Comment on ConvertJavaStringToUTF8() / GetStringUTFChars()

base/android/linker/legacy_linker_jni.cc

 // Copyright 2014 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.
 
 // This is the Android-specific Chromium linker, a tiny shared library
 // implementing a custom dynamic linker that can be used to load the
 // real Chromium libraries (e.g. libcontentshell.so).
 
 // The main point of this linker is to be able to share the RELRO
 // section of libcontentshell.so (or equivalent) between the browser and
@@ skipping 53 matching lines @@
 
  private:
   char* ptr_;
   size_t size_;
 };
 
 String::String(JNIEnv* env, jstring str) {
   size_ = env->GetStringUTFLength(str);
   ptr_ = static_cast<char*>(::malloc(size_ + 1));
 
-  // Note: the result contains Java "modified UTF-8" bytes.
-  // Good enough for the linker though.
+  // Note: This runs before browser native code is loaded, and so cannot
+  // rely on anything from base/. This means that we must use
+  // GetStringUTFChars() and not base::android::ConvertJavaStringToUTF8().
+  //
+  // GetStringUTFChars() suffices because the only strings used here are
+  // paths to APK files or names of shared libraries, all of which are
+  // plain ASCII, defined and hard-coded by the Chromium Android build.
+  //
+  // For more: see
+  //   https://crbug.com/508876
+  //
+  // Note: GetStringUTFChars() returns Java UTF-8 bytes. This is good
+  // enough for the linker though.
   const char* bytes = env->GetStringUTFChars(str, NULL);
   ::memcpy(ptr_, bytes, size_);
   ptr_[size_] = '\0';
 
   env->ReleaseStringUTFChars(str, bytes);
 }
 
 // Return true iff |address| is a valid address for the target CPU.
 bool IsValidAddress(jlong address) {
   return static_cast<jlong>(static_cast<size_t>(address)) == address;
@@ skipping 671 matching lines @@
   crazy_context_t* context = GetCrazyContext();
   crazy_context_set_java_vm(context, vm, JNI_VERSION_1_4);
 
   // Register the function that the crazy linker can call to post code
   // for later execution.
   crazy_context_set_callback_poster(context, &PostForLaterExecution, NULL);
 
   LOG_INFO("%s: Done", __FUNCTION__);
   return JNI_VERSION_1_4;
 }