1
 2
 3
 4
 5
 6
 7
 8
 9
10

// oopDesc is the top baseclass for objects classes. The {name}Desc classes describe
// the format of Java objects so the fields can be accessed from C++.
// oopDesc is abstract.
class oopDesc {
 private:
  volatile markWord _mark;
  union _metadata {
    Klass*      _klass;
    narrowKlass _compressed_klass;
  } _metadata;

1
2
3
4

class arrayOopDesc : public oopDesc {
  // Accessors for array length.  There's not a member variable for
  // it; see length_offset_in_bytes().
  int length() {...    

1
2

class objArrayOopDesc : public arrayOopDesc {
    Klass* element_klass();

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15

// gcc warns about applying offsetof() to non-POD object or calculating
// offset directly when base address is null. The -Wno-invalid-offsetof
// option could be used to suppress this warning, but we instead just
// avoid the use of offsetof().
//
// FIXME: This macro is complex and rather arcane. Perhaps we should
// use offsetof() instead, with the invalid-offsetof warning
// temporarily disabled.
#define offset_of(klass,field)                          \
([]() {                                                 \
  char space[sizeof (klass)] ATTRIBUTE_ALIGNED(16);     \
  klass* dummyObj = (klass*)space;                      \
  char* c = (char*)(void*)&dummyObj->field;             \
  return (size_t)(c - space);                           \
}())

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96

// This table encapsulates the debugging information required by the
// serviceability agent in order to run. Specifically, we need to
// understand the layout of certain C data structures (offsets, in
// bytes, of their fields.)
//
// There are alternatives for the design of this mechanism, including
// parsing platform-specific debugging symbols from a debug build into
// a program database. While this current mechanism can be considered
// to be a workaround for the inability to debug arbitrary C and C++
// programs at the present time, it does have certain advantages.
// First, it is platform-independent, which will vastly simplify the
// initial bringup of the system both now and on future platforms.
// Second, it is embedded within the VM, as opposed to being in a
// separate program database; experience has shown that whenever
// portions of a system are decoupled, version skew is problematic.
// Third, generating a program database, for example for a product
// build, would probably require two builds to be done: the desired
// product build as well as an intermediary build with the PRODUCT
// flag turned on but also compiled with -g, leading to a doubling of
// the time required to get a serviceability agent-debuggable product
// build. Fourth, and very significantly, this table probably
// preserves more information about field types than stabs do; for
// example, it preserves the fact that a field is a "jlong" rather
// than transforming the type according to the typedef in jni_md.h,
// which allows the Java-side code to identify "Java-sized" fields in
// C++ data structures. If the symbol parsing mechanism was redone
// using stabs, it might still be necessary to have a table somewhere
// containing this information.
//
// Do not change the sizes or signedness of the integer values in
// these data structures; they are fixed over in the serviceability
// agent's Java code (for bootstrapping).

typedef struct {
  const char* typeName;            // The type name containing the given field (example: "Klass")
  const char* fieldName;           // The field name within the type           (example: "_name")
  const char* typeString;          // Quoted name of the type of this field (example: "Symbol*";
                                   // parsed in Java to ensure type correctness
  int32_t  isStatic;               // Indicates whether following field is an offset or an address
  uint64_t offset;                 // Offset of field within structure; only used for nonstatic fields
  void* address;                   // Address of field; only used for static fields
                                   // ("offset" can not be reused because of apparent solstudio compiler bug
                                   // in generation of initializer data)
} VMStructEntry;

typedef struct {
  const char* typeName;            // Type name (example: "Method")
  const char* superclassName;      // Superclass name, or null if none (example: "oopDesc")
  int32_t isOopType;               // Does this type represent an oop typedef? (i.e., "Method*" or
                                   // "Klass*", but NOT "Method")
  int32_t isIntegerType;           // Does this type represent an integer type (of arbitrary size)?
  int32_t isUnsigned;              // If so, is it unsigned?
  uint64_t size;                   // Size, in bytes, of the type
} VMTypeEntry;

// This class is a friend of most classes, to be able to access
// private fields
class VMStructs {
public:
  // The last entry is identified over in the serviceability agent by
  // the fact that it has a null fieldName
  static VMStructEntry localHotSpotVMStructs[];
  ...

  // The last entry is identified over in the serviceability agent by
  // the fact that it has a null typeName
  static VMTypeEntry   localHotSpotVMTypes[];
  ...

  /**
   * Table of addresses.
   */
  static VMAddressEntry localHotSpotVMAddresses[];
  ...
}    

// This utility macro quotes the passed string
#define QUOTE(x) #x

//--------------------------------------------------------------------------------
// VMStructEntry macros
//

// This macro generates a VMStructEntry line for a nonstatic field
#define GENERATE_NONSTATIC_VM_STRUCT_ENTRY(typeName, fieldName, type)              \
 { QUOTE(typeName), QUOTE(fieldName), QUOTE(type), 0, offset_of(typeName, fieldName), nullptr },

//--------------------------------------------------------------------------------
// VMTypeEntry macros
//

#define GENERATE_VM_TYPE_ENTRY(type, superclass) \
 { QUOTE(type), QUOTE(superclass), 0, 0, 0, sizeof(type) },

#define GENERATE_TOPLEVEL_VM_TYPE_ENTRY(type) \
 { QUOTE(type), nullptr,              0, 0, 0, sizeof(type) },

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72

//--------------------------------------------------------------------------------
// VM_STRUCTS
//
// This list enumerates all of the fields the serviceability agent
// needs to know about. Be sure to see also the type table below this one.
// NOTE that there are platform-specific additions to this table in
// vmStructs_<os>_<cpu>.hpp.

#define VM_STRUCTS(nonstatic_field, \
                   static_field, \
                   static_ptr_volatile_field, \
                   unchecked_nonstatic_field, \
                   volatile_nonstatic_field, \
                   ...) \
  /******************************************************************/ \
  /* OopDesc and Klass hierarchies (NOTE: MethodData* incomplete)   */ \
  /******************************************************************/ \
  volatile_nonstatic_field(oopDesc, _mark, markWord) \
  volatile_nonstatic_field(oopDesc, _metadata._klass, Klass*) \
  volatile_nonstatic_field(oopDesc, _metadata._compressed_klass, narrowKlass) \
  ...

      
      
//--------------------------------------------------------------------------------
// VM_TYPES
//
// This list must enumerate at least all of the types in the above
// list. For the types in the above list, the entry below must have
// exactly the same spacing since string comparisons are done in the
// code which verifies the consistency of these tables (in the debug
// build).
//
// In addition to the above types, this list is required to enumerate
// the JNI's java types, which are used to indicate the size of Java
// fields in this VM to the SA. Further, oop types are currently
// distinguished by name (i.e., ends with "oop") over in the SA.
//
// The declare_toplevel_type macro should be used to declare types
// which do not have a superclass.
//
// The declare_integer_type and declare_unsigned_integer_type macros
// are required in order to properly identify C integer types over in
// the SA. They should be used for any type which is otherwise opaque
// and which it is necessary to coerce into an integer value. This
// includes, for example, the type uintptr_t. Note that while they
// will properly identify the type's size regardless of the platform,
// since it is does not seem possible to deduce or check signedness at
// compile time using the pointer comparison tricks, it is currently
// required that the given types have the same signedness across all
// platforms.
//
// NOTE that there are platform-specific additions to this table in
// vmStructs_<os>_<cpu>.hpp.

#define VM_TYPES(declare_type,                                            \
                 declare_toplevel_type,                                   \
                 declare_oop_type,                                        \
                 declare_integer_type,                                    \
                 declare_unsigned_integer_type,                           \
                 declare_c1_toplevel_type,                                \
                 declare_c2_type,                                         \
                 declare_c2_toplevel_type)                                \
...                                                                       \
  /******************************************/                            \
  /* OopDesc hierarchy (NOTE: some missing) */                            \
  /******************************************/                            \
                                                                          \
  declare_toplevel_type(oopDesc)                                          \
    declare_type(arrayOopDesc, oopDesc)                                   \
      declare_type(objArrayOopDesc, arrayOopDesc)                         \
    declare_type(instanceOopDesc, oopDesc)                                \

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40

//
// Instantiation of VMStructEntries, VMTypeEntries and VMIntConstantEntries
//

// These initializers are allowed to access private fields in classes
// as long as class VMStructs is a friend
VMStructEntry VMStructs::localHotSpotVMStructs[] = {

  VM_STRUCTS(GENERATE_NONSTATIC_VM_STRUCT_ENTRY,
             GENERATE_STATIC_VM_STRUCT_ENTRY,
             GENERATE_STATIC_PTR_VOLATILE_VM_STRUCT_ENTRY,
             GENERATE_UNCHECKED_NONSTATIC_VM_STRUCT_ENTRY,
             GENERATE_NONSTATIC_VM_STRUCT_ENTRY, // <---
             GENERATE_NONPRODUCT_NONSTATIC_VM_STRUCT_ENTRY,
             GENERATE_C1_NONSTATIC_VM_STRUCT_ENTRY,
             GENERATE_C2_NONSTATIC_VM_STRUCT_ENTRY,
             GENERATE_C1_UNCHECKED_STATIC_VM_STRUCT_ENTRY,
             GENERATE_C2_UNCHECKED_STATIC_VM_STRUCT_ENTRY)
...
}

VMTypeEntry VMStructs::localHotSpotVMTypes[] = {

  VM_TYPES(GENERATE_VM_TYPE_ENTRY,
           GENERATE_TOPLEVEL_VM_TYPE_ENTRY,
           GENERATE_OOP_VM_TYPE_ENTRY,
           GENERATE_INTEGER_VM_TYPE_ENTRY,
           GENERATE_UNSIGNED_INTEGER_VM_TYPE_ENTRY,
           GENERATE_C1_TOPLEVEL_VM_TYPE_ENTRY,
           GENERATE_C2_VM_TYPE_ENTRY,
           GENERATE_C2_TOPLEVEL_VM_TYPE_ENTRY)
...
}

extern "C" {
...
JNIEXPORT VMStructEntry* gHotSpotVMStructs = VMStructs::localHotSpotVMStructs;
JNIEXPORT VMTypeEntry* gHotSpotVMTypes = VMStructs::localHotSpotVMTypes;
...
}    

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35

VMStructEntry VMStructs::localHotSpotVMStructs[] = {
...
    {"oopDesc", "_mark", "markWord", 0, 
     ([](){ 
        char space[sizeof (oopDesc)] __attribute__((aligned(16)));
        oopDesc* dummyObj = (oopDesc*)space; 
        char* c = (char*)(void*)&dummyObj->_mark; 
        return (size_t)(c - space); 
     }()),//call a lamda expression to get offset of field within structure
     nullptr},
    {"oopDesc", "_metadata._klass", "Klass*", 0, ([](){ char space[sizeof (oopDesc)] __attribute__((aligned(16))); oopDesc* dummyObj = (oopDesc*)space; char* c = (char*)(void*)&dummyObj->_metadata._klass; return (size_t)(c - space); }()),
     nullptr},
    {"oopDesc", "_metadata._compressed_klass", "narrowKlass", 0, ([](){ char space[sizeof (oopDesc)] __attribute__((aligned(16))); oopDesc* dummyObj = (oopDesc*)space; char* c = (char*)(void*)&dummyObj->_metadata._compressed_klass; return (size_t)(c - space); }()),
     nullptr},
...
}


VMTypeEntry VMStructs::localHotSpotVMTypes[] = {
    ...
    {"oopDesc", nullptr, 0, 0, 0, sizeof(oopDesc)}, 
    {"arrayOopDesc", "oopDesc", 0, 0, 0, sizeof(arrayOopDesc)}, 
    {"objArrayOopDesc", "arrayOopDesc", 0, 0, 0, sizeof(objArrayOopDesc)}, 
    {"instanceOopDesc", "oopDesc", 0, 0, 0, sizeof(instanceOopDesc)}, 
    {"ArrayKlass", "Klass", 0, 0, 0, sizeof(ArrayKlass)}, 
    {"ObjArrayKlass", "ArrayKlass", 0, 0, 0, sizeof(ObjArrayKlass)}, 
    ...
}

extern "C" {
...
__attribute__((visibility("default"))) VMStructEntry *gHotSpotVMStructs = VMStructs::localHotSpotVMStructs;
__attribute__((visibility("default"))) VMTypeEntry *gHotSpotVMTypes = VMStructs::localHotSpotVMTypes;
...
}    

1
2
3
4
5
6

// These are the CPU-specific fields, types and integer
// constants required by the Serviceability Agent. This file is
// referenced by vmStructs.cpp.

#define VM_STRUCTS_CPU(nonstatic_field, static_field, unchecked_nonstatic_field, volatile_nonstatic_field, nonproduct_nonstatic_field, c2_nonstatic_field, unchecked_c1_static_field, unchecked_c2_static_field)            \
  volatile_nonstatic_field(JavaFrameAnchor, _last_Java_fp, intptr_t*)

1
2
3
4
5

// These are the OS-specific fields, types and integer
// constants required by the Serviceability Agent. This file is
// referenced by vmStructs.cpp.

#define VM_STRUCTS_OS(nonstatic_field, static_field, unchecked_nonstatic_field, volatile_nonstatic_field, nonproduct_nonstatic_field, c2_nonstatic_field, unchecked_c1_static_field, unchecked_c2_static_field)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11

// These are the OS and CPU-specific fields, types and integer
// constants required by the Serviceability Agent. This file is
// referenced by vmStructs.cpp.

#define VM_STRUCTS_OS_CPU(nonstatic_field, static_field, unchecked_nonstatic_field, volatile_nonstatic_field, nonproduct_nonstatic_field, c2_nonstatic_field, unchecked_c1_static_field, unchecked_c2_static_field) \
 \
  /******************************/ \
  /* Threads (NOTE: incomplete) */ \
  /******************************/ \
  nonstatic_field(OSThread, _thread_id, OSThread::thread_id_t) \
  nonstatic_field(OSThread, _pthread_id, pthread_t)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16

// JavaThreadState keeps track of which part of the code a thread is executing in. This
// information is needed by the safepoint code.
enum JavaThreadState {
  _thread_uninitialized     =  0, // should never happen (missing initialization)
  _thread_new               =  2, // just starting up, i.e., in process of being initialized
  _thread_new_trans         =  3, // corresponding transition state (not used, included for completeness)
  _thread_in_native         =  4, // running in native code
  _thread_in_native_trans   =  5, // corresponding transition state
  _thread_in_vm             =  6, // running in VM
  _thread_in_vm_trans       =  7, // corresponding transition state
  _thread_in_Java           =  8, // running in Java or in stub code
  _thread_in_Java_trans     =  9, // corresponding transition state (not used, included for completeness)
  _thread_blocked           = 10, // blocked in vm
  _thread_blocked_trans     = 11, // corresponding transition state
  _thread_max_state         = 12  // maximum thread state+1 - used for statistics allocation
};

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35

/** <P> This is the cross-platform TypeDataBase used by the Oop
    hierarchy. The decision was made to make this cross-platform by
    having the VM export the necessary symbols via a built-in table;
    see src/share/vm/runtime/vmStructs.[ch]pp for more details. </P>

    <P> <B>WARNING</B>: clients should refer to this class through the
    TypeDataBase interface and not directly to the HotSpotTypeDataBase
    type. </P>

    <P> NOTE: since we are fetching the sizes of the Java primitive types
 */

public class HotSpotTypeDataBase extends BasicTypeDataBase {  
  ...    
  private void readVMTypes() {
    // Get the variables we need in order to traverse the VMTypeEntry[]
    ...
    // Fetch the address of the VMTypeEntry*. We get this symbol first
    // and try to use it to make sure that symbol lookup is working.
    Address entryAddr = lookupInProcess("gHotSpotVMTypes");
    //    System.err.println("gHotSpotVMTypes address = " + entryAddr);
    // Dereference this once to get the pointer to the first VMTypeEntry
    //    dumpMemory(entryAddr, 80);
    entryAddr = entryAddr.getAddressAt(0);
    ...
  }
  ...
  private void readVMStructs() {
    ...
    // Fetch the address of the VMStructEntry*
    Address entryAddr = lookupInProcess("gHotSpotVMStructs");
    // Dereference this once to get the pointer to the first VMStructEntry
    entryAddr = entryAddr.getAddressAt(0);
    ...
  }

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20

public class Oop {
  static {
    VM.registerVMInitializedObserver(new Observer() {
        public void update(Observable o, Object data) {
          initialize(VM.getVM().getTypeDataBase());
        }
      });
  }

  private static synchronized void initialize(TypeDataBase db) throws WrongTypeException {
    Type type  = db.lookupType("oopDesc");
    mark       = new CIntField(type.getCIntegerField("_mark"), 0);
    klass      = new MetadataField(type.getAddressField("_metadata._klass"), 0);
    compressedKlass  = new NarrowKlassField(type.getAddressField("_metadata._compressed_klass"), 0);
    headerSize = type.getSize();
  }
    
  private static CIntField mark;
  private static MetadataField  klass;
  private static NarrowKlassField compressedKlass;