Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright 1997-2009 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

  * CA 95054 USA or visit www.sun.com if you need additional information or

  * have any questions.

  *

  */

 // This class is used internally by nmethods, to cache

 // exception/pc/handler information.

 class ExceptionCache : public CHeapObj {

   friend class VMStructs;

  private:

   static address _unwind_handler;

   enum { cache_size = 16 };

   klassOop _exception_type;

   address  _pc[cache_size];

   address  _handler[cache_size];

   int      _count;

   ExceptionCache* _next;

   address pc_at(int index)                     { assert(index >= 0 && index < count(),""); return _pc[index]; }

   void    set_pc_at(int index, address a)      { assert(index >= 0 && index < cache_size,""); _pc[index] = a; }

   address handler_at(int index)                { assert(index >= 0 && index < count(),""); return _handler[index]; }

   void    set_handler_at(int index, address a) { assert(index >= 0 && index < cache_size,""); _handler[index] = a; }

   int     count()                              { return _count; }

   void    increment_count()                    { _count++; }

  public:

   ExceptionCache(Handle exception, address pc, address handler);

   klassOop  exception_type()                { return _exception_type; }

   klassOop* exception_type_addr()           { return &_exception_type; }

   ExceptionCache* next()                    { return _next; }

   void      set_next(ExceptionCache *ec)    { _next = ec; }

   address match(Handle exception, address pc);

   bool    match_exception_with_space(Handle exception) ;

   address test_address(address addr);

   bool    add_address_and_handler(address addr, address handler) ;

   static address unwind_handler() { return _unwind_handler; }

 };

 // cache pc descs found in earlier inquiries

 class PcDescCache VALUE_OBJ_CLASS_SPEC {

   friend class VMStructs;

  private:

   enum { cache_size = 4 };

   PcDesc* _last_pc_desc;         // most recent pc_desc found

   PcDesc* _pc_descs[cache_size]; // last cache_size pc_descs found

  public:

   PcDescCache() { debug_only(_last_pc_desc = NULL); }

   void    reset_to(PcDesc* initial_pc_desc);

   PcDesc* find_pc_desc(int pc_offset, bool approximate);

   void    add_pc_desc(PcDesc* pc_desc);

   PcDesc* last_pc_desc() { return _last_pc_desc; }

 };

 // nmethods (native methods) are the compiled code versions of Java methods.

 struct nmFlags {

   friend class VMStructs;

   unsigned int version:8;                 // version number (0 = first version)

   unsigned int level:4;                   // optimization level

   unsigned int age:4;                     // age (in # of sweep steps)

   unsigned int state:2;                   // {alive, zombie, unloaded)

   unsigned int isUncommonRecompiled:1;    // recompiled because of uncommon trap?

   unsigned int isToBeRecompiled:1;        // to be recompiled as soon as it matures

   unsigned int hasFlushedDependencies:1;  // Used for maintenance of dependencies

   unsigned int markedForReclamation:1;    // Used by NMethodSweeper

   unsigned int has_unsafe_access:1;       // May fault due to unsafe access.

   void clear();

 };

 // A nmethod contains:

 //  - header                 (the nmethod structure)

 //  [Relocation]

 //  - relocation information

 //  - constant part          (doubles, longs and floats used in nmethod)

 //  [Code]

 //  - code body

 //  - exception handler

 //  - stub code

 //  [Debugging information]

 //  - oop array

 //  - data array

 //  - pcs

 //  [Exception handler table]

 //  - handler entry point array

 //  [Implicit Null Pointer exception table]

 //  - implicit null table array

 class Dependencies;

 class ExceptionHandlerTable;

 class ImplicitExceptionTable;

 class AbstractCompiler;

 class xmlStream;

 class nmethod : public CodeBlob {

   friend class VMStructs;

   friend class NMethodSweeper;

   friend class CodeCache;  // non-perm oops

  private:

   // Shared fields for all nmethod's

   static int _zombie_instruction_size;

   methodOop _method;

   int       _entry_bci;        // != InvocationEntryBci if this nmethod is an on-stack replacement method

   // To support simple linked-list chaining of nmethods:

   nmethod*  _osr_link;         // from instanceKlass::osr_nmethods_head

   nmethod*  _scavenge_root_link; // from CodeCache::scavenge_root_nmethods

   static nmethod* volatile _oops_do_mark_nmethods;

   nmethod*        volatile _oops_do_mark_link;

   AbstractCompiler* _compiler; // The compiler which compiled this nmethod

   // Offsets for different nmethod parts

   int _exception_offset;

   // All deoptee's will resume execution at this location described by this offset

   int _deoptimize_offset;

 #ifdef HAVE_DTRACE_H

   int _trap_offset;

 #endif // def HAVE_DTRACE_H

   int _stub_offset;

   int _consts_offset;

   int _scopes_data_offset;

   int _scopes_pcs_offset;

   int _dependencies_offset;

   int _handler_table_offset;

   int _nul_chk_table_offset;

   int _nmethod_end_offset;

   // location in frame (offset for sp) that deopt can store the original

   // pc during a deopt.

   int _orig_pc_offset;

   int _compile_id;                     // which compilation made this nmethod

   int _comp_level;                     // compilation level

   // offsets for entry points

   address _entry_point;                // entry point with class check

   address _verified_entry_point;       // entry point without class check

   address _osr_entry_point;            // entry point for on stack replacement

   nmFlags flags;           // various flags to keep track of nmethod state

   bool _markedForDeoptimization;       // Used for stack deoptimization

   enum { alive        = 0,

          not_entrant  = 1, // uncommon trap has happened but activations may still exist

          zombie       = 2,

          unloaded     = 3 };

   // used by jvmti to track if an unload event has been posted for this nmethod.

   bool _unload_reported;

   jbyte _scavenge_root_state;

   NOT_PRODUCT(bool _has_debug_info; )

   // Nmethod Flushing lock (if non-zero, then the nmethod is not removed)

   jint  _lock_count;

   // not_entrant method removal. Each mark_sweep pass will update

   // this mark to current sweep invocation count if it is seen on the

   // stack.  An not_entrant method can be removed when there is no

   // more activations, i.e., when the _stack_traversal_mark is less than

   // current sweep traversal index.

   long _stack_traversal_mark;

   ExceptionCache *_exception_cache;

   PcDescCache     _pc_desc_cache;

   // These are only used for compiled synchronized native methods to

   // locate the owner and stack slot for the BasicLock so that we can

   // properly revoke the bias of the owner if necessary. They are

   // needed because there is no debug information for compiled native

   // wrappers and the oop maps are insufficient to allow

   // frame::retrieve_receiver() to work. Currently they are expected

   // to be byte offsets from the Java stack pointer for maximum code

   // sharing between platforms. Note that currently biased locking

   // will never cause Class instances to be biased but this code

   // handles the static synchronized case as well.

   ByteSize _compiled_synchronized_native_basic_lock_owner_sp_offset;

   ByteSize _compiled_synchronized_native_basic_lock_sp_offset;

   friend class nmethodLocker;

   // For native wrappers

   nmethod(methodOop method,

           int nmethod_size,

           CodeOffsets* offsets,

           CodeBuffer *code_buffer,

           int frame_size,

           ByteSize basic_lock_owner_sp_offset, /* synchronized natives only */

           ByteSize basic_lock_sp_offset,       /* synchronized natives only */

           OopMapSet* oop_maps);

 #ifdef HAVE_DTRACE_H

   // For native wrappers

   nmethod(methodOop method,

           int nmethod_size,

           CodeOffsets* offsets,

           CodeBuffer *code_buffer,

           int frame_size);

 #endif // def HAVE_DTRACE_H

   // Creation support

   nmethod(methodOop method,

           int nmethod_size,

           int compile_id,

           int entry_bci,

           CodeOffsets* offsets,

           int orig_pc_offset,

           DebugInformationRecorder *recorder,

           Dependencies* dependencies,

           CodeBuffer *code_buffer,

           int frame_size,

           OopMapSet* oop_maps,

           ExceptionHandlerTable* handler_table,

           ImplicitExceptionTable* nul_chk_table,

           AbstractCompiler* compiler,

           int comp_level);

   // helper methods

   void* operator new(size_t size, int nmethod_size);

   const char* reloc_string_for(u_char* begin, u_char* end);

   void make_not_entrant_or_zombie(int state);

   void inc_decompile_count();

   // used to check that writes to nmFlags are done consistently.

   static void check_safepoint() PRODUCT_RETURN;

   // Used to manipulate the exception cache

   void add_exception_cache_entry(ExceptionCache* new_entry);

   ExceptionCache* exception_cache_entry_for_exception(Handle exception);

   // Inform external interfaces that a compiled method has been unloaded

   inline void post_compiled_method_unload();

  public:

   // create nmethod with entry_bci

   static nmethod* new_nmethod(methodHandle method,

                               int compile_id,

                               int entry_bci,

                               CodeOffsets* offsets,

                               int orig_pc_offset,

                               DebugInformationRecorder* recorder,

                               Dependencies* dependencies,

                               CodeBuffer *code_buffer,

                               int frame_size,

                               OopMapSet* oop_maps,

                               ExceptionHandlerTable* handler_table,

                               ImplicitExceptionTable* nul_chk_table,

                               AbstractCompiler* compiler,

                               int comp_level);

   static nmethod* new_native_nmethod(methodHandle method,

                                      CodeBuffer *code_buffer,

                                      int vep_offset,

                                      int frame_complete,

                                      int frame_size,

                                      ByteSize receiver_sp_offset,

                                      ByteSize basic_lock_sp_offset,

                                      OopMapSet* oop_maps);

 #ifdef HAVE_DTRACE_H

   // The method we generate for a dtrace probe has to look

   // like an nmethod as far as the rest of the system is concerned

   // which is somewhat unfortunate.

   static nmethod* new_dtrace_nmethod(methodHandle method,

                                      CodeBuffer *code_buffer,

                                      int vep_offset,

                                      int trap_offset,

                                      int frame_complete,

                                      int frame_size);

   int trap_offset() const      { return _trap_offset; }

   address trap_address() const { return code_begin() + _trap_offset; }

 #endif // def HAVE_DTRACE_H

   // accessors

   methodOop method() const                        { return _method; }

   AbstractCompiler* compiler() const              { return _compiler; }

 #ifndef PRODUCT

   bool has_debug_info() const                     { return _has_debug_info; }

   void set_has_debug_info(bool f)                 { _has_debug_info = false; }

 #endif // NOT PRODUCT

   // type info

   bool is_nmethod() const                         { return true; }

   bool is_java_method() const                     { return !method()->is_native(); }

   bool is_native_method() const                   { return method()->is_native(); }

   bool is_osr_method() const                      { return _entry_bci != InvocationEntryBci; }

   bool is_compiled_by_c1() const;

   bool is_compiled_by_c2() const;

   // boundaries for different parts

   address code_begin         () const             { return _entry_point; }

   address code_end           () const             { return           header_begin() + _stub_offset          ; }

   address exception_begin    () const             { return           header_begin() + _exception_offset     ; }

   address deopt_handler_begin() const             { return           header_begin() + _deoptimize_offset    ; }

   address stub_begin         () const             { return           header_begin() + _stub_offset          ; }

   address stub_end           () const             { return           header_begin() + _consts_offset        ; }

   address consts_begin       () const             { return           header_begin() + _consts_offset        ; }

   address consts_end         () const             { return           header_begin() + _scopes_data_offset   ; }

   address scopes_data_begin  () const             { return           header_begin() + _scopes_data_offset   ; }

   address scopes_data_end    () const             { return           header_begin() + _scopes_pcs_offset    ; }

   PcDesc* scopes_pcs_begin   () const             { return (PcDesc*)(header_begin() + _scopes_pcs_offset   ); }

   PcDesc* scopes_pcs_end     () const             { return (PcDesc*)(header_begin() + _dependencies_offset); }

   address dependencies_begin () const             { return           header_begin() + _dependencies_offset ; }

   address dependencies_end   () const             { return           header_begin() + _handler_table_offset ; }

   address handler_table_begin() const             { return           header_begin() + _handler_table_offset ; }

   address handler_table_end  () const             { return           header_begin() + _nul_chk_table_offset   ; }

   address nul_chk_table_begin() const             { return           header_begin() + _nul_chk_table_offset ; }

   address nul_chk_table_end  () const             { return           header_begin() + _nmethod_end_offset   ; }

   int code_size         () const                  { return      code_end         () -      code_begin         (); }

   int stub_size         () const                  { return      stub_end         () -      stub_begin         (); }

   int consts_size       () const                  { return      consts_end       () -      consts_begin       (); }

   int scopes_data_size  () const                  { return      scopes_data_end  () -      scopes_data_begin  (); }

   int scopes_pcs_size   () const                  { return (intptr_t)scopes_pcs_end   () - (intptr_t)scopes_pcs_begin   (); }

   int dependencies_size () const                  { return      dependencies_end () -      dependencies_begin (); }

   int handler_table_size() const                  { return      handler_table_end() -      handler_table_begin(); }

   int nul_chk_table_size() const                  { return      nul_chk_table_end() -      nul_chk_table_begin(); }

   int total_size        () const;

   bool code_contains         (address addr) const { return code_begin         () <= addr && addr < code_end         (); }

   bool stub_contains         (address addr) const { return stub_begin         () <= addr && addr < stub_end         (); }

   bool consts_contains       (address addr) const { return consts_begin       () <= addr && addr < consts_end       (); }

   bool scopes_data_contains  (address addr) const { return scopes_data_begin  () <= addr && addr < scopes_data_end  (); }

   bool scopes_pcs_contains   (PcDesc* addr) const { return scopes_pcs_begin   () <= addr && addr < scopes_pcs_end   (); }

   bool handler_table_contains(address addr) const { return handler_table_begin() <= addr && addr < handler_table_end(); }

   bool nul_chk_table_contains(address addr) const { return nul_chk_table_begin() <= addr && addr < nul_chk_table_end(); }

   // entry points

   address entry_point() const                     { return _entry_point;             } // normal entry point

   address verified_entry_point() const            { return _verified_entry_point;    } // if klass is correct

   // flag accessing and manipulation

   bool  is_in_use() const                         { return flags.state == alive; }

   bool  is_alive() const                          { return flags.state == alive || flags.state == not_entrant; }

   bool  is_not_entrant() const                    { return flags.state == not_entrant; }

   bool  is_zombie() const                         { return flags.state == zombie; }

   bool  is_unloaded() const                       { return flags.state == unloaded;   }

   // Make the nmethod non entrant. The nmethod will continue to be alive.

   // It is used when an uncommon trap happens.

   void  make_not_entrant()                        { make_not_entrant_or_zombie(not_entrant); }

   void  make_zombie()                             { make_not_entrant_or_zombie(zombie); }

   // used by jvmti to track if the unload event has been reported

   bool  unload_reported()                         { return _unload_reported; }

   void  set_unload_reported()                     { _unload_reported = true; }

   bool  is_marked_for_deoptimization() const      { return _markedForDeoptimization; }

   void  mark_for_deoptimization()                 { _markedForDeoptimization = true; }

   void  make_unloaded(BoolObjectClosure* is_alive, oop cause);

   bool has_dependencies()                         { return dependencies_size() != 0; }

   void flush_dependencies(BoolObjectClosure* is_alive);

   bool  has_flushed_dependencies()                { return flags.hasFlushedDependencies; }

   void  set_has_flushed_dependencies()            {

     check_safepoint();

     assert(!has_flushed_dependencies(), "should only happen once");

     flags.hasFlushedDependencies = 1;

   }

   bool  is_marked_for_reclamation() const         { return flags.markedForReclamation; }

   void  mark_for_reclamation()                    { check_safepoint(); flags.markedForReclamation = 1; }

   void  unmark_for_reclamation()                  { check_safepoint(); flags.markedForReclamation = 0; }

   bool  has_unsafe_access() const                 { return flags.has_unsafe_access; }

   void  set_has_unsafe_access(bool z)             { flags.has_unsafe_access = z; }

   int   level() const                             { return flags.level; }

   void  set_level(int newLevel)                   { check_safepoint(); flags.level = newLevel; }

   int   comp_level() const                        { return _comp_level; }

   int   version() const                           { return flags.version; }

   void  set_version(int v);

   // Non-perm oop support

   bool  on_scavenge_root_list() const                  { return (_scavenge_root_state & 1) != 0; }

  protected:

   enum { npl_on_list = 0x01, npl_marked = 0x10 };

   void  set_on_scavenge_root_list()                    { _scavenge_root_state = npl_on_list; }

   void  clear_on_scavenge_root_list()                  { _scavenge_root_state = 0; }

   // assertion-checking and pruning logic uses the bits of _scavenge_root_state

 #ifndef PRODUCT

   void  set_scavenge_root_marked()                     { _scavenge_root_state |= npl_marked; }

   void  clear_scavenge_root_marked()                   { _scavenge_root_state &= ~npl_marked; }

   bool  scavenge_root_not_marked()                     { return (_scavenge_root_state &~ npl_on_list) == 0; }

   // N.B. there is no positive marked query, and we only use the not_marked query for asserts.

 #endif //PRODUCT

   nmethod* scavenge_root_link() const                  { return _scavenge_root_link; }

   void     set_scavenge_root_link(nmethod *n)          { _scavenge_root_link = n; }

  public:

   // Sweeper support

   long  stack_traversal_mark()                    { return _stack_traversal_mark; }

   void  set_stack_traversal_mark(long l)          { _stack_traversal_mark = l; }

   // Exception cache support

   ExceptionCache* exception_cache() const         { return _exception_cache; }

   void set_exception_cache(ExceptionCache *ec)    { _exception_cache = ec; }

   address handler_for_exception_and_pc(Handle exception, address pc);

   void add_handler_for_exception_and_pc(Handle exception, address pc, address handler);

   void remove_from_exception_cache(ExceptionCache* ec);

   // implicit exceptions support

   address continuation_for_implicit_exception(address pc);

   // On-stack replacement support

   int   osr_entry_bci() const                     { assert(_entry_bci != InvocationEntryBci, "wrong kind of nmethod"); return _entry_bci; }

   address  osr_entry() const                      { assert(_entry_bci != InvocationEntryBci, "wrong kind of nmethod"); return _osr_entry_point; }

   void  invalidate_osr_method();

   nmethod* osr_link() const                       { return _osr_link; }

   void     set_osr_link(nmethod *n)               { _osr_link = n; }

   // tells whether frames described by this nmethod can be deoptimized

   // note: native wrappers cannot be deoptimized.

   bool can_be_deoptimized() const { return is_java_method(); }

   // Inline cache support

   void clear_inline_caches();

   void cleanup_inline_caches();

   bool inlinecache_check_contains(address addr) const {

     return (addr >= instructions_begin() && addr < verified_entry_point());

   }

   // unlink and deallocate this nmethod

   // Only NMethodSweeper class is expected to use this. NMethodSweeper is not

   // expected to use any other private methods/data in this class.

  protected:

   void flush();

  public:

   // If returning true, it is unsafe to remove this nmethod even though it is a zombie

   // nmethod, since the VM might have a reference to it. Should only be called from a  safepoint.

   bool is_locked_by_vm() const                    { return _lock_count >0; }

   // See comment at definition of _last_seen_on_stack

   void mark_as_seen_on_stack();

   bool can_not_entrant_be_converted();

   // Evolution support. We make old (discarded) compiled methods point to new methodOops.

   void set_method(methodOop method) { _method = method; }

   // GC support

   void do_unloading(BoolObjectClosure* is_alive, OopClosure* keep_alive,

                     bool unloading_occurred);

   bool can_unload(BoolObjectClosure* is_alive, OopClosure* keep_alive,

                   oop* root, bool unloading_occurred);

   void preserve_callee_argument_oops(frame fr, const RegisterMap *reg_map,

                                      OopClosure* f);

   virtual void oops_do(OopClosure* f) { oops_do(f, false); }

   void         oops_do(OopClosure* f, bool do_strong_roots_only);

   bool detect_scavenge_root_oops();

   void verify_scavenge_root_oops() PRODUCT_RETURN;

   bool test_set_oops_do_mark();

   static void oops_do_marking_prologue();

   static void oops_do_marking_epilogue();

   static bool oops_do_marking_is_active() { return _oops_do_mark_nmethods != NULL; }

   DEBUG_ONLY(bool test_oops_do_mark() { return _oops_do_mark_link != NULL; })

   // ScopeDesc for an instruction

   ScopeDesc* scope_desc_at(address pc);

  private:

   ScopeDesc* scope_desc_in(address begin, address end);

   address* orig_pc_addr(const frame* fr ) { return (address*) ((address)fr->unextended_sp() + _orig_pc_offset); }

   PcDesc* find_pc_desc_internal(address pc, bool approximate);

   PcDesc* find_pc_desc(address pc, bool approximate) {

     PcDesc* desc = _pc_desc_cache.last_pc_desc();

     if (desc != NULL && desc->pc_offset() == pc - instructions_begin()) {

       return desc;

     }

     return find_pc_desc_internal(pc, approximate);

   }

  public:

   // ScopeDesc retrieval operation

   PcDesc* pc_desc_at(address pc)   { return find_pc_desc(pc, false); }

   // pc_desc_near returns the first PcDesc at or after the givne pc.

   PcDesc* pc_desc_near(address pc) { return find_pc_desc(pc, true); }

  public:

   // copying of debugging information

   void copy_scopes_pcs(PcDesc* pcs, int count);

   void copy_scopes_data(address buffer, int size);

   // deopt

   // return true is the pc is one would expect if the frame is being deopted.

   bool is_deopt_pc(address pc);

   // Accessor/mutator for the original pc of a frame before a frame was deopted.

   address get_original_pc(const frame* fr) { return *orig_pc_addr(fr); }

   void    set_original_pc(const frame* fr, address pc) { *orig_pc_addr(fr) = pc; }

   // jvmti support:

   void post_compiled_method_load_event();

   // verify operations

   void verify();

   void verify_scopes();

   void verify_interrupt_point(address interrupt_point);

   // printing support

   void print()                          const;

   void print_code();

   void print_relocations()                        PRODUCT_RETURN;

   void print_pcs()                                PRODUCT_RETURN;

   void print_scopes()                             PRODUCT_RETURN;

   void print_dependencies()                       PRODUCT_RETURN;

   void print_value_on(outputStream* st) const     PRODUCT_RETURN;

   void print_calls(outputStream* st)              PRODUCT_RETURN;

   void print_handler_table()                      PRODUCT_RETURN;

   void print_nul_chk_table()                      PRODUCT_RETURN;

   void print_nmethod(bool print_code);

   void print_on(outputStream* st, const char* title) const;

   // Logging

   void log_identity(xmlStream* log) const;

   void log_new_nmethod() const;

   void log_state_change(int state) const;

   // Prints a comment for one native instruction (reloc info, pc desc)

   void print_code_comment_on(outputStream* st, int column, address begin, address end);

   static void print_statistics()                  PRODUCT_RETURN;

   // Compiler task identification.  Note that all OSR methods

   // are numbered in an independent sequence if CICountOSR is true,

   // and native method wrappers are also numbered independently if

   // CICountNative is true.

   int  compile_id() const                         { return _compile_id; }

   const char* compile_kind() const;

   // For debugging

   // CompiledIC*    IC_at(char* p) const;

   // PrimitiveIC*   primitiveIC_at(char* p) const;

   oop embeddedOop_at(address p);

   // tells if any of this method's dependencies have been invalidated

   // (this is expensive!)

   bool check_all_dependencies();

   // tells if this compiled method is dependent on the given changes,

   // and the changes have invalidated it

   bool check_dependency_on(DepChange& changes);

   // Evolution support. Tells if this compiled method is dependent on any of

   // methods m() of class dependee, such that if m() in dependee is replaced,

   // this compiled method will have to be deoptimized.

   bool is_evol_dependent_on(klassOop dependee);

   // Fast breakpoint support. Tells if this compiled method is

   // dependent on the given method. Returns true if this nmethod

   // corresponds to the given method as well.

   bool is_dependent_on_method(methodOop dependee);

   // is it ok to patch at address?

   bool is_patchable_at(address instr_address);

   // UseBiasedLocking support

   ByteSize compiled_synchronized_native_basic_lock_owner_sp_offset() {

     return _compiled_synchronized_native_basic_lock_owner_sp_offset;

   }

   ByteSize compiled_synchronized_native_basic_lock_sp_offset() {

     return _compiled_synchronized_native_basic_lock_sp_offset;

   }

   // support for code generation

   static int verified_entry_point_offset()        { return offset_of(nmethod, _verified_entry_point); }

   static int osr_entry_point_offset()             { return offset_of(nmethod, _osr_entry_point); }

   static int entry_bci_offset()                   { return offset_of(nmethod, _entry_bci); }

 };

 // Locks an nmethod so its code will not get removed, even if it is a zombie/not_entrant method

 class nmethodLocker : public StackObj {

   nmethod* _nm;

   static void lock_nmethod(nmethod* nm);   // note: nm can be NULL

   static void unlock_nmethod(nmethod* nm); // (ditto)

  public:

   nmethodLocker(address pc); // derive nm from pc

   nmethodLocker(nmethod *nm) { _nm = nm; lock_nmethod(_nm); }

   nmethodLocker() { _nm = NULL; }

   ~nmethodLocker() { unlock_nmethod(_nm); }

   nmethod* code() { return _nm; }

   void set_code(nmethod* new_nm) {

     unlock_nmethod(_nm);   // note:  This works even if _nm==new_nm.

     _nm = new_nm;

     lock_nmethod(_nm);

   }

 };