标签：lang java -- fields 0x0000 源码 oop offset Class

先打断点systemDictionary.cpp 1915行

Universe::fixup_mirrors(CHECK);

进入

void Universe::fixup_mirrors(TRAPS) {
  // Bootstrap problem: all classes gets a mirror (java.lang.Class instance) assigned eagerly,
  // but we cannot do that for classes created before java.lang.Class is loaded. Here we simply
  // walk over permanent objects created so far (mostly classes) and fixup their mirrors. Note
  // that the number of objects allocated at this point is very small.
  assert(SystemDictionary::Class_klass_loaded(), "java.lang.Class should be loaded");
  HandleMark hm(THREAD);
  // Cache the start of the static fields
  InstanceMirrorKlass::init_offset_of_static_fields();

  GrowableArray <Klass*>* list = java_lang_Class::fixup_mirror_list();
  int list_length = list->length();
  for (int i = 0; i < list_length; i++) {
    Klass* k = list->at(i);
    assert(k->is_klass(), "List should only hold classes");
    EXCEPTION_MARK;
    KlassHandle kh(THREAD, k);
    java_lang_Class::fixup_mirror(kh, CATCH);
}
  delete java_lang_Class::fixup_mirror_list();
  java_lang_Class::set_fixup_mirror_list(NULL);
}

给红色打断点,当i=12的时候进入java.lang.String类的解析

void java_lang_Class::fixup_mirror(KlassHandle k, TRAPS) {
  assert(InstanceMirrorKlass::offset_of_static_fields() != 0, "must have been computed already");

  // If the offset was read from the shared archive, it was fixed up already
  if (!k->is_shared()) {
    if (k->oop_is_instance()) {
      // During bootstrap, java.lang.Class wasn't loaded so static field
      // offsets were computed without the size added it.  Go back and
      // update all the static field offsets to included the size.
        for (JavaFieldStream fs(InstanceKlass::cast(k())); !fs.done(); fs.next()) {
        if (fs.access_flags().is_static()) {
          int real_offset = fs.offset() + InstanceMirrorKlass::offset_of_static_fields();
          fs.set_offset(real_offset);
        }
      }
    }
  }
  create_mirror(k, Handle(NULL), CHECK);
}

给紫色的构造器

JavaFieldStream(instanceKlassHandle k): FieldStreamBase(k->fields(), k->constants(), 0, k->java_fields_count()) {}

  FieldStreamBase(Array<u2>* fields, constantPoolHandle constants, int start, int limit) {
    _fields = fields;
    _constants = constants;
    _index = start;
    int num_fields = init_generic_signature_start_slot();
    if (limit < start) {
      _limit = num_fields;
    } else {
      _limit = limit;
    }
  }

打印对象

(gdb) p fields
$25 = (Array<unsigned short> *) 0x7f28e0a03280

(gdb) x/36h fields
0x7f28e0a03280: 0x001f 0x0000 0x0012 0x0098 0x0099 0x0000 {{ 0x0031 0x0000
0x7f28e0a03290: 0x0002 0x009a 0x009b 0x0000 }}{{ 0x0041 0x0000 0x001a 0x009c
0x7f28e0a032a0: 0x009d 0x009f}}{{ 0x0021 0x0000 0x001a 0x00a1 0x00a2 0x0000
0x7f28e0a032b0: 0x0001 0x0000 0x0819 0x00a3 0x00a4 0x0000 }}{{0x0011 0x0000
0x7f28e0a032c0: 0x00a6 0x0000 0x0000 0x0000}}

标签：lang,java,--,fields,0x0000,源码,oop,offset,Class
来源： https://www.cnblogs.com/zytcomeon/p/14638408.html

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