Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -164,7 +164,7 @@
 # We support running instrumented tests when we're not cross compiling
 # and target a UNIX-like system or Windows.
 # We can run tests on Android even when we are cross-compiling.
-if(("${CMAKE_HOST_SYSTEM}" STREQUAL "${CMAKE_SYSTEM}" AND (UNIX OR MSVC)) OR ANDROID
+if(("${CMAKE_HOST_SYSTEM}" STREQUAL "${CMAKE_SYSTEM}" AND (UNIX OR WIN32)) OR ANDROID
    OR COMPILER_RT_EMULATOR)
   option(COMPILER_RT_CAN_EXECUTE_TESTS "Can we execute instrumented tests" ON)
 else()
Index: lib/builtins/CMakeLists.txt
===================================================================
--- lib/builtins/CMakeLists.txt
+++ lib/builtins/CMakeLists.txt
@@ -154,6 +154,12 @@
   x86_64/floatundixf.S
   ${GENERIC_SOURCES})
 
+if(WIN32)
+  set(x86_64_SOURCES
+      ${x86_64_SOURCES}
+      x86_64/chkstk.S)
+endif()
+
 set(i386_SOURCES
   i386/ashldi3.S
   i386/ashrdi3.S
@@ -171,6 +177,12 @@
   i386/umoddi3.S
   ${GENERIC_SOURCES})
 
+if(WIN32)
+  set(i386_SOURCES
+      ${i386_SOURCES}
+      i386/chkstk.S)
+endif()
+
 set(i686_SOURCES
   ${i386_SOURCES})
 
@@ -260,7 +272,7 @@
 
 add_custom_target(builtins)
 
-if (NOT WIN32)
+if (NOT MSVC)
   foreach (arch x86_64 i386 i686 arm)
     if (CAN_TARGET_${arch})
       # Filter out generic versions of routines that are re-implemented in
Index: lib/builtins/enable_execute_stack.c
===================================================================
--- lib/builtins/enable_execute_stack.c
+++ lib/builtins/enable_execute_stack.c
@@ -10,7 +10,9 @@
 
 #include "int_lib.h"
 
+#ifndef _WIN32
 #include <sys/mman.h>
+#endif
 
 /* #include "config.h"
  * FIXME: CMake - include when cmake system is ready.
@@ -18,9 +20,14 @@
  */
 #define HAVE_SYSCONF 1
 
+#ifdef _WIN32
+#include <windef.h>
+#include <winbase.h>
+#else
 #ifndef __APPLE__
 #include <unistd.h>
 #endif /* __APPLE__ */
+#endif /* _WIN32 */
 
 #if __LP64__
 	#define TRAMPOLINE_SIZE 48
@@ -40,6 +47,12 @@
 __enable_execute_stack(void* addr)
 {
 
+#if _WIN32
+	MEMORY_BASIC_INFORMATION mbi;
+	if (!VirtualQuery (addr, &mbi, sizeof(mbi)))
+		return; /* We should probably assert here because there is no return value */
+	VirtualProtect (mbi.BaseAddress, mbi.RegionSize, PAGE_EXECUTE_READWRITE, &mbi.Protect);
+#else
 #if __APPLE__
 	/* On Darwin, pagesize is always 4096 bytes */
 	const uintptr_t pageSize = 4096;
@@ -55,4 +68,5 @@
 	unsigned char* endPage = (unsigned char*)((p+TRAMPOLINE_SIZE+pageSize) & pageAlignMask);
 	size_t length = endPage - startPage;
 	(void) mprotect((void *)startPage, length, PROT_READ | PROT_WRITE | PROT_EXEC);
+#endif
 }
Index: lib/builtins/i386/chkstk.S
===================================================================
--- /dev/null
+++ lib/builtins/i386/chkstk.S
@@ -0,0 +1,34 @@
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+ 
+#include "../assembly.h"
+
+// _chkstk routine
+// This routine is windows specific
+// http://msdn.microsoft.com/en-us/library/ms648426.aspx
+
+#ifdef __i386__
+
+.text
+.balign 4
+DEFINE_COMPILERRT_FUNCTION(__chkstk_ms)
+        push   %ecx
+        push   %eax
+        cmp    $0x1000,%eax
+        lea    12(%esp),%ecx
+        jb     1f
+2:
+        sub    $0x1000,%ecx
+        orl    $0,(%ecx)
+        sub    $0x1000,%eax
+        cmp    $0x1000,%eax
+        ja     2b
+1:
+        sub    %eax,%ecx
+        orl    $0,(%ecx)
+        pop    %eax
+        pop    %ecx
+        ret
+END_COMPILERRT_FUNCTION(__chkstk_ms)
+
+#endif // __i386__
Index: lib/builtins/x86_64/chkstk.S
===================================================================
--- /dev/null
+++ lib/builtins/x86_64/chkstk.S
@@ -0,0 +1,39 @@
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+ 
+#include "../assembly.h"
+
+// _chkstk routine
+// This routine is windows specific
+// http://msdn.microsoft.com/en-us/library/ms648426.aspx
+
+// Notes from r227519
+// MSVC x64s __chkstk and cygmings ___chkstk_ms do not adjust %rsp
+// themselves. It also does not clobber %rax so we can reuse it when
+// adjusting %rsp.
+
+#ifdef __x86_64__
+
+.text
+.balign 4
+DEFINE_COMPILERRT_FUNCTION(___chkstk_ms)
+        push   %rcx
+        push   %rax
+        cmp    $0x1000,%rax
+        lea    24(%rsp),%rcx
+        jb     1f
+2:
+        sub    $0x1000,%rcx
+        orl    $0,(%ecx)
+        sub    $0x1000,%rax
+        cmp    $0x1000,%rax
+        ja     2b
+1:
+        sub    %rax,%rcx
+        orl    $0,(%rcx)
+        pop    %rax
+        pop    %rcx
+        ret
+END_COMPILERRT_FUNCTION(___chkstk_ms)
+
+#endif // __x86_64__