JPH086821A - Microprocessor - Google Patents

Abstract

PURPOSE:To detect an error of a program which accesses a tentative variable that is not present any more. CONSTITUTION:The program is so generated that the addresses of all data access are above the address of a stack painter 5. Comparing the address of the stack painter 5 with an address of data access, the address of correct data access is above the address of the stack pointer 5. A comparator 4 compares the address of the stack pointer 5 with the address of data access at all times and a processor exception is generated when the large/small relation between the addresses is inverted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microprocessor for detecting a program error.

[0002]

2. Description of the Related Art In a conventional microprocessor,
When an incorrect memory access is performed due to a program error, the memory access error is detected by comparing the segment limit values or by checking the accessibility of paging.

[0003]

In this conventional microprocessor, even if a temporary variable that does not already exist is used due to a program error after the temporary variable is secured on the stack, used, and released, this is still used. It could not be detected.

An object of the present invention is to provide a microprocessor that detects an error in a program that accesses a temporary variable that does not already exist.

[0005]

A microprocessor according to the present invention comprises a register group including a stack pointer, an execution unit capable of receiving an exception notification signal, an address unit for generating a data access address, a stack pointer value and an address. And a comparator which compares the data access addresses generated by the units and passes the result to the execution unit.

[0006]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the microprocessor of the present invention. In this embodiment, a register group 1 including a stack pointer 5, an execution unit 2,
It is composed of an address unit 3 and a comparator 4. The stack pointer 5 and the address unit 3 are respectively connected to two inputs of the comparator 4, and the output of the comparator 4 is connected to the execution unit 2. .

In this embodiment, the register group 1 is a set of registers including the stack pointer 5. The stack pointer 5 is a register indicating memory access in push / pop operation of the stack. The execution unit 2 executes the program and receives an exception notification signal. The address unit 3 generates an address for memory access. The comparator 4 compares the address generated by the address unit 3 with the value of the stack pointer 5, and when the value is incorrect, notifies the execution unit 2 of it.

Next, the operation of this embodiment will be described.

FIG. 2 is a conceptual diagram of the operation of this embodiment. In this embodiment, all data accessed by the program is programmed so that it is always on the upper address side of the stack pointer. As a result, all correct data accesses are made to the same address or higher addresses as compared with the stack pointer value, and all data accesses lower than the stack pointer value can be regarded as errors.

When a temporary variable area is secured on the stack from the state shown in FIG. 2A, the state shown in FIG. 2B is obtained. At this time, since the temporary variable area is equal to or larger than the stack pointer value, the access is successful. When the temporary variable area is released, the state shown in FIG. At this time, when the data is accessed to the area of the temporary variable that has been released and does not already exist, the address is smaller than the value of the stack pointer, so the comparator 4 detects that the data access is invalid. can do.

[0012]

As described above, according to the present invention, by comparing the value of the stack pointer and the address of the data access, it is possible to detect the error of the program of accessing the released temporary variable. Have.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a microprocessor of the present invention.

FIG. 2 is an operation conceptual diagram of the present embodiment.

[Explanation of symbols]

 1 register group 2 execution unit 3 address unit 4 comparator 5 stack pointer

Claims (3)

[Claims] 1. A register group including a stack pointer, an execution unit capable of receiving an exception notification signal, an address unit for generating a data access address, a stack pointer value and a data access address generated by the address unit are compared. And a comparator for passing a result to an execution unit. 2. A result of programming such that all data accessed by a program are always on the upper address side of the stack pointer value, and the comparator regards all data access on the lower side of the stack pointer value as an error. Is passed to the execution unit. 3. A data access to an area of a temporary variable which does not already exist when the area of the temporary variable is secured on the stack so as to be equal to or larger than the value of the stack pointer and the area of the temporary variable is released. 3. The microprocessor according to claim 2, wherein a result which regards all as an error is passed to the execution unit.