runtime/entrypoints_order_test.cc

/*
 * Copyright (C) 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <memory>
#include <setjmp.h>

#include "base/macros.h"
#include "common_runtime_test.h"
#include "thread.h"

// This test checks the offsets of values in the thread TLS and entrypoint structures. A failure
// of this test means that offsets have changed from the last update of the test. This indicates
// that an oat version bump may be in order, and some defines should be carefully checked (or their
// corresponding tests run).

namespace art {

// OFFSETOF_MEMBER uses reinterpret_cast. This means it is not a constexpr. So we cannot use
// compile-time assertions. Once we find another way, adjust the define accordingly.
#define CHECKED(expr, name) \
  EXPECT_TRUE(expr) << #name

// Macro to check whether two fields have an expected difference in offsets.  The error is named
// name.
#define EXPECT_OFFSET_DIFF(first_type, first_field, second_type, second_field, diff, name) \
  CHECKED(OFFSETOF_MEMBER(second_type, second_field) \
          - OFFSETOF_MEMBER(first_type, first_field) == diff, name)

// Helper macro for when the fields are from the same type.
#define EXPECT_OFFSET_DIFFNP(type, first_field, second_field, diff) \
  EXPECT_OFFSET_DIFF(type, first_field, type, second_field, diff, \
                     type ## _ ## first_field ## _ ## second_field)

// Helper macro for when the fields are from the same type and in the same member of said type.
#define EXPECT_OFFSET_DIFFP(type, prefix, first_field, second_field, diff) \
  EXPECT_OFFSET_DIFF(type, prefix . first_field, type, prefix . second_field, diff, \
                     type ## _ ## prefix ## _ ## first_field ## _ ## second_field)

// Macro to check whether two fields have at least an expected difference in offsets.  The error is
// named name.
#define EXPECT_OFFSET_DIFF_GT(first_type, first_field, second_type, second_field, diff, name) \
  CHECKED(OFFSETOF_MEMBER(second_type, second_field) \
          - OFFSETOF_MEMBER(first_type, first_field) >= diff, name)

// Helper macro for when the fields are from the same type.
#define EXPECT_OFFSET_DIFF_GT3(type, first_field, second_field, diff, name) \
  EXPECT_OFFSET_DIFF_GT(type, first_field, type, second_field, diff, name)

class EntrypointsOrderTest : public CommonRuntimeTest {
 protected:
  void CheckThreadOffsets() {
    CHECKED(OFFSETOF_MEMBER(Thread, tls32_.state_and_flags) == 0, thread_flags_at_zero);
    EXPECT_OFFSET_DIFFP(Thread, tls32_, state_and_flags, suspend_count, 4);
    EXPECT_OFFSET_DIFFP(Thread, tls32_, suspend_count, debug_suspend_count, 4);
    EXPECT_OFFSET_DIFFP(Thread, tls32_, debug_suspend_count, thin_lock_thread_id, 4);
    EXPECT_OFFSET_DIFFP(Thread, tls32_, thin_lock_thread_id, tid, 4);
    EXPECT_OFFSET_DIFFP(Thread, tls32_, tid, daemon, 4);
    EXPECT_OFFSET_DIFFP(Thread, tls32_, daemon, throwing_OutOfMemoryError, 4);
    EXPECT_OFFSET_DIFFP(Thread, tls32_, throwing_OutOfMemoryError, no_thread_suspension, 4);
    EXPECT_OFFSET_DIFFP(Thread, tls32_, no_thread_suspension, thread_exit_check_count, 4);
    EXPECT_OFFSET_DIFFP(Thread, tls32_, thread_exit_check_count,
                        is_exception_reported_to_instrumentation_, 4);
    EXPECT_OFFSET_DIFFP(Thread, tls32_, is_exception_reported_to_instrumentation_,
                        handling_signal_, 4);

    // TODO: Better connection. Take alignment into account.
    EXPECT_OFFSET_DIFF_GT3(Thread, tls32_.thread_exit_check_count, tls64_.trace_clock_base, 4,
                           thread_tls32_to_tls64);

    EXPECT_OFFSET_DIFFP(Thread, tls64_, trace_clock_base, deoptimization_return_value, 8);
    EXPECT_OFFSET_DIFFP(Thread, tls64_, deoptimization_return_value, stats, 8);

    // TODO: Better connection. Take alignment into account.
    EXPECT_OFFSET_DIFF_GT3(Thread, tls64_.stats, tlsPtr_.card_table, 8, thread_tls64_to_tlsptr);

    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, card_table, exception, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, exception, stack_end, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, stack_end, managed_stack, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, managed_stack, suspend_trigger, sizeof(ManagedStack));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, suspend_trigger, jni_env, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, jni_env, self, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, self, opeer, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, opeer, jpeer, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, jpeer, stack_begin, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, stack_begin, stack_size, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, stack_size, throw_location, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, throw_location, stack_trace_sample, sizeof(ThrowLocation));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, stack_trace_sample, wait_next, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, wait_next, monitor_enter_object, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, monitor_enter_object, top_handle_scope, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, top_handle_scope, class_loader_override, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, class_loader_override, long_jump_context, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, long_jump_context, instrumentation_stack, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, instrumentation_stack, debug_invoke_req, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, debug_invoke_req, single_step_control, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, single_step_control, deoptimization_shadow_frame,
                        sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, deoptimization_shadow_frame,
                        shadow_frame_under_construction, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, shadow_frame_under_construction, name, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, name, pthread_self, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, pthread_self, last_no_thread_suspension_cause,
                        sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, last_no_thread_suspension_cause, checkpoint_functions,
                        sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, checkpoint_functions, interpreter_entrypoints,
                        sizeof(void*) * 3);

    // Skip across the entrypoints structures.

    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, thread_local_start, thread_local_pos, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, thread_local_pos, thread_local_end, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, thread_local_end, thread_local_objects, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, thread_local_objects, rosalloc_runs, sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, rosalloc_runs, thread_local_alloc_stack_top,
                        sizeof(void*) * kNumRosAllocThreadLocalSizeBrackets);
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, thread_local_alloc_stack_top, thread_local_alloc_stack_end,
                        sizeof(void*));
    EXPECT_OFFSET_DIFFP(Thread, tlsPtr_, thread_local_alloc_stack_end, held_mutexes, sizeof(void*));
    EXPECT_OFFSET_DIFF(Thread, tlsPtr_.held_mutexes, Thread, wait_mutex_,
                       sizeof(void*) * kLockLevelCount + sizeof(void*), thread_tlsptr_end);
  }

  void CheckInterpreterEntryPoints() {
    CHECKED(OFFSETOF_MEMBER(InterpreterEntryPoints, pInterpreterToInterpreterBridge) == 0,
            InterpreterEntryPoints_start_with_i2i);
    EXPECT_OFFSET_DIFFNP(InterpreterEntryPoints, pInterpreterToInterpreterBridge,
                         pInterpreterToCompiledCodeBridge, sizeof(void*));
    CHECKED(OFFSETOF_MEMBER(InterpreterEntryPoints, pInterpreterToCompiledCodeBridge)
            + sizeof(void*) == sizeof(InterpreterEntryPoints), InterpreterEntryPoints_all);
  }

  void CheckJniEntryPoints() {
    CHECKED(OFFSETOF_MEMBER(JniEntryPoints, pDlsymLookup) == 0,
            JniEntryPoints_start_with_dlsymlookup);
    CHECKED(OFFSETOF_MEMBER(JniEntryPoints, pDlsymLookup)
            + sizeof(void*) == sizeof(JniEntryPoints), JniEntryPoints_all);
  }

  void CheckQuickEntryPoints() {
    CHECKED(OFFSETOF_MEMBER(QuickEntryPoints, pAllocArray) == 0,
                QuickEntryPoints_start_with_allocarray);
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pAllocArray, pAllocArrayResolved, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pAllocArrayResolved, pAllocArrayWithAccessCheck,
                         sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pAllocArrayWithAccessCheck, pAllocObject, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pAllocObject, pAllocObjectResolved, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pAllocObjectResolved, pAllocObjectInitialized,
                         sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pAllocObjectInitialized, pAllocObjectWithAccessCheck,
                         sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pAllocObjectWithAccessCheck, pCheckAndAllocArray,
                         sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pCheckAndAllocArray, pCheckAndAllocArrayWithAccessCheck,
                         sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pCheckAndAllocArrayWithAccessCheck,
                         pInstanceofNonTrivial, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pInstanceofNonTrivial, pCheckCast, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pCheckCast, pInitializeStaticStorage, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pInitializeStaticStorage, pInitializeTypeAndVerifyAccess,
                         sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pInitializeTypeAndVerifyAccess, pInitializeType,
                         sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pInitializeType, pResolveString, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pResolveString, pSet8Instance, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pSet8Instance, pSet8Static, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pSet8Static, pSet16Instance, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pSet16Instance, pSet16Static, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pSet16Static, pSet32Instance, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pSet32Instance, pSet32Static, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pSet32Static, pSet64Instance, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pSet64Instance, pSet64Static, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pSet64Static, pSetObjInstance, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pSetObjInstance, pSetObjStatic, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pSetObjStatic, pGetByteInstance, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGetByteInstance, pGetBooleanInstance, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGetBooleanInstance, pGetByteStatic, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGetByteStatic, pGetBooleanStatic, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGetBooleanStatic, pGetShortInstance, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGetShortInstance, pGetCharInstance, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGetCharInstance, pGetShortStatic, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGetShortStatic, pGetCharStatic, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGetCharStatic, pGet32Instance, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGet32Instance, pGet32Static, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGet32Static, pGet64Instance, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGet64Instance, pGet64Static, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGet64Static, pGetObjInstance, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGetObjInstance, pGetObjStatic, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pGetObjStatic, pAputObjectWithNullAndBoundCheck,
                         sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pAputObjectWithNullAndBoundCheck,
                         pAputObjectWithBoundCheck, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pAputObjectWithBoundCheck, pAputObject, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pAputObject, pHandleFillArrayData, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pHandleFillArrayData, pJniMethodStart, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pJniMethodStart, pJniMethodStartSynchronized,
                         sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pJniMethodStartSynchronized, pJniMethodEnd,
                         sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pJniMethodEnd, pJniMethodEndSynchronized, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pJniMethodEndSynchronized, pJniMethodEndWithReference,
                         sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pJniMethodEndWithReference,
                         pJniMethodEndWithReferenceSynchronized, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pJniMethodEndWithReferenceSynchronized,
                         pQuickGenericJniTrampoline, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pQuickGenericJniTrampoline, pLockObject, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pLockObject, pUnlockObject, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pUnlockObject, pCmpgDouble, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pCmpgDouble, pCmpgFloat, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pCmpgFloat, pCmplDouble, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pCmplDouble, pCmplFloat, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pCmplFloat, pFmod, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pFmod, pL2d, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pL2d, pFmodf, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pFmodf, pL2f, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pL2f, pD2iz, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pD2iz, pF2iz, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pF2iz, pIdivmod, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pIdivmod, pD2l, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pD2l, pF2l, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pF2l, pLdiv, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pLdiv, pLmod, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pLmod, pLmul, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pLmul, pShlLong, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pShlLong, pShrLong, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pShrLong, pUshrLong, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pUshrLong, pIndexOf, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pIndexOf, pStringCompareTo, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pStringCompareTo, pMemcpy, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pMemcpy, pQuickImtConflictTrampoline, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pQuickImtConflictTrampoline, pQuickResolutionTrampoline,
                         sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pQuickResolutionTrampoline, pQuickToInterpreterBridge,
                         sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pQuickToInterpreterBridge,
                         pInvokeDirectTrampolineWithAccessCheck, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pInvokeDirectTrampolineWithAccessCheck,
                         pInvokeInterfaceTrampolineWithAccessCheck, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pInvokeInterfaceTrampolineWithAccessCheck,
                         pInvokeStaticTrampolineWithAccessCheck, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pInvokeStaticTrampolineWithAccessCheck,
                         pInvokeSuperTrampolineWithAccessCheck, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pInvokeSuperTrampolineWithAccessCheck,
                         pInvokeVirtualTrampolineWithAccessCheck, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pInvokeVirtualTrampolineWithAccessCheck,
                         pTestSuspend, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pTestSuspend, pDeliverException, sizeof(void*));

    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pDeliverException, pThrowArrayBounds, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pThrowArrayBounds, pThrowDivZero, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pThrowDivZero, pThrowNoSuchMethod, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pThrowNoSuchMethod, pThrowNullPointer, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pThrowNullPointer, pThrowStackOverflow, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pThrowStackOverflow, pA64Load, sizeof(void*));
    EXPECT_OFFSET_DIFFNP(QuickEntryPoints, pA64Load, pA64Store, sizeof(void*));

    CHECKED(OFFSETOF_MEMBER(QuickEntryPoints, pA64Store)
            + sizeof(void*) == sizeof(QuickEntryPoints), QuickEntryPoints_all);
  }
};

TEST_F(EntrypointsOrderTest, ThreadOffsets) {
  CheckThreadOffsets();
}

TEST_F(EntrypointsOrderTest, InterpreterEntryPoints) {
  CheckInterpreterEntryPoints();
}

TEST_F(EntrypointsOrderTest, JniEntryPoints) {
  CheckJniEntryPoints();
}

TEST_F(EntrypointsOrderTest, QuickEntryPoints) {
  CheckQuickEntryPoints();
}

}  // namespace art