadow_memory_dynamic_address;
 
   // Manually wrap __asan_init as we need to initialize
   // __asan_option_detect_stack_use_after_return afterwards.
   void __asan_init() {
-    typedef void (*fntype)();
+     typedef void (*fntype)(int*, uptr*);
     static fntype fn = 0;
     // __asan_init is expected to be called by only one thread.
     if (fn) return;
 
-    fn = (fntype)getRealProcAddressOrDie("__asan_init");
-    fn();
-    __asan_option_detect_stack_use_after_return =
-        (__asan_should_detect_stack_use_after_return() != 0);
+    fn = (fntype)getRealProcAddressOrDie("__asan_init_from_dll");
+    fn(&__asan_option_detect_stack_use_after_return,
+       &__asan_shadow_memory_dynamic_address);
 
     InterceptHooks();
   }
Index: lib/asan/asan_win_dynamic_runtime_thunk.cc
===================================================================
--- lib/asan/asan_win_dynamic_runtime_thunk.cc
+++ lib/asan/asan_win_dynamic_runtime_thunk.cc
@@ -34,23 +34,6 @@
 #pragma section(".CRT$XTY", long, read)  // NOLINT
 
 ////////////////////////////////////////////////////////////////////////////////
-// Define a copy of __asan_option_detect_stack_use_after_return that should be
-// used when linking an MD runtime with a set of object files on Windows.
-//
-// The ASan MD runtime dllexports '__asan_option_detect_stack_use_after_return',
-// so normally we would just dllimport it.  Unfortunately, the dllimport
-// attribute adds __imp_ prefix to the symbol name of a variable.
-// Since in general we don't know if a given TU is going to be used
-// with a MT or MD runtime and we don't want to use ugly __imp_ names on Windows
-// just to work around this issue, let's clone the variable that is constant
-// after initialization anyways.
-extern "C" {
-__declspec(dllimport) int __asan_should_detect_stack_use_after_return();
-int __asan_option_detect_stack_use_after_return =
-    __asan_should_detect_stack_use_after_return();
-}
-
-////////////////////////////////////////////////////////////////////////////////
 // For some reason, the MD CRT doesn't call the C/C++ terminators during on DLL
 // unload or on exit.  ASan relies on LLVM global_dtors to call
 // __asan_unregister_globals on these events, which unfortunately doesn't work
Index: lib/sanitizer_common/sanitizer_common.h
===================================================================
--- lib/sanitizer_common/sanitizer_common.h
+++ lib/sanitizer_common/sanitizer_common.h
@@ -98,6 +98,9 @@
 bool MprotectNoAccess(uptr addr, uptr size);
 bool MprotectReadOnly(uptr addr, uptr size);
 
+// Find an available address space.
+uptr FindAvailableMemoryRange(uptr size, uptr alignment, uptr left_padding);
+
 // Used to check if we can map shadow memory to a fixed location.
 bool MemoryRangeIsAvailable(uptr range_start, uptr range_end);
 void ReleaseMemoryToOS(uptr addr, uptr size);
Index: lib/sanitizer_common/sanitizer_win.cc
===================================================================
--- lib/sanitizer_common/sanitizer_win.cc
+++ lib/sanitizer_common/sanitizer_win.cc
@@ -249,6 +249,26 @@
   // FIXME: add madvise-analog when we move to 64-bits.
 }
 
+uptr FindAvailableMemoryRange(uptr size, uptr alignment, uptr left_padding) {
+  uptr address = 0;
+  while (true) {
+    MEMORY_BASIC_INFORMATION info;
+    if (!::VirtualQuery((void*)address, &info, sizeof(info)))
+      return 0;
+
+    if (info.State == MEM_FREE) {
+      uptr shadow_address = RoundUpTo((uptr)info.BaseAddress + left_padding,
+                                      alignment);
+      if (shadow_address + size < (uptr)info.BaseAddress + info.RegionSize)
+        return shadow_address;
+    }
+
+    // Move to the next region.
+    address = (uptr)info.BaseAddress + info.RegionSize;
+  }
+  return 0;
+}
+
 bool MemoryRangeIsAvailable(uptr range_start, uptr range_end) {
   MEMORY_BASIC_INFORMATION mbi;
   CHECK(VirtualQuery((void *)range_start, &mbi, sizeof(mbi)));