[Merge M49] Remove XP-specific code from file_pre_reader_win.cc.

BUG=547794

Review URL: https://codereview.chromium.org/1659113002

Cr-Commit-Position: refs/heads/master@{#373352}
(cherry picked from commit bb4fe7af38b6a9cee46b095e18810295d18e6523)

TBR=gab@chromium.org

Review URL: https://codereview.chromium.org/1730883002 .

Cr-Commit-Position: refs/branch-heads/2623@{#489}
Cr-Branched-From: 92d77538a86529ca35f9220bd3cd512cbea1f086-refs/heads/master@{#369907}

2 files changed, 11 insertions, 87 deletions

diff --git a/chrome/app/file_pre_reader_win.cc b/chrome/app/file_pre_reader_win.cc
index 7d57244..bfade83 100644
--- a/chrome/app/file_pre_reader_win.cc
+++ b/chrome/app/file_pre_reader_win.cc
@@ -5,101 +5,28 @@
 #include "chrome/app/file_pre_reader_win.h"
 
 #include <windows.h>
-#include <stdint.h>
 
 #include "base/files/file.h"
 #include "base/files/memory_mapped_file.h"
-#include "base/logging.h"
-#include "base/scoped_native_library.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, uint32_t length) {
-  DCHECK(base_addr);
-  DCHECK_GT(length, static_cast<uint32_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
 
 void PreReadFile(const base::FilePath& file_path) {
   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;
-
-    const DWORD kStepSize = 1024 * 1024;
-    char* buffer = reinterpret_cast<char*>(
-        ::VirtualAlloc(nullptr, kStepSize, MEM_COMMIT, PAGE_READWRITE));
-    if (!buffer)
-      return;
-
-    while (file.ReadAtCurrentPos(buffer, kStepSize) > 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, 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);
-    ::SetErrorMode(previous_error_mode | SEM_FAILCRITICALERRORS);
-
-    base::ScopedNativeLibrary dll_module(::LoadLibraryExW(
-        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.is_valid())
-      return;
+  base::File file(file_path, base::File::FLAG_OPEN | base::File::FLAG_READ |
+                                 base::File::FLAG_SEQUENTIAL_SCAN);
+  if (!file.IsValid())
+    return;
 
-    base::win::PEImage pe_image(dll_module.get());
-    if (!pe_image.VerifyMagic())
-      return;
+  const DWORD kStepSize = 1024 * 1024;
+  char* buffer = reinterpret_cast<char*>(
+      ::VirtualAlloc(nullptr, kStepSize, MEM_COMMIT, PAGE_READWRITE));
+  if (!buffer)
+    return;
 
-    // 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 uint32_t dll_module_length = nt_headers->OptionalHeader.SizeOfImage;
+  while (file.ReadAtCurrentPos(buffer, kStepSize) > 0) {}
 
-    // Page in the module.
-    TouchPagesInRange(dll_module.get(), dll_module_length);
-  }
+  ::VirtualFree(buffer, 0, MEM_RELEASE);
 }
 
 void PreReadMemoryMappedFile(const base::MemoryMappedFile& memory_mapped_file,
diff --git a/chrome/app/file_pre_reader_win.h b/chrome/app/file_pre_reader_win.h
index da88ba4..85912b8 100644
--- a/chrome/app/file_pre_reader_win.h
+++ b/chrome/app/file_pre_reader_win.h
@@ -14,9 +14,6 @@ class MemoryMappedFile;
 }
 
 // Reads |file_path| to avoid touching the disk when the file is actually used.
-// The function checks the Windows version to determine which pre-reading
-// mechanism to use. On Vista+, chunks of 1 MB are read into a buffer. On XP,
-// pre-reading non-PE files is not supported.
 void PreReadFile(const base::FilePath& file_path);
 
 // Reads |memory_mapped_file| to avoid touching the disk when the mapped file is