Digital Equipment Corporation

R Kim Peterson

John R Ellis

Benn L Schreiber

Charles G Nylander

Stephen R Greenwood

Disclosed is a position independent code system that enables a programmable digital data processing system to invoke and execute procedures and access data that are loaded into system memory at addresses that are not specified by the program code and are not determined until the program code is compiled, linked and loaded into system memory. The coded call sequence instructions that are provided by the disclosed position independent code allow a procedure to call another procedure and are based upon the value that is stored in a dedicated register (or equivalent memory space) of the system and memory offset pointers, which are determined during system compilation and linking of program code and which indicate the memory location of the calling procedure and the call sequence of the calling procedure relative to the memory location at which the system stores the address of the procedure being called. When a call sequence is executed, the address of the called procedure is transferred to the dedicated register. Similar position independent code instructions are utilized for accessing a data set that is stored in memory external to the procedure, without transferring the address of the accessed data to the dedicated register. Compatibility between procedures that employ the disclosed position independent code and programmed code that is written for use with prior art position dependent code can be established by supplementing and modifying the position dependent code procedures during compilation and linking.

Position independent code location system

A procedure state descriptor system for generating state reports of the progress of the invocation process for procedures executed on a digital data processing system is disclosed. The procedure state descriptor system includes a procedure descriptor generator process that generates a procedure descriptor for each procedure. Each procedure descriptor contains a number of offset values that are offset addresses from the start of the procedure to locations in the procedure that are the demarcations between states of the invocation process for the procedure. When a particular procedure is invoked for execution, a procedure state analyzation process accesses the procedure descriptor offset values for the procedure, the memory address of the start of the procedure, and the address of the next instruction to be executed in the procedure. The procedure state analyzation process then determines the difference between the address of the instruction to be next executed and the starting address of the procedure. The difference between the two addresses is compared to the offset values to determine the state of the invocation process for the procedure. As the result of selected state determinations, the procedure state analyzation process also may review the next instruction to be executed by the invoked procedure. The instruction is reviewed to determine if it is a specific type of instruction indicating that the procedure was in still another invocation state.

Procedure state descriptor system for digital data processors

A method and arrangement for providing each thread of execution (28, 30, 32 and 34) of a multi-threading digital data processing environment with private copies of each set of initialization data (regions 60-1 through 60-4 and 62-1 through 62-4) that is required by procedures (44, 46) which are executed in the context of more than one of the threads. The regions (duplicate data copies) are generated from templates (56, 58) that include a base or original copy of the required set of initialization data. The templates are formulated during operation of the digital data processing system to compile, link and load the procedures and are each identified by a region descriptor (72) which includes a region index (a non-negative integer) and the memory address of the template. Regions are created when the initialization data of the region is required by a procedure that is executing within the context of a thread (i.e., regions are created on an as needed basis) and the memory address of each region is stored in a thread address array (70) so that subsequent access by procedures executing in the context of the same thread can be made using the region descriptor. To conserve system memory, the thread address array is not established in memory until the corresponding thread is being executed and a procedure of the thread requires initialization data (i.e., a region for that thread is to be created).

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Seattle, WA, United States of America

R Kim Peterson