METHOD FOR PROTECTING USER-MANAGED MEMORY USING AN EXCEPTION

• US 20090271763A1
• Filed: 04/29/2008
• Published: 10/29/2009
• Est. Priority Date: 04/29/2008
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Shyamasundar, Rudrapatna K., Varma, Pradeep
• Granted Patent: US 8,347,061 B2
• Time in Patent Office: Days
• US Class Current: 717/114
• CPC Class Codes: G06F 12/023 Free address space management
• CPC Class Codes: G06F 12/0253 Garbage collection, i.e. reclamation of unreferenced memory
• CPC Class Codes: G06F 12/145 the protection being virtual, e.g. for virtual blocks or segments before a translation mechanism
• CPC Class Codes: G06F 2212/702 Conservative garbage collection

Abstract

Techniques for providing safe user-managed memory are provided The techniques include performing memory allocation in constant time, performing memory de-allocation in constant time, performing memory access overhead for safety checking in constant time, and using the memory allocation, memory de-allocation and memory access overhead to protect at least one memory access, user-specified allocation and de-allocation with at least one exception for said user-managed memory.

Claims

1. A method for providing safe user-managed memory, comprising the steps of:

performing memory allocation in constant time;

performing memory de-allocation in constant time;

performing memory access overhead for safety checking in constant time; and

using the memory allocation, memory de-allocation and memory access overhead to protect at least one memory access, user-specified allocation and de-allocation with at least one exception for said user-managed memory.

2. An exception protection system for user-specified memory management, wherein the system comprises:

a mechanism for memory allocation;

a mechanism for memory de-allocation;

a mechanism for memory access overhead; and

a mechanism for using the memory allocation, memory de-allocation and memory access overhead to protect one or more memory accesses and user-specified allocation and de-allocation with at least one exception for said user-specified memory.

3. The system of claim 2, wherein the exception protection system is object-version based.

4. The system of claim 3, wherein one or mole object versions used in the exception protection system are designed for recycling using a conservative garbage collector so that unbounded protected heap recycling during a program run can take place.

5. The system of claim 2, wherein the exception protection system comprises an ability for real-time operation.

6. The system of claim 2, further comprising a synchronization cost in a context of at least one multi-core machine, comprising:

a constant number of at least one synchronization step for memory allocation and de-allocation; and

no synchronization overhead for memory read and memory write access.

7. The system of claim 2, wherein the exception mechanism is interoperable with unprotected user-specified memory management, with support for:

at least one distinct heap space for protected and unprotected memories;

unprotected access override to protect at least one object for gaining speed at expense of dynamic exception checking; and

allocation of at least one object from an un-protected heap for faster allocation and later unprotected access.

8. The system of claim 7, further comprising obtaining backwards compatibility of the system via unprotected user-specified memory management.

9. The system of claim 7, wherein a choice of heap size for protected and un-protected memory is carried out using profiling data from at least one program run.

10. The system of claim 2, wherein the exception mechanism is interoperable with automatic memory management, with support for at least one distinct heap space for protected and automatically-managed memories.

11. The system of claim 2, further comprising real-time application of the exception mechanism, with protection maximized subject to resource availability within at least one real-time constraint.

12. The system of claim 2, further comprising virtualizing a protected heap so that at least one pointer bit not used for indexing into the heap can be used for encoding at least one object version that reflect a number of times object space has been re-used by at least one of the memory allocator and memory de-allocator.

13. The system of claim 2, further comprising at least one pointer to an exception-protected heap, wherein the at least one pointer is encoded to carry at least one object version bit and at least one offset bit into a protected heap.

14. The system of claim 13, wherein the encoded pointer occupies a space of standard scalar size (for example, one machine word or two machine words) to obtain atomic hardware support over one or more encoded pointers and one or more meaningful casts between pointers and other scalar types.

15. The system of claim 2, further comprising at least one pointer to an unprotected heap from user code, wherein the at least one pointer is at least one standard language pointer, with access to an unprotected heap via at least one language pointer being as fast as in at least one standard language implementation.

16. The system of claim 2, further comprising a garbage collector with safe user de-allocation override and deferred garbage collection due to memory virtualization through at least one version number.

17. The system of claim 16, wherein a user provides the garbage collector programmatically.

18. A computer program product comprising a computer readable medium having computer readable program code for providing safe user-managed memory, said computer program product including:

computer readable program code for performing memory allocation in constant time;

computer readable program code for performing memory de-allocation in constant time;

computer readable program code for performing memory access overhead for safety checking in constant time; and

computer readable program code for using the memory allocation, memory de-allocation and memory access overhead to protect at least one memory access, user-specified allocation and de-allocation with at least one exception for said user-managed memory.

19. A system for providing safe user-managed memory, comprising:

a memory; and

at least one processor coupled to said memory and operative to;

perform memory allocation in constant time;

perform memory de-allocation in constant time;

perform memory access overhead for safety checking in constant time; and

use the memory allocation, memory de-allocation and memory access overhead to protect at least one memory access, user-specified allocation and de-allocation with at least one exception for said user-managed memory.