1 /*
   2  * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #ifndef SHARE_CODE_VTABLESTUBS_HPP
  26 #define SHARE_CODE_VTABLESTUBS_HPP
  27 
  28 #include "asm/macroAssembler.hpp"
  29 #include "code/vmreg.hpp"
  30 #include "memory/allocation.hpp"
  31 
  32 // A VtableStub holds an individual code stub for a pair (vtable index, #args) for either itables or vtables
  33 // There's a one-to-one relationship between a VtableStub and such a pair.
  34 
  35 // A word on VtableStub sizing:
  36 //   Such a vtable/itable stub consists of the instance data
  37 //   and an immediately following CodeBuffer.
  38 //   Unfortunately, the required space for the code buffer varies, depending on
  39 //   the setting of compile time macros (PRODUCT, ASSERT, ...) and of command line
  40 //   parameters. Actual data may have an influence on the size as well.
  41 //
  42 //   A simple approximation for the VtableStub size would be to just take a value
  43 //   "large enough" for all circumstances - a worst case estimate.
  44 //   As there can exist many stubs - and they never go away - we certainly don't
  45 //   want to waste more code cache space than absolutely necessary.
  46 //
  47 //   We need a different approach which, as far as possible, should be independent
  48 //   from or adaptive to code size variations. These variations may be caused by
  49 //   changed compile time or run time switches as well as by changed emitter code.
  50 //
  51 //   Here is the idea:
  52 //   For the first stub we generate, we allocate a "large enough" code buffer.
  53 //   Once all instructions are emitted, we know the actual size of the stub.
  54 //   Remembering that size allows us to allocate a tightly matching code buffer
  55 //   for all subsequent stubs. That covers all "static variance", i.e. all variance
  56 //   that is due to compile time macros, command line parameters, machine capabilities,
  57 //   and other influences which are immutable for the life span of the vm.
  58 //
  59 //   Life isn't always that easy. Code size may depend on actual data, "load constant"
  60 //   being an example for that. All code segments with such "dynamic variance" require
  61 //   additional care. We need to know or estimate the worst case code size for each
  62 //   such segment. With that knowledge, we can maintain a "slop counter" in the
  63 //   platform-specific stub emitters. It accumulates the difference between worst-case
  64 //   and actual code size. When the stub is fully generated, the actual stub size is
  65 //   adjusted (increased) by the slop counter value.
  66 //
  67 //   As a result, we allocate all but the first code buffers with the same, tightly matching size.
  68 //
  69 
  70 // VtableStubs creates the code stubs for compiled calls through vtables.
  71 // There is one stub per (vtable index, args_size) pair, and the stubs are
  72 // never deallocated. They don't need to be GCed because they contain no oops.
  73 class VtableStub;
  74 
  75 class VtableStubs : AllStatic {
  76  public:                                         // N must be public (some compilers need this for _table)
  77   enum {
  78     N    = 256,                                  // size of stub table; must be power of two
  79     mask = N - 1
  80   };
  81 
  82  private:
  83   friend class VtableStub;
  84   static VtableStub* _table[N];                  // table of existing stubs
  85   static int         _number_of_vtable_stubs;    // number of stubs created so far (for statistics)
  86   static int         _vtab_stub_size;            // current size estimate for vtable stub (quasi-constant)
  87   static int         _itab_stub_size;            // current size estimate for itable stub (quasi-constant)
  88 
  89   static VtableStub* create_vtable_stub(int vtable_index);
  90   static VtableStub* create_itable_stub(int vtable_index);
  91   static VtableStub* lookup            (bool is_vtable_stub, int vtable_index);
  92   static void        enter             (bool is_vtable_stub, int vtable_index, VtableStub* s);
  93   static inline uint hash              (bool is_vtable_stub, int vtable_index);
  94   static address     find_stub         (bool is_vtable_stub, int vtable_index);
  95   static void        bookkeeping(MacroAssembler* masm, outputStream* out, VtableStub* s,
  96                                  address npe_addr, address ame_addr,   bool is_vtable_stub,
  97                                  int     index,    int     slop_bytes, int  index_dependent_slop);
  98   static int         code_size_limit(bool is_vtable_stub);
  99   static void        check_and_set_size_limit(bool is_vtable_stub,
 100                                               int   code_size,
 101                                               int   padding);
 102 
 103  public:
 104   static address     find_vtable_stub(int vtable_index) { return find_stub(true,  vtable_index); }
 105   static address     find_itable_stub(int itable_index) { return find_stub(false, itable_index); }
 106 
 107   static VtableStub* entry_point(address pc);                        // vtable stub entry point for a pc
 108   static bool        contains(address pc);                           // is pc within any stub?
 109   static VtableStub* stub_containing(address pc);                    // stub containing pc or NULL
 110   static int         number_of_vtable_stubs() { return _number_of_vtable_stubs; }
 111   static void        initialize();
 112   static void        vtable_stub_do(void f(VtableStub*));            // iterates over all vtable stubs
 113 };
 114 
 115 
 116 class VtableStub {
 117  private:
 118   friend class VtableStubs;
 119 
 120   static address _chunk;             // For allocation
 121   static address _chunk_end;         // For allocation
 122   static VMReg   _receiver_location; // Where to find receiver
 123 
 124   VtableStub*    _next;              // Pointer to next entry in hash table
 125   const short    _index;             // vtable index
 126   short          _ame_offset;        // Where an AbstractMethodError might occur
 127   short          _npe_offset;        // Where a NullPointerException might occur
 128   bool           _is_vtable_stub;    // True if vtable stub, false, is itable stub
 129   /* code follows here */            // The vtableStub code
 130 
 131   void* operator new(size_t size, int code_size) throw();
 132 
 133   VtableStub(bool is_vtable_stub, int index)
 134         : _next(NULL), _index(index), _ame_offset(-1), _npe_offset(-1),
 135           _is_vtable_stub(is_vtable_stub) {}
 136   VtableStub* next() const                       { return _next; }
 137   int index() const                              { return _index; }
 138   static VMReg receiver_location()               { return _receiver_location; }
 139   void set_next(VtableStub* n)                   { _next = n; }
 140 
 141  public:
 142   address code_begin() const                     { return (address)(this + 1); }
 143   address code_end() const                       { return code_begin() + VtableStubs::code_size_limit(_is_vtable_stub); }
 144   address entry_point() const                    { return code_begin(); }
 145   static int entry_offset()                      { return sizeof(class VtableStub); }
 146 
 147   bool matches(bool is_vtable_stub, int index) const {
 148     return _index == index && _is_vtable_stub == is_vtable_stub;
 149   }
 150   bool contains(address pc) const                { return code_begin() <= pc && pc < code_end(); }
 151 
 152  private:
 153   void set_exception_points(address npe_addr, address ame_addr) {
 154     _npe_offset = npe_addr - code_begin();
 155     _ame_offset = ame_addr - code_begin();
 156     assert(is_abstract_method_error(ame_addr),   "offset must be correct");
 157     assert(is_null_pointer_exception(npe_addr),  "offset must be correct");
 158     assert(!is_abstract_method_error(npe_addr),  "offset must be correct");
 159     assert(!is_null_pointer_exception(ame_addr), "offset must be correct");
 160   }
 161 
 162   // platform-dependent routines
 163   static int  pd_code_alignment();
 164   // CNC: Removed because vtable stubs are now made with an ideal graph
 165   // static bool pd_disregard_arg_size();
 166 
 167   static void align_chunk() {
 168     uintptr_t off = (uintptr_t)( _chunk + sizeof(VtableStub) ) % pd_code_alignment();
 169     if (off != 0)  _chunk += pd_code_alignment() - off;
 170   }
 171 
 172  public:
 173   // Query
 174   bool is_itable_stub()                          { return !_is_vtable_stub; }
 175   bool is_vtable_stub()                          { return  _is_vtable_stub; }
 176   bool is_abstract_method_error(address epc)     { return epc == code_begin()+_ame_offset; }
 177   bool is_null_pointer_exception(address epc)    { return epc == code_begin()+_npe_offset; }
 178 
 179   void print_on(outputStream* st) const;
 180   void print() const;
 181 
 182 };
 183 
 184 #endif // SHARE_CODE_VTABLESTUBS_HPP