Apparatus for executing a plurality of program segments having different object code types in a single program or processor environment

• US 6,256,658 B1
• Filed: 03/22/1995
• Issued: 07/03/2001
• Est. Priority Date: 12/18/1992
• Status: Expired due to Term

• Current Assignee: Apple Computer Incorporated (Apple Inc.)
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Traut, Eric P., Parent, Sean R., Jones, Bruce K., Mourey, Jean-Charles D., Eidt, Erik L., Lillich, Alan W.
• Primary Examiner(s): BANANKHAH, MAJID A
• Application Number:
  US08/409,477
• Time in Patent Office: 2,295 Days
• Field of Search: 709/100, 709/101, 709/104, 709/106, 709/102, 709/103, 709/108, 712/244, 712/245, 703/26
• US Class Current: 718/100
• CPC Class Codes: G06F 9/4484 Executing subprograms
• CPC Class Codes: G06F 9/45504 Abstract machines for programme code execution, e.g. Java virtual machine [JVM], interpreters, emulators

Abstract

The invention provides a method and apparatus for switching between execution of a plurality of object code types having different conventions for invoking program procedures and performing stack manipulations. The invention may also be used to switch between different calling conventions within a single object code type. Briefly according to the invention, a computer system comprises a routine descriptor, a stack switch frame, a mode switching mechanism for switching from a first processor, code or calling convention type to a second processor, code or calling convention type and means for executing instructions in various code types.

A routine descriptor describes a program or code segment and its code type and calling conventions. A routine descriptor contains, among other information, a “mixed mode” field which is set to a specific, predetermined value such as a value indicating an instruction which is not legal in the runtime environment of a first processor, code or calling convention type. When that instruction is encountered, control is transferred to the mode switching mechanism. A routine descriptor also contains a “procedure information” field which is set to a value indicating the convention for invoking a program segment and performing appropriate stack manipulations.

When a routine calls a routine having a different stack model, the mode switching mechanism uses a stack switch frame to provide a transition between the two different stack types.

Claims

1. A method for executing a plurality of modes in a program or processor environment in a computer system having at least one central processing unit and a memory, said method comprising the steps of:

allocating memory space for a routine descriptor;

setting a pointer to the address of the routine descriptor,

setting contents of a first field in the routine descriptor equal to a nonvalid instruction, the field being positioned in the routine descriptor such that the pointer to the routine descriptor points to the contents of the field;

executing contents of the field;

switching from a first mode to a second mode when executing contents of the field which are equal to a nonvalid instruction; and

after further processing returning to the first mode.

2. A method defined in claim 1 further comprising the steps of:

setting contents of a procedure pointer field in the routine descriptor to the address of the routine being described by the routine descriptor; and

after switching to the second mode, executing the routine addressed by the procedure pointer field.

3. A method for executing a plurality of modes to a processor environment in a computer system having at least one central processing unit and a memory, said method comprising the steps of:

allocating memory space for a routine descriptor;

setting a pointer to the address of the first routine descriptor;

setting contents of a mixed mode field in the first routine descriptor equal to a specific predetermined instruction;

executing contents of the field;

switching from a first mode to a second mode when executing contents of the mixed mode field which are equal to a nonvalid instruction;

setting contents of a selector field in the first routine descriptor to a type of mode switching operation to be performed after switching to the second mode;

after switching to the second mode, performing the operation indicated by the contents of the selector field;

allocating a second routine descriptor;

setting the selector field in the second routine descriptor to a value indicating a return to the first mode operation;

allocating a stack switch frame;

saving values of registers in the stack switch frame;

determining if the routine being described by the first routine descriptor is register-based or stack-based and if the routine is register-based, moving input parameters from first mode registers and putting them into second mode registers;

putting information into the stack switch frame;

if the routine returns a value, allocating space in the stack switch frame for it;

putting paramters into the stack switch frame;

setting a return address in the stack switch frame equal to the address of the second routine descriptor;

executing the routine described by the first routine descriptor;

checking the selector field of the second routine descriptor; and

when the selector field of the second routine descriptor indicates a return operation, returning to the first mode.

4. An article of manufacture for use in a system that includes a processor, the system capable of of executing a plurality of modes, the article comprising:

memory that can be accessed by the processor; and

data stored in the memory, the data comprising;

a mixed mode field for differentiating between modes, said mixed mode field capable of specifying at least a first and second state, said mixed mode field being set to a specific, predetermined value when in said second state;

means for specifying a software routine; and

a procedure information field for indicating a mechanism capable of initiating the execution of the specified software routine and for specifying one or more characteristics of parameters to be used by the executing specified software routine.

5. An article of manufacture as defined in claim 4, said data further comprising a selector field for indicating an operation to be performed.

6. An article of manufacture as defined in claim 4, said data further comprising:

a stack arranged so that it can be accessed by the processor, said stack having a first stack frame associated with a first code segment and a second stack frame associated with a second code segment, said first and second stack frames having different formats; and

a stack switch frame, positioned between said first and said second stack frames, said stack switch frame having a first segment referencing the first stack frame, a second segment having parameters in a format of the second stack frame, said parameters having been converted from a format of the first stack frame, and a third segment specifying information so that the stack switch frame is in a format that can be referenced by the second stack frame.