This is the bottom-most interface which abstracts address access for both debugging and introspection. In the situation of debugging a target VM, these routines can throw the specified RuntimeExceptions to indicate failure and allow recovery of the debugging system. If these are used for introspecting the current VM and implementing functionality in it, however, it is expected that these kinds of failures will not occur and, in fact, a crash will occur if the situation arises where they would have been thrown.
Addresses are immutable. Further, it was decided not to expose the representation of the Address (and provide a corresponding factory method from, for example, long to Address). Unfortunately, because of the existence of C and "reuse" of low bits of pointers, it is occasionally necessary to perform logical operations like masking off the low bits of an "address". While these operations could be used to generate arbitrary Address objects, allowing this is not the intent of providing these operations.
This interface is able to fetch all Java primitive types, addresses, oops, and C integers of arbitrary size (see @see sun.jvm.hotspot.types.CIntegerType for further discussion). Note that the result of the latter is restricted to fitting into a 64-bit value and the high-order bytes will be silently discarded if too many bytes are requested.
Implementations may have restrictions, for example that the Java-related routines may not be called until a certain point in the bootstrapping process once the sizes of the Java primitive types are known. (The current implementation has that property.)
A note of warning: in C addresses, when represented as integers, are usually represented with unsigned types. Unfortunately, there are no unsigned primitive types in Java, so care will have to be taken in the implementation of this interface if using longs as the representation for 64-bit correctness. This is not so simple for the comparison operators.
*/ public interface Address { /** This is stated explicitly here because it is important for implementations to understand that equals() and hashCode() must absolutely, positively work properly -- i.e., two Address objects representing the same address are both equal (via equals()) and have the same hash code. */ public boolean equals(Object arg); /** This is stated explicitly here because it is important for implementations to understand that equals() and hashCode() must absolutely, positively work properly -- i.e., two Address objects representing the same address are both equal (via equals()) and have the same hash code. */ public int hashCode(); // // C/C++-related routines // public long getCIntegerAt (long offset, long numBytes, boolean isUnsigned) throws UnmappedAddressException, UnalignedAddressException; /** This returns null if the address at the given offset is NULL. */ public Address getAddressAt (long offset) throws UnmappedAddressException, UnalignedAddressException; /** Returns the decoded address at the given offset */ public Address getCompOopAddressAt (long offset) throws UnmappedAddressException, UnalignedAddressException; // // Java-related routines // public boolean getJBooleanAt (long offset) throws UnmappedAddressException, UnalignedAddressException; public byte getJByteAt (long offset) throws UnmappedAddressException, UnalignedAddressException; public char getJCharAt (long offset) throws UnmappedAddressException, UnalignedAddressException; public double getJDoubleAt (long offset) throws UnmappedAddressException, UnalignedAddressException; public float getJFloatAt (long offset) throws UnmappedAddressException, UnalignedAddressException; public int getJIntAt (long offset) throws UnmappedAddressException, UnalignedAddressException; public long getJLongAt (long offset) throws UnmappedAddressException, UnalignedAddressException; public short getJShortAt (long offset) throws UnmappedAddressException, UnalignedAddressException; /** This returns null if the address at the given offset is NULL. */ public OopHandle getOopHandleAt (long offset) throws UnmappedAddressException, UnalignedAddressException, NotInHeapException; public OopHandle getCompOopHandleAt (long offset) throws UnmappedAddressException, UnalignedAddressException, NotInHeapException; // // C/C++-related mutators. These throw UnmappedAddressException if // the target is read-only (for example, a core file rather than an // active process), if the target address is unmapped, or if it is // read-only. The implementation may supply extra detail messages. // /** Sets a C integer numBytes in size at the specified offset. Note that there is no "unsigned" flag for the accessor since the value will not be sign-extended; the number of bytes are simply copied from the value into the target address space. */ public void setCIntegerAt(long offset, long numBytes, long value); /** Sets an Address at the specified location. */ public void setAddressAt(long offset, Address value); // // Java-related mutators -- see above. // public void setJBooleanAt (long offset, boolean value) throws UnmappedAddressException, UnalignedAddressException; public void setJByteAt (long offset, byte value) throws UnmappedAddressException, UnalignedAddressException; public void setJCharAt (long offset, char value) throws UnmappedAddressException, UnalignedAddressException; public void setJDoubleAt (long offset, double value) throws UnmappedAddressException, UnalignedAddressException; public void setJFloatAt (long offset, float value) throws UnmappedAddressException, UnalignedAddressException; public void setJIntAt (long offset, int value) throws UnmappedAddressException, UnalignedAddressException; public void setJLongAt (long offset, long value) throws UnmappedAddressException, UnalignedAddressException; public void setJShortAt (long offset, short value) throws UnmappedAddressException, UnalignedAddressException; public void setOopHandleAt (long offset, OopHandle value) throws UnmappedAddressException, UnalignedAddressException; // // Arithmetic operations -- necessary evil. // /** This throws an UnsupportedOperationException if this address happens to actually be an OopHandle, because interior object pointers are not allowed. Negative offsets are allowed and handle the subtraction case. */ public Address addOffsetTo (long offset) throws UnsupportedOperationException; /** This method had to be added in order to support heap iteration in the debugging system, and is effectively the dangerous operation of allowing interior object pointers. For this reason it was kept as a separate API and its use is forbidden in the non-debugging (i.e., reflective system) case. It is strongly recommended that this not be called by clients: it is currently wrapped up in the Space's iteration mechanism. */ public OopHandle addOffsetToAsOopHandle(long offset) throws UnsupportedOperationException; /** Performs the subtraction "this - arg", returning the resulting offset in bytes. Note that this must handle a null argument properly, and can be used to convert an Address into a long for further manipulation, but that the reverse conversion is not possible. (FIXME: any signed/unsigned issues? Should this work for OopHandles?) */ public long minus(Address arg); /** Performs unsigned comparison "this < arg". (FIXME: should this work for OopHandles?) */ public boolean lessThan (Address arg); /** Performs unsigned comparison "this <= arg". (FIXME: should this work for OopHandles?) */ public boolean lessThanOrEqual (Address arg); /** Performs unsigned comparison "this > arg". (FIXME: should this work for OopHandles?) */ public boolean greaterThan (Address arg); /** Performs unsigned comparison "this >= arg". (FIXME: should this work for OopHandles?) */ public boolean greaterThanOrEqual(Address arg); /** This throws an UnsupportedOperationException if this address happens to actually be an OopHandle. Performs a logical "and" operation of the bits of the address and the mask (least significant bits of the Address and the mask are aligned) and returns the result as an Address. Returns null if the result was zero. */ public Address andWithMask(long mask) throws UnsupportedOperationException; /** This throws an UnsupportedOperationException if this address happens to actually be an OopHandle. Performs a logical "or" operation of the bits of the address and the mask (least significant bits of the Address and the mask are aligned) and returns the result as an Address. Returns null if the result was zero. */ public Address orWithMask(long mask) throws UnsupportedOperationException; /** This throws an UnsupportedOperationException if this address happens to actually be an OopHandle. Performs a logical "exclusive or" operation of the bits of the address and the mask (least significant bits of the Address and the mask are aligned) and returns the result as an Address. Returns null if the result was zero. */ public Address xorWithMask(long mask) throws UnsupportedOperationException; }