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

base/native_library_mac.mm

Index: base/native_library_mac.mm
diff --git a/base/native_library_mac.mm b/base/native_library_mac.mm
index eec586b863588d9856cc0221da1e73973e10e8de..80fcb4f6e57a5de9d4ec004bd78f3671ee616629 100644
--- a/base/native_library_mac.mm
+++ b/base/native_library_mac.mm
@@ -5,9 +5,15 @@
 #include "base/native_library.h"
 
 #include <dlfcn.h>
+#include <mach/task_info.h>
+#include <mach-o/dyld_images.h>
+#include <mach-o/getsect.h>
+
+#import <Foundation/Foundation.h>
 
 #include "base/file_util.h"
-#include "base/files/file_path.h"
+#include "base/logging.h"
+#include "base/mac/mac_util.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/string_util.h"
 #include "base/threading/thread_restrictions.h"
@@ -15,6 +21,53 @@
 
 namespace base {
 
+static bool ImageContainsObjectiveC(const base::FilePath& library_path) {
+  // Get the dyld info from the kernel, which will contain the array of all
+  // loaded modules.
+  task_dyld_info_data_t task_dyld_info;

[Scott Hess - ex-Googler, 2013/03/12 20:43:53]

I'm having a mental-model issue with this.  Usually I'd expect to see a
vm_deallocate() for large structures the kernel returns.  Is all_image_info_addr
some direct kernel structure?  How the heck is it safe to iterate, given that
task_t could be some other process?

[Mark Mentovai, 2013/03/12 20:51:03]

shess wrote:
task_dyld_info contains pointers into task’s address space. If you’re in a
different task, you need to call mach_vm_read to get at its memory (and then
obviously mach_vm_deallocate it when you’re done with it). If you’re the task,
you can take advantage of the fact that a pointer in your address space is, um,
a valid pointer to your own address space.

[Scott Hess - ex-Googler, 2013/03/12 20:55:01]

So, is this thread safe?  Perhaps implicitly, because load/unload can only
happen on the main thread?

+  mach_msg_type_number_t count = TASK_DYLD_INFO_COUNT;
+  kern_return_t result = task_info(mach_task_self(), TASK_DYLD_INFO,
+      reinterpret_cast<task_info_t>(&task_dyld_info), &count);
+  if (result != KERN_SUCCESS) {
+    VLOG(1) << "Failed to get TASK_DYLD_INFO: " << result;
+    return false;
+  }
+
+  const char* const library_path_c = library_path.value().c_str();
+
+  // Search the array of loaded images for the |library_path| that is being
+  // tested for ObjC.
+  struct dyld_all_image_infos* infos =
+      reinterpret_cast<struct dyld_all_image_infos*>(
+          task_dyld_info.all_image_info_addr);
+  for (uint32_t i = 0; i < infos->infoArrayCount; ++i) {
+    const struct dyld_image_info image_info = infos->infoArray[i];
+    if (strcmp(image_info.imageFilePath, library_path_c) != 0)
+      continue;
+
+    // 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_info.imageLoadAddress),
+        SEG_DATA, "__objc_imageinfo");
+#else
+    const section* section = getsectbynamefromheader(
+        image_info.imageLoadAddress, SEG_OBJC, "__image_info");
+#endif
+    return section != NULL;
+  }
+
+  VLOG(1) << "Could not find image info for " << library_path_c;
+
+  return false;
+}
+
 // static
 NativeLibrary LoadNativeLibrary(const base::FilePath& library_path,
                                 std::string* error) {
@@ -27,6 +80,7 @@ NativeLibrary LoadNativeLibrary(const base::FilePath& library_path,
     NativeLibrary native_lib = new NativeLibraryStruct();
     native_lib->type = DYNAMIC_LIB;
     native_lib->dylib = dylib;
+    native_lib->image_path = library_path;
     return native_lib;
   }
   base::mac::ScopedCFTypeRef<CFURLRef> url(
@@ -45,17 +99,32 @@ NativeLibrary LoadNativeLibrary(const base::FilePath& library_path,
   native_lib->type = BUNDLE;
   native_lib->bundle = bundle;
   native_lib->bundle_resource_ref = CFBundleOpenBundleResourceMap(bundle);
+
+  base::mac::ScopedCFTypeRef<CFURLRef> executable_url(
+      CFBundleCopyExecutableURL(bundle));
+  NSURL* executable_url_ns = base::mac::CFToNSCast(executable_url);
+  native_lib->image_path =
+      base::FilePath([[executable_url_ns path] fileSystemRepresentation]);
   return native_lib;
 }
 
 // static
 void UnloadNativeLibrary(NativeLibrary library) {
-  if (library->type == BUNDLE) {
-    CFBundleCloseBundleResourceMap(library->bundle,
-                                   library->bundle_resource_ref);
-    CFRelease(library->bundle);
+  if (ImageContainsObjectiveC(library->image_path)) {
+    VLOG(2) << "Not unloading NativeLibrary at "
+            << library->image_path.MaybeAsASCII()
+            << " because it contains an Objective-C segment.";
+    // 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.
   } else {
-    dlclose(library->dylib);
+    if (library->type == BUNDLE) {
+      CFBundleCloseBundleResourceMap(library->bundle,
+                                     library->bundle_resource_ref);
+      CFRelease(library->bundle);
+    } else {
+      dlclose(library->dylib);
+    }
   }
   delete library;
 }