Patent Grant
11847476
When a new version of a computer system (a “new device”) is released it is desirable for the applications written for a previous version of the system (a “legacy device”) to run flawlessly on the new device. This capability is often referred to as “backwards compatibility” with respect to “legacy applications”. Even if the new device is capable of executing legacy applications created for the legacy device, the new device may still fail to be backwards compatible when running those applications. Differences in performance of the hardware components of the new device and legacy device can cause errors in synchronization on the new device. Such differences in performance can arise, e.g., from differences in capabilities of the central processing unit (CPU) of the new device relative to the legacy device. For example, if the CPU on the new device is faster than the CPU on the legacy device, data still being used by another component of the new device may be prematurely overwritten by the CPU.
The teachings of the present disclosure can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:
The disadvantages associated with the prior art are overcome by aspects of the present disclosure relating to a method in which a computing device responds to a call from an application for information regarding a processor on the computing device by returning information regarding a different processor than the processor on the computing device.
Although the following detailed description contains many specific details for the purposes of illustration, anyone of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the claimed invention. Accordingly, the exemplary embodiments of the invention described below are set forth without any loss of generality to, and without imposing limitations upon, the claimed invention.
Introduction
To address problems resulting from differences in CPU behavior relative to a legacy device, a new device may mimic certain capabilities of the legacy device CPU when running legacy applications. A key feature of the ability to mimic a legacy device is to fool the legacy application into acting as though it is running on a legacy device. Since many applications are designed to be run on different processors, modern processors often implement an opcode or a register that allows a software application to discover details of the processor. To facilitate backwards compatibility, a processor on a new device can execute the opcode or supply the register value in such a way that different processor information is returned in response to a call from a legacy application. The different information is referred to herein as a “Spoofed Processor ID”. The spoofed processor ID would selectively identify certain features of the new device as being either different from ones that are actually supported or not being supported at all when in fact they are.
Method
The method 100 depicted in the flow diagram shown in
The information returned by the processor to the requesting application 101 would vary based on whether the application 101 is a legacy application or a new application, i.e., one written to run on the device. If the requesting application 101 is a new application, the processor returns true processor information, e.g., the correct processor ID 103 for the processor on the device running the application, as indicated at 106. If the requesting application 101 is a legacy application, the processor returns spoofed processor information, e.g., a spoofed processor ID 105, as indicated at 108. The returned information may identify certain features that are in fact supported by the processor as not being supported, or specify that the processor running the application is a legacy processor.
By way of example and not by way of limitation, the spoofed processor ID 105 may be returned by a modified CPUID instruction, which is an opcode supported by the x86 architecture. By using the CPUID opcode, software can determine processor type and the presence of features such as implementation of the various SSE instruction set architectures. On the x86 architecture the CPUID opcode is the bytes 0Fh and A2h and the value in the EAX register, and in some cases the ECX register, specifies what information to return.
In assembly language the CPUID instruction takes no parameters and instead implicitly uses the EAX register to determine the main category of information returned, which is commonly called the CPUID leaf. An application calling CPUID with EAX=0 will receive in the EAX register the highest EAX calling parameter (leaf) that the CPU supports in return, and other registers contain a vendor ID that identifies the CPU manufacturer. To obtain extended function information CPUID may be called with the most significant bit of EAX set. To determine the highest extended function calling parameter, CPUID may be called with EAX=80000000h. Some leaves also have sub-leaves, which are selected via the ECX register before calling CPUID.
Calling CPUID with EAX=1 returns information on the CPU's stepping model, model, and family information in EAX (also called the signature of a CPU), feature flags in EDX and ECX, and additional feature info in EBX. Calling CPUID with EAX=2 returns a list of descriptors indicating cache and translation lookaside buffer (TLB) capabilities in EAX, EBX, ECX and EDX registers. Other EAX values return information such as processor serial number, thread/core and cache topology, extended features, processor brand, L1 cache and TLB identifiers, extended L2 cache features, power management feature identifiers, and virtual and physical address sizes. A program of the type shown in
CPU
The processor ID spoofing capability shown in
In the particular implementation shown in
In alternative implementations there may be two different processor ID programs, one for legacy applications and one for new device application. In such implementations, the CPU 200 may selectively run one program or the other when executing the CPUID instruction depending on whether the application it is running is a legacy application or a new device application. In other alternative implementations, the processor ID program may be implemented by special dedicated hardware, e.g., certain aspects of returning the processor ID information may be implemented by hardware logic rather than microcode stored in ROM 218. In other alternative implementations, the microcode may be stored in Random Access Memory (RAM) rather than in ROM.
System
A CPU of the type shown in
The device 300 runs the application 101 by executing its instructions on the CPU 200 and GPU 302. Portions of the application 101 may be loaded into memory 312. In one particular implementation, the CPUID instruction is implemented by microcode that contains a processor ID program and two different sets of processor ID data, e.g., as discussed above with respect to
As noted above, in alternative implementations there may be two different processor ID programs, one for legacy applications and one for new device application. In such implementations, the CPU 200 may selectively run one program or the other when executing the CPUID instruction depending on whether the application it is running is a legacy application or a new device application. In other alternative implementations, a single processor ID program may return processor ID data that differs in some specifics depending on whether the querying program is a legacy application or a new device application. In other alternative implementations, the processor ID code 216 may be implemented by special dedicated hardware, e.g., certain aspects of returning the processor ID information may be implemented by hardware logic rather than microcode stored in a ROM 218 of a CPU core 202. In other alternative implementations, the microcode may be stored in Random Access Memory (RAM), e.g., main memory 312 rather than in ROM.
Returning spoofed processor feature information can facilitate resolution of backward compatibility issues by preventing an application from taking advantage of features that, even though they are supported, might cause timing issues if a legacy application attempts to use them.
While the above is a complete description of the preferred embodiments of the present invention, it is possible to use various alternatives, modifications, and equivalents. Therefore, the scope of the present invention should be determined not with reference to the above description but should, instead, be determined with reference to the appended claims, along with their full scope of equivalents. Any feature, whether preferred or not, may be combined with any other feature, whether preferred or not. In the claims that follow, the indefinite article “A” or “An” refers to a quantity of one or more of the item following the article, except where expressly stated otherwise. The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase “means for”. Any element in a claim that does not explicitly state “means for” performing a specified function, is not to be interpreted as a “means” or “step” clause as specified in 35 USC § 112(f).
This application is a continuation of U.S. Patent Application 15/411,310 filed Jan. 20, 2017 (now U.S. Pat. No. 11,068,291), the entire contents of which are incorporated herein by reference. U.S. patent application Ser. No. 15/411,310 claims the benefit of prior to commonly-assigned, U.S. Provisional application No. 62/286,280, filed Jan. 22, 2016 the entire contents of which are herein incorporated by reference.
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| Number | Date | Country | |
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| 20210365282 A1 | Nov 2021 | US |
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 15411310 | Jan 2017 | US |
| Child | 17379550 | US |
