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* version 2 for more details (a copy is included in the LICENSE file that
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#ifndef SHARE_VM_CODE_VTABLESTUBS_HPP
#define SHARE_VM_CODE_VTABLESTUBS_HPP
#include "asm/macroAssembler.hpp"
#include "code/vmreg.hpp"
#include "memory/allocation.hpp"
// A VtableStub holds an individual code stub for a pair (vtable index, #args) for either itables or vtables
// There's a one-to-one relationship between a VtableStub and such a pair.
// A word on VtableStub sizing:
// Such a vtable/itable stub consists of the instance data
// and an immediately following CodeBuffer.
// Unfortunately, the required space for the code buffer varies, depending on
// the setting of compile time macros (PRODUCT, ASSERT, ...) and of command line
// parameters. Actual data may have an influence on the size as well.
//
// A simple approximation for the VtableStub size would be to just take a value
// "large enough" for all circumstances - a worst case estimate.
// As there can exist many stubs - and they never go away - we certainly don't
// want to waste more code cache space than absolutely necessary.
//
// We need a different approach which, as far as possible, should be independent
// from or adaptive to code size variations. These variations may be caused by
// changed compile time or run time switches as well as by changed emitter code.
//
// Here is the idea:
// For the first stub we generate, we allocate a "large enough" code buffer.
// Once all instructions are emitted, we know the actual size of the stub.
// Remembering that size allows us to allocate a tightly matching code buffer
// for all subsequent stubs. That covers all "static variance", i.e. all variance
// that is due to compile time macros, command line parameters, machine capabilities,
// and other influences which are immutable for the life span of the vm.
//
// Life isn't always that easy. Code size may depend on actual data, "load constant"
// being an example for that. All code segments with such "dynamic variance" require
// additional care. We need to know or estimate the worst case code size for each
// such segment. With that knowledge, we can maintain a "slop counter" in the
// platform-specific stub emitters. It accumulates the difference between worst-case
// and actual code size. When the stub is fully generated, the actual stub size is
// adjusted (increased) by the slop counter value.
//
// As a result, we allocate all but the first code buffers with the same, tightly matching size.
//
// VtableStubs creates the code stubs for compiled calls through vtables.
// There is one stub per (vtable index, args_size) pair, and the stubs are
// never deallocated. They don't need to be GCed because they contain no oops.
class VtableStub;
class VtableStubs : AllStatic {
public: // N must be public (some compilers need this for _table)
enum {
N = 256, // size of stub table; must be power of two
mask = N - 1
};
private:
friend class VtableStub;
static VtableStub* _table[N]; // table of existing stubs
static int _number_of_vtable_stubs; // number of stubs created so far (for statistics)
static int _vtab_stub_size; // current size estimate for vtable stub (quasi-constant)
static int _itab_stub_size; // current size estimate for itable stub (quasi-constant)
static VtableStub* create_vtable_stub(int vtable_index);
static VtableStub* create_itable_stub(int vtable_index);
static VtableStub* lookup (bool is_vtable_stub, int vtable_index);
static void enter (bool is_vtable_stub, int vtable_index, VtableStub* s);
static inline uint hash (bool is_vtable_stub, int vtable_index);
static address find_stub (bool is_vtable_stub, int vtable_index);
static void bookkeeping(MacroAssembler* masm, outputStream* out, VtableStub* s,
address npe_addr, address ame_addr, bool is_vtable_stub,
int index, int slop_bytes, int index_dependent_slop);
static int code_size_limit(bool is_vtable_stub);
static void check_and_set_size_limit(bool is_vtable_stub,
int code_size,
int padding);
public:
static address find_vtable_stub(int vtable_index) { return find_stub(true, vtable_index); }
static address find_itable_stub(int itable_index) { return find_stub(false, itable_index); }
static VtableStub* entry_point(address pc); // vtable stub entry point for a pc
static bool contains(address pc); // is pc within any stub?
static VtableStub* stub_containing(address pc); // stub containing pc or NULL
static int number_of_vtable_stubs() { return _number_of_vtable_stubs; }
static void initialize();
static void vtable_stub_do(void f(VtableStub*)); // iterates over all vtable stubs
};
class VtableStub {
private:
friend class VtableStubs;
static address _chunk; // For allocation
static address _chunk_end; // For allocation
static VMReg _receiver_location; // Where to find receiver
VtableStub* _next; // Pointer to next entry in hash table
const short _index; // vtable index
short _ame_offset; // Where an AbstractMethodError might occur
short _npe_offset; // Where a NullPointerException might occur
bool _is_vtable_stub; // True if vtable stub, false, is itable stub
/* code follows here */ // The vtableStub code
void* operator new(size_t size, int code_size) throw();
VtableStub(bool is_vtable_stub, int index)
: _next(NULL), _index(index), _ame_offset(-1), _npe_offset(-1),
_is_vtable_stub(is_vtable_stub) {}
VtableStub* next() const { return _next; }
int index() const { return _index; }
static VMReg receiver_location() { return _receiver_location; }
void set_next(VtableStub* n) { _next = n; }
public:
address code_begin() const { return (address)(this + 1); }
address code_end() const { return code_begin() + VtableStubs::code_size_limit(_is_vtable_stub); }
address entry_point() const { return code_begin(); }
static int entry_offset() { return sizeof(class VtableStub); }
bool matches(bool is_vtable_stub, int index) const {
return _index == index && _is_vtable_stub == is_vtable_stub;
}
bool contains(address pc) const { return code_begin() <= pc && pc < code_end(); }
private:
void set_exception_points(address npe_addr, address ame_addr) {
_npe_offset = npe_addr - code_begin();
_ame_offset = ame_addr - code_begin();
assert(is_abstract_method_error(ame_addr), "offset must be correct");
assert(is_null_pointer_exception(npe_addr), "offset must be correct");
assert(!is_abstract_method_error(npe_addr), "offset must be correct");
assert(!is_null_pointer_exception(ame_addr), "offset must be correct");
}
// platform-dependent routines
static int pd_code_alignment();
// CNC: Removed because vtable stubs are now made with an ideal graph
// static bool pd_disregard_arg_size();
static void align_chunk() {
uintptr_t off = (uintptr_t)( _chunk + sizeof(VtableStub) ) % pd_code_alignment();
if (off != 0) _chunk += pd_code_alignment() - off;
}
public:
// Query
bool is_itable_stub() { return !_is_vtable_stub; }
bool is_vtable_stub() { return _is_vtable_stub; }
bool is_abstract_method_error(address epc) { return epc == code_begin()+_ame_offset; }
bool is_null_pointer_exception(address epc) { return epc == code_begin()+_npe_offset; }
void print_on(outputStream* st) const;
void print() const { print_on(tty); }
};
#endif // SHARE_VM_CODE_VTABLESTUBS_HPP