jdk-24/hotspot/src/share/vm/runtime/vmStructs.hpp

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
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 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
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// 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: "symbolOopDesc*";
                                   // 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 SparcWorks compiler bug
                                   // in generation of initializer data)
} VMStructEntry;

typedef struct {
  const char* typeName;            // Type name (example: "methodOopDesc")
  const char* superclassName;      // Superclass name, or null if none (example: "oopDesc")
  int32_t isOopType;               // Does this type represent an oop typedef? (i.e., "methodOop" or
                                   // "klassOop", but NOT "methodOopDesc")
  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;

typedef struct {
  const char* name;                // Name of constant (example: "_thread_in_native")
  int32_t value;                   // Value of constant
} VMIntConstantEntry;

typedef struct {
  const char* name;                // Name of constant (example: "_thread_in_native")
  uint64_t value;                  // Value of constant
} VMLongConstantEntry;

// 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 integer constants required by the serviceability agent.
  // The last entry is identified over in the serviceability agent by
  // the fact that it has a NULL typeName
  static VMIntConstantEntry localHotSpotVMIntConstants[];

  // Table of long constants required by the serviceability agent.
  // The last entry is identified over in the serviceability agent by
  // the fact that it has a NULL typeName
  static VMLongConstantEntry localHotSpotVMLongConstants[];

  // This is used to run any checking code necessary for validation of
  // the data structure (debug build only)
  static void init();

private:
  // Look up a type in localHotSpotVMTypes using strcmp() (debug build only).
  // Returns 1 if found, 0 if not.
  //  debug_only(static int findType(const char* typeName);)
  static int findType(const char* typeName);
};