JPS62232054A - Controlling system for stack frame descriptor - Google Patents

Abstract

PURPOSE:To effectively protect a stack frame descriptor from erroneous writing by controlling a stack frame descriptor in a segment different from a segment on a main memory in which a stack frame is formed and writing by procedure is prohibited based on memory protecting function by an operating system. CONSTITUTION:A stack frame 11 used by a main procedure is secured in a segment 10 of a main memory address space. A stack frame descriptor 21 of the stack frame 11 is different from the segment 10, and secured in other segment 20 in which writing by procedure is made impossible by memory protecting function of an operating system based on a technique such as a memory protecting key, etc. Further, a current stack frame descriptor pointer P for designating the stack frame descriptor 21 of main procedure in execution is secured in a general-purpose register, etc., in a CPU.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stack frame descriptor management method applied to an electronic computer system, and in particular to a method for managing stack frame descriptors while protecting them from destruction due to erroneous writing. This is related to the method of doing so.

Conventional TechnologyFor each procedure that makes up a program written in a high-level language such as ALGOL or PASCAL, a stack frame containing a work area and a stack frame descriptor management area is stored in main memory prior to the start of processing. It is reserved and released when processing ends.

The stack frame descriptor contains stack frame management information such as the size of the stack frame and its start address,
Procedure control information such as argument addresses and return addresses to the calling procedure, the contents of various registers of the calling procedure, exception conditions, the address of the exception handling routine, and the running ring value if a ring protection mechanism is used. A device consisting of procedure environment information such as There is a risk that the stack frame descriptor may be destroyed by writing. If the stack frame descriptor is destroyed, it becomes impossible to manage the stack frame, and normal operation of the program is no longer guaranteed.

Generally, in computer systems, the operating system takes storage protection measures such as dividing the main memory address space into segments and assigning a storage protection key to each segment. However, since the stack frame, which includes the work area secured by each procedure and the stack frame descriptor management area, is often formed within the same segment or across consecutive segments, the above operating system does not take storage protection measures. It is often ineffective.

According to the patent application (Japanese Patent Application No. 60-169413) entitled "Error writing prevention circuit" related to the applicant's earlier application, the memory retention S in the stack frame! A register that displays the area,
An invention has been disclosed in which a stack frame descriptor is protected from erroneous writing by detecting writing of data to a protected area based on the contents of this register and the write address and disabling a circuit to invalidate this.

Problems to be Solved by the Invention Although the erroneous write prevention circuit according to the above-mentioned prior application can effectively protect the stack frame descriptor from erroneous writes, there is a problem in that some hardware must be added.

Means for Solving the Constituent Problems of the Invention The stack frame descriptor management method of the present invention, which solves the problems of the above-mentioned prior art, manages stack frame descriptors by
By storing the stack frame in a segment that is different from the segment in which it is formed and that procedures are prohibited from writing to based on operating system storage protection, the operating system can use existing It is configured to effectively protect the stack frame descriptor from erroneous writing by utilizing the storage protection function of .

Hereinafter, the operation of the present invention will be explained in detail together with examples.

Embodiment FIG. 1 is a conceptual diagram showing the usage status of the main memory address space in the execution state of the main procedure in an embodiment of the present invention.

A stack frame 11 used by the main procedure is reserved in segment 10 of the main memory address space. The stack frame descriptor 21 of this stack frame 11 is different from the segment 10 and is based on the operating system's memory protection 3! based on techniques such as memory protection keys. The functionality allows other segments that are not writable by procedures (the "stack frame management segment")
20). Further, a current stack frame descriptor pointer P for specifying the stack frame descriptor 21 of the main procedure being executed is secured in a general-purpose register or the like within the CPU.

Prior to execution of the main procedure, a stack frame reservation routine is executed, and first, a stack frame 11 of variable length or fixed length size is secured within the segment 10. Subsequently, one of the stack frame descriptor storage areas provided in the stack frame management segment 20 that is free is selected, and the stack frame management information, procedure control information, and procedure environment of the calling procedure are stored here. A stack frame descriptor 21 consisting of information is stored and saved. Furthermore, the contents of the current stack frame descriptor pointer P are changed to point to the newly secured stack frame descriptor 21.

Based on the storage protection function of the operating system, writing into the stack frame management segment 20 is only permitted by the stack frame allocation routine described above and the stack frame release routine described below.
Writing to this segment by procedures is prohibited.

Among the fields constituting the stack frame descriptor 21, a is a field that stores a pointer to the stack frame descriptor of the calling procedure, b is a field that stores the start address of the stack frame 11,
C is a field that stores the size of stack frame 11, d is a field that stores argument addresses in stack frame 11, e is a field that stores the return address to the calling procedure, and f is the contents of various registers at the time of calling. This is the evacuation field. Further, arguments passed to the sub-procedure are stored in an argument area within the stack frame 11.

In the stack frame descriptor 21 of the main procedure, since there is no calling procedure, the pointer a to the stack frame descriptor of the calling procedure
, argument address storage field d, return address storage field e for the calling procedure, and save field f for various register contents are all invalid.

Assume that the main procedure calls the subprocedure under these conditions. When a new stack frame securing routine is executed in response to a sub-procedure call, the usage status of the main memory address space changes to that shown in FIG. 2.

That is, by executing the stack frame allocation routine, stack frame 1 used by the subprocedure is first allocated.
2 is reserved in segment 10. Next, the stack frame descriptor 22 of this stack frame 12 is stored in a free area within the stack frame management segment 30. Stack frame 1 secured in segment 10
The start address of 2 is stored in the start address storage field b of the segment descriptor 22, and the size m is stored in the size storage field C. The address of the argument passed from the main procedure is stored in the argument address storage field d. Further, the return address X to the main procedure is stored in the field e, and the contents of various registers at the time the sub procedure is called are stored in the register content save field f.

Finally, the current stack frame descriptor pointer P
The contents are saved in the pointer save field a of the stack frame descriptor 21 of the calling procedure, and then the contents are changed to a value pointing to the stack frame descriptor 31 of the sub-procedure. When this stack frame allocation routine ends, execution of the subprocedure begins.

When processing of the subsequent procedure is completed, the stack frame release routine frees the stack frame 12 and restores the procedure control information and the procedure environment information of the calling procedure.

That is, the return address X is taken out from the return address storage field e to the calling procedure of the stack frame descriptor 22, and the contents of the save field f of the contents of various registers are returned to the corresponding register. Further, the value saved in field a of the stack frame descriptor 31 of the calling procedure is returned to the current stack frame descriptor pointer P. Finally, the stack frame descriptor 31 that is no longer needed is released on the stack frame management segment 30, and the usage state of the main memory address space returns to the state shown in FIG.

Effects of the Invention As explained in detail above, the stack frame descriptor management method of the present invention allows the stack frame descriptor to be written in a manner that is different from the main memory segment in which the stack frame is formed and which cannot be written by the operating system. Since the configuration is such that management is performed within a segment that is prohibited based on the system's memory protection function, it is possible to use the existing memory protection function of the operating system without adding any hardware to prevent errors in stack frame descriptors. It can be effectively protected from writing.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing the usage status of the main memory address space during execution of the main procedure in an embodiment of the present invention;
The figure is a conceptual diagram for explaining the usage status of the main memory address space after the sub-procedure is called by the main procedure. 10.20... Different segments of main memory address space, 11... Stack frame allocated to main procedure, 12... Stack frame allocated to sub procedure, 21... Descriptor of stack frame 11, 2
2. Descriptor of stack frame 12, P. Pointer pointing to the current stack frame descriptor, a. Pointer storage field for the stack frame descriptor in the calling program, b. Storage field for the stack frame address. C: Storage field for stack frame size d: Storage field for argument address, e: Storage field for return address to caller field

Claims (1)

[Claims] In a computer system in which a main memory address space is divided into segments and memory protection is performed for each segment by an operating system, stack frame management information, procedure control information, and environment information of a calling procedure are stored. A stack frame descriptor comprising a stack frame descriptor managed in a segment that is different from the segment in which the stack frame is formed and in which writing by a procedure is prohibited based on a memory protection function of the operating system. management method.