Retargetable instruction set simulators

A system, comprising:

• hardware including a processor;
• and
• a computer-readable medium having stored thereon a generic instruction model, the generic instruction model executable by the processor in an instruction set simulator (ISS), the generic instruction model comprising an instruction specification used to interpret each instruction in an instruction set architecture (ISA), wherein the instruction set simulator is configured to perform
• generating decoder source code for an original input application, prior to a simulation time, by decoding each instruction of a plurality of instructions in the original input application, wherein the decoding comprises:
• identifying a plurality of unique instruction patterns in the original input application;
• selecting an appropriate template from a plurality of templates for each unique instruction pattern of the plurality of unique instruction patterns, wherein each template of the plurality of templates is configured to implement a functionality of an instruction contained within an instruction class, the instruction class describing a set of instructions of the instruction set architecture having a common behavior;
• generating a customized template for each instruction of the plurality of instructions by extracting values from each instruction and assigning the extracted values to parameters within the template;
• instantiating the customized template;
• and
• appending the customized template and corresponding instantiation code into the decoder source code;
• compiling the decoder source code including optimizing the decoder source code through partial evaluation to generate an optimized decoder having optimized decoded instructions of the original input application;
• executing the optimized decoder to simulate the original input application, comprising:
• loading, at a simulation time, the optimized decoded instructions of the original input application into instruction memory;
• fetching, at a run time, an instruction binary of the optimized decoded instruction from instruction memory;
• determining, at the runtime, whether the fetched instruction binary has been modified since a time of decoding;
• if the fetched instruction binary has been modified since a time of decoding:
• decoding, at the runtime, the modified instruction to generate a redecoded instruction by selecting one of an optimized decoded template or a decoding mechanism comprising function pointers;
• and
• executing one of the decoded instruction or the redecoded instruction.

A non-transitory computer readable medium having stored thereon a set of instructions executable by a machine to perform operations for simulating an instruction set architecture (ISA), said operations comprising:

• generating decoder source code for an original input application, prior to a simulation time, by decoding each instruction of a plurality of instructions in the original input application, wherein the decoding comprises:
• identifying a plurality of unique instruction patterns in the original input application;
• selecting an appropriate template from a plurality of templates for each unique instruction pattern of the plurality of unique instruction patterns, wherein each template of the plurality of templates is configured to implement a functionality of an instruction contained within an instruction class, the instruction class describing a set of instructions of the instruction set architecture having a common behavior;
• generating a customized template for each instruction of the plurality of instructions by extracting values from each instruction and assigning the extracted values to parameters within the template;
• instantiating the customized template;
• and
• appending the customized template and corresponding instantiation code into the decoder source code;
• compiling the decoder source code including optimizing the decoder source code through partial evaluation to generate an optimized decoder having optimized decoded instructions of the original input application;
• executing the optimized decoder to simulate the original input application, comprising:
• loading, at a simulation time, the optimized decoded instructions of the original input application into instruction memory;
• fetching, at a run time, an instruction binary of the optimized decoded instruction from instruction memory;
• determining, at the runtime, whether the fetched instruction binary has been modified since a time of decoding;
• if the fetched instruction binary has been modified since a time of decoding:
• decoding, at the runtime, the modified instruction to generate a redecoded instruction by selecting one of an optimized decoded template or a decoding mechanism comprising function pointers;
• and
• executing one of the decoded instruction or the redecoded instruction.