Transform ImagePreReader into PreReadFile.

chrome/app/file_pre_reader_win.cc

Index: chrome/app/file_pre_reader_win.cc
diff --git a/chrome/app/file_pre_reader_win.cc b/chrome/app/file_pre_reader_win.cc
new file mode 100644
index 0000000000000000000000000000000000000000..467f45ff4f9e1902c051d66342ec295aa7c247ec
--- /dev/null
+++ b/chrome/app/file_pre_reader_win.cc
@@ -0,0 +1,104 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/app/file_pre_reader_win.h"
+
+#include <windows.h>
+
+#include "base/files/file.h"
+#include "base/logging.h"
+#include "base/threading/thread_restrictions.h"
+#include "base/win/pe_image.h"
+#include "base/win/windows_version.h"
+
+namespace {
+
+// A helper function to touch all pages in the range
+// [base_addr, base_addr + length).
+void TouchPagesInRange(const void* base_addr, size_t length) {
+  DCHECK(base_addr);
+  DCHECK_GT(length, static_cast<size_t>(0));
+
+  // Get the system info so we know the page size. Also, make sure we use a
+  // non-zero value for the page size; GetSystemInfo() is hookable/patchable,
+  // and you never know what shenanigans someone could get up to.
+  SYSTEM_INFO system_info = {};
+  ::GetSystemInfo(&system_info);
+  if (system_info.dwPageSize == 0)
+    system_info.dwPageSize = 4096;
+
+  // We don't want to read outside the byte range (which could trigger an
+  // access violation), so let's figure out the exact locations of the first
+  // and final bytes we want to read.
+  volatile uint8_t const* touch_ptr =
+      reinterpret_cast<uint8_t const*>(base_addr);
+  volatile uint8_t const* final_touch_ptr = touch_ptr + length - 1;
+
+  // Read the memory in the range [touch_ptr, final_touch_ptr] with a stride
+  // of the system page size, to ensure that it's been paged in.
+  uint8_t dummy;
+  for (; touch_ptr < final_touch_ptr; touch_ptr += system_info.dwPageSize)
+    dummy = *touch_ptr;
+  dummy = *final_touch_ptr;
+}
+
+}  // namespace
+
+bool PreReadFile(const base::FilePath& file_path, int step_size) {
+  DCHECK_GT(step_size, 0);
+  base::ThreadRestrictions::AssertIOAllowed();
+
+  if (base::win::GetVersion() > base::win::VERSION_XP) {
+    // Vista+ branch. On these OSes, the forced reads through the file actually
+    // slows warm starts. The solution is to sequentially read file contents.
+    base::File file(file_path, base::File::FLAG_OPEN | base::File::FLAG_READ |
+                                   base::File::FLAG_SEQUENTIAL_SCAN);
+    if (!file.IsValid())
+      return false;
+
+    char* buffer = reinterpret_cast<char*>(::VirtualAlloc(
+        nullptr, static_cast<DWORD>(step_size), MEM_COMMIT, PAGE_READWRITE));
+    if (!buffer)
+      return false;
+
+    while (file.ReadAtCurrentPos(buffer, step_size) > 0) {}
+
+    ::VirtualFree(buffer, 0, MEM_RELEASE);
+  } else {
+    // WinXP branch. Here, reading the DLL from disk doesn't do what we want so
+    // instead we pull the pages into memory and touch pages at a stride. We use
+    // the system's page size as the stride, ignoring the passed in |step_size|,
+    // to make sure each page in the range is touched.
+
+    // Don't show an error popup when |file_path| is not a valid PE file.
+    UINT previous_error_mode = ::SetErrorMode(SEM_FAILCRITICALERRORS);

[grt (UTC plus 2), 2015/11/10 19:29:10]

does the pre-read happen before ChromeMainDelegate::SandboxInitialized runs? i
see that it adds in FAILCRITICALERRORS.

+    ::SetErrorMode(previous_error_mode | SEM_FAILCRITICALERRORS);
+
+    HMODULE dll_module = ::LoadLibraryExW(

[grt (UTC plus 2), 2015/11/10 19:29:10]

use
    ScopedNativeLibrary dll_module(::LoadLibraryExW(...));
to avoid the leak on line 90 (and remove the call to FreeLibrary on line 100).

+        file_path.value().c_str(), NULL,
+        LOAD_WITH_ALTERED_SEARCH_PATH | DONT_RESOLVE_DLL_REFERENCES);
+
+    ::SetErrorMode(previous_error_mode);
+
+    // Pre-reading non-PE files is not supported on XP.
+    if (!dll_module)
+      return false;
+
+    base::win::PEImage pe_image(dll_module);
+    if (!pe_image.VerifyMagic())
+      return false;
+
+    // We don't want to read past the end of the module (which could trigger
+    // an access violation), so make sure to check the image size.
+    PIMAGE_NT_HEADERS nt_headers = pe_image.GetNTHeaders();
+    const size_t dll_module_length =

[grt (UTC plus 2), 2015/11/10 19:29:10]

SizeOfImage is a 32-bit unsigned int for both 32-bit and 64-bit images. Can you
get rid of this cast if you change TouchPagesInRange so that it takes the length
as uint32_t?

+        static_cast<size_t>(nt_headers->OptionalHeader.SizeOfImage);
+
+    // Page in then release the module.
+    TouchPagesInRange(dll_module, dll_module_length);
+    ::FreeLibrary(dll_module);
+  }
+
+  return true;
+}