Using short references to access program elements in a large address space

• US 20030229769A1
• Filed: 06/07/2002
• Published: 12/11/2003
• Est. Priority Date: 06/07/2002
• Status: Active Grant

• Current Assignee: Oracle America, Inc. (Oracle Corporation)
• Original Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Inventors: Montemayor, Oscar A.
• Granted Patent: US 6,865,659 B2
• Time in Patent Office: Days
• US Class Current: 711/206
• CPC Class Codes: G06F 12/0292 using tables or multilevel address translation means G06F12/023 takes precedence; address translation in virtual memory systems G06F12/10
• CPC Class Codes: G06F 12/0623 for memory modules
• CPC Class Codes: G06F 9/44521 Dynamic linking or loading; Link editing at or after load time, e.g. Java class loading
• CPC Class Codes: G06Q 20/341 Active cards, i.e. cards including their own processing means, e.g. including an IC or chip
• CPC Class Codes: G06Q 20/3576 Multiple memory zones on card
• CPC Class Codes: G07F 7/1008 Active credit-cards provided with means to personalise their use, e.g. with PIN-introduction/comparison system

Abstract

One embodiment of the present invention provides a system that accesses a desired element during execution of a program. During operation, the system receives a reference to the desired element. The system determines if the reference is an internal reference to a location in a local package that is currently executing, or an external reference to a location in an external package. If the reference is an external reference, the system uses an index component of the reference to lookup an address for the desired element in a global reference table. Next, the system uses the address to access the desired element. Note that the address retrieved from the global reference table is larger than the reference, which allows the address to access a larger address space than is possible to access with the reference alone.

Claims

1. A method for accessing a desired element during execution of a program, comprising:

receiving a reference to the desired element during execution of the program;

determining if the reference is an internal reference to a location in a local package that is currently executing, or an external reference to a location in an external package;

if the reference is an external reference, using an index component from the reference to lookup an address for the desired element in a global reference table; and

using the address to access the desired element;

wherein the address retrieved from the global reference table is larger than the reference, thereby allowing the address to access a larger address space than is possible to access with the reference alone.

2. The method of claim 1, wherein if the reference is an internal reference, the method further comprises:

determining a base address of a component in which the desired element is located; and

adding an offset of the reference to the base address to produce the address for the desired element.

3. The method of claim 2, wherein determining the base address of the component involves:

obtaining an identifier for the local package that is currently executing;

using the identifier to lookup an entry in a package location table, wherein the entry points to a component location table for the local package; and

examining the component location table to determine the base address of the component.

4. The method of claim 3, wherein examining the component location table involves first examining an instruction preceding the reference to determine which component the desired element is located in.

5. The method of claim 1, further comprising installing a new package, wherein installing the new package involves:

calculating element addresses for all exported references associated with the new package;

adding the element addresses to the global reference table; and

replacing all external references within the new package with references to entries in the global reference table, wherein the entries in the global reference table contain element addresses for the desired elements.

6. The method of claim 1, wherein determining if the reference is an internal reference or an external reference involves examining a reserved bit within the reference, wherein the reserved bit indicates whether the reference is an internal reference or an external reference.

7. The method of claim 1, wherein looking up the address for the desired element in the global reference table involves retrieving an absolute address for the desired element from the global reference table.

8. The method of claim 1, wherein looking up the address for the desired element in the global reference table involves retrieving a relative address for the desired element from the global reference table, wherein the relative address specifies an offset relative to a base address of a component containing the desired element.

9. The method of claim 1, wherein the desired element can include:

a class record;

a static field; and

a method.

10. The method of claim 1, wherein the reference is 16 bits in size and the address retrieved from the global reference table is 32 bits in size.

11. The method of claim 1, wherein the global reference table is stored as a multi-level table so that the entire global reference table does not have to be allocated at once.

12. The method of claim 1, wherein a given package includes:

a static field component containing static fields;

a class component containing class records;

a method component containing methods;

an export component; and

an import component.

13. A computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for accessing a desired element during execution of a program, the method comprising:

receiving a reference to the desired element during execution of the program;

determining if the reference is an internal reference to a location in a local package that is currently executing, or an external reference to a location in an external package;

if the reference is an external reference, using an index component from the reference to lookup an address for the desired element in a global reference table; and

using the address to access the desired element;

wherein the address retrieved from the global reference table is larger than the reference, thereby allowing the address to access a larger address space than is possible to access with the reference alone.

14. The computer-readable storage medium of claim 13, wherein if the reference is an internal reference, the method further comprises:

determining a base address of a component in which the desired element is located; and

adding an offset of the reference to the base address to produce the address for the desired element.

15. The computer-readable storage medium of claim 14, wherein determining the base address of the component involves:

obtaining an identifier for the local package that is currently executing;

using the identifier to lookup an entry in a package location table, wherein the entry points to a component location table for the local package; and

examining the component location table to determine the base address of the component.

16. The computer-readable storage medium of claim 15, wherein examining the component location table involves first examining an instruction preceding the reference to determine which component the desired element is located in.

17. The computer-readable storage medium of claim 13, wherein the method further comprises installing a new package, wherein installing the new package involves:

calculating element addresses for all exported references associated with the new package;

adding the element addresses to the global reference table; and

replacing all external references within the new package with references to entries in the global reference table, wherein the entries in the global reference table contain element addresses for the desired elements.

18. The computer-readable storage medium of claim 13, wherein determining if the reference is an internal reference or an external reference involves examining a reserved bit within the reference, wherein the reserved bit indicates whether the reference is an internal reference or an external reference.

19. The computer-readable storage medium of claim 13, wherein looking up the address for the desired element in the global reference table involves retrieving an absolute address for the desired element from the global reference table.

20. The computer-readable storage medium of claim 13, wherein looking up the address for the desired element in the global reference table involves retrieving a relative address for the desired element from the global reference table, wherein the relative address specifies an offset relative to a base address of a component containing the desired element.

21. The computer-readable storage medium of claim 13, wherein the desired element can include:

a class record;

a static field; and

a method.

22. The computer-readable storage medium of claim 13, wherein the reference is 16 bits in size and the address retrieved from the global reference table is 32 bits in size.

23. The computer-readable storage medium of claim 13, wherein the global reference table is stored as a multi-level table so that the entire global reference table does not have to be allocated at once.

24. The computer-readable storage medium of claim 13, wherein a given package includes:

a static field component containing static fields;

a class component containing class records;

a method component containing methods;

an export component; and

an import component.

25. An apparatus that facilitates accessing a desired element during execution of a program, comprising:

an execution mechanism that is configured to receive a reference to the desired element during execution of the program; and

an address resolution mechanism that is configured to determine if the reference is an internal reference to a location in a local package that is currently executing, or an external reference to a location in an external package;

wherein if the reference is an external reference, the address resolution mechanism is configured to use an index component from the reference to lookup an address for the desired element in a global reference table;

wherein the execution mechanism is additionally configured to use the address to access the desired element;

wherein the address retrieved from the global reference table is larger than the reference, thereby allowing the address to access a larger address space than is possible to access with the reference alone.

26. The apparatus of claim 25, wherein if the reference is an internal reference, the address resolution mechanism is additionally configured to:

determine a base address of a component in which the desired element is located; and

to

add an offset of the reference to the base address to produce the address for the desired element.

27. The apparatus of claim 26, wherein while determining the base address of the component, the address resolution mechanism is configured to:

obtain an identifier for the local package that is currently executing;

use the identifier to lookup an entry in a package location table, wherein the entry points to a component location table for the local package; and

to

examine the component location table to determine the base address of the component.

28. The apparatus of claim 27, wherein while examining the component location table, the address resolution mechanism is configured to first examine an instruction preceding the reference to determine which component the desired element is located in.

29. The apparatus of claim 25, further comprising a package installation mechanism that is configured to:

receive a new package to be installed;

calculate element addresses for all exported references associated with the new package;

add the element addresses to the global reference table; and

to

replace all external references within the new package with references to entries in the global reference table, wherein the entries in the global reference table contain element addresses for the desired elements.

30. The apparatus of claim 25, wherein while determining if the reference is an internal reference or an external reference, the address resolution mechanism is configured to examine a reserved bit within the reference, wherein the reserved bit indicates whether the reference is an internal reference or an external reference.

31. The apparatus of claim 25, wherein while looking up the address for the desired element in the global reference table, the address resolution mechanism is configured to retrieve an absolute address for the desired element from the global reference table.

32. The apparatus of claim 25, wherein while looking up the address for the desired element in the global reference table, the address resolution mechanism is configured to retrieve a relative address for the desired element from the global reference table, wherein the relative address specifies an offset relative to a base address of a component containing the desired element.

33. The apparatus of claim 25, wherein the desired element can include:

a class record;

a static field; and

a method.

34. The apparatus of claim 25, wherein the reference is 16 bits in size and the address retrieved from the global reference table is 32 bits in size.

35. The apparatus of claim 25, wherein the global reference table is stored as a multi-level table so that the entire global reference table does not have to be allocated at once.

36. The apparatus of claim 25, wherein a given package includes:

a static field component containing static fields;

a class component containing class records;

a method component containing methods;

an export component; and

an import component.

37. A means for accessing a desired element during execution of a program, comprising:

an execution means for receiving receive a reference to the desired element during execution of the program;

a determining means for determining if the reference is an internal reference to a location in a local package that is currently executing, or an external reference to a location in an external package;

a lookup means, wherein if the reference is an external reference, the lookup uses an index component from the reference to lookup an address for the desired element in a global reference table; and

wherein the execution means is additionally uses the address to access the desired element;

wherein the address retrieved from the global reference table is larger than the reference, thereby allowing the address to access a larger address space than is possible to access with the reference alone.