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*/
// this function computes the vtable size (including the size needed for miranda // methods) and the number of miranda methods in this class. // Note on Miranda methods: Let's say there is a class C that implements // interface I, and none of C's superclasses implements I. // Let's say there is an abstract method m in I that neither C // nor any of its super classes implement (i.e there is no method of any access, // with the same name and signature as m), then m is a Miranda method which is // entered as a public abstract method in C's vtable. From then on it should // treated as any other public method in C for method over-ride purposes. void klassVtable::compute_vtable_size_and_num_mirandas( int* vtable_length_ret, int* num_new_mirandas,
GrowableArray<Method*>* all_mirandas, const Klass* super,
Array<Method*>* methods, AccessFlags class_flags, u2 major_version,
Handle classloader, Symbol* classname, Array<InstanceKlass*>* local_interfaces) {
NoSafepointVerifier nsv;
// set up default result values int vtable_length = 0;
// start off with super's vtable length
vtable_length = super == NULL ? 0 : super->vtable_length();
// go thru each method in the methods table to see if it needs a new entry int len = methods->length(); for (int i = 0; i < len; i++) {
Method* method = methods->at(i);
if (needs_new_vtable_entry(method, super, classloader, classname, class_flags, major_version)) {
assert(!method->is_private(), "private methods should not need a vtable entry");
vtable_length += vtableEntry::size(); // we need a new entry
}
}
GrowableArray<Method*> new_mirandas(20); // compute the number of mirandas methods that must be added to the end
get_mirandas(&new_mirandas, all_mirandas, super, methods, NULL, local_interfaces,
class_flags.is_interface());
*num_new_mirandas = new_mirandas.length();
// Interfaces do not need interface methods in their vtables // This includes miranda methods and during later processing, default methods if (!class_flags.is_interface()) {
vtable_length += *num_new_mirandas * vtableEntry::size();
}
if (Universe::is_bootstrapping() && vtable_length == 0) { // array classes don't have their superclass set correctly during // bootstrapping
vtable_length = Universe::base_vtable_size();
}
if (super == NULL && vtable_length != Universe::base_vtable_size()) { if (Universe::is_bootstrapping()) { // Someone is attempting to override java.lang.Object incorrectly on the // bootclasspath. The JVM cannot recover from this error including throwing // an exception
vm_exit_during_initialization("Incompatible definition of java.lang.Object");
} else { // Someone is attempting to redefine java.lang.Object incorrectly. The // only way this should happen is from // SystemDictionary::resolve_from_stream(), which will detect this later // and throw a security exception. So don't assert here to let // the exception occur.
vtable_length = Universe::base_vtable_size();
}
}
assert(vtable_length % vtableEntry::size() == 0, "bad vtable length");
assert(vtable_length >= Universe::base_vtable_size(), "vtable too small");
*vtable_length_ret = vtable_length;
}
// Copy super class's vtable to the first part (prefix) of this class's vtable, // and return the number of entries copied. Expects that 'super' is the Java // super class (arrays can have "array" super classes that must be skipped). int klassVtable::initialize_from_super(Klass* super) { if (super == NULL) { return 0;
} elseif (is_preinitialized_vtable()) { // A shared class' vtable is preinitialized at dump time. No need to copy // methods from super class for shared class, as that was already done // during archiving time. However, if Jvmti has redefined a class, // copy super class's vtable in case the super class has changed. return super->vtable().length();
} else { // copy methods from superKlass
klassVtable superVtable = super->vtable();
assert(superVtable.length() <= _length, "vtable too short"); #ifdef ASSERT
superVtable.verify(tty, true); #endif
superVtable.copy_vtable_to(table()); if (log_develop_is_enabled(Trace, vtables)) {
ResourceMark rm;
log_develop_trace(vtables)("copy vtable from %s to %s size %d",
super->internal_name(), klass()->internal_name(),
_length);
} return superVtable.length();
}
}
if (Universe::is_bootstrapping()) {
assert(!is_shared, "sanity"); // just clear everything for (int i = 0; i < _length; i++) table()[i].clear(); return;
}
int super_vtable_len = initialize_from_super(super); if (_klass->is_array_klass()) {
assert(super_vtable_len == _length, "arrays shouldn't introduce new methods");
} else {
assert(_klass->is_instance_klass(), "must be InstanceKlass");
Array<Method*>* methods = ik()->methods(); int len = methods->length(); int initialized = super_vtable_len;
// Check each of this class's methods against super; // if override, replace in copy of super vtable, otherwise append to end for (int i = 0; i < len; i++) { // update_inherited_vtable can stop for gc - ensure using handles
methodHandle mh(current, methods->at(i));
if (needs_new_entry) {
put_method_at(mh(), initialized);
mh->set_vtable_index(initialized); // set primary vtable index
initialized++;
}
}
// update vtable with default_methods
Array<Method*>* default_methods = ik()->default_methods(); if (default_methods != NULL) {
len = default_methods->length(); if (len > 0) {
Array<int>* def_vtable_indices = ik()->default_vtable_indices();
assert(def_vtable_indices != NULL, "should be created");
assert(def_vtable_indices->length() == len, "reinit vtable len?"); for (int i = 0; i < len; i++) { bool needs_new_entry;
{ // Reduce the scope of this handle so that it is fetched again. // The methodHandle keeps it from being deleted by RedefineClasses while // we're using it.
methodHandle mh(current, default_methods->at(i));
assert(!mh->is_private(), "private interface method in the default method list");
needs_new_entry = update_inherited_vtable(current, mh, super_vtable_len, i, supers);
}
// needs new entry if (needs_new_entry) { // Refetch this default method in case of redefinition that might // happen during constraint checking in the update_inherited_vtable call above.
Method* method = default_methods->at(i);
put_method_at(method, initialized); if (is_preinitialized_vtable()) { // At runtime initialize_vtable is rerun for a shared class // (loaded by the non-boot loader) as part of link_class_impl(). // The dumptime vtable index should be the same as the runtime index.
assert(def_vtable_indices->at(i) == initialized, "dump time vtable index is different from runtime index");
} else {
def_vtable_indices->at_put(i, initialized); //set vtable index
}
initialized++;
}
}
}
}
// add miranda methods; it will also return the updated initialized // Interfaces do not need interface methods in their vtables // This includes miranda methods and during later processing, default methods if (!ik()->is_interface()) {
initialized = fill_in_mirandas(current, initialized);
}
// In class hierarchies where the accessibility is not increasing (i.e., going from private -> // package_private -> public/protected), the vtable might actually be smaller than our initial // calculation, for classfile versions for which we do not do transitive override // calculations. if (ik()->major_version() >= VTABLE_TRANSITIVE_OVERRIDE_VERSION) {
assert(initialized == _length, "vtable initialization failed");
} else {
assert(initialized <= _length, "vtable initialization failed"); for(;initialized < _length; initialized++) {
table()[initialized].clear();
}
}
NOT_PRODUCT(verify(tty, true));
}
}
// Returns true iff super_method can be overridden by a method in targetclassname // See JLS 8.4.8.1 // Assumes name-signature match // Note that the InstanceKlass of the method in the targetclassname has not always been created yet staticbool can_be_overridden(Method* super_method, Handle targetclassloader, Symbol* targetclassname) { // Private methods can not be overridden
assert(!super_method->is_private(), "shouldn't call with a private method");
// If super method is accessible, then override if ((super_method->is_protected()) ||
(super_method->is_public())) { returntrue;
} // Package-private methods are not inherited outside of package
assert(super_method->is_package_private(), "must be package private"); return(super_method->method_holder()->is_same_class_package(targetclassloader(), targetclassname));
}
// Called for cases where a method does not override its superclass' vtable entry // For bytecodes not produced by javac together it is possible that a method does not override // the superclass's method, but might indirectly override a super-super class's vtable entry // If none found, return a null superk, else return the superk of the method this does override // For public and protected methods: if they override a superclass, they will // also be overridden themselves appropriately. // Private methods do not override, and are not overridden and are not in the vtable. // Package Private methods are trickier: // e.g. P1.A, pub m // P2.B extends A, package private m // P1.C extends B, public m // P1.C.m needs to override P1.A.m and can not override P2.B.m // Therefore: all package private methods need their own vtable entries for // them to be the root of an inheritance overriding decision // Package private methods may also override other vtable entries
InstanceKlass* klassVtable::find_transitive_override(InstanceKlass* initialsuper, const methodHandle& target_method, int vtable_index,
Handle target_loader,
Symbol* target_classname) {
if (can_be_overridden(super_method, target_loader, target_classname)) { if (log_develop_is_enabled(Trace, vtables)) {
ResourceMark rm;
LogTarget(Trace, vtables) lt;
LogStream ls(lt); char* sig = target_method()->name_and_sig_as_C_string();
ls.print("transitive overriding superclass %s with %s index %d, original flags: ",
super_method->method_holder()->internal_name(),
sig, vtable_index);
super_method->print_linkage_flags(&ls);
ls.print("overriders flags: ");
target_method->print_linkage_flags(&ls);
ls.cr();
}
break; // return found superk
}
} else { // super class has no vtable entry here, stop transitive search
superk = (InstanceKlass*)NULL; break;
} // if no override found yet, continue to search up
superk = superk->super() == NULL ? NULL : InstanceKlass::cast(superk->super());
}
return superk;
}
staticvoid log_vtables(int i, bool overrides, const methodHandle& target_method,
Klass* target_klass, Method* super_method) { #ifndef PRODUCT if (log_develop_is_enabled(Trace, vtables)) {
ResourceMark rm;
LogTarget(Trace, vtables) lt;
LogStream ls(lt); char* sig = target_method()->name_and_sig_as_C_string(); if (overrides) {
ls.print("overriding with %s index %d, original flags: ",
sig, i);
} else {
ls.print("NOT overriding with %s index %d, original flags: ",
sig, i);
}
super_method->print_linkage_flags(&ls);
ls.print("overriders flags: ");
target_method->print_linkage_flags(&ls);
ls.cr();
} #endif
}
// Update child's copy of super vtable for overrides // OR return true if a new vtable entry is required. // Only called for InstanceKlass's, i.e. not for arrays // If that changed, could not use _klass as handle for klass bool klassVtable::update_inherited_vtable(Thread* current, const methodHandle& target_method, int super_vtable_len, int default_index,
GrowableArray<InstanceKlass*>* supers) { bool allocate_new = true;
// default methods are non-private concrete methods in superinterfaces which are added // to the vtable with their real method_holder. // Since vtable and itable indices share the same storage, don't touch // the default method's real vtable/itable index. // default_vtable_indices stores the vtable value relative to this inheritor if (default_index >= 0 ) {
is_default = true;
def_vtable_indices = klass->default_vtable_indices();
assert(!target_method->is_private(), "private interface method flagged as default");
assert(def_vtable_indices != NULL, "def vtable alloc?");
assert(default_index <= def_vtable_indices->length(), "def vtable len?");
} else {
assert(klass == target_method->method_holder(), "caller resp."); // Initialize the method's vtable index to "nonvirtual". // If we allocate a vtable entry, we will update it to a non-negative number.
target_method->set_vtable_index(Method::nonvirtual_vtable_index);
}
// Private, static and <init> methods are never in if (target_method->is_private() || target_method->is_static() ||
(target_method->name()->fast_compare(vmSymbols::object_initializer_name()) == 0)) { returnfalse;
}
if (target_method->is_final_method(klass->access_flags())) { // a final method never needs a new entry; final methods can be statically // resolved and they have to be present in the vtable only if they override // a super's method, in which case they re-use its entry
allocate_new = false;
} elseif (klass->is_interface()) {
allocate_new = false; // see note below in needs_new_vtable_entry // An interface never allocates new vtable slots, only inherits old ones. // This method will either be assigned its own itable index later, // or be assigned an inherited vtable index in the loop below. // default methods inherited by classes store their vtable indices // in the inheritor's default_vtable_indices. // default methods inherited by interfaces may already have a // valid itable index, if so, don't change it. // Overpass methods in an interface will be assigned an itable index later // by an inheriting class. if ((!is_default || !target_method->has_itable_index())) {
target_method->set_vtable_index(Method::pending_itable_index);
}
}
// we need a new entry if there is no superclass
Klass* super = klass->super(); if (super == NULL) { return allocate_new;
}
// search through the vtable and update overridden entries // Since check_signature_loaders acquires SystemDictionary_lock // which can block for gc, once we are in this loop, use handles // For classfiles built with >= jdk7, we now look for transitive overrides
Symbol* name = target_method->name();
Symbol* signature = target_method->signature();
Symbol* target_classname = target_klass->name(); for(int i = 0; i < super_vtable_len; i++) {
Method* super_method; if (is_preinitialized_vtable()) { // If this is a shared class, the vtable is already in the final state (fully // initialized). Need to look at the super's vtable.
klassVtable superVtable = super->vtable();
super_method = superVtable.method_at(i);
} else {
super_method = method_at(i);
} // Check if method name matches. Ignore match if klass is an interface and the // matching method is a non-public java.lang.Object method. (See JVMS 5.4.3.4) // This is safe because the method at this slot should never get invoked. // (TBD: put in a method to throw NoSuchMethodError if this slot is ever used.) if (super_method->name() == name && super_method->signature() == signature &&
(!klass->is_interface() ||
!SystemDictionary::is_nonpublic_Object_method(super_method))) {
// get super_klass for method_holder for the found method
InstanceKlass* super_klass = super_method->method_holder();
// Whether the method is being overridden bool overrides = false;
// private methods are also never overridden if (!super_method->is_private() &&
(is_default ||
can_be_overridden(super_method, target_loader, target_classname) ||
(klass->major_version() >= VTABLE_TRANSITIVE_OVERRIDE_VERSION &&
(super_klass = find_transitive_override(super_klass,
target_method, i, target_loader,
target_classname)) != NULL))) {
// Package private methods always need a new entry to root their own // overriding. They may also override other methods. if (!target_method->is_package_private()) {
allocate_new = false;
}
// Set the vtable index before the constraint check safepoint, which potentially // redefines this method if this method is a default method belonging to a // super class or interface.
put_method_at(target_method(), i); // Save super for constraint checking. if (supers != NULL) {
supers->at_put(i, super_klass);
}
overrides = true; if (!is_default) {
target_method->set_vtable_index(i);
} else { if (def_vtable_indices != NULL) { if (is_preinitialized_vtable()) { // At runtime initialize_vtable is rerun as part of link_class_impl() // for a shared class loaded by the non-boot loader. // The dumptime vtable index should be the same as the runtime index.
assert(def_vtable_indices->at(default_index) == i, "dump time vtable index is different from runtime index");
} else {
def_vtable_indices->at_put(default_index, i);
}
}
assert(super_method->is_default_method() || super_method->is_overpass()
|| super_method->is_abstract(), "default override error");
}
} else {
overrides = false;
}
log_vtables(i, overrides, target_method, target_klass, super_method);
}
} return allocate_new;
}
void klassVtable::put_method_at(Method* m, int index) {
assert(!m->is_private(), "private methods should not be in vtable");
JVMTI_ONLY(assert(!m->is_old() || ik()->is_being_redefined(), "old methods should not be in vtable")); if (is_preinitialized_vtable()) { // At runtime initialize_vtable is rerun as part of link_class_impl() // for shared class loaded by the non-boot loader to obtain the loader // constraints based on the runtime classloaders' context. The dumptime // method at the vtable index should be the same as the runtime method.
assert(table()[index].method() == m, "archived method is different from the runtime method");
} else { if (log_develop_is_enabled(Trace, vtables)) {
ResourceMark rm;
LogTarget(Trace, vtables) lt;
LogStream ls(lt); constchar* sig = (m != NULL) ? m->name_and_sig_as_C_string() : "";
ls.print("adding %s at index %d, flags: ", sig, index); if (m != NULL) {
m->print_linkage_flags(&ls);
}
ls.cr();
}
table()[index].set(m);
}
}
void klassVtable::check_constraints(GrowableArray<InstanceKlass*>* supers, TRAPS) {
assert(supers->length() == length(), "lengths are different"); // For each method in the vtable, check constraints against any super class // if overridden. for (int i = 0; i < length(); i++) {
methodHandle target_method(THREAD, unchecked_method_at(i));
InstanceKlass* super_klass = supers->at(i); if (target_method() != NULL && super_klass != NULL) { // Do not check loader constraints for overpass methods because overpass // methods are created by the jvm to throw exceptions. if (!target_method->is_overpass()) { // Override vtable entry if passes loader constraint check // if loader constraint checking requested // No need to visit his super, since he and his super // have already made any needed loader constraints. // Since loader constraints are transitive, it is enough // to link to the first super, and we get all the others.
Handle super_loader(THREAD, super_klass->class_loader());
InstanceKlass* target_klass = target_method->method_holder();
Handle target_loader(THREAD, target_klass->class_loader());
if (target_loader() != super_loader()) {
ResourceMark rm(THREAD);
Symbol* failed_type_symbol =
SystemDictionary::check_signature_loaders(target_method->signature(),
_klass,
target_loader, super_loader, true); if (failed_type_symbol != NULL) {
stringStream ss;
ss.print("loader constraint violation for class %s: when selecting " "overriding method '", _klass->external_name());
target_method->print_external_name(&ss),
ss.print("' the class loader %s of the " "selected method's type %s, and the class loader %s for its super " "type %s have different Class objects for the type %s used in the signature (%s; %s)",
target_klass->class_loader_data()->loader_name_and_id(),
target_klass->external_name(),
super_klass->class_loader_data()->loader_name_and_id(),
super_klass->external_name(),
failed_type_symbol->as_klass_external_name(),
target_klass->class_in_module_of_loader(false, true),
super_klass->class_in_module_of_loader(false, true));
THROW_MSG(vmSymbols::java_lang_LinkageError(), ss.as_string());
}
}
}
}
}
}
void klassVtable::initialize_vtable_and_check_constraints(TRAPS) { // Save a superclass from each vtable entry to do constraint checking
ResourceMark rm(THREAD);
GrowableArray<InstanceKlass*>* supers = new GrowableArray<InstanceKlass*>(_length, _length, NULL);
initialize_vtable(supers);
check_constraints(supers, CHECK);
}
// Find out if a method "m" with superclass "super", loader "classloader" and // name "classname" needs a new vtable entry. Let P be a class package defined // by "classloader" and "classname". // NOTE: The logic used here is very similar to the one used for computing // the vtables indices for a method. We cannot directly use that function because, // we allocate the InstanceKlass at load time, and that requires that the // superclass has been loaded. // However, the vtable entries are filled in at link time, and therefore // the superclass' vtable may not yet have been filled in. bool klassVtable::needs_new_vtable_entry(Method* target_method, const Klass* super,
Handle classloader,
Symbol* classname,
AccessFlags class_flags,
u2 major_version) { if (class_flags.is_interface()) { // Interfaces do not use vtables, except for java.lang.Object methods, // so there is no point to assigning // a vtable index to any of their local methods. If we refrain from doing this, // we can use Method::_vtable_index to hold the itable index returnfalse;
}
if (target_method->is_final_method(class_flags) || // a final method never needs a new entry; final methods can be statically // resolved and they have to be present in the vtable only if they override // a super's method, in which case they re-use its entry
(target_method->is_private()) || // private methods don't need to be in vtable
(target_method->is_static()) || // static methods don't need to be in vtable
(target_method->name()->fast_compare(vmSymbols::object_initializer_name()) == 0) // <init> is never called dynamically-bound
) { returnfalse;
}
// Concrete interface methods do not need new entries, they override // abstract method entries using default inheritance rules if (target_method->method_holder() != NULL &&
target_method->method_holder()->is_interface() &&
!target_method->is_abstract()) {
assert(target_method->is_default_method(), "unexpected interface method type"); returnfalse;
}
// we need a new entry if there is no superclass if (super == NULL) { returntrue;
}
// Package private methods always need a new entry to root their own // overriding. This allows transitive overriding to work. if (target_method->is_package_private()) { returntrue;
}
// search through the super class hierarchy to see if we need // a new entry
Symbol* name = target_method->name();
Symbol* signature = target_method->signature(); const Klass* k = super;
Method* super_method = NULL;
InstanceKlass *holder = NULL;
Method* recheck_method = NULL; bool found_pkg_prvt_method = false; while (k != NULL) { // lookup through the hierarchy for a method with matching name and sign.
super_method = InstanceKlass::cast(k)->lookup_method(name, signature); if (super_method == NULL) { break; // we still have to search for a matching miranda method
} // get the class holding the matching method
InstanceKlass* superk = super_method->method_holder(); // we want only instance method matches // ignore private methods found via lookup_method since they do not participate in overriding, // and since we do override around them: e.g. a.m pub/b.m private/c.m pub, // ignore private, c.m pub does override a.m pub // For classes that were not javac'd together, we also do transitive overriding around // methods that have less accessibility if (!super_method->is_static() &&
!super_method->is_private()) { if (can_be_overridden(super_method, classloader, classname)) { returnfalse; // else keep looking for transitive overrides
} // If we get here then one of the super classes has a package private method // that will not get overridden because it is in a different package. But, // that package private method does "override" any matching methods in super // interfaces, so there will be no miranda vtable entry created. So, set flag // to TRUE for use below, in case there are no methods in super classes that // this target method overrides.
assert(super_method->is_package_private(), "super_method must be package private");
assert(!superk->is_same_class_package(classloader(), classname), "Must be different packages");
found_pkg_prvt_method = true;
}
// Start with lookup result and continue to search up, for versions supporting transitive override if (major_version >= VTABLE_TRANSITIVE_OVERRIDE_VERSION) {
k = superk->super(); // haven't found an override match yet; continue to look
} else { break;
}
}
// If found_pkg_prvt_method is set, then the ONLY matching method in the // superclasses is package private in another package. That matching method will // prevent a miranda vtable entry from being created. Because the target method can not // override the package private method in another package, then it needs to be the root // for its own vtable entry. if (found_pkg_prvt_method) { returntrue;
}
// if the target method is public or protected it may have a matching // miranda method in the super, whose entry it should re-use. // Actually, to handle cases that javac would not generate, we need // this check for all access permissions. const InstanceKlass *sk = InstanceKlass::cast(super); if (sk->has_miranda_methods()) { if (sk->lookup_method_in_all_interfaces(name, signature, Klass::DefaultsLookupMode::find) != NULL) { returnfalse; // found a matching miranda; we do not need a new entry
}
} returntrue; // found no match; we need a new entry
}
// Support for miranda methods
// get the vtable index of a miranda method with matching "name" and "signature" int klassVtable::index_of_miranda(Symbol* name, Symbol* signature) { // search from the bottom, might be faster for (int i = (length() - 1); i >= 0; i--) {
Method* m = table()[i].method(); if (is_miranda_entry_at(i) &&
m->name() == name && m->signature() == signature) { return i;
}
} return Method::invalid_vtable_index;
}
// check if an entry at an index is miranda // requires that method m at entry be declared ("held") by an interface. bool klassVtable::is_miranda_entry_at(int i) {
Method* m = method_at(i);
InstanceKlass* holder = m->method_holder();
// miranda methods are public abstract instance interface methods in a class's vtable if (holder->is_interface()) {
assert(m->is_public(), "should be public");
assert(ik()->implements_interface(holder) , "this class should implement the interface"); if (is_miranda(m, ik()->methods(), ik()->default_methods(), ik()->super(), klass()->is_interface())) { returntrue;
}
} returnfalse;
}
// Check if a method is a miranda method, given a class's methods array, // its default_method table and its super class. // "Miranda" means an abstract non-private method that would not be // overridden for the local class. // A "miranda" method should only include non-private interface // instance methods, i.e. not private methods, not static methods, // not default methods (concrete interface methods), not overpass methods. // If a given class already has a local (including overpass) method, a // default method, or any of its superclasses has the same which would have // overridden an abstract method, then this is not a miranda method. // // Miranda methods are checked multiple times. // Pass 1: during class load/class file parsing: before vtable size calculation: // include superinterface abstract and default methods (non-private instance). // We include potential default methods to give them space in the vtable. // During the first run, the current instanceKlass has not yet been // created, the superclasses and superinterfaces do have instanceKlasses // but may not have vtables, the default_methods list is empty, no overpasses. // Default method generation uses the all_mirandas array as the starter set for // maximally-specific default method calculation. So, for both classes and // interfaces, it is necessary that the first pass will find all non-private // interface instance methods, whether or not they are concrete. // // Pass 2: recalculated during vtable initialization: only include abstract methods. // The goal of pass 2 is to walk through the superinterfaces to see if any of // the superinterface methods (which were all abstract pre-default methods) // need to be added to the vtable. // With the addition of default methods, we have three new challenges: // overpasses, static interface methods and private interface methods. // Static and private interface methods do not get added to the vtable and // are not seen by the method resolution process, so we skip those. // Overpass methods are already in the vtable, so vtable lookup will // find them and we don't need to add a miranda method to the end of // the vtable. So we look for overpass methods and if they are found we // return false. Note that we inherit our superclasses vtable, so // the superclass' search also needs to use find_overpass so that if // one is found we return false. // False means - we don't need a miranda method added to the vtable. // // During the second run, default_methods is set up, so concrete methods from // superinterfaces with matching names/signatures to default_methods are already // in the default_methods list and do not need to be appended to the vtable // as mirandas. Abstract methods may already have been handled via // overpasses - either local or superclass overpasses, which may be // in the vtable already. // // Pass 3: They are also checked by link resolution and selection, // for invocation on a method (not interface method) reference that // resolves to a method with an interface as its method_holder. // Used as part of walking from the bottom of the vtable to find // the vtable index for the miranda method. // // Part of the Miranda Rights in the US mean that if you do not have // an attorney one will be appointed for you. bool klassVtable::is_miranda(Method* m, Array<Method*>* class_methods,
Array<Method*>* default_methods, const Klass* super, bool is_interface) { if (m->is_static() || m->is_private() || m->is_overpass()) { returnfalse;
}
Symbol* name = m->name();
Symbol* signature = m->signature();
// First look in local methods to see if already covered if (InstanceKlass::find_local_method(class_methods, name, signature,
Klass::OverpassLookupMode::find,
Klass::StaticLookupMode::skip,
Klass::PrivateLookupMode::skip) != NULL)
{ returnfalse;
}
// Check local default methods if ((default_methods != NULL) &&
(InstanceKlass::find_method(default_methods, name, signature) != NULL))
{ returnfalse;
}
// Iterate on all superclasses, which should be InstanceKlasses. // Note that we explicitly look for overpasses at each level. // Overpasses may or may not exist for supers for pass 1, // they should have been created for pass 2 and later.
for (const Klass* cursuper = super; cursuper != NULL; cursuper = cursuper->super())
{
Method* found_mth = InstanceKlass::cast(cursuper)->find_local_method(name, signature,
Klass::OverpassLookupMode::find,
Klass::StaticLookupMode::skip,
Klass::PrivateLookupMode::skip); // Ignore non-public methods in java.lang.Object if klass is an interface. if (found_mth != NULL && (!is_interface ||
!SystemDictionary::is_nonpublic_Object_method(found_mth))) { returnfalse;
}
}
returntrue;
}
// Scans current_interface_methods for miranda methods that do not // already appear in new_mirandas, or default methods, and are also not defined-and-non-private // in super (superclass). These mirandas are added to all_mirandas if it is // not null; in addition, those that are not duplicates of miranda methods // inherited by super from its interfaces are added to new_mirandas. // Thus, new_mirandas will be the set of mirandas that this class introduces, // all_mirandas will be the set of all mirandas applicable to this class // including all defined in superclasses. void klassVtable::add_new_mirandas_to_lists(
GrowableArray<Method*>* new_mirandas, GrowableArray<Method*>* all_mirandas,
Array<Method*>* current_interface_methods, Array<Method*>* class_methods,
Array<Method*>* default_methods, const Klass* super, bool is_interface) {
// iterate thru the current interface's method to see if it a miranda int num_methods = current_interface_methods->length(); for (int i = 0; i < num_methods; i++) {
Method* im = current_interface_methods->at(i); bool is_duplicate = false; int num_of_current_mirandas = new_mirandas->length(); // check for duplicate mirandas in different interfaces we implement for (int j = 0; j < num_of_current_mirandas; j++) {
Method* miranda = new_mirandas->at(j); if ((im->name() == miranda->name()) &&
(im->signature() == miranda->signature())) {
is_duplicate = true; break;
}
}
if (!is_duplicate) { // we don't want duplicate miranda entries in the vtable if (is_miranda(im, class_methods, default_methods, super, is_interface)) { // is it a miranda at all? const InstanceKlass *sk = InstanceKlass::cast(super); // check if it is a duplicate of a super's miranda if (sk->lookup_method_in_all_interfaces(im->name(), im->signature(), Klass::DefaultsLookupMode::find) == NULL) {
new_mirandas->append(im);
} if (all_mirandas != NULL) {
all_mirandas->append(im);
}
}
}
}
}
// iterate thru the local interfaces looking for a miranda int num_local_ifs = local_interfaces->length(); for (int i = 0; i < num_local_ifs; i++) {
InstanceKlass *ik = local_interfaces->at(i);
add_new_mirandas_to_lists(new_mirandas, all_mirandas,
ik->methods(), class_methods,
default_methods, super, is_interface); // iterate thru each local's super interfaces
Array<InstanceKlass*>* super_ifs = ik->transitive_interfaces(); int num_super_ifs = super_ifs->length(); for (int j = 0; j < num_super_ifs; j++) {
InstanceKlass *sik = super_ifs->at(j);
add_new_mirandas_to_lists(new_mirandas, all_mirandas,
sik->methods(), class_methods,
default_methods, super, is_interface);
}
}
}
// Discover miranda methods ("miranda" = "interface abstract, no binding"), // and append them into the vtable starting at index initialized, // return the new value of initialized. // Miranda methods use vtable entries, but do not get assigned a vtable_index // The vtable_index is discovered by searching from the end of the vtable int klassVtable::fill_in_mirandas(Thread* current, int initialized) {
ResourceMark rm(current);
GrowableArray<Method*> mirandas(20);
get_mirandas(&mirandas, NULL, ik()->super(), ik()->methods(),
ik()->default_methods(), ik()->local_interfaces(),
klass()->is_interface()); for (int i = 0; i < mirandas.length(); i++) { if (log_develop_is_enabled(Trace, vtables)) {
Method* meth = mirandas.at(i);
LogTarget(Trace, vtables) lt;
LogStream ls(lt); if (meth != NULL) { char* sig = meth->name_and_sig_as_C_string();
ls.print("fill in mirandas with %s index %d, flags: ",
sig, initialized);
meth->print_linkage_flags(&ls);
ls.cr();
}
}
put_method_at(mirandas.at(i), initialized);
++initialized;
} return initialized;
}
// Copy this class's vtable to the vtable beginning at start. // Used to copy superclass vtable to prefix of subclass's vtable. void klassVtable::copy_vtable_to(vtableEntry* start) {
Copy::disjoint_words((HeapWord*)table(), (HeapWord*)start, _length * vtableEntry::size());
}
#if INCLUDE_JVMTI bool klassVtable::adjust_default_method(int vtable_index, Method* old_method, Method* new_method) { // If old_method is default, find this vtable index in default_vtable_indices // and replace that method in the _default_methods list bool updated = false;
Array<Method*>* default_methods = ik()->default_methods(); if (default_methods != NULL) { int len = default_methods->length(); for (int idx = 0; idx < len; idx++) { if (vtable_index == ik()->default_vtable_indices()->at(idx)) { if (default_methods->at(idx) == old_method) {
default_methods->at_put(idx, new_method);
updated = true;
} break;
}
}
} return updated;
}
// search the vtable for uses of either obsolete or EMCP methods void klassVtable::adjust_method_entries(bool * trace_name_printed) { int prn_enabled = 0;
ResourceMark rm;
for (int index = 0; index < length(); index++) {
Method* old_method = unchecked_method_at(index); if (old_method == NULL || !old_method->is_old()) { continue; // skip uninteresting entries
}
assert(!old_method->is_deleted(), "vtable methods may not be deleted");
// For default methods, need to update the _default_methods array // which can only have one method entry for a given signature bool updated_default = false; if (old_method->is_default_method()) {
updated_default = adjust_default_method(index, old_method, new_method);
}
// Initialize a itableMethodEntry void itableMethodEntry::initialize(InstanceKlass* klass, Method* m) { if (m == NULL) return;
#ifdef ASSERT if (MetaspaceShared::is_in_shared_metaspace((void*)&_method) &&
!MetaspaceShared::remapped_readwrite() &&
m->method_holder()->verified_at_dump_time() &&
klass->verified_at_dump_time()) { // At runtime initialize_itable is rerun as part of link_class_impl() // for a shared class loaded by the non-boot loader. // The dumptime itable method entry should be the same as the runtime entry. // For a shared old class which was not linked during dump time, we can't compare the dumptime // itable method entry with the runtime entry.
assert(_method == m, "sanity");
} #endif
_method = m;
}
if (klass->itable_length() > 0) {
itableOffsetEntry* offset_entry = (itableOffsetEntry*)klass->start_of_itable(); if (offset_entry != NULL && offset_entry->interface_klass() != NULL) { // Check that itable is initialized // First offset entry points to the first method_entry
intptr_t* method_entry = (intptr_t *)(((address)klass) + offset_entry->offset());
intptr_t* end = klass->end_of_itable();
// The length of the itable was either zero, or it has not yet been initialized.
_table_offset = 0;
_size_offset_table = 0;
_size_method_table = 0;
}
staticint initialize_count = 0;
// Initialization void klassItable::initialize_itable(GrowableArray<Method*>* supers) { if (_klass->is_interface()) { // This needs to go after vtable indices are assigned but // before implementors need to know the number of itable indices.
assign_itable_indices_for_interface(InstanceKlass::cast(_klass));
}
// Cannot be setup doing bootstrapping, interfaces don't have // itables, and klass with only ones entry have empty itables if (Universe::is_bootstrapping() ||
_klass->is_interface() ||
_klass->itable_length() == itableOffsetEntry::size()) return;
// There's always an extra itable entry so we can null-terminate it.
guarantee(size_offset_table() >= 1, "too small"); int num_interfaces = size_offset_table() - 1; if (num_interfaces > 0) { if (log_develop_is_enabled(Debug, itables)) {
ResourceMark rm;
log_develop_debug(itables)("%3d: Initializing itables for %s", ++initialize_count,
_klass->name()->as_C_string());
}
// Iterate through all interfaces for(int i = 0; i < num_interfaces; i++) {
itableOffsetEntry* ioe = offset_entry(i);
InstanceKlass* interf = ioe->interface_klass();
assert(interf != NULL && ioe->offset() != 0, "bad offset entry in itable");
initialize_itable_for_interface(ioe->offset(), interf, supers,
(ioe->offset() - offset_entry(0)->offset())/wordSize);
}
} // Check that the last entry is empty
itableOffsetEntry* ioe = offset_entry(size_offset_table() - 1);
guarantee(ioe->interface_klass() == NULL && ioe->offset() == 0, "terminator entry missing");
}
if (method_holder_loader() != interface_loader()) {
ResourceMark rm(THREAD);
Symbol* failed_type_symbol =
SystemDictionary::check_signature_loaders(target->signature(),
_klass,
method_holder_loader,
interface_loader, true); if (failed_type_symbol != NULL) {
stringStream ss;
ss.print("loader constraint violation in interface itable" " initialization for class %s: when selecting method '",
_klass->external_name());
interface_method->print_external_name(&ss),
ss.print("' the class loader %s for super interface %s, and the class" " loader %s of the selected method's %s, %s have" " different Class objects for the type %s used in the signature (%s; %s)",
interf->class_loader_data()->loader_name_and_id(),
interf->external_name(),
method_holder->class_loader_data()->loader_name_and_id(),
method_holder->external_kind(),
method_holder->external_name(),
failed_type_symbol->as_klass_external_name(),
interf->class_in_module_of_loader(false, true),
method_holder->class_in_module_of_loader(false, true));
THROW_MSG(vmSymbols::java_lang_LinkageError(), ss.as_string());
}
}
}
ime++;
}
}
void klassItable::initialize_itable_and_check_constraints(TRAPS) { // Save a super interface from each itable entry to do constraint checking
ResourceMark rm(THREAD);
GrowableArray<Method*>* supers = new GrowableArray<Method*>(_size_method_table, _size_method_table, NULL);
initialize_itable(supers);
check_constraints(supers, CHECK);
}
inlinebool interface_method_needs_itable_index(Method* m) { if (m->is_static()) returnfalse; // e.g., Stream.empty if (m->is_initializer()) returnfalse; // <init> or <clinit> if (m->is_private()) returnfalse; // uses direct call // If an interface redeclares a method from java.lang.Object, // it should already have a vtable index, don't touch it. // e.g., CharSequence.toString (from initialize_vtable) // if (m->has_vtable_index()) return false; // NO! returntrue;
}
int klassItable::assign_itable_indices_for_interface(InstanceKlass* klass) { // an interface does not have an itable, but its methods need to be numbered if (log_develop_is_enabled(Trace, itables)) {
ResourceMark rm;
log_develop_debug(itables)("%3d: Initializing itable indices for interface %s",
++initialize_count, klass->name()->as_C_string());
}
Array<Method*>* methods = klass->methods(); int nof_methods = methods->length(); int ime_num = 0; for (int i = 0; i < nof_methods; i++) {
Method* m = methods->at(i); if (interface_method_needs_itable_index(m)) {
assert(!m->is_final_method(), "no final interface methods"); // If m is already assigned a vtable index, do not disturb it. if (log_develop_is_enabled(Trace, itables)) {
ResourceMark rm;
LogTarget(Trace, itables) lt;
LogStream ls(lt);
assert(m != NULL, "methods can never be null"); constchar* sig = m->name_and_sig_as_C_string(); if (m->has_vtable_index()) {
ls.print("vtable index %d for method: %s, flags: ", m->vtable_index(), sig);
} else {
ls.print("itable index %d for method: %s, flags: ", ime_num, sig);
}
m->print_linkage_flags(&ls);
ls.cr();
} if (!m->has_vtable_index()) { // A shared method could have an initialized itable_index that // is < 0.
assert(m->vtable_index() == Method::pending_itable_index ||
m->is_shared(), "set by initialize_vtable");
m->set_itable_index(ime_num); // Progress to next itable entry
ime_num++;
}
}
}
assert(ime_num == method_count_for_interface(klass), "proper sizing"); return ime_num;
}
int klassItable::method_count_for_interface(InstanceKlass* interf) {
assert(interf->is_interface(), "must be");
Array<Method*>* methods = interf->methods(); int nof_methods = methods->length(); int length = 0; while (nof_methods > 0) {
Method* m = methods->at(nof_methods-1); if (m->has_itable_index()) {
length = m->itable_index() + 1; break;
}
nof_methods -= 1;
} #ifdef ASSERT int nof_methods_copy = nof_methods; while (nof_methods_copy > 0) {
Method* mm = methods->at(--nof_methods_copy);
assert(!mm->has_itable_index() || mm->itable_index() < length, "");
} #endif//ASSERT // return the rightmost itable index, plus one; or 0 if no methods have // itable indices return length;
}
int ime_count = method_count_for_interface(interf); for (int i = 0; i < nof_methods; i++) {
Method* m = methods->at(i);
Method* target = NULL; if (m->has_itable_index()) { // This search must match the runtime resolution, i.e. selection search for invokeinterface // to correctly enforce loader constraints for interface method inheritance. // Private methods are skipped as a private class method can never be the implementation // of an interface method. // Invokespecial does not perform selection based on the receiver, so it does not use // the cached itable.
target = LinkResolver::lookup_instance_method_in_klasses(_klass, m->name(), m->signature(),
Klass::PrivateLookupMode::skip);
} if (target == NULL || !target->is_public() || target->is_abstract() || target->is_overpass()) {
assert(target == NULL || !target->is_overpass() || target->is_public(), "Non-public overpass method!"); // Entry does not resolve. Leave it empty for AbstractMethodError or other error. if (!(target == NULL) && !target->is_public()) { // Stuff an IllegalAccessError throwing method in there instead.
itableOffsetEntry::method_entry(_klass, method_table_offset)[m->itable_index()].
initialize(_klass, Universe::throw_illegal_access_error());
}
} else {
int ime_num = m->itable_index();
assert(ime_num < ime_count, "oob");
// Save super interface method to perform constraint checks. // The method is in the error message, that's why. if (supers != NULL) {
supers->at_put(start_offset + ime_num, m);
}
#if INCLUDE_JVMTI // search the itable for uses of either obsolete or EMCP methods void klassItable::adjust_method_entries(bool * trace_name_printed) {
ResourceMark rm;
itableMethodEntry* ime = method_entry(0);
for (int i = 0; i < _size_method_table; i++, ime++) {
Method* old_method = ime->method(); if (old_method == NULL || !old_method->is_old()) { continue; // skip uninteresting entries
}
assert(!old_method->is_deleted(), "itable methods may not be deleted");
Method* new_method = old_method->get_new_method();
ime->initialize(_klass, new_method);
// an itable should never contain old or obsolete methods bool klassItable::check_no_old_or_obsolete_entries() {
ResourceMark rm;
itableMethodEntry* ime = method_entry(0);
for (int i = 0; i < _size_method_table; i++) {
Method* m = ime->method(); if (m != NULL &&
(NOT_PRODUCT(!m->is_valid() ||) m->is_old() || m->is_obsolete())) {
log_trace(redefine, class, update, itables)
("itable check found old method entry: class: %s old: %d obsolete: %d, method: %s",
_klass->external_name(), m->is_old(), m->is_obsolete(), m->external_name()); returnfalse;
}
ime++;
} returntrue;
}
void klassItable::dump_itable() {
itableMethodEntry* ime = method_entry(0);
tty->print_cr("itable dump --"); for (int i = 0; i < _size_method_table; i++) {
Method* m = ime->method(); if (m != NULL) {
tty->print(" (%5d) ", i);
m->access_flags().print_on(tty); if (m->is_default_method()) {
tty->print("default ");
}
tty->print(" -- ");
m->print_name(tty);
tty->cr();
}
ime++;
}
} #endif// INCLUDE_JVMTI
// Setup class InterfaceVisiterClosure : public StackObj { public: virtualvoid doit(InstanceKlass* intf, int method_count) = 0;
};
// Visit all interfaces with at least one itable method void visit_all_interfaces(Array<InstanceKlass*>* transitive_intf, InterfaceVisiterClosure *blk) { // Handle array argument for(int i = 0; i < transitive_intf->length(); i++) {
InstanceKlass* intf = transitive_intf->at(i);
assert(intf->is_interface(), "sanity check");
// Find no. of itable methods int method_count = 0; // method_count = klassItable::method_count_for_interface(intf);
Array<Method*>* methods = intf->methods(); if (methods->length() > 0) { for (int i = methods->length(); --i >= 0; ) { if (interface_method_needs_itable_index(methods->at(i))) {
method_count++;
}
}
}
// Visit all interfaces which either have any methods or can participate in receiver type check. // We do not bother to count methods in transitive interfaces, although that would allow us to skip // this step in the rare case of a zero-method interface extending another zero-method interface. if (method_count > 0 || intf->transitive_interfaces()->length() > 0) {
blk->doit(intf, method_count);
}
}
}
class CountInterfacesClosure : public InterfaceVisiterClosure { private: int _nof_methods; int _nof_interfaces; public:
CountInterfacesClosure() { _nof_methods = 0; _nof_interfaces = 0; }
int nof_methods() const { return _nof_methods; } int nof_interfaces() const { return _nof_interfaces; }
void doit(InstanceKlass* intf, int method_count) { int offset = ((address)_method_entry) - _klass_begin;
_offset_entry->initialize(intf, offset);
_offset_entry++;
_method_entry += method_count;
}
};
int klassItable::compute_itable_size(Array<InstanceKlass*>* transitive_interfaces) { // Count no of interfaces and total number of interface methods
CountInterfacesClosure cic;
visit_all_interfaces(transitive_interfaces, &cic);
// There's always an extra itable entry so we can null-terminate it. int itable_size = calc_itable_size(cic.nof_interfaces() + 1, cic.nof_methods());
return itable_size;
}
// Fill out offset table and interface klasses into the itable space void klassItable::setup_itable_offset_table(InstanceKlass* klass) { if (klass->itable_length() == 0) return;
assert(!klass->is_interface(), "Should have zero length itable");
// Count no of interfaces and total number of interface methods
CountInterfacesClosure cic;
visit_all_interfaces(klass->transitive_interfaces(), &cic); int nof_methods = cic.nof_methods(); int nof_interfaces = cic.nof_interfaces();
// Add one extra entry so we can null-terminate the table
nof_interfaces++;
assert(compute_itable_size(klass->transitive_interfaces()) ==
calc_itable_size(nof_interfaces, nof_methods), "mismatch calculation of itable size");
// Fill-out offset table
itableOffsetEntry* ioe = (itableOffsetEntry*)klass->start_of_itable();
itableMethodEntry* ime = (itableMethodEntry*)(ioe + nof_interfaces);
intptr_t* end = klass->end_of_itable();
--> --------------------
--> maximum size reached
--> --------------------
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