diff --git a/include/llvm/System/Memory.h b/include/llvm/System/Memory.h
index b4ebf0e87f8..8c1c37a07cc 100644
--- a/include/llvm/System/Memory.h
+++ b/include/llvm/System/Memory.h
@@ -57,6 +57,10 @@ namespace sys {
                                      const MemoryBlock *NearBlock,
                                      std::string *ErrMsg = 0);
 
+      static MemoryBlock AllocateRW(unsigned NumBytes,
+                                    const MemoryBlock *NearBlock,
+                                    std::string *ErrMsg = 0);
+
       /// This method releases a block of Read/Write/Execute memory that was
       /// allocated with the AllocateRWX method. It should not be used to
       /// release any memory block allocated any other way.
@@ -66,6 +70,7 @@ namespace sys {
       /// @throws std::string if an error occurred.
       /// @brief Release Read/Write/Execute memory.
       static bool ReleaseRWX(MemoryBlock &block, std::string *ErrMsg = 0);
+      
     /// @}
   };
 }
diff --git a/lib/System/Unix/Memory.inc b/lib/System/Unix/Memory.inc
index afa8f03117f..164988793f7 100644
--- a/lib/System/Unix/Memory.inc
+++ b/lib/System/Unix/Memory.inc
@@ -67,6 +67,53 @@ llvm::sys::Memory::AllocateRWX(unsigned NumBytes, const MemoryBlock* NearBlock,
   return result;
 }
 
+/// AllocateRWMemory - Allocate a slab of memory with read/write permissions. 
+/// This memory needs to have executable permissions set before it can be used
+/// to execute JIT'ed code.
+llvm::sys::MemoryBlock 
+llvm::sys::Memory::AllocateRW(unsigned NumBytes, const MemoryBlock* NearBlock,
+                               std::string *ErrMsg) {
+  if (NumBytes == 0) return MemoryBlock();
+
+  long pageSize = Process::GetPageSize();
+  unsigned NumPages = (NumBytes+pageSize-1)/pageSize;
+
+  int fd = -1;
+#ifdef NEED_DEV_ZERO_FOR_MMAP
+  static int zero_fd = open("/dev/zero", O_RDWR);
+  if (zero_fd == -1) {
+    MakeErrMsg(ErrMsg, "Can't open /dev/zero device");
+    return MemoryBlock();
+  }
+  fd = zero_fd;
+#endif
+
+  int flags = MAP_PRIVATE |
+#ifdef HAVE_MMAP_ANONYMOUS
+  MAP_ANONYMOUS
+#else
+  MAP_ANON
+#endif
+  ;
+
+  void* start = NearBlock ? (unsigned char*)NearBlock->base() + 
+                            NearBlock->size() : 0;
+
+  void *pa = ::mmap(start, pageSize*NumPages, PROT_READ|PROT_WRITE,
+                    flags, fd, 0);
+  if (pa == MAP_FAILED) {
+    if (NearBlock) //Try again without a near hint
+      return AllocateRWX(NumBytes, 0);
+
+    MakeErrMsg(ErrMsg, "Can't allocate RWX Memory");
+    return MemoryBlock();
+  }
+  MemoryBlock result;
+  result.Address = pa;
+  result.Size = NumPages*pageSize;
+  return result;
+}
+
 bool llvm::sys::Memory::ReleaseRWX(MemoryBlock &M, std::string *ErrMsg) {
   if (M.Address == 0 || M.Size == 0) return false;
   if (0 != ::munmap(M.Address, M.Size))
diff --git a/lib/System/Win32/Memory.inc b/lib/System/Win32/Memory.inc
index eed2b100e6d..12627521a3d 100644
--- a/lib/System/Win32/Memory.inc
+++ b/lib/System/Win32/Memory.inc
@@ -46,6 +46,29 @@ MemoryBlock Memory::AllocateRWX(unsigned NumBytes,
   return result;
 }
 
+MemoryBlock Memory::AllocateRW(unsigned NumBytes,
+                                const MemoryBlock *NearBlock,
+                                std::string *ErrMsg) {
+  if (NumBytes == 0) return MemoryBlock();
+
+  static const long pageSize = Process::GetPageSize();
+  unsigned NumPages = (NumBytes+pageSize-1)/pageSize;
+
+  //FIXME: support NearBlock if ever needed on Win64.
+
+  void *pa = VirtualAlloc(NULL, NumPages*pageSize, MEM_COMMIT,
+                  PAGE_READWRITE);
+  if (pa == NULL) {
+    MakeErrMsg(ErrMsg, "Can't allocate RWX Memory: ");
+    return MemoryBlock();
+  }
+
+  MemoryBlock result;
+  result.Address = pa;
+  result.Size = NumPages*pageSize;
+  return result;
+}
+
 bool Memory::ReleaseRWX(MemoryBlock &M, std::string *ErrMsg) {
   if (M.Address == 0 || M.Size == 0) return false;
   if (!VirtualFree(M.Address, 0, MEM_RELEASE))