Emulated memory management

• US 7,403,887 B1
• Filed: 01/14/2004
• Issued: 07/22/2008
• Est. Priority Date: 01/14/2004
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Bishop, Alan G., Taillefer, Martin, Dyer, Landon
• Primary Examiner(s): Rodriguez; Paul L
• Assistant Examiner(s): Janakiraman; Nithya
• Application Number:
  US10/759,773
• Time in Patent Office: 1,651 Days
• Field of Search: 703/26
• US Class Current: 703/26
• CPC Class Codes: G06F 12/1009 using page tables, e.g. page table structures

Abstract

A first software program executing on a computing device emulates a second computing device executing a software program using emulated memory. The first software program permits the second software program to perform an operation on a contiguous portion of the emulated memory only when a pointer and a table entry both contain the same identifier, thus protecting against common types of memory usage errors in the second software program. The pointer has an address to the contiguous portion. The table entry maps to the contiguous portion. A plurality of table entries map to a respective plurality of contiguous portions of the emulated memory. A plurality of the pointers each contain the address to a respective contiguous portion of the emulated memory as well as containing an identifier corresponding to the respective contiguous portion of the emulated memory. The second computing device can be high or low in resources.

Claims

1. A method of emulating memory management of a low resource computing device with an emulator application running on a high resource computing device, the method comprising:

allocating one or more contiguous portions of emulated memory on the high resource computing device, wherein each contiguous portion has an address;

assigning an identifier to each address, wherein the identifier is assigned by a memory manager associated with the emulator application;

entering each identifier into a table, wherein each identifier is mapped to its corresponding address;

producing one or more pointers, wherein each of the one or more pointers includes an identifier and points to an address corresponding to the identifier; and

emulating a memory access operation, wherein the emulating comprises;

attempting to access a contiguous portion of the emulated memory having a first address;

comparing a first identifier in a pointer associated with the first address with a second identifier included in the table, the second identifier being mapped to the first address, and

accessing the contiguous portion of emulated memory associated with the first address when the first and second identifiers are the same.

2. The method as defined in claim 1, wherein the entering is performed by the memory manager associated with the emulator application.

3. The method as defined in claim 1, further comprising outputting a diagnostic when the first and second identifiers are not the same.

4. The method as defined in claim 1, wherein the low resource computing device is selected from the group consisting of:

a personal computer (PC);

a workstation;

a server;

a set top box;

a video game console;

a Personal Digital Assistant (PDA);

a cellular telephone;

a handheld computing device; and

a computing device having less memory and/or computing resources than that of another computing device executing the emulator application.

5. A computer-readable medium comprising instructions that, when executed by a computer, performs the method of claim 1.

6. A method for emulating at least some of the operational characteristics of a low resource computing device using resources of a high resource computing device comprising:

making a call to a memory manager for an emulated memory access operation to an allocated contiguous portion of emulated memory, wherein a generation count has been assigned by the memory manager for the emulated memory access operation to;

a plurality of table entries corresponding to a respective plurality of said allocated contiguous portions of emulated memory, and

a plurality of pointers each including an address to a respective said allocated contiguous portion of emulated memory;

comparing the generation count;

in the pointer including the address to the allocated contiguous portion of emulated memory; and

in the table entry corresponding to the allocated contiguous portion of emulated memory;

if the respective said generation counts in the comparison do not match, then outputting a diagnostic; and

if the respective said generation counts in the comparison match, removing the generation count from the pointer specified by the memory manager for the emulated memory access operation during the performing of the emulated memory access operation for which the memory manager was called.

7. The method as defined in claim 6, further comprising:

performing the emulated memory access operation for which the memory manager was called when there is a match of the respective said generation counts; and

preventing the performance of the emulated memory access operation for which the memory manager was called when the respective said generation counts of the comparison do not match.

8. The method as defined in claim 7, further comprising, when there is a match and the emulated memory access operation is not a read or a write operation, incrementing the generation count in both:

the pointer including the address to the allocated contiguous portion of emulated memory; and

the table entry corresponding to the allocated contiguous portion of emulated memory.

9. The method as defined in claim 6, wherein the emulated memory access operation is selected from the group consisting of:

a read operation;

a write operation;

a reallocation operation; and

an operation to free one or more of said allocated contiguous portions of emulated memory.

10. The method as defined in claim 6, further comprising, prior to the making of the call:

making a call to the memory manager for to allocate a contiguous portion of emulated memory;

receiving one said pointer from the memory manager that includes the address of the allocated contiguous portion of emulated memory;

performing the allocation of the contiguous portion of emulated memory; and

inserting the generation count;

in the;

the pointer including the address to the one said allocated contiguous portion of emulated memory; and

the plurality of table entries corresponding to the one said allocated contiguous portion of emulated memory.

11. In a first computing device executing a first application for the emulation of a second computing device executing a second application, a method comprising:

making a call from the second application to a memory manager for an emulated memory access operation to an allocated contiguous portion of emulated memory used by the second application and including a plurality of said allocated contiguous portions, wherein;

a generation count is in a plurality of table entries corresponding to a respective plurality of said allocated contiguous portions of emulated memory, the generation count being entered into the plurality of table entries by the first application;

a generation count is in a plurality of pointers each including an address to a respective said allocated contiguous portion of emulated memory, the generation count being included in the plurality of pointers by the first application;

for the emulated memory access operation, the memory manager uses the address in the pointer that corresponds to the allocated contiguous portion in emulated memory after removal of the generation count from the pointer; and

prior to performing the emulated memory access operation to the allocated contiguous portion of emulated memory;

comparing the generation count;

in the pointer including the address of the allocated contiguous portion of the emulated memory; and

in the table entry corresponding to the allocated contiguous portion of the emulated memory;

outputting a diagnostic when the respective said generation counts of the comparison do not match.

12. The method as defined in claim 11, further comprising:

performing the emulated memory access operation for which the memory manager was called when there is a match of the respective said generation counts; and

preventing the performance of the emulated memory access operation for which the memory manager was called when the respective said generation counts of the comparison do not match.

13. The method as defined in claim 12 further comprising, when there is a match of the respective said generation counts and the emulated memory access operation is not a read operation or a write operation, incrementing the generation count in both:

the pointer including the address to the allocated contiguous portion of emulated memory; and

the table entry corresponding to the allocated contiguous portion of emulated memory.

14. The method as defined in claim 11, further comprising, when:

the comparison finds that there is a match of the respective said generation counts; and

the emulated memory access operation is neither a read operation nor a write operation;

performing the emulated memory access operation for which the memory manager was called and during which the generation count is removed from the pointer used by the memory manager.

15. The method as defined in claim 11, wherein the emulated memory access operation is selected from the group consisting of:

a read operation;

a write operation;

a reallocation operation; and

an operation to free one or more of said allocated contiguous portions of emulated memory.

16. The method as defined in claim 11, further comprising, prior to the making of the call by the second application to the memory manager for the emulated memory access operation:

making a call by the second application to the memory manager for an allocation of said allocated contiguous portion of emulated memory;

receiving one said pointer from the memory manager that includes an address to said allocated contiguous portion of emulated memory;

performing an allocation of said allocated contiguous portions of emulated memory; and

incrementing the generation count in both;

the pointer including the address to said allocated contiguous portion of emulated memory; and

the table entry corresponding to said allocated contiguous portion of emulated memory.

17. The method as defined in claim 11, wherein the second computing device is selected from the group consisting of:

a PC;

a workstation;

a server;

a set top box;

a video game console;

a PDA;

a cellular telephone;

a handheld computing device;

a consumer electronic device having a processor and memory; and

a client having less memory and/or computing resources than that of the first computing device.

18. A computer-readable medium comprising instructions that, when executed by a computer, performs the method of claim 11.

19. A computer-readable medium including instructions for execution by a computer, wherein the instructions comprise:

first logic calling for an emulated memory access operation with respect to a first of a contiguous portion of an emulated memory for which there is;

a corresponding table entry in a table having a plurality of said table entries that map to respective other said portions of the emulated memory, wherein each said table entry includes an identifier, and further wherein each identifier is entered into its corresponding table entry by an emulator application; and

a corresponding pointer to a plurality of pointers each including an identifier and an address to a respective said contiguous portion of the emulated memory, wherein each identifier is entered into its corresponding pointer by the emulator application;

second logic, in response to the first logic, such that, if the identifier in the table entry corresponding to the first said contiguous portion is the same as the identifier in the pointer corresponding to the first said portion, then;

the emulated memory access operation is performed with respect to the first said contiguous portion of the emulated memory.

20. The computer-readable medium as defined in claim 19, wherein the emulated memory access operation is selected from the group consisting of:

a read operation;

a write operation;

a reallocation operation; and

an operation to free one or more of said portions of the emulated memory.

21. The computer-readable medium as defined in claim 19, wherein the performance of the memory operation further comprises removing the identifier from the pointer corresponding to the first said contiguous portion during the performance of the memory operation.

22. The computer-readable medium as defined in claim 19, wherein the second logic is further configured to identically change the identifier in both the table entry corresponding to the first said portion and the pointer corresponding to the first said portion when the emulated memory access operation is neither a read operation nor a write operation.