Adjust how we assign vtable indexes during class loading.
Only populate the super vtable set in the edge case of a super class
overriding a method from a new interface.
Test: test.py
Bug: 211854716
Bug: 233545487
Change-Id: I350f545df1cb193cd50a76e85b582c5bff9c15cc
diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index c8dbc75..a598d27 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -37,6 +37,7 @@
#include "art_method-inl.h"
#include "barrier.h"
#include "base/arena_allocator.h"
+#include "base/arena_bit_vector.h"
#include "base/casts.h"
#include "base/file_utils.h"
#include "base/hash_map.h"
@@ -7976,40 +7977,7 @@
super_vtable_buffer_ptr,
super_vtable_buffer_size,
allocator_.Adapter());
- ArrayRef<uint32_t> same_signature_vtable_lists;
- // Insert the first `mirror::Object::kVTableLength` indexes with pre-calculated hashes.
- DCHECK_GE(super_vtable_length, mirror::Object::kVTableLength);
- for (uint32_t i = 0; i != mirror::Object::kVTableLength; ++i) {
- size_t hash = class_linker_->object_virtual_method_hashes_[i];
- // There are no duplicate signatures in `java.lang.Object`, so use `HashSet<>::PutWithHash()`.
- // This avoids equality comparison for the three `java.lang.Object.wait()` overloads.
- super_vtable_signatures.PutWithHash(i, hash);
- }
- // Insert the remaining indexes, check for duplicate signatures.
- if (super_vtable_length > mirror::Object::kVTableLength) {
- for (size_t i = mirror::Object::kVTableLength; i < super_vtable_length; ++i) {
- // Use `super_vtable_accessor` for getting the method for hash calculation.
- // Letting `HashSet<>::insert()` use the internal accessor copy in the hash
- // function prevents the compiler from optimizing this properly because the
- // compiler cannot prove that the accessor copy is immutable.
- size_t hash = ComputeMethodHash(super_vtable_accessor.GetVTableEntry(i));
- auto [it, inserted] = super_vtable_signatures.InsertWithHash(i, hash);
- if (UNLIKELY(!inserted)) {
- if (same_signature_vtable_lists.empty()) {
- same_signature_vtable_lists = ArrayRef<uint32_t>(
- allocator_.AllocArray<uint32_t>(super_vtable_length), super_vtable_length);
- std::fill_n(same_signature_vtable_lists.data(), super_vtable_length, dex::kDexNoIndex);
- same_signature_vtable_lists_ = same_signature_vtable_lists;
- }
- DCHECK_LT(*it, i);
- same_signature_vtable_lists[i] = *it;
- *it = i;
- }
- }
- }
- // For each declared virtual method, look for a superclass virtual method
- // to override and assign a new vtable index if no method was overridden.
DeclaredVirtualSignatureSet declared_virtual_signatures(
kMinLoadFactor,
kMaxLoadFactor,
@@ -8018,8 +7986,22 @@
declared_virtuals_buffer_ptr,
declared_virtuals_buffer_size,
allocator_.Adapter());
+
+ ArrayRef<uint32_t> same_signature_vtable_lists;
const bool is_proxy_class = klass->IsProxyClass();
size_t vtable_length = super_vtable_length;
+
+ // Record which declared methods are overriding a super method.
+ ArenaBitVector initialized_methods(&allocator_, num_virtual_methods, /* expandable= */ false);
+
+ // Note: our sets hash on the method name, and therefore we pay a high
+ // performance price when a class has many overloads.
+ //
+ // We populate the declared_virtual_signatures instead of the
+ // super_vtable_signatures (which is only lazy populated in case of interface
+ // overriding, see below). This makes sure that we pay the performance price
+ // only on that class, and not on its subclasses (except in the case of
+ // interface overriding, see below).
for (size_t i = 0; i != num_virtual_methods; ++i) {
ArtMethod* virtual_method = klass->GetVirtualMethodDuringLinking(i, kPointerSize);
DCHECK(!virtual_method->IsStatic()) << virtual_method->PrettyMethod();
@@ -8028,57 +8010,65 @@
: virtual_method;
size_t hash = ComputeMethodHash(signature_method);
declared_virtual_signatures.PutWithHash(i, hash);
- auto it = super_vtable_signatures.FindWithHash(signature_method, hash);
- if (it != super_vtable_signatures.end()) {
- size_t super_index = *it;
- DCHECK_LT(super_index, super_vtable_length);
- ArtMethod* super_method = super_vtable_accessor.GetVTableEntry(super_index);
- // Historical note: Before Android 4.1, an inaccessible package-private
- // superclass method would have been incorrectly overridden.
- bool overrides = klass->CanAccessMember(super_method->GetDeclaringClass(),
- super_method->GetAccessFlags());
- if (overrides && super_method->IsFinal()) {
- sants.reset();
- ThrowLinkageError(klass, "Method %s overrides final method in class %s",
- virtual_method->PrettyMethod().c_str(),
- super_method->GetDeclaringClassDescriptor());
- return 0u;
- }
- if (UNLIKELY(!same_signature_vtable_lists.empty())) {
- // We may override more than one method according to JLS, see b/211854716 .
- // We record the highest overridden vtable index here so that we can walk
- // the list to find other overridden methods when constructing the vtable.
- // However, we walk all the methods to check for final method overriding.
- size_t current_index = super_index;
- while (same_signature_vtable_lists[current_index] != dex::kDexNoIndex) {
- DCHECK_LT(same_signature_vtable_lists[current_index], current_index);
- current_index = same_signature_vtable_lists[current_index];
- ArtMethod* current_method = super_vtable_accessor.GetVTableEntry(current_index);
- if (klass->CanAccessMember(current_method->GetDeclaringClass(),
- current_method->GetAccessFlags())) {
- if (current_method->IsFinal()) {
- sants.reset();
- ThrowLinkageError(klass, "Method %s overrides final method in class %s",
- virtual_method->PrettyMethod().c_str(),
- current_method->GetDeclaringClassDescriptor());
- return 0u;
- }
- if (!overrides) {
- overrides = true;
- super_index = current_index;
- super_method = current_method;
- }
- }
- }
- }
- if (overrides) {
- virtual_method->SetMethodIndex(super_index);
- continue;
- }
+ }
+
+ // Loop through each super vtable method and see if they are overridden by a method we added to
+ // the hash table.
+ for (size_t j = 0; j < super_vtable_length; ++j) {
+ // Search the hash table to see if we are overridden by any method.
+ ArtMethod* super_method = super_vtable_accessor.GetVTableEntry(j);
+ if (!klass->CanAccessMember(super_method->GetDeclaringClass(),
+ super_method->GetAccessFlags())) {
+ // Continue on to the next method since this one is package private and cannot be overridden.
+ // Before Android 4.1, the package-private method super_method might have been incorrectly
+ // overridden.
+ continue;
}
- // The method does not override any method from superclass, so it needs a new vtable index.
- virtual_method->SetMethodIndex(vtable_length);
- ++vtable_length;
+ size_t hash = (j < mirror::Object::kVTableLength)
+ ? class_linker_->object_virtual_method_hashes_[j]
+ : ComputeMethodHash(super_method);
+ auto it = declared_virtual_signatures.FindWithHash(super_method, hash);
+ if (it == declared_virtual_signatures.end()) {
+ continue;
+ }
+ ArtMethod* virtual_method = klass->GetVirtualMethodDuringLinking(*it, kPointerSize);
+ if (super_method->IsFinal()) {
+ sants.reset();
+ ThrowLinkageError(klass, "Method %s overrides final method in class %s",
+ virtual_method->PrettyMethod().c_str(),
+ super_method->GetDeclaringClassDescriptor());
+ return 0u;
+ }
+ if (initialized_methods.IsBitSet(*it)) {
+ // The method is overriding two methods: one public, and one package private.
+ // We record that information to later set the method in the vtable
+ // location that isn't the method index.
+ if (same_signature_vtable_lists.empty()) {
+ same_signature_vtable_lists = ArrayRef<uint32_t>(
+ allocator_.AllocArray<uint32_t>(super_vtable_length), super_vtable_length);
+ std::fill_n(same_signature_vtable_lists.data(), super_vtable_length, dex::kDexNoIndex);
+ same_signature_vtable_lists_ = same_signature_vtable_lists;
+ }
+ same_signature_vtable_lists[j] = virtual_method->GetMethodIndexDuringLinking();
+ } else {
+ initialized_methods.SetBit(*it);
+ }
+ // Make sure the vtable index of the method is the vtable index of the overridden
+ // method that is public. We know that index is the largest one, a we can
+ // only start with a package private in the superclass hierarchy, and then have a new
+ // index in a closer superclass.
+ // This makes sure we find the public version when looking for interface
+ // (see code below).
+ virtual_method->SetMethodIndex(j);
+ }
+
+ // Add the non-overridden methods at the end.
+ for (size_t i = 0; i < num_virtual_methods; ++i) {
+ if (!initialized_methods.IsBitSet(i)) {
+ ArtMethod* local_method = klass->GetVirtualMethodDuringLinking(i, kPointerSize);
+ local_method->SetMethodIndex(vtable_length);
+ vtable_length++;
+ }
}
// Assign vtable indexes for interface methods in new interfaces and store them
@@ -8105,24 +8095,34 @@
vtable_method = klass->GetVirtualMethodDuringLinking(*it1, kPointerSize);
found = true;
} else {
- auto it2 = super_vtable_signatures.FindWithHash(interface_method, hash);
- if (it2 != super_vtable_signatures.end()) {
- // If there are multiple vtable methods with the same signature, the one with
- // the highest vtable index is not nessarily the one in most-derived class.
- // Find the most-derived method. See b/211854716 .
- vtable_method = super_vtable_accessor.GetVTableEntry(*it2);
- if (UNLIKELY(!same_signature_vtable_lists.empty())) {
- size_t current_index = *it2;
- while (same_signature_vtable_lists[current_index] != dex::kDexNoIndex) {
- DCHECK_LT(same_signature_vtable_lists[current_index], current_index);
- current_index = same_signature_vtable_lists[current_index];
- ArtMethod* current_method = super_vtable_accessor.GetVTableEntry(current_index);
- ObjPtr<mirror::Class> current_class = current_method->GetDeclaringClass();
- if (current_class->IsSubClass(vtable_method->GetDeclaringClass())) {
- vtable_method = current_method;
- }
+ // This situation should be rare (a superclass implements a method
+ // declared in an interface this class is inheriting). Only in this case
+ // do we lazily populate the super_vtable_signatures.
+ if (super_vtable_signatures.empty()) {
+ for (size_t k = 0; k < super_vtable_length; ++k) {
+ ArtMethod* super_method = super_vtable_accessor.GetVTableEntry(k);
+ if (!klass->CanAccessMember(super_method->GetDeclaringClass(),
+ super_method->GetAccessFlags())) {
+ continue;
+ }
+ size_t super_hash = (k < mirror::Object::kVTableLength)
+ ? class_linker_->object_virtual_method_hashes_[k]
+ : ComputeMethodHash(super_method);
+ auto [it, inserted] = super_vtable_signatures.InsertWithHash(k, super_hash);
+ if (UNLIKELY(!inserted)) {
+ // If there is an existing method with the same name and
+ // signature, this means we have a package-private version and a
+ // public version. When setting up vtable indexes, we make sure
+ // the public version has the highest index, and therefore we only
+ // record the public version here. This makes sure we don't get
+ // the package-private version in the lookup below.
+ *it = k;
}
}
+ }
+ auto it2 = super_vtable_signatures.FindWithHash(interface_method, hash);
+ if (it2 != super_vtable_signatures.end()) {
+ vtable_method = super_vtable_accessor.GetVTableEntry(*it2);
found = true;
}
}
@@ -8484,8 +8484,15 @@
uint32_t vtable_index = virtual_method.GetMethodIndexDuringLinking();
vtable->SetElementPtrSize(vtable_index, &virtual_method, kPointerSize);
if (UNLIKELY(vtable_index < same_signature_vtable_lists.size())) {
- // We may override more than one method according to JLS, see b/211854716 .
- // If we do, arbitrarily update the method index to the lowest overridden vtable index.
+ // We may override more than one method according to JLS, see b/211854716.
+ // We really only expect one or two methods overridden, not more: one for
+ // package-private visibility, and one for public visibility.
+ // In AssignVTableIndexes, we make sure the vtable index of a method that
+ // overrides two methods is the same vtable index as the public one.
+ // This makes sure we find the public version when looking for interface
+ // method overriding.
+ // FIXME: Change this while loop into code that only expects two
+ // entries.
while (same_signature_vtable_lists[vtable_index] != dex::kDexNoIndex) {
DCHECK_LT(same_signature_vtable_lists[vtable_index], vtable_index);
vtable_index = same_signature_vtable_lists[vtable_index];
@@ -8494,7 +8501,6 @@
current_method->GetAccessFlags())) {
DCHECK(!current_method->IsFinal());
vtable->SetElementPtrSize(vtable_index, &virtual_method, kPointerSize);
- virtual_method.SetMethodIndex(vtable_index);
}
}
}