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How to find the native method from the JVM source code?


How to find the native method from the JVM source code?

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How to find the native method from the JVM source code?
Tag : java , By : cjdavis
Date : November 27 2020, 11:01 PM

Any of those help JNI implementation of the above methods is in JDK repository, not in HotSpot, see src/share/native/java/lang/ClassLoader.c
However, these methods eventually call back to JVM through HotSpot-specific JVM_DefineClassWithSource API. The implementation of this JVM function is in HotSpot repository, see src/share/vm/prims/jvm.cpp

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Where can I find the native source code of android API of camera?


Tag : android , By : n1ckless_id
Date : March 29 2020, 07:55 AM
Any of those help The android sources are here: https://android.googlesource.com.
This posting might also be informative: https://groups.google.com/group/android-platform/browse_thread/thread/8995288acaa30018?fwc=1

Where can I find javascript native functions source code?


Tag : javascript , By : Marcos de Carvalho
Date : March 29 2020, 07:55 AM
hope this fix your issue where can I find the source code of native js functions, for example I want to look at eval() function , In the JavaScript engine's source code.

Is it possible to find the source for a Java native method?


Tag : java , By : Raghaw
Date : March 29 2020, 07:55 AM
I wish this help you I have found the clone() method of Object in Java: , From jdk/src/share/native/java/lang/Object.c
static JNINativeMethod methods[] = {
    {"hashCode",    "()I",                    (void *)&JVM_IHashCode},
    {"wait",        "(J)V",                   (void *)&JVM_MonitorWait},
    {"notify",      "()V",                    (void *)&JVM_MonitorNotify},
    {"notifyAll",   "()V",                    (void *)&JVM_MonitorNotifyAll},
    {"clone",       "()Ljava/lang/Object;",   (void *)&JVM_Clone},
};
JVM_ENTRY(jobject, JVM_Clone(JNIEnv* env, jobject handle))
  JVMWrapper("JVM_Clone");
  Handle obj(THREAD, JNIHandles::resolve_non_null(handle));
  const KlassHandle klass (THREAD, obj->klass());
  JvmtiVMObjectAllocEventCollector oam;

#ifdef ASSERT
  // Just checking that the cloneable flag is set correct
  if (obj->is_javaArray()) {
    guarantee(klass->is_cloneable(), "all arrays are cloneable");
  } else {
    guarantee(obj->is_instance(), "should be instanceOop");
    bool cloneable = klass->is_subtype_of(SystemDictionary::Cloneable_klass());
    guarantee(cloneable == klass->is_cloneable(), "incorrect cloneable flag");
  }
#endif

  // Check if class of obj supports the Cloneable interface.
  // All arrays are considered to be cloneable (See JLS 20.1.5)
  if (!klass->is_cloneable()) {
    ResourceMark rm(THREAD);
    THROW_MSG_0(vmSymbols::java_lang_CloneNotSupportedException(), klass->external_name());
  }

  // Make shallow object copy
  const int size = obj->size();
  oop new_obj = NULL;
  if (obj->is_javaArray()) {
    const int length = ((arrayOop)obj())->length();
    new_obj = CollectedHeap::array_allocate(klass, size, length, CHECK_NULL);
  } else {
    new_obj = CollectedHeap::obj_allocate(klass, size, CHECK_NULL);
  }
  // 4839641 (4840070): We must do an oop-atomic copy, because if another thread
  // is modifying a reference field in the clonee, a non-oop-atomic copy might
  // be suspended in the middle of copying the pointer and end up with parts
  // of two different pointers in the field.  Subsequent dereferences will crash.
  // 4846409: an oop-copy of objects with long or double fields or arrays of same
  // won't copy the longs/doubles atomically in 32-bit vm's, so we copy jlongs instead
  // of oops.  We know objects are aligned on a minimum of an jlong boundary.
  // The same is true of StubRoutines::object_copy and the various oop_copy
  // variants, and of the code generated by the inline_native_clone intrinsic.
  assert(MinObjAlignmentInBytes >= BytesPerLong, "objects misaligned");
  Copy::conjoint_jlongs_atomic((jlong*)obj(), (jlong*)new_obj,
                               (size_t)align_object_size(size) / HeapWordsPerLong);
  // Clear the header
  new_obj->init_mark();

  // Store check (mark entire object and let gc sort it out)
  BarrierSet* bs = Universe::heap()->barrier_set();
  assert(bs->has_write_region_opt(), "Barrier set does not have write_region");
  bs->write_region(MemRegion((HeapWord*)new_obj, size));

  // Caution: this involves a java upcall, so the clone should be
  // "gc-robust" by this stage.
  if (klass->has_finalizer()) {
    assert(obj->is_instance(), "should be instanceOop");
    new_obj = instanceKlass::register_finalizer(instanceOop(new_obj), CHECK_NULL);
  }

  return JNIHandles::make_local(env, oop(new_obj));
JVM_END

Java native method source code


Tag : java , By : RinKaMan
Date : March 29 2020, 07:55 AM
this one helps. You can download OpenJdk source code here.
In the folder jdk\src\share you can get source code.
void objArrayKlass::copy_array(arrayOop s, int src_pos, arrayOop d,
                           int dst_pos, int length, TRAPS) {
assert(s->is_objArray(), "must be obj array");

if (!d->is_objArray()) {
  THROW(vmSymbols::java_lang_ArrayStoreException());
}

// Check is all offsets and lengths are non negative
if (src_pos < 0 || dst_pos < 0 || length < 0) {
  THROW(vmSymbols::java_lang_ArrayIndexOutOfBoundsException());
}
// Check if the ranges are valid
if  ( (((unsigned int) length + (unsigned int) src_pos) > (unsigned int) s->length())
   || (((unsigned int) length + (unsigned int) dst_pos) > (unsigned int) d->length()) )   {
  THROW(vmSymbols::java_lang_ArrayIndexOutOfBoundsException());
}

// Special case. Boundary cases must be checked first
// This allows the following call: copy_array(s, s.length(), d.length(), 0).
// This is correct, since the position is supposed to be an 'in between point', i.e., s.length(),
// points to the right of the last element.
if (length==0) {
  return;
}
if (UseCompressedOops) {
  narrowOop* const src = objArrayOop(s)->obj_at_addr<narrowOop>(src_pos);
  narrowOop* const dst = objArrayOop(d)->obj_at_addr<narrowOop>(dst_pos);
  do_copy<narrowOop>(s, src, d, dst, length, CHECK);
} else {
  oop* const src = objArrayOop(s)->obj_at_addr<oop>(src_pos);
  oop* const dst = objArrayOop(d)->obj_at_addr<oop>(dst_pos);
  do_copy<oop> (s, src, d, dst, length, CHECK);
  }
}

Adding a native method to OpenJDK source code


Tag : java , By : boonchew
Date : March 29 2020, 07:55 AM
this will help I am trying add a custom native method(free) to OpenJDK source, so I can call that method as System.free() from inside the user Application. , Your symbol (JVM_Free) is not exported. Take a look here (t vs. T)
> nm libjvm.dylib | grep JVM_GC
000000000041508c T _JVM_GC

vs.

> nm libjvm.dylib | grep JVM_Free
000000000041517a t _JVM_Free
{JDK13ROOT}/make/hotspot/symbols/symbols-unix
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