diff --git a/lib/System/Win32/MappedFile.cpp b/lib/System/Win32/MappedFile.cpp
index d106eb16ad2..3112a93a8d3 100644
--- a/lib/System/Win32/MappedFile.cpp
+++ b/lib/System/Win32/MappedFile.cpp
@@ -2,37 +2,132 @@
 // 
 //                     The LLVM Compiler Infrastructure
 //
-// This file was developed by Reid Spencer and is distributed under the 
+// This file was developed by Jeff Cohen and is distributed under the 
 // University of Illinois Open Source License. See LICENSE.TXT for details.
 // 
 //===----------------------------------------------------------------------===//
 //
-// This file provides the Win32 specific implementation of the MappedFile
-// concept.
+// This file provides the Win32 implementation of the MappedFile concept.
 //
 //===----------------------------------------------------------------------===//
 
+//===----------------------------------------------------------------------===//
+//=== WARNING: Implementation here must contain only Win32 code.
+//===----------------------------------------------------------------------===//
+
 #include "Win32.h"
+#include "llvm/System/MappedFile.h"
+#include "llvm/System/Process.h"
+
+namespace llvm {
+using namespace sys;
+
+struct sys::MappedFileInfo {
+  HANDLE hFile;
+  HANDLE hMapping;
+  size_t size;
+};
 
 void MappedFile::initialize() {
+  assert(!info_);
+  info_ = new MappedFileInfo;
+  info_->hFile = INVALID_HANDLE_VALUE;
+  info_->hMapping = NULL;
+
+  DWORD mode = options_ & WRITE_ACCESS ? GENERIC_WRITE : GENERIC_READ;
+  DWORD disposition = options_ & WRITE_ACCESS ? OPEN_ALWAYS : OPEN_EXISTING;
+  DWORD share = options_ & WRITE_ACCESS ? FILE_SHARE_WRITE : FILE_SHARE_READ;
+  share = options_ & SHARED_MAPPING ? share : 0;
+  info_->hFile = CreateFile(path_.c_str(), mode, share, NULL, disposition,
+                            FILE_ATTRIBUTE_NORMAL, NULL);
+  if (info_->hFile == INVALID_HANDLE_VALUE) {
+    delete info_;
+    info_ = NULL;
+    ThrowError(std::string("Can't open file: ") + path_.get());
+  }
+
+  LARGE_INTEGER size;
+  if (!GetFileSizeEx(info_->hFile, &size) ||
+      (info_->size = size_t(size.QuadPart), info_->size != size.QuadPart)) {
+    CloseHandle(info_->hFile);
+    delete info_;
+    info_ = NULL;
+    ThrowError(std::string("Can't get size of file: ") + path_.get());
+  }
 }
 
 void MappedFile::terminate() {
+  unmap();
+  if (info_->hFile != INVALID_HANDLE_VALUE)
+    CloseHandle(info_->hFile);
+  delete info_;
+  info_ = NULL;
 }
 
 void MappedFile::unmap() {
+  assert(info_ && "MappedFile not initialized");
+  if (isMapped()) {
+    UnmapViewOfFile(base_);
+    base_ = NULL;
+  }
+  if (info_->hMapping != INVALID_HANDLE_VALUE) {
+    CloseHandle(info_->hMapping);
+    info_->hMapping = NULL;
+  }
 }
 
 void* MappedFile::map() {
-  static char junk[4096];
-  return junk;
+  if (!isMapped()) {
+    DWORD prot = PAGE_READONLY;
+    if (options_ & EXEC_ACCESS)
+      prot = SEC_IMAGE;
+    else if (options_ & WRITE_ACCESS)
+      prot = PAGE_READWRITE;
+    info_->hMapping = CreateFileMapping(info_->hFile, NULL, prot, 0, 0, NULL);
+    if (info_->hMapping == NULL)
+      ThrowError(std::string("Can't map file: ") + path_.get());
+
+    prot = (options_ & WRITE_ACCESS) ? FILE_MAP_WRITE : FILE_MAP_READ;
+    base_ = MapViewOfFileEx(info_->hMapping, prot, 0, 0, 0, NULL);
+    if (base_ == NULL) {
+      CloseHandle(info_->hMapping);
+      info_->hMapping = NULL;
+      ThrowError(std::string("Can't map file: ") + path_.get());
+    }
+  }
+  return base_;
 }
 
 size_t MappedFile::size() {
-  return 4096;
+  assert(info_ && "MappedFile not initialized");
+  return info_->size;
 }
 
 void MappedFile::size(size_t new_size) {
+  assert(info_ && "MappedFile not initialized");
+
+  // Take the mapping out of memory.
+  unmap();
+
+  // Adjust the new_size to a page boundary.
+  size_t pagesizem1 = Process::GetPageSize() - 1;
+  new_size = (new_size + pagesizem1) & ~pagesizem1;
+
+  // If the file needs to be extended, do so.
+  if (new_size > info_->size) {
+    LARGE_INTEGER eof;
+    eof.QuadPart = new_size;
+    if (!SetFilePointerEx(info_->hFile, eof, NULL, FILE_BEGIN))
+      ThrowError(std::string("Can't set end of file: ") + path_.get());
+    if (!SetEndOfFile(info_->hFile))
+      ThrowError(std::string("Can't set end of file: ") + path_.get());
+    info_->size = new_size;
+  }
+
+  // Remap the file.
+  map();
+}
+
 }
 
 // vim: sw=2 smartindent smarttab tw=80 autoindent expandtab
diff --git a/lib/System/Win32/MappedFile.inc b/lib/System/Win32/MappedFile.inc
index d106eb16ad2..3112a93a8d3 100644
--- a/lib/System/Win32/MappedFile.inc
+++ b/lib/System/Win32/MappedFile.inc
@@ -2,37 +2,132 @@
 // 
 //                     The LLVM Compiler Infrastructure
 //
-// This file was developed by Reid Spencer and is distributed under the 
+// This file was developed by Jeff Cohen and is distributed under the 
 // University of Illinois Open Source License. See LICENSE.TXT for details.
 // 
 //===----------------------------------------------------------------------===//
 //
-// This file provides the Win32 specific implementation of the MappedFile
-// concept.
+// This file provides the Win32 implementation of the MappedFile concept.
 //
 //===----------------------------------------------------------------------===//
 
+//===----------------------------------------------------------------------===//
+//=== WARNING: Implementation here must contain only Win32 code.
+//===----------------------------------------------------------------------===//
+
 #include "Win32.h"
+#include "llvm/System/MappedFile.h"
+#include "llvm/System/Process.h"
+
+namespace llvm {
+using namespace sys;
+
+struct sys::MappedFileInfo {
+  HANDLE hFile;
+  HANDLE hMapping;
+  size_t size;
+};
 
 void MappedFile::initialize() {
+  assert(!info_);
+  info_ = new MappedFileInfo;
+  info_->hFile = INVALID_HANDLE_VALUE;
+  info_->hMapping = NULL;
+
+  DWORD mode = options_ & WRITE_ACCESS ? GENERIC_WRITE : GENERIC_READ;
+  DWORD disposition = options_ & WRITE_ACCESS ? OPEN_ALWAYS : OPEN_EXISTING;
+  DWORD share = options_ & WRITE_ACCESS ? FILE_SHARE_WRITE : FILE_SHARE_READ;
+  share = options_ & SHARED_MAPPING ? share : 0;
+  info_->hFile = CreateFile(path_.c_str(), mode, share, NULL, disposition,
+                            FILE_ATTRIBUTE_NORMAL, NULL);
+  if (info_->hFile == INVALID_HANDLE_VALUE) {
+    delete info_;
+    info_ = NULL;
+    ThrowError(std::string("Can't open file: ") + path_.get());
+  }
+
+  LARGE_INTEGER size;
+  if (!GetFileSizeEx(info_->hFile, &size) ||
+      (info_->size = size_t(size.QuadPart), info_->size != size.QuadPart)) {
+    CloseHandle(info_->hFile);
+    delete info_;
+    info_ = NULL;
+    ThrowError(std::string("Can't get size of file: ") + path_.get());
+  }
 }
 
 void MappedFile::terminate() {
+  unmap();
+  if (info_->hFile != INVALID_HANDLE_VALUE)
+    CloseHandle(info_->hFile);
+  delete info_;
+  info_ = NULL;
 }
 
 void MappedFile::unmap() {
+  assert(info_ && "MappedFile not initialized");
+  if (isMapped()) {
+    UnmapViewOfFile(base_);
+    base_ = NULL;
+  }
+  if (info_->hMapping != INVALID_HANDLE_VALUE) {
+    CloseHandle(info_->hMapping);
+    info_->hMapping = NULL;
+  }
 }
 
 void* MappedFile::map() {
-  static char junk[4096];
-  return junk;
+  if (!isMapped()) {
+    DWORD prot = PAGE_READONLY;
+    if (options_ & EXEC_ACCESS)
+      prot = SEC_IMAGE;
+    else if (options_ & WRITE_ACCESS)
+      prot = PAGE_READWRITE;
+    info_->hMapping = CreateFileMapping(info_->hFile, NULL, prot, 0, 0, NULL);
+    if (info_->hMapping == NULL)
+      ThrowError(std::string("Can't map file: ") + path_.get());
+
+    prot = (options_ & WRITE_ACCESS) ? FILE_MAP_WRITE : FILE_MAP_READ;
+    base_ = MapViewOfFileEx(info_->hMapping, prot, 0, 0, 0, NULL);
+    if (base_ == NULL) {
+      CloseHandle(info_->hMapping);
+      info_->hMapping = NULL;
+      ThrowError(std::string("Can't map file: ") + path_.get());
+    }
+  }
+  return base_;
 }
 
 size_t MappedFile::size() {
-  return 4096;
+  assert(info_ && "MappedFile not initialized");
+  return info_->size;
 }
 
 void MappedFile::size(size_t new_size) {
+  assert(info_ && "MappedFile not initialized");
+
+  // Take the mapping out of memory.
+  unmap();
+
+  // Adjust the new_size to a page boundary.
+  size_t pagesizem1 = Process::GetPageSize() - 1;
+  new_size = (new_size + pagesizem1) & ~pagesizem1;
+
+  // If the file needs to be extended, do so.
+  if (new_size > info_->size) {
+    LARGE_INTEGER eof;
+    eof.QuadPart = new_size;
+    if (!SetFilePointerEx(info_->hFile, eof, NULL, FILE_BEGIN))
+      ThrowError(std::string("Can't set end of file: ") + path_.get());
+    if (!SetEndOfFile(info_->hFile))
+      ThrowError(std::string("Can't set end of file: ") + path_.get());
+    info_->size = new_size;
+  }
+
+  // Remap the file.
+  map();
+}
+
 }
 
 // vim: sw=2 smartindent smarttab tw=80 autoindent expandtab