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 /*

  * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * 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

  * published by the Free Software Foundation.

  *

  * 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.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 /*

  * This file has been modified by Loongson Technology in 2015. These

  * modifications are Copyright (c) 2015 Loongson Technology, and are made

  * available on the same license terms set forth above.

  */

 #ifndef SHARE_VM_CODE_RELOCINFO_HPP

 #define SHARE_VM_CODE_RELOCINFO_HPP

 #include "memory/allocation.hpp"

 #include "utilities/top.hpp"

 class NativeMovConstReg;

 // Types in this file:

 //    relocInfo

 //      One element of an array of halfwords encoding compressed relocations.

 //      Also, the source of relocation types (relocInfo::oop_type, ...).

 //    Relocation

 //      A flyweight object representing a single relocation.

 //      It is fully unpacked from the compressed relocation array.

 //    metadata_Relocation, ... (subclasses of Relocation)

 //      The location of some type-specific operations (metadata_addr, ...).

 //      Also, the source of relocation specs (metadata_Relocation::spec, ...).

 //    oop_Relocation, ... (subclasses of Relocation)

 //      oops in the code stream (strings, class loaders)

 //      Also, the source of relocation specs (oop_Relocation::spec, ...).

 //    RelocationHolder

 //      A ValueObj type which acts as a union holding a Relocation object.

 //      Represents a relocation spec passed into a CodeBuffer during assembly.

 //    RelocIterator

 //      A StackObj which iterates over the relocations associated with

 //      a range of code addresses.  Can be used to operate a copy of code.

 //    BoundRelocation

 //      An _internal_ type shared by packers and unpackers of relocations.

 //      It pastes together a RelocationHolder with some pointers into

 //      code and relocInfo streams.

 // Notes on relocType:

 //

 // These hold enough information to read or write a value embedded in

 // the instructions of an CodeBlob.  They're used to update:

 //

 //   1) embedded oops     (isOop()          == true)

 //   2) inline caches     (isIC()           == true)

 //   3) runtime calls     (isRuntimeCall()  == true)

 //   4) internal word ref (isInternalWord() == true)

 //   5) external word ref (isExternalWord() == true)

 //

 // when objects move (GC) or if code moves (compacting the code heap).

 // They are also used to patch the code (if a call site must change)

 //

 // A relocInfo is represented in 16 bits:

 //   4 bits indicating the relocation type

 //  12 bits indicating the offset from the previous relocInfo address

 //

 // The offsets accumulate along the relocInfo stream to encode the

 // address within the CodeBlob, which is named RelocIterator::addr().

 // The address of a particular relocInfo always points to the first

 // byte of the relevant instruction (and not to any of its subfields

 // or embedded immediate constants).

 //

 // The offset value is scaled appropriately for the target machine.

 // (See relocInfo_<arch>.hpp for the offset scaling.)

 //

 // On some machines, there may also be a "format" field which may provide

 // additional information about the format of the instruction stream

 // at the corresponding code address.  The format value is usually zero.

 // Any machine (such as Intel) whose instructions can sometimes contain

 // more than one relocatable constant needs format codes to distinguish

 // which operand goes with a given relocation.

 //

 // If the target machine needs N format bits, the offset has 12-N bits,

 // the format is encoded between the offset and the type, and the

 // relocInfo_<arch>.hpp file has manifest constants for the format codes.

 //

 // If the type is "data_prefix_tag" then the offset bits are further encoded,

 // and in fact represent not a code-stream offset but some inline data.

 // The data takes the form of a counted sequence of halfwords, which

 // precedes the actual relocation record.  (Clients never see it directly.)

 // The interpetation of this extra data depends on the relocation type.

 //

 // On machines that have 32-bit immediate fields, there is usually

 // little need for relocation "prefix" data, because the instruction stream

 // is a perfectly reasonable place to store the value.  On machines in

 // which 32-bit values must be "split" across instructions, the relocation

 // data is the "true" specification of the value, which is then applied

 // to some field of the instruction (22 or 13 bits, on SPARC).

 //

 // Whenever the location of the CodeBlob changes, any PC-relative

 // relocations, and any internal_word_type relocations, must be reapplied.

 // After the GC runs, oop_type relocations must be reapplied.

 //

 //

 // Here are meanings of the types:

 //

 // relocInfo::none -- a filler record

 //   Value:  none

 //   Instruction: The corresponding code address is ignored

 //   Data:  Any data prefix and format code are ignored

 //   (This means that any relocInfo can be disabled by setting

 //   its type to none.  See relocInfo::remove.)

 //

 // relocInfo::oop_type, relocInfo::metadata_type -- a reference to an oop or meta data

 //   Value:  an oop, or else the address (handle) of an oop

 //   Instruction types: memory (load), set (load address)

 //   Data:  []       an oop stored in 4 bytes of instruction

 //          [n]      n is the index of an oop in the CodeBlob's oop pool

 //          [[N]n l] and l is a byte offset to be applied to the oop

 //          [Nn Ll]  both index and offset may be 32 bits if necessary

 //   Here is a special hack, used only by the old compiler:

 //          [[N]n 00] the value is the __address__ of the nth oop in the pool

 //   (Note that the offset allows optimal references to class variables.)

 //

 // relocInfo::internal_word_type -- an address within the same CodeBlob

 // relocInfo::section_word_type -- same, but can refer to another section

 //   Value:  an address in the CodeBlob's code or constants section

 //   Instruction types: memory (load), set (load address)

 //   Data:  []     stored in 4 bytes of instruction

 //          [[L]l] a relative offset (see [About Offsets] below)

 //   In the case of section_word_type, the offset is relative to a section

 //   base address, and the section number (e.g., SECT_INSTS) is encoded

 //   into the low two bits of the offset L.

 //

 // relocInfo::external_word_type -- a fixed address in the runtime system

 //   Value:  an address

 //   Instruction types: memory (load), set (load address)

 //   Data:  []   stored in 4 bytes of instruction

 //          [n]  the index of a "well-known" stub (usual case on RISC)

 //          [Ll] a 32-bit address

 //

 // relocInfo::runtime_call_type -- a fixed subroutine in the runtime system

 //   Value:  an address

 //   Instruction types: PC-relative call (or a PC-relative branch)

 //   Data:  []   stored in 4 bytes of instruction

 //

 // relocInfo::static_call_type -- a static call

 //   Value:  an CodeBlob, a stub, or a fixup routine

 //   Instruction types: a call

 //   Data:  []

 //   The identity of the callee is extracted from debugging information.

 //   //%note reloc_3

 //

 // relocInfo::virtual_call_type -- a virtual call site (which includes an inline

 //                                 cache)

 //   Value:  an CodeBlob, a stub, the interpreter, or a fixup routine

 //   Instruction types: a call, plus some associated set-oop instructions

 //   Data:  []       the associated set-oops are adjacent to the call

 //          [n]      n is a relative offset to the first set-oop

 //          [[N]n l] and l is a limit within which the set-oops occur

 //          [Nn Ll]  both n and l may be 32 bits if necessary

 //   The identity of the callee is extracted from debugging information.

 //

 // relocInfo::opt_virtual_call_type -- a virtual call site that is statically bound

 //

 //    Same info as a static_call_type. We use a special type, so the handling of

 //    virtuals and statics are separated.

 //

 //

 //   The offset n points to the first set-oop.  (See [About Offsets] below.)

 //   In turn, the set-oop instruction specifies or contains an oop cell devoted

 //   exclusively to the IC call, which can be patched along with the call.

 //

 //   The locations of any other set-oops are found by searching the relocation

 //   information starting at the first set-oop, and continuing until all

 //   relocations up through l have been inspected.  The value l is another

 //   relative offset.  (Both n and l are relative to the call's first byte.)

 //

 //   The limit l of the search is exclusive.  However, if it points within

 //   the call (e.g., offset zero), it is adjusted to point after the call and

 //   any associated machine-specific delay slot.

 //

 //   Since the offsets could be as wide as 32-bits, these conventions

 //   put no restrictions whatever upon code reorganization.

 //

 //   The compiler is responsible for ensuring that transition from a clean

 //   state to a monomorphic compiled state is MP-safe.  This implies that

 //   the system must respond well to intermediate states where a random

 //   subset of the set-oops has been correctly from the clean state

 //   upon entry to the VEP of the compiled method.  In the case of a

 //   machine (Intel) with a single set-oop instruction, the 32-bit

 //   immediate field must not straddle a unit of memory coherence.

 //   //%note reloc_3

 //

 // relocInfo::static_stub_type -- an extra stub for each static_call_type

 //   Value:  none

 //   Instruction types: a virtual call:  { set_oop; jump; }

 //   Data:  [[N]n]  the offset of the associated static_call reloc

 //   This stub becomes the target of a static call which must be upgraded

 //   to a virtual call (because the callee is interpreted).

 //   See [About Offsets] below.

 //   //%note reloc_2

 //

 // For example:

 //

 //   INSTRUCTIONS                        RELOC: TYPE    PREFIX DATA

 //   ------------                               ----    -----------

 // sethi      %hi(myObject),  R               oop_type [n(myObject)]

 // ld      [R+%lo(myObject)+fldOffset], R2    oop_type [n(myObject) fldOffset]

 // add R2, 1, R2

 // st  R2, [R+%lo(myObject)+fldOffset]        oop_type [n(myObject) fldOffset]

 //%note reloc_1

 //

 // This uses 4 instruction words, 8 relocation halfwords,

 // and an entry (which is sharable) in the CodeBlob's oop pool,

 // for a total of 36 bytes.

 //

 // Note that the compiler is responsible for ensuring the "fldOffset" when

 // added to "%lo(myObject)" does not overflow the immediate fields of the

 // memory instructions.

 //

 //

 // [About Offsets] Relative offsets are supplied to this module as

 // positive byte offsets, but they may be internally stored scaled

 // and/or negated, depending on what is most compact for the target

 // system.  Since the object pointed to by the offset typically

 // precedes the relocation address, it is profitable to store

 // these negative offsets as positive numbers, but this decision

 // is internal to the relocation information abstractions.

 //

 class Relocation;

 class CodeBuffer;

 class CodeSection;

 class RelocIterator;

 class relocInfo VALUE_OBJ_CLASS_SPEC {

   friend class RelocIterator;

  public:

   enum relocType {

     none                    =  0, // Used when no relocation should be generated

     oop_type                =  1, // embedded oop

     virtual_call_type       =  2, // a standard inline cache call for a virtual send

     opt_virtual_call_type   =  3, // a virtual call that has been statically bound (i.e., no IC cache)

     static_call_type        =  4, // a static send

     static_stub_type        =  5, // stub-entry for static send  (takes care of interpreter case)

     runtime_call_type       =  6, // call to fixed external routine

     external_word_type      =  7, // reference to fixed external address

     internal_word_type      =  8, // reference within the current code blob

     section_word_type       =  9, // internal, but a cross-section reference

     poll_type               = 10, // polling instruction for safepoints

     poll_return_type        = 11, // polling instruction for safepoints at return

     metadata_type           = 12, // metadata that used to be oops

     trampoline_stub_type    = 13, // stub-entry for trampoline

 #ifndef MIPS64

     yet_unused_type_1       = 14, // Still unused

 #else

     internal_pc_type        = 14, // tag for internal data,??

 #endif

     data_prefix_tag         = 15, // tag for a prefix (carries data arguments)

     type_mask               = 15  // A mask which selects only the above values

   };

  protected:

   unsigned short _value;

   enum RawBitsToken { RAW_BITS };

   relocInfo(relocType type, RawBitsToken ignore, int bits)

     : _value((type << nontype_width) + bits) { }

   relocInfo(relocType type, RawBitsToken ignore, int off, int f)

     : _value((type << nontype_width) + (off / (unsigned)offset_unit) + (f << offset_width)) { }

  public:

   // constructor

   relocInfo(relocType type, int offset, int format = 0)

 #ifndef ASSERT

   {

     (*this) = relocInfo(type, RAW_BITS, offset, format);

   }

 #else

   // Put a bunch of assertions out-of-line.

   ;

 #endif

   #define APPLY_TO_RELOCATIONS(visitor) \

     visitor(oop) \

     visitor(metadata) \

     visitor(virtual_call) \

     visitor(opt_virtual_call) \

     visitor(static_call) \

     visitor(static_stub) \

     visitor(runtime_call) \

     visitor(external_word) \

     visitor(internal_word) \

     visitor(poll) \

     visitor(poll_return) \

     visitor(trampoline_stub) \

     NOT_MIPS64(visitor(section_word)) MIPS64_ONLY(visitor(internal_pc)) \

  public:

   enum {

     value_width             = sizeof(unsigned short) * BitsPerByte,

     type_width              = 4,   // == log2(type_mask+1)

     nontype_width           = value_width - type_width,

     datalen_width           = nontype_width-1,

     datalen_tag             = 1 << datalen_width,  // or-ed into _value

     datalen_limit           = 1 << datalen_width,

     datalen_mask            = (1 << datalen_width)-1

   };

   // accessors

  public:

   relocType  type()       const { return (relocType)((unsigned)_value >> nontype_width); }

   int  format()           const { return format_mask==0? 0: format_mask &

                                          ((unsigned)_value >> offset_width); }

   int  addr_offset()      const { assert(!is_prefix(), "must have offset");

                                   return (_value & offset_mask)*offset_unit; }

  protected:

   const short* data()     const { assert(is_datalen(), "must have data");

                                   return (const short*)(this + 1); }

   int          datalen()  const { assert(is_datalen(), "must have data");

                                   return (_value & datalen_mask); }

   int         immediate() const { assert(is_immediate(), "must have immed");

                                   return (_value & datalen_mask); }

  public:

   static int addr_unit()        { return offset_unit; }

   static int offset_limit()     { return (1 << offset_width) * offset_unit; }

   void set_type(relocType type);

   void set_format(int format);

   void remove() { set_type(none); }

  protected:

   bool is_none()                const { return type() == none; }

   bool is_prefix()              const { return type() == data_prefix_tag; }

   bool is_datalen()             const { assert(is_prefix(), "must be prefix");

                                         return (_value & datalen_tag) != 0; }

   bool is_immediate()           const { assert(is_prefix(), "must be prefix");

                                         return (_value & datalen_tag) == 0; }

  public:

   // Occasionally records of type relocInfo::none will appear in the stream.

   // We do not bother to filter these out, but clients should ignore them.

   // These records serve as "filler" in three ways:

   //  - to skip large spans of unrelocated code (this is rare)

   //  - to pad out the relocInfo array to the required oop alignment

   //  - to disable old relocation information which is no longer applicable

   inline friend relocInfo filler_relocInfo();

   // Every non-prefix relocation may be preceded by at most one prefix,

   // which supplies 1 or more halfwords of associated data.  Conventionally,

   // an int is represented by 0, 1, or 2 halfwords, depending on how

   // many bits are required to represent the value.  (In addition,

   // if the sole halfword is a 10-bit unsigned number, it is made

   // "immediate" in the prefix header word itself.  This optimization

   // is invisible outside this module.)

   inline friend relocInfo prefix_relocInfo(int datalen);

  protected:

   // an immediate relocInfo optimizes a prefix with one 10-bit unsigned value

   static relocInfo immediate_relocInfo(int data0) {

     assert(fits_into_immediate(data0), "data0 in limits");

     return relocInfo(relocInfo::data_prefix_tag, RAW_BITS, data0);

   }

   static bool fits_into_immediate(int data0) {

     return (data0 >= 0 && data0 < datalen_limit);

   }

  public:

   // Support routines for compilers.

   // This routine takes an infant relocInfo (unprefixed) and

   // edits in its prefix, if any.  It also updates dest.locs_end.

   void initialize(CodeSection* dest, Relocation* reloc);

   // This routine updates a prefix and returns the limit pointer.

   // It tries to compress the prefix from 32 to 16 bits, and if

   // successful returns a reduced "prefix_limit" pointer.

   relocInfo* finish_prefix(short* prefix_limit);

   // bit-packers for the data array:

   // As it happens, the bytes within the shorts are ordered natively,

   // but the shorts within the word are ordered big-endian.

   // This is an arbitrary choice, made this way mainly to ease debugging.

   static int data0_from_int(jint x)         { return x >> value_width; }

   static int data1_from_int(jint x)         { return (short)x; }

   static jint jint_from_data(short* data) {

     return (data[0] << value_width) + (unsigned short)data[1];

   }

   static jint short_data_at(int n, short* data, int datalen) {

     return datalen > n ? data[n] : 0;

   }

   static jint jint_data_at(int n, short* data, int datalen) {

     return datalen > n+1 ? jint_from_data(&data[n]) : short_data_at(n, data, datalen);

   }

   // Update methods for relocation information

   // (since code is dynamically patched, we also need to dynamically update the relocation info)

   // Both methods takes old_type, so it is able to performe sanity checks on the information removed.

   static void change_reloc_info_for_address(RelocIterator *itr, address pc, relocType old_type, relocType new_type);

   static void remove_reloc_info_for_address(RelocIterator *itr, address pc, relocType old_type);

   // Machine dependent stuff

 #ifdef TARGET_ARCH_x86

 # include "relocInfo_x86.hpp"

 #endif

 #ifdef TARGET_ARCH_sparc

 # include "relocInfo_sparc.hpp"

 #endif

 #ifdef TARGET_ARCH_zero

 # include "relocInfo_zero.hpp"

 #endif

 #ifdef TARGET_ARCH_arm

 # include "relocInfo_arm.hpp"

 #endif

 #ifdef TARGET_ARCH_ppc

 # include "relocInfo_ppc.hpp"

 #endif

 #ifdef TARGET_ARCH_mips

 # include "relocInfo_mips.hpp"

 #endif

  protected:

   // Derived constant, based on format_width which is PD:

   enum {

     offset_width       = nontype_width - format_width,

     offset_mask        = (1<<offset_width) - 1,

     format_mask        = (1<<format_width) - 1

   };

  public:

   enum {

     // Conservatively large estimate of maximum length (in shorts)

     // of any relocation record.

     // Extended format is length prefix, data words, and tag/offset suffix.

     length_limit       = 1 + 1 + (3*BytesPerWord/BytesPerShort) + 1,

     have_format        = format_width > 0

   };

 };

 #define FORWARD_DECLARE_EACH_CLASS(name)              \

 class name##_Relocation;

 APPLY_TO_RELOCATIONS(FORWARD_DECLARE_EACH_CLASS)

 #undef FORWARD_DECLARE_EACH_CLASS

 inline relocInfo filler_relocInfo() {

   return relocInfo(relocInfo::none, relocInfo::offset_limit() - relocInfo::offset_unit);

 }

 inline relocInfo prefix_relocInfo(int datalen = 0) {

   assert(relocInfo::fits_into_immediate(datalen), "datalen in limits");

   return relocInfo(relocInfo::data_prefix_tag, relocInfo::RAW_BITS, relocInfo::datalen_tag | datalen);

 }

 // Holder for flyweight relocation objects.

 // Although the flyweight subclasses are of varying sizes,

 // the holder is "one size fits all".

 class RelocationHolder VALUE_OBJ_CLASS_SPEC {

   friend class Relocation;

   friend class CodeSection;

  private:

   // this preallocated memory must accommodate all subclasses of Relocation

   // (this number is assertion-checked in Relocation::operator new)

   enum { _relocbuf_size = 5 };

   void* _relocbuf[ _relocbuf_size ];

  public:

   Relocation* reloc() const { return (Relocation*) &_relocbuf[0]; }

   inline relocInfo::relocType type() const;

   // Add a constant offset to a relocation.  Helper for class Address.

   RelocationHolder plus(int offset) const;

   inline RelocationHolder();                // initializes type to none

   inline RelocationHolder(Relocation* r);   // make a copy

   static const RelocationHolder none;

 };

 // A RelocIterator iterates through the relocation information of a CodeBlob.

 // It is a variable BoundRelocation which is able to take on successive

 // values as it is advanced through a code stream.

 // Usage:

 //   RelocIterator iter(nm);

 //   while (iter.next()) {

 //     iter.reloc()->some_operation();

 //   }

 // or:

 //   RelocIterator iter(nm);

 //   while (iter.next()) {

 //     switch (iter.type()) {

 //      case relocInfo::oop_type          :

 //      case relocInfo::ic_type           :

 //      case relocInfo::prim_type         :

 //      case relocInfo::uncommon_type     :

 //      case relocInfo::runtime_call_type :

 //      case relocInfo::internal_word_type:

 //      case relocInfo::external_word_type:

 //      ...

 //     }

 //   }

 class RelocIterator : public StackObj {

   enum { SECT_LIMIT = 3 };  // must be equal to CodeBuffer::SECT_LIMIT, checked in ctor

   friend class Relocation;

   friend class relocInfo;       // for change_reloc_info_for_address only

   typedef relocInfo::relocType relocType;

  private:

   address    _limit;   // stop producing relocations after this _addr

   relocInfo* _current; // the current relocation information

   relocInfo* _end;     // end marker; we're done iterating when _current == _end

   nmethod*   _code;    // compiled method containing _addr

   address    _addr;    // instruction to which the relocation applies

   short      _databuf; // spare buffer for compressed data

   short*     _data;    // pointer to the relocation's data

   short      _datalen; // number of halfwords in _data

   char       _format;  // position within the instruction

   // Base addresses needed to compute targets of section_word_type relocs.

   address    _section_start[SECT_LIMIT];

   address    _section_end  [SECT_LIMIT];

   void set_has_current(bool b) {

     _datalen = !b ? -1 : 0;

     debug_only(_data = NULL);

   }

   void set_current(relocInfo& ri) {

     _current = &ri;

     set_has_current(true);

   }

   RelocationHolder _rh; // where the current relocation is allocated

   relocInfo* current() const { assert(has_current(), "must have current");

                                return _current; }

   void set_limits(address begin, address limit);

   void advance_over_prefix();    // helper method

   void initialize_misc();

   void initialize(nmethod* nm, address begin, address limit);

   RelocIterator() { initialize_misc(); }

  public:

   // constructor

   RelocIterator(nmethod* nm,     address begin = NULL, address limit = NULL);

   RelocIterator(CodeSection* cb, address begin = NULL, address limit = NULL);

   // get next reloc info, return !eos

   bool next() {

     _current++;

     assert(_current <= _end, "must not overrun relocInfo");

     if (_current == _end) {

       set_has_current(false);

       return false;

     }

     set_has_current(true);

     if (_current->is_prefix()) {

       advance_over_prefix();

       assert(!current()->is_prefix(), "only one prefix at a time");

     }

     _addr += _current->addr_offset();

     if (_limit != NULL && _addr >= _limit) {

       set_has_current(false);

       return false;

     }

     if (relocInfo::have_format)  _format = current()->format();

     return true;

   }

   // accessors

   address      limit()        const { return _limit; }

   void     set_limit(address x);

   relocType    type()         const { return current()->type(); }

   int          format()       const { return (relocInfo::have_format) ? current()->format() : 0; }

   address      addr()         const { return _addr; }

   nmethod*     code()         const { return _code; }

   short*       data()         const { return _data; }

   int          datalen()      const { return _datalen; }

   bool     has_current()      const { return _datalen >= 0; }

   void       set_addr(address addr) { _addr = addr; }

   bool   addr_in_const()      const;

   address section_start(int n) const {

     assert(_section_start[n], "must be initialized");

     return _section_start[n];

   }

   address section_end(int n) const {

     assert(_section_end[n], "must be initialized");

     return _section_end[n];

   }

   // The address points to the affected displacement part of the instruction.

   // For RISC, this is just the whole instruction.

   // For Intel, this is an unaligned 32-bit word.

   // type-specific relocation accessors:  oop_Relocation* oop_reloc(), etc.

   #define EACH_TYPE(name)                               \

   inline name##_Relocation* name##_reloc();

   APPLY_TO_RELOCATIONS(EACH_TYPE)

   #undef EACH_TYPE

   // generic relocation accessor; switches on type to call the above

   Relocation* reloc();

   // CodeBlob's have relocation indexes for faster random access:

   static int locs_and_index_size(int code_size, int locs_size);

   // Store an index into [dest_start+dest_count..dest_end).

   // At dest_start[0..dest_count] is the actual relocation information.

   // Everything else up to dest_end is free space for the index.

   static void create_index(relocInfo* dest_begin, int dest_count, relocInfo* dest_end);

 #ifndef PRODUCT

  public:

   void print();

   void print_current();

 #endif

 };

 // A Relocation is a flyweight object allocated within a RelocationHolder.

 // It represents the relocation data of relocation record.

 // So, the RelocIterator unpacks relocInfos into Relocations.

 class Relocation VALUE_OBJ_CLASS_SPEC {

   friend class RelocationHolder;

   friend class RelocIterator;

  private:

   static void guarantee_size();

   // When a relocation has been created by a RelocIterator,

   // this field is non-null.  It allows the relocation to know

   // its context, such as the address to which it applies.

   RelocIterator* _binding;

  protected:

   RelocIterator* binding() const {

     assert(_binding != NULL, "must be bound");

     return _binding;

   }

   void set_binding(RelocIterator* b) {

     assert(_binding == NULL, "must be unbound");

     _binding = b;

     assert(_binding != NULL, "must now be bound");

   }

   Relocation() {

     _binding = NULL;

   }

   static RelocationHolder newHolder() {

     return RelocationHolder();

   }

  public:

   void* operator new(size_t size, const RelocationHolder& holder) throw() {

     if (size > sizeof(holder._relocbuf)) guarantee_size();

     assert((void* const *)holder.reloc() == &holder._relocbuf[0], "ptrs must agree");

     return holder.reloc();

   }

   // make a generic relocation for a given type (if possible)

   static RelocationHolder spec_simple(relocInfo::relocType rtype);

   // here is the type-specific hook which writes relocation data:

   virtual void pack_data_to(CodeSection* dest) { }

   // here is the type-specific hook which reads (unpacks) relocation data:

   virtual void unpack_data() {

     assert(datalen()==0 || type()==relocInfo::none, "no data here");

   }

   static bool is_reloc_index(intptr_t index) {

     return 0 < index && index < os::vm_page_size();

   }

  protected:

   // Helper functions for pack_data_to() and unpack_data().

   // Most of the compression logic is confined here.

   // (The "immediate data" mechanism of relocInfo works independently

   // of this stuff, and acts to further compress most 1-word data prefixes.)

   // A variable-width int is encoded as a short if it will fit in 16 bits.

   // The decoder looks at datalen to decide whether to unpack short or jint.

   // Most relocation records are quite simple, containing at most two ints.

   static bool is_short(jint x) { return x == (short)x; }

   static short* add_short(short* p, int x)  { *p++ = x; return p; }

   static short* add_jint (short* p, jint x) {

     *p++ = relocInfo::data0_from_int(x); *p++ = relocInfo::data1_from_int(x);

     return p;

   }

   static short* add_var_int(short* p, jint x) {   // add a variable-width int

     if (is_short(x))  p = add_short(p, x);

     else              p = add_jint (p, x);

     return p;

   }

   static short* pack_1_int_to(short* p, jint x0) {

     // Format is one of:  [] [x] [Xx]

     if (x0 != 0)  p = add_var_int(p, x0);

     return p;

   }

   int unpack_1_int() {

     assert(datalen() <= 2, "too much data");

     return relocInfo::jint_data_at(0, data(), datalen());

   }

   // With two ints, the short form is used only if both ints are short.

   short* pack_2_ints_to(short* p, jint x0, jint x1) {

     // Format is one of:  [] [x y?] [Xx Y?y]

     if (x0 == 0 && x1 == 0) {

       // no halfwords needed to store zeroes

     } else if (is_short(x0) && is_short(x1)) {

       // 1-2 halfwords needed to store shorts

       p = add_short(p, x0); if (x1!=0) p = add_short(p, x1);

     } else {

       // 3-4 halfwords needed to store jints

       p = add_jint(p, x0);             p = add_var_int(p, x1);

     }

     return p;

   }

   void unpack_2_ints(jint& x0, jint& x1) {

     int    dlen = datalen();

     short* dp  = data();

     if (dlen <= 2) {

       x0 = relocInfo::short_data_at(0, dp, dlen);

       x1 = relocInfo::short_data_at(1, dp, dlen);

     } else {

       assert(dlen <= 4, "too much data");

       x0 = relocInfo::jint_data_at(0, dp, dlen);

       x1 = relocInfo::jint_data_at(2, dp, dlen);

     }

   }

  protected:

   // platform-dependent utilities for decoding and patching instructions

   void       pd_set_data_value       (address x, intptr_t off, bool verify_only = false); // a set or mem-ref

   void       pd_verify_data_value    (address x, intptr_t off) { pd_set_data_value(x, off, true); }

   address    pd_call_destination     (address orig_addr = NULL);

   void       pd_set_call_destination (address x);

   // this extracts the address of an address in the code stream instead of the reloc data

   address* pd_address_in_code       ();

   // this extracts an address from the code stream instead of the reloc data

   address  pd_get_address_from_code ();

   // these convert from byte offsets, to scaled offsets, to addresses

   static jint scaled_offset(address x, address base) {

     int byte_offset = x - base;

     int offset = -byte_offset / relocInfo::addr_unit();

     assert(address_from_scaled_offset(offset, base) == x, "just checkin'");

     return offset;

   }

   static jint scaled_offset_null_special(address x, address base) {

     // Some relocations treat offset=0 as meaning NULL.

     // Handle this extra convention carefully.

     if (x == NULL)  return 0;

     assert(x != base, "offset must not be zero");

     return scaled_offset(x, base);

   }

   static address address_from_scaled_offset(jint offset, address base) {

     int byte_offset = -( offset * relocInfo::addr_unit() );

     return base + byte_offset;

   }

   // these convert between indexes and addresses in the runtime system

   static int32_t runtime_address_to_index(address runtime_address);

   static address index_to_runtime_address(int32_t index);

   // helpers for mapping between old and new addresses after a move or resize

   address old_addr_for(address newa, const CodeBuffer* src, CodeBuffer* dest);

   address new_addr_for(address olda, const CodeBuffer* src, CodeBuffer* dest);

   void normalize_address(address& addr, const CodeSection* dest, bool allow_other_sections = false);

  public:

   // accessors which only make sense for a bound Relocation

   address  addr()         const { return binding()->addr(); }

   nmethod* code()         const { return binding()->code(); }

   bool     addr_in_const() const { return binding()->addr_in_const(); }

  protected:

   short*   data()         const { return binding()->data(); }

   int      datalen()      const { return binding()->datalen(); }

   int      format()       const { return binding()->format(); }

  public:

   virtual relocInfo::relocType type()            { return relocInfo::none; }

   // is it a call instruction?

   virtual bool is_call()                         { return false; }

   // is it a data movement instruction?

   virtual bool is_data()                         { return false; }

   // some relocations can compute their own values

   virtual address  value();

   // all relocations are able to reassert their values

   virtual void set_value(address x);

   virtual void clear_inline_cache()              { }

   // This method assumes that all virtual/static (inline) caches are cleared (since for static_call_type and

   // ic_call_type is not always posisition dependent (depending on the state of the cache)). However, this is

   // probably a reasonable assumption, since empty caches simplifies code reloacation.

   virtual void fix_relocation_after_move(const CodeBuffer* src, CodeBuffer* dest) { }

   void print();

 };

 // certain inlines must be deferred until class Relocation is defined:

 inline RelocationHolder::RelocationHolder() {

   // initialize the vtbl, just to keep things type-safe

   new(*this) Relocation();

 }

 inline RelocationHolder::RelocationHolder(Relocation* r) {

   // wordwise copy from r (ok if it copies garbage after r)

   for (int i = 0; i < _relocbuf_size; i++) {

     _relocbuf[i] = ((void**)r)[i];

   }

 }

 relocInfo::relocType RelocationHolder::type() const {

   return reloc()->type();

 }

 // A DataRelocation always points at a memory or load-constant instruction..

 // It is absolute on most machines, and the constant is split on RISCs.

 // The specific subtypes are oop, external_word, and internal_word.

 // By convention, the "value" does not include a separately reckoned "offset".

 class DataRelocation : public Relocation {

  public:

   bool          is_data()                      { return true; }

   // both target and offset must be computed somehow from relocation data

   virtual int    offset()                      { return 0; }

   address         value()                      = 0;

   void        set_value(address x)             { set_value(x, offset()); }

   void        set_value(address x, intptr_t o) {

     if (addr_in_const())

       *(address*)addr() = x;

     else

       pd_set_data_value(x, o);

   }

   void        verify_value(address x) {

     if (addr_in_const())

       assert(*(address*)addr() == x, "must agree");

     else

       pd_verify_data_value(x, offset());

   }

   // The "o" (displacement) argument is relevant only to split relocations

   // on RISC machines.  In some CPUs (SPARC), the set-hi and set-lo ins'ns

   // can encode more than 32 bits between them.  This allows compilers to

   // share set-hi instructions between addresses that differ by a small

   // offset (e.g., different static variables in the same class).

   // On such machines, the "x" argument to set_value on all set-lo

   // instructions must be the same as the "x" argument for the

   // corresponding set-hi instructions.  The "o" arguments for the

   // set-hi instructions are ignored, and must not affect the high-half

   // immediate constant.  The "o" arguments for the set-lo instructions are

   // added into the low-half immediate constant, and must not overflow it.

 };

 // A CallRelocation always points at a call instruction.

 // It is PC-relative on most machines.

 class CallRelocation : public Relocation {

  public:

   bool is_call() { return true; }

   address  destination()                    { return pd_call_destination(); }

   void     set_destination(address x); // pd_set_call_destination

   void     fix_relocation_after_move(const CodeBuffer* src, CodeBuffer* dest);

   address  value()                          { return destination();  }

   void     set_value(address x)             { set_destination(x); }

 };

 class oop_Relocation : public DataRelocation {

   relocInfo::relocType type() { return relocInfo::oop_type; }

  public:

   // encode in one of these formats:  [] [n] [n l] [Nn l] [Nn Ll]

   // an oop in the CodeBlob's oop pool

   static RelocationHolder spec(int oop_index, int offset = 0) {

     assert(oop_index > 0, "must be a pool-resident oop");

     RelocationHolder rh = newHolder();

     new(rh) oop_Relocation(oop_index, offset);

     return rh;

   }

   // an oop in the instruction stream

   static RelocationHolder spec_for_immediate() {

     const int oop_index = 0;

     const int offset    = 0;    // if you want an offset, use the oop pool

     RelocationHolder rh = newHolder();

     new(rh) oop_Relocation(oop_index, offset);

     return rh;

   }

  private:

   jint _oop_index;                  // if > 0, index into CodeBlob::oop_at

   jint _offset;                     // byte offset to apply to the oop itself

   oop_Relocation(int oop_index, int offset) {

     _oop_index = oop_index; _offset = offset;

   }

   friend class RelocIterator;

   oop_Relocation() { }

  public:

   int oop_index() { return _oop_index; }

   int offset()    { return _offset; }

   // data is packed in "2_ints" format:  [i o] or [Ii Oo]

   void pack_data_to(CodeSection* dest);

   void unpack_data();

   void fix_oop_relocation();        // reasserts oop value

   void verify_oop_relocation();

   address value()  { return (address) *oop_addr(); }

   bool oop_is_immediate()  { return oop_index() == 0; }

   oop* oop_addr();                  // addr or &pool[jint_data]

   oop  oop_value();                 // *oop_addr

   // Note:  oop_value transparently converts Universe::non_oop_word to NULL.

 };

 // copy of oop_Relocation for now but may delete stuff in both/either

 class metadata_Relocation : public DataRelocation {

   relocInfo::relocType type() { return relocInfo::metadata_type; }

  public:

   // encode in one of these formats:  [] [n] [n l] [Nn l] [Nn Ll]

   // an metadata in the CodeBlob's metadata pool

   static RelocationHolder spec(int metadata_index, int offset = 0) {

     assert(metadata_index > 0, "must be a pool-resident metadata");

     RelocationHolder rh = newHolder();

     new(rh) metadata_Relocation(metadata_index, offset);

     return rh;

   }

   // an metadata in the instruction stream

   static RelocationHolder spec_for_immediate() {

     const int metadata_index = 0;

     const int offset    = 0;    // if you want an offset, use the metadata pool

     RelocationHolder rh = newHolder();

     new(rh) metadata_Relocation(metadata_index, offset);

     return rh;

   }

  private:

   jint _metadata_index;            // if > 0, index into nmethod::metadata_at

   jint _offset;                     // byte offset to apply to the metadata itself

   metadata_Relocation(int metadata_index, int offset) {

     _metadata_index = metadata_index; _offset = offset;

   }

   friend class RelocIterator;

   metadata_Relocation() { }

   // Fixes a Metadata pointer in the code. Most platforms embeds the

   // Metadata pointer in the code at compile time so this is empty

   // for them.

   void pd_fix_value(address x);

  public:

   int metadata_index() { return _metadata_index; }

   int offset()    { return _offset; }

   // data is packed in "2_ints" format:  [i o] or [Ii Oo]

   void pack_data_to(CodeSection* dest);

   void unpack_data();

   void fix_metadata_relocation();        // reasserts metadata value

   void verify_metadata_relocation();

   address value()  { return (address) *metadata_addr(); }

   bool metadata_is_immediate()  { return metadata_index() == 0; }

   Metadata**   metadata_addr();                  // addr or &pool[jint_data]

   Metadata*    metadata_value();                 // *metadata_addr

   // Note:  metadata_value transparently converts Universe::non_metadata_word to NULL.

 };

  #ifdef MIPS64

  // to handle the set_last_java_frame pc

  class internal_pc_Relocation : public Relocation {

   relocInfo::relocType type() { return relocInfo::internal_pc_type; }

   public:

    address pc() {pd_get_address_from_code();}

          //void     fix_relocation_at_move(intptr_t delta);

          void     fix_relocation_after_move(const CodeBuffer* src, CodeBuffer* dest);

  };

  #endif

 class virtual_call_Relocation : public CallRelocation {

   relocInfo::relocType type() { return relocInfo::virtual_call_type; }

  public:

   // "cached_value" points to the first associated set-oop.

   // The oop_limit helps find the last associated set-oop.

   // (See comments at the top of this file.)

   static RelocationHolder spec(address cached_value) {

     RelocationHolder rh = newHolder();

     new(rh) virtual_call_Relocation(cached_value);

     return rh;

   }

   virtual_call_Relocation(address cached_value) {

     _cached_value = cached_value;

     assert(cached_value != NULL, "first oop address must be specified");

   }

  private:

   address _cached_value;               // location of set-value instruction

   friend class RelocIterator;

   virtual_call_Relocation() { }

  public:

   address cached_value();

   // data is packed as scaled offsets in "2_ints" format:  [f l] or [Ff Ll]

   // oop_limit is set to 0 if the limit falls somewhere within the call.

   // When unpacking, a zero oop_limit is taken to refer to the end of the call.

   // (This has the effect of bringing in the call's delay slot on SPARC.)

   void pack_data_to(CodeSection* dest);

   void unpack_data();

   void clear_inline_cache();

 };

 class opt_virtual_call_Relocation : public CallRelocation {

   relocInfo::relocType type() { return relocInfo::opt_virtual_call_type; }

  public:

   static RelocationHolder spec() {

     RelocationHolder rh = newHolder();

     new(rh) opt_virtual_call_Relocation();

     return rh;

   }

  private:

   friend class RelocIterator;

   opt_virtual_call_Relocation() { }

  public:

   void clear_inline_cache();

   // find the matching static_stub

   address static_stub();

 };

 class static_call_Relocation : public CallRelocation {

   relocInfo::relocType type() { return relocInfo::static_call_type; }

  public:

   static RelocationHolder spec() {

     RelocationHolder rh = newHolder();

     new(rh) static_call_Relocation();

     return rh;

   }

  private:

   friend class RelocIterator;

   static_call_Relocation() { }

  public:

   void clear_inline_cache();

   // find the matching static_stub

   address static_stub();

 };

 class static_stub_Relocation : public Relocation {

   relocInfo::relocType type() { return relocInfo::static_stub_type; }

  public:

   static RelocationHolder spec(address static_call) {

     RelocationHolder rh = newHolder();

     new(rh) static_stub_Relocation(static_call);

     return rh;

   }

  private:

   address _static_call;             // location of corresponding static_call

   static_stub_Relocation(address static_call) {

     _static_call = static_call;

   }

   friend class RelocIterator;

   static_stub_Relocation() { }

  public:

   void clear_inline_cache();

   address static_call() { return _static_call; }

   // data is packed as a scaled offset in "1_int" format:  [c] or [Cc]

   void pack_data_to(CodeSection* dest);

   void unpack_data();

 };

 class runtime_call_Relocation : public CallRelocation {

   relocInfo::relocType type() { return relocInfo::runtime_call_type; }

  public:

   static RelocationHolder spec() {

     RelocationHolder rh = newHolder();

     new(rh) runtime_call_Relocation();

     return rh;

   }

  private:

   friend class RelocIterator;

   runtime_call_Relocation() { }

  public:

 };

 // Trampoline Relocations.

 // A trampoline allows to encode a small branch in the code, even if there

 // is the chance that this branch can not reach all possible code locations.

 // If the relocation finds that a branch is too far for the instruction

 // in the code, it can patch it to jump to the trampoline where is

 // sufficient space for a far branch. Needed on PPC.

 class trampoline_stub_Relocation : public Relocation {

   relocInfo::relocType type() { return relocInfo::trampoline_stub_type; }

  public:

   static RelocationHolder spec(address static_call) {

     RelocationHolder rh = newHolder();

     return (new (rh) trampoline_stub_Relocation(static_call));

   }

  private:

   address _owner;    // Address of the NativeCall that owns the trampoline.

   trampoline_stub_Relocation(address owner) {

     _owner = owner;

   }

   friend class RelocIterator;

   trampoline_stub_Relocation() { }

  public:

   // Return the address of the NativeCall that owns the trampoline.

   address owner() { return _owner; }

   void pack_data_to(CodeSection * dest);

   void unpack_data();

   // Find the trampoline stub for a call.

   static address get_trampoline_for(address call, nmethod* code);

 };

 class external_word_Relocation : public DataRelocation {

   relocInfo::relocType type() { return relocInfo::external_word_type; }

  public:

   static RelocationHolder spec(address target) {

     assert(target != NULL, "must not be null");

     RelocationHolder rh = newHolder();

     new(rh) external_word_Relocation(target);

     return rh;

   }

   // Use this one where all 32/64 bits of the target live in the code stream.

   // The target must be an intptr_t, and must be absolute (not relative).

   static RelocationHolder spec_for_immediate() {

     RelocationHolder rh = newHolder();

     new(rh) external_word_Relocation(NULL);

     return rh;

   }

   // Some address looking values aren't safe to treat as relocations

   // and should just be treated as constants.

   static bool can_be_relocated(address target) {

     return target != NULL && !is_reloc_index((intptr_t)target);

   }

  private:

   address _target;                  // address in runtime

   external_word_Relocation(address target) {

     _target = target;

   }

   friend class RelocIterator;

   external_word_Relocation() { }

  public:

   // data is packed as a well-known address in "1_int" format:  [a] or [Aa]

   // The function runtime_address_to_index is used to turn full addresses

   // to short indexes, if they are pre-registered by the stub mechanism.

   // If the "a" value is 0 (i.e., _target is NULL), the address is stored

   // in the code stream.  See external_word_Relocation::target().

   void pack_data_to(CodeSection* dest);

   void unpack_data();

   void fix_relocation_after_move(const CodeBuffer* src, CodeBuffer* dest);

   address  target();        // if _target==NULL, fetch addr from code stream

   address  value()          { return target(); }

 };

 class internal_word_Relocation : public DataRelocation {

   relocInfo::relocType type() { return relocInfo::internal_word_type; }

  public:

   static RelocationHolder spec(address target) {

     assert(target != NULL, "must not be null");

     RelocationHolder rh = newHolder();

     new(rh) internal_word_Relocation(target);

     return rh;

   }

   // use this one where all the bits of the target can fit in the code stream:

   static RelocationHolder spec_for_immediate() {

     RelocationHolder rh = newHolder();

     new(rh) internal_word_Relocation(NULL);

     return rh;

   }

   internal_word_Relocation(address target) {

     _target  = target;

     _section = -1;  // self-relative

   }

  protected:

   address _target;                  // address in CodeBlob

   int     _section;                 // section providing base address, if any

   friend class RelocIterator;

   internal_word_Relocation() { }

   // bit-width of LSB field in packed offset, if section >= 0

   enum { section_width = 2 }; // must equal CodeBuffer::sect_bits

  public:

   // data is packed as a scaled offset in "1_int" format:  [o] or [Oo]

   // If the "o" value is 0 (i.e., _target is NULL), the offset is stored

   // in the code stream.  See internal_word_Relocation::target().

   // If _section is not -1, it is appended to the low bits of the offset.

   void pack_data_to(CodeSection* dest);

   void unpack_data();

   void fix_relocation_after_move(const CodeBuffer* src, CodeBuffer* dest);

   address  target();        // if _target==NULL, fetch addr from code stream

   int      section()        { return _section;   }

   address  value()          { return target();   }

 };

 class section_word_Relocation : public internal_word_Relocation {

   relocInfo::relocType type() { return relocInfo::section_word_type; }

  public:

   static RelocationHolder spec(address target, int section) {

     RelocationHolder rh = newHolder();

     new(rh) section_word_Relocation(target, section);

     return rh;

   }

   section_word_Relocation(address target, int section) {

     assert(target != NULL, "must not be null");

     assert(section >= 0, "must be a valid section");

     _target  = target;

     _section = section;

   }

   //void pack_data_to -- inherited

   void unpack_data();

  private:

   friend class RelocIterator;

   section_word_Relocation() { }

 };

 class poll_Relocation : public Relocation {

   bool          is_data()                      { return true; }

   relocInfo::relocType type() { return relocInfo::poll_type; }

   void     fix_relocation_after_move(const CodeBuffer* src, CodeBuffer* dest);

 };

 class poll_return_Relocation : public Relocation {

   bool          is_data()                      { return true; }

   relocInfo::relocType type() { return relocInfo::poll_return_type; }

   void     fix_relocation_after_move(const CodeBuffer* src, CodeBuffer* dest);

 };

 // We know all the xxx_Relocation classes, so now we can define these:

 #define EACH_CASE(name)                                         \

 inline name##_Relocation* RelocIterator::name##_reloc() {       \

   assert(type() == relocInfo::name##_type, "type must agree");  \

   /* The purpose of the placed "new" is to re-use the same */   \

   /* stack storage for each new iteration. */                   \

   name##_Relocation* r = new(_rh) name##_Relocation();          \

   r->set_binding(this);                                         \

   r->name##_Relocation::unpack_data();                          \

   return r;                                                     \

 }

 APPLY_TO_RELOCATIONS(EACH_CASE);

 #undef EACH_CASE

 inline RelocIterator::RelocIterator(nmethod* nm, address begin, address limit) {

   initialize(nm, begin, limit);

 }

 #endif // SHARE_VM_CODE_RELOCINFO_HPP