Packages

  • package root
    Definition Classes
    root
  • package org
    Definition Classes
    root
  • package opalj

    OPAL is a Scala-based framework for the static analysis, manipulation and creation of Java bytecode.

    OPAL is a Scala-based framework for the static analysis, manipulation and creation of Java bytecode. OPAL is designed with performance, scalability and adaptability in mind.

    Its main components are:

    • a library (Common) which provides generally useful data-structures and algorithms for static analyses.
    • a framework for parsing Java bytecode (Bytecode Infrastructure) that can be used to create arbitrary representations.
    • a library to create a one-to-one in-memory representation of Java bytecode (Bytecode Disassembler).
    • a library to create a representation of Java bytecode that facilitates writing simple static analyses (Bytecode Representation - org.opalj.br).
    • a scalable, easily customizable framework for the abstract interpretation of Java bytecode (Abstract Interpretation Framework - org.opalj.ai).
    • a library to extract dependencies between code elements and to facilitate checking architecture definitions.
    • a library for the lightweight manipulation and creation of Java bytecode.

    General Design Decisions

    Thread Safety

    Unless explicitly noted, OPAL is thread safe. I.e., the classes defined by OPAL can be considered to be thread safe unless otherwise stated. (For example, it is possible to read and process class files concurrently without explicit synchronization on the client side.)

    No null Values

    Unless explicitly noted, OPAL does not null values I.e., fields that are accessible will never contain null values and methods will never return null. If a method accepts null as a value for a parameter or returns a null value it is always explicitly documented. In general, the behavior of methods that are passed null values is undefined unless explicitly documented.

    No Typecasts for Collections

    For efficiency reasons, OPAL sometimes uses mutable data-structures internally. After construction time, these data-structures are generally represented using their generic interfaces (e.g., scala.collection.{Set,Map}). However, a downcast (e.g., to add/remove elements) is always forbidden as it would effectively prevent thread-safety. Furthermore, the concrete data-structure is always considered an implementation detail and may change at any time.

    Assertions

    OPAL makes heavy use of Scala's Assertion Facility to facilitate writing correct code. Hence, for production builds (after thorough testing(!)) it is highly recommend to build OPAL again using -Xdisable-assertions.

    Definition Classes
    org
  • package ai

    Implementation of an abstract interpretation (ai) framework – also referred to as OPAL.

    Implementation of an abstract interpretation (ai) framework – also referred to as OPAL.

    Please note, that OPAL/the abstract interpreter just refers to the classes and traits defined in this package (ai). The classes and traits defined in the sub-packages (in particular in domain) are not considered to be part of the core of OPAL/the abstract interpreter.

    Definition Classes
    opalj
    Note

    This framework assumes that the analyzed bytecode is valid; i.e., the JVM's bytecode verifier would be able to verify the code. Furthermore, load-time errors (e.g., LinkageErrors) are – by default – completely ignored to facilitate the analysis of parts of a project. In general, if the presented bytecode is not valid, the result is undefined (i.e., OPAL may report meaningless results, crash or run indefinitely).

    See also

    org.opalj.ai.Domain - The core interface between the abstract interpretation framework and the abstract domain that is responsible for performing the abstract computations.

    org.opalj.ai.AI - Implements the abstract interpreter that processes a methods code and uses an analysis-specific domain to perform the abstract computations.

  • trait ValuesDomain extends AnyRef

    Defines the concept of a value in a Domain.

    Defines the concept of a value in a Domain.

    Definition Classes
    ai
    See also

    Domain For an explanation of the underlying concepts and ideas.

  • DomainIllegalValue
  • DomainReferenceValue
  • DomainReturnAddressValue
  • DomainReturnAddressValues
  • DomainTypedValue
  • DomainValue
  • IllegalValue
  • RETValue
  • ReferenceValue
  • ReturnAddressValue
  • ReturnAddressValues
  • TypedValue
  • Value
t

org.opalj.ai.ValuesDomain

ReferenceValue

trait ReferenceValue extends TypedValue[ReferenceType] with IsReferenceValue[DomainReferenceValue]

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  1. ReferenceValue
  2. IsReferenceValue
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Abstract Value Members

  1. abstract def baseValues: Traversable[DomainReferenceValue]

    In general an IsReferenceValue abstracts over all potential values and this information is sufficient for subsequent analyses; but in some cases, analyzing the set of underlying values may increase the overall precision and this set is returned by this function.

    In general an IsReferenceValue abstracts over all potential values and this information is sufficient for subsequent analyses; but in some cases, analyzing the set of underlying values may increase the overall precision and this set is returned by this function. In other words: if baseValues is nonEmpty, then the properties returned by this value are derived from the base values, but still maybe more specific. For example,

    Object o = _;
    if(...) o = f() else o = g();
    // when we reach this point, we generally don't know if the values returned by f and g
    // are non-null; hence, o is potentially null.
    if(o != null)
     // Now, we know that o is not null, but we still don't know if the values returned
     // by f OR g were null and we cannot establish that when we don't know to which value
     // o is actually referring to.
     u(o);
    returns

    The set of values this reference value abstracts over. The set is empty if this value is already a base value.

    Definition Classes
    IsReferenceValue
    Note

    A reference value which belongs to the base values by some other reference value never has itself as a direct base value.

  2. abstract def doJoin(pc: PC, value: DomainValue): Update[DomainValue]

    Joins this value and the given value.

    Joins this value and the given value.

    Join is called whenever an instruction is evaluated more than once and, hence, the values found on the paths need to be joined. This method is, however, only called if the two values are two different objects ((this ne value) === true), but both values have the same computational type.

    This basically implements the join operator of complete lattices.

    Example

    For example, joining a DomainValue that represents the integer value 0 with a DomainValue that represents the integer value 1 may return a new DomainValue that precisely captures the range [0..1] or that captures all positive integer values or just some integer value.

    Contract

    this value is always the value that was previously used to perform subsequent computations/analyses. Hence, if this value subsumes the given value, the result has to be either NoUpdate or a MetaInformationUpdate. In case that the given value subsumes this value, the result has to be a StructuralUpdate with the given value as the new value. Hence, this join operation is not commutative. If a new (more abstract) abstract value is created that represents both values the result always has to be a StructuralUpdate. If the result is a StructuralUpdate the framework will continue with the interpretation.

    The termination of the abstract interpretation directly depends on the fact that at some point all (abstract) values are fixed and don't change anymore. Hence, it is important that the type of the update is only a org.opalj.ai.StructuralUpdate if the value has changed in a way relevant for future computations/analyses involving this value. In other words, when two values are joined it has to be ensured that no fall back to a previous value occurs. E.g., if you join the existing integer value 0 and the given value 1 and the result would be 1, then it must be ensured that a subsequent join with the value 0 will not result in the value 0 again.

    Conceptually, the join of an object with itself has to return the object itself. Note, that this is a conceptual requirement as such a call (this.doJoin(..,this)) will not be performed by the abstract interpretation framework; this case is handled by the join method. However, if the join object is also used by the implementation of the domain itself, it may be necessary to explicitly handle self-joins.

    Performance

    In general, the domain should try to minimize the number of objects that it uses to represent values. That is, two values that are conceptually equal should – whenever possible – use only one object. This has a significant impact on functions such as join.

    pc

    The program counter of the instruction where the paths converge.

    value

    The "new" domain value with which this domain value should be joined. The given value and this value are guaranteed to have the same computational type, but are not reference equal.

    Attributes
    protected[this]
    Definition Classes
    Value
  3. abstract def summarize(pc: PC): DomainValue

    Creates a summary of this value.

    Creates a summary of this value.

    In general, creating a summary of a value may be useful/required for values that are potentially returned by a called method and which will then be used by the calling method. For example, it may be useful to precisely track the flow of values within a method to be able to distinguish between all sources of a value (E.g., to be able to distinguish between a NullPointerException created by instruction A and another one created by instruction B (A != B).) However, from the caller perspective it may be absolutely irrelevant where/how the value was created in the called method and, hence, keeping all information would just waste memory and a summary may be sufficient.

    Definition Classes
    Value
    Note

    This method is predefined to facilitate the development of project-wide analyses.

  4. abstract def upperTypeBound: UIDSet[_ <: ReferenceType]

    The upper bound of the value's type.

    The upper bound of the value's type. The upper bound is empty if this value is null (i.e., isNull == Yes). The upper bound is only guaranteed to contain exactly one type if the type is precise. (i.e., isPrecise == true). Otherwise, the upper type bound may contain one or more types that are not known to be in an inheritance relation, but which will correctly approximate the runtime type.

    Definition Classes
    IsReferenceValue
    Note

    If only a part of a project is analyzed, the class hierarchy may be fragmented and it may happen that two classes that are indeed in an inheritance relation – if we would analyze the complete project – are part of the upper type bound.

  5. abstract def valueType: Option[ReferenceType]

    The type kind of the values, if the value has a specific type kind; None if and only if the underlying value is null.

    The type kind of the values, if the value has a specific type kind; None if and only if the underlying value is null.

    returns

    The type/the upper type bound of the value. If the type is a base type, then the type is necessarily precise. In case of a reference type the type may be an upper type bound or may be precise. In the latter case, using the concrete domain it may be possible to get further information. If the underlying value is null, None is returned.

    Definition Classes
    TypedValue

Concrete Value Members

  1. final def !=(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  2. final def ##(): Int
    Definition Classes
    AnyRef → Any
  3. final def ==(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  4. def abstractsOver(other: DomainValue): Boolean

    Returns true iff the abstract state represented by this value abstracts over the state of the given value.

    Returns true iff the abstract state represented by this value abstracts over the state of the given value. In other words if every possible runtime value represented by the given value is also represented by this value.

    The abstract state generally encompasses every information that would be considered during a join of this value and the other value and that could lead to an Update.

    This method is reflexive, I.e., every value abstracts over itself.

    TheIllegalValue only abstracts over itself.

    Definition Classes
    Value
    Note

    abstractsOver is only defined for comparable values where both values have the same computational type.

    Implementation

    The default implementation relies on this domain value's join method. Overriding this method is, hence, primarily meaningful for performance reasons.

    See also

    isMorePreciseThan

  5. def adapt(target: TargetDomain, origin: ValueOrigin): (target)#DomainValue

    Adapts this value to the given domain (default: throws a domain exception that adaptation is not supported).

    Adapts this value to the given domain (default: throws a domain exception that adaptation is not supported). This method needs to be overridden by concrete Value classes to support the adaptation for a specific domain.

    Supporting the adapt method is primarily necessary when you want to analyze a method that is called by the currently analyzed method and you need to adapt this domain's values (the actual parameters of the method) to the domain used for analyzing the called method.

    Additionally, the adapt method is OPAL's main mechanism to enable dynamic domain-adaptation. I.e., to make it possible to change the abstract domain at runtime if the analysis time takes too long using a (more) precise domain.

    Definition Classes
    Value
    Annotations
    @throws( ... )
    Note

    The abstract interpretation framework does not use/call this method. This method is solely predefined to facilitate the development of project-wide analyses.

  6. final def allValues: Traversable[DomainReferenceValue]

    The set of base values this values abstracts over.

    The set of base values this values abstracts over. This set is never empty and contains this value if this value does not (further) abstract over other reference values.

    Definition Classes
    IsReferenceValue
    Note

    Primarily defined as a convenience interface.

  7. final def asDomainReferenceValue: DomainReferenceValue

    returns

    The represented reference value if and only if this value represents a reference value.

    Definition Classes
    ReferenceValueValue
  8. final def asInstanceOf[T0]: T0
    Definition Classes
    Any
  9. def clone(): AnyRef
    Attributes
    protected[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @native() @throws( ... )
  10. final def computationalType: ComputationalType

    Returns ComputationalTypeReference.

    Returns ComputationalTypeReference.

    Definition Classes
    ReferenceValueValue
  11. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  12. def equals(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  13. def finalize(): Unit
    Attributes
    protected[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( classOf[java.lang.Throwable] )
  14. final def getClass(): Class[_]
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  15. def hashCode(): Int
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  16. final def isInstanceOf[T0]: Boolean
    Definition Classes
    Any
  17. def isMorePreciseThan(other: DomainValue): Boolean

    Returns true iff the abstract state represented by this value is strictly more precise than the state of the given value.

    Returns true iff the abstract state represented by this value is strictly more precise than the state of the given value. In other words if every possible runtime value represented by this value is also represented by the given value, but both are not equal; in other words, this method is irreflexive.

    The considered abstract state generally encompasses every information that would be considered during a join of this value and the other value and that could lead to a StructuralUpdate.

    other

    Another DomainValue with the same computational type as this value. (The IllegalValue has no computational type and, hence, a comparison with an IllegalValue is not well defined.)

    Definition Classes
    Value
    Note

    It is recommended to overwrite this method for performance reasons, as the default implementation relies on join.

    See also

    abstractsOver

  18. def isNull: Answer

    If Yes the value is known to always be null at runtime.

    If Yes the value is known to always be null at runtime. In this case the upper bound is (has to be) empty. If the answer is Unknown then the analysis was not able to statically determine whether the value is null or is not null. In this case the upper bound is expected to be non-empty. If the answer is No then the value is statically known not to be null. In this case, the upper bound may precisely identify the runtime type or still just identify an upper bound.

    This default implementation always returns Unknown; this is a sound over-approximation.

    returns

    Unknown.

    Definition Classes
    IsReferenceValue
    Note

    This method is expected to be overridden by subtypes.

  19. def isPrecise: Boolean

    Returns true if the type information is precise.

    Returns true if the type information is precise. I.e., the type returned by upperTypeBound precisely models the runtime type of the value. If, isPrecise returns true, the type of this value can generally be assumed to represent a class type (not an interface type) or an array type. However, this domain also supports the case that isPrecise returns true even though the associated type identifies an interface type or an abstract class type. The later case may be interesting in the context of classes that are generated at run time.

    This default implementation always returns false.

    returns

    false

    Definition Classes
    IsReferenceValue
    Note

    This method is expected to be overridden by subtypes.

    ,

    isPrecise is always true if this value is known to be null.

  20. final def isPrimitiveValue: Boolean

    True in case of a value with primitive type; undefined if the type is unknown.

    True in case of a value with primitive type; undefined if the type is unknown.

    Definition Classes
    IsReferenceValueTypeInformation
  21. final def isReferenceValue: Boolean

    True if the value has a reference type; undefined if the type is unknown.

    True if the value has a reference type; undefined if the type is unknown.

    Definition Classes
    IsReferenceValueTypeInformation
  22. final def isUnknownValue: Boolean

    Returns true if no type information is available.

    Returns true if no type information is available.

    Definition Classes
    KnownTypeTypeInformation
  23. def isValueSubtypeOf(referenceType: ReferenceType): Answer

    Tests if the type of this value is potentially a subtype of the specified reference type under the assumption that this value is not null.

    Tests if the type of this value is potentially a subtype of the specified reference type under the assumption that this value is not null. This test takes the precision of the type information into account. That is, if the currently available type information is not precise and the given type has a subtype that is always a subtype of the current upper type bound, then Unknown is returned. Given that it may be computationally intensive to determine whether two types have a common subtype it may be better to just return Unknown in case that this type and the given type are not in a direct inheritance relationship.

    Basically, this method implements the same semantics as the ClassHierarchy's isSubtypeOf method, but it additionally checks if the type of this value could be a subtype of the given supertype. I.e., if this value's type identifies a supertype of the given supertype and that type is not known to be precise, the answer is Unknown.

    For example, assume that the type of this reference value is java.util.Collection and we know/have to assume that this is only an upper bound. In this case an answer is No if and only if it is impossible that the runtime type is a subtype of the given supertype. This condition holds, for example, for java.io.File which is not a subclass of java.util.Collection and which does not have any further subclasses (in the JDK). I.e., the classes java.io.File and java.util.Collection are not in an inheritance relationship. However, if the specified supertype would be java.util.List the answer would be unknown.

    returns

    This default implementation always returns Unknown.

    Definition Classes
    IsReferenceValue
    Note

    This method is expected to be overridden by subtypes.

    ,

    The function isValueSubtypeOf is not defined if isNull returns Yes; if isNull is Unknown then the result is given under the assumption that the value is not null at runtime. In other words, if this value represents null this method is not supported.

  24. def join(pc: PC, that: DomainValue): Update[DomainValue]

    Checks that the given value and this value are compatible with regard to its computational type and – if so – calls doJoin.

    Checks that the given value and this value are compatible with regard to its computational type and – if so – calls doJoin.

    See doJoin(PC,DomainValue) for details.

    pc

    The program counter of the instruction where the paths converge.

    that

    The "new" domain value with which this domain value should be joined. The caller has to ensure that the given value and this value are guaranteed to be two different objects.

    returns

    MetaInformationUpdateIllegalValue or the result of calling doJoin.

    Definition Classes
    Value
    Note

    It is in general not recommended/needed to override this method.

  25. final def ne(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  26. final def notify(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  27. final def notifyAll(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  28. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  29. def toString(): String
    Definition Classes
    AnyRef → Any
  30. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  31. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  32. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @native() @throws( ... )

Inherited from TypedValue[ReferenceType]

Inherited from KnownType

Inherited from TypeInformation

Inherited from Value

Inherited from AnyRef

Inherited from Any

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