RUNTIME CHECKING OF DYNAMIC SUBRANGES

• US 20100174893A1
• Filed: 01/05/2009
• Published: 07/08/2010
• Est. Priority Date: 01/05/2009
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Rivera, Jose G.
• Granted Patent: US 7,962,729 B2
• Time in Patent Office: Days
• US Class Current: 712/244
• CPC Class Codes: G06F 9/30014 with variable precision
• CPC Class Codes: G06F 9/38 Concurrent instruction execution, e.g. pipeline or look ahead

Abstract

Software defects (e.g., array access out of bounds, stack overflow, infinite loops, and data corruption) occur due to integer values falling outside their expected range. Because programming languages do not include range-checking instructions as part of their language, to detect software defects and ensure that the code runs smoothly, programmers generally use 1) runtime assertions and/or 2) sub-range data types. However, these techniques cause additional conditional branches, incur additional overhead, and decrease processor performance. Processors comprising a range checking hardware feature supported by machine instructions for runtime integer range checking can eliminate the conditional branches generated during runtime integer range checks. Programming language extensions for the range checking hardware can allow dynamic range bounds to be defined during runtime without decreasing the processor'"'"'s performance. This can allow for easier programming and code that is easier to maintain.

Claims

1. A method comprising:

determining a target register, wherein an instruction indicates operations to modify contents of the target register;

determining a lower range bound value and an upper range bound value for the target register, wherein a set of one or more range bound registers indicate the upper range bound value and the lower range bound value;

determining, based on the lower range bound value and the upper range bound value, that a value to be stored in the target register is invalid; and

generating a range checking exception, wherein the range checking exception indicates that the value to be stored in the target register violates any one of the lower and the upper range bound values.

2. The method of claim 1, further comprising determining a type of range checking indicated by range status registers for the target register.

3. The method of claim 2, wherein the range status registers indicate any one or more of whether range checking is performed using signed or unsigned arithmetic and whether inclusive or exclusive range bounds are applied on the target register.

4. The method of claim 3, wherein each bit of the range status registers corresponds to one of a plurality of registers.

5. The method of claim 1, wherein the set of one or more range bound registers that indicate the upper range bound value and the lower range bound value comprises any one of an extended range bound register indicating the lower and the upper range bound value a pair of distinct registers, one of which indicates the lower range bound value and the other of which indicates the upper range bound value.

6. The method of claim 1, wherein setting a range checking flag in a machine status register (MSR) globally enables range checking for a plurality of registers.

7. The method of claim 1, wherein the set of one or more range bound registers are modified using any one of special machine instructions for assigning, saving, restoring, and clearing the lower and upper range bound values for the target register.

8. The method of claim 1, further comprising:

determining, based on the lower range bound value and the upper range bound value, that a value in the target register is invalid; and

generating a range checking exception, wherein the range checking exception indicates that the value stored in the target register violates at least one of the lower and the upper range bound values.

9. The method of claim 8, wherein the generating the range checking exception further comprises removing the invalid value from the target register.

10. One or more machine-readable media having stored therein a program product, which when executed a set of one or more processor units causes the set of one or more processor units to perform operations that comprise:

determining a target register, wherein an instruction indicates operations to modify contents of the target register;

determining a lower range bound value and an upper range bound value for the target register, wherein a set of one or more range bound registers indicates the upper range bound value and the lower range bound value;

determining, based on the lower range bound and the upper range bound values, that a value to be stored in the target register is invalid; and

generating a range checking exception, wherein the range checking exception indicates that the value to be stored in the target register violates any one of the lower and the upper range bound values.

11. The machine-readable media of claim 10 wherein the operations further comprise determining a type of range checking indicated by range status registers for the target register.

12. The machine-readable media of claim 11, wherein the range status registers indicate any one or more of whether range checking is performed using signed or unsigned arithmetic and whether inclusive or exclusive range bounds are applied on the target register.

13. The machine-readable media of claim 12, wherein each bit of the range status registers corresponds to one of a plurality of registers.

14. The machine-readable media of claim 10, wherein the set of one or more range bound registers that indicate the upper range bound value and the lower range bound value comprises any one of an extended range bound register indicating the lower and the upper range bound value a pair of distinct registers, one of which indicates the lower range bound value and the other of which indicates the upper range bound value.

15. The machine-readable media of claim 10, wherein setting a range checking flag in a machine status register globally enables range checking for a plurality of registers.

16. The machine-readable media of claim 10, wherein the set of one or more range bound registers are modified using any one of special machine instructions for assigning, saving, restoring, and clearing the lower and upper range bound values for the target register.

17. The machine-readable media of claim 10, wherein the operations further comprise:

determining, based on the lower range bound value and the upper range bound value, that a value in the target register is invalid; and

generating a range checking exception, wherein the range checking exception indicates that the value stored in the target register violates at least one of the lower and the upper range bound values.

18. The machine-readable media of claim 17, wherein said operation of generating the range checking exception further comprises removing the invalid value from the target register.

19. An apparatus comprising:

one or more registers;

one or more range checking registers comprising a set of one or more range bound registers indicating an upper and a lower range bound value for the registers;

an arithmetic and logic unit operable to perform arithmetic and logic operations on one or more of the registers; and

a range checking unit operable to

determine a target register, wherein an instruction indicates operations to modify contents of the target register;

determine a lower range bound value and an upper range bound value for the target register, wherein the set of one or more range bound registers indicate the upper range bound value and the lower range bound value;

determine, based on the lower range bound and the upper range bound values, that a value to be stored in the target register is invalid; and

generate a range checking exception, wherein the range checking exception indicates that the value to be stored in the target register violates any one of the lower and the upper range bound values.

20. The apparatus of claim 19, wherein the range checking unit comprises one or more machine-readable media.