[Mac] Do not unload base::NativeLibary-ies if they contain ObjC segments.

base/native_library_mac.mm

 // Copyright (c) 2011 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 "base/native_library.h"
 
 #include <dlfcn.h>
+#include <mach-o/getsect.h>
 
 #include "base/file_util.h"
 #include "base/files/file_path.h"
+#include "base/logging.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/string_util.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/utf_string_conversions.h"
 
 namespace base {
 
+static bool ImageContainsObjectiveC(const struct mach_header* image_header) {
+  // See if the the image contains an "ObjC image info" segment. This method
+  // of testing is used in _CFBundleGrokObjcImageInfoFromFile in
+  // CF-744/CFBundle.c, around lines 2447-2474.
+  //
+  // In 32-bit images, ObjC can be recognized in __OBJC,__image_info, whereas
+  // in 64-bit, the data is in __DATA,__objc_imageinfo.
+#if __LP64__
+  const section_64* section = getsectbynamefromheader_64(
+      reinterpret_cast<const struct mach_header_64*>(image_header),
+      SEG_DATA, "__objc_imageinfo");
+#else
+  const section* section = getsectbynamefromheader(
+      image_header, SEG_OBJC, "__image_info");
+#endif
+  return section != NULL;
+}
+
 // static
 NativeLibrary LoadNativeLibrary(const base::FilePath& library_path,
                                 std::string* error) {
   // dlopen() etc. open the file off disk.
   if (library_path.Extension() == "dylib" ||
       !file_util::DirectoryExists(library_path)) {
     void* dylib = dlopen(library_path.value().c_str(), RTLD_LAZY);
     if (!dylib)
       return NULL;
     NativeLibrary native_lib = new NativeLibraryStruct();
     native_lib->type = DYNAMIC_LIB;
     native_lib->dylib = dylib;
+    native_lib->objc_status = OBJC_UNKNOWN;
     return native_lib;
   }
   base::mac::ScopedCFTypeRef<CFURLRef> url(
       CFURLCreateFromFileSystemRepresentation(
           kCFAllocatorDefault,
           (const UInt8*)library_path.value().c_str(),
           library_path.value().length(),
           true));
   if (!url)
     return NULL;
   CFBundleRef bundle = CFBundleCreate(kCFAllocatorDefault, url.get());
   if (!bundle)
     return NULL;
 
   NativeLibrary native_lib = new NativeLibraryStruct();
   native_lib->type = BUNDLE;
   native_lib->bundle = bundle;
   native_lib->bundle_resource_ref = CFBundleOpenBundleResourceMap(bundle);
+  native_lib->objc_status = OBJC_UNKNOWN;
   return native_lib;
 }
 
 // static
 void UnloadNativeLibrary(NativeLibrary library) {
-  if (library->type == BUNDLE) {
-    CFBundleCloseBundleResourceMap(library->bundle,
-                                   library->bundle_resource_ref);
-    CFRelease(library->bundle);
+  if (library->objc_status == OBJC_NOT_PRESENT) {
+    if (library->type == BUNDLE) {
+      CFBundleCloseBundleResourceMap(library->bundle,
+                                     library->bundle_resource_ref);
+      CFRelease(library->bundle);
+    } else {
+      dlclose(library->dylib);
+    }
   } else {
-    dlclose(library->dylib);
+    VLOG(2) <<
+        "Not unloading NativeLibrary because it contains an ObjC segment.";

[Mark Mentovai, 2013/03/14 18:22:36]

This message isn’t strictly correct if the status is still OBJC_UNKNOWN.

[Robert Sesek, 2013/03/14 18:27:38]

Done.

+    // Deliberately do not CFRelease the bundle or dlclose the dylib because
+    // doing so can corrupt the ObjC runtime method caches. See
+    // http://crbug.com/172319 for details.
   }
   delete library;
 }
 
 // static
 void* GetFunctionPointerFromNativeLibrary(NativeLibrary library,
                                           const char* name) {
+  void* function_pointer = NULL;
+
+  // Get the function pointer using the right API for the type.
   if (library->type == BUNDLE) {
     base::mac::ScopedCFTypeRef<CFStringRef> symbol_name(
         CFStringCreateWithCString(kCFAllocatorDefault, name,
                                   kCFStringEncodingUTF8));
-    return CFBundleGetFunctionPointerForName(library->bundle, symbol_name);
+    function_pointer = CFBundleGetFunctionPointerForName(library->bundle,
+                                                         symbol_name);
+  } else {
+    function_pointer = dlsym(library->dylib, name);
   }
-  return dlsym(library->dylib, name);
+
+  // If this library hasn't been tested for having ObjC, get the mach_header
+  // for the library and see if it has an ObjC segment.
+  if (library->objc_status == OBJC_UNKNOWN) {

[Mark Mentovai, 2013/03/14 18:22:36]

&& function_pointer

[Robert Sesek, 2013/03/14 18:27:38]

Done.

+    Dl_info info;
+    if (dladdr(function_pointer, &info)) {
+      const struct mach_header* header =
+          reinterpret_cast<const struct mach_header*>(info.dli_fbase);

[Scott Hess - ex-Googler, 2013/03/14 18:30:39]

I think that you should pass in a void* (or whatever) and have the 32-bit and
64-bit versions each have a custom crazy undocumented cast, rather than having
the cast in two places.

Heck, pass function_pointer in and let the test code handle all the crazy.

[Robert Sesek, 2013/03/14 20:41:25]

Done.

+      library->objc_status =
+          ImageContainsObjectiveC(header) ? OBJC_PRESENT : OBJC_NOT_PRESENT;
+    }
+  }
+
+  return function_pointer;
 }
 
 // static
 string16 GetNativeLibraryName(const string16& name) {
   return name + ASCIIToUTF16(".dylib");
 }
 
 }  // namespace base