JPH04266126A - Control system for subroutine call - Google Patents

Abstract

PURPOSE:To prevent the runaway of a program caused by execution of a transfer control instruction which calls the subroutine included in an unlinked compiling unit. CONSTITUTION:An instruction 4 transfers 'program counter value + byte number of instruction 3 + byte number of instruction 5' to a stack (steps 1 and 5). An instruction 3 shifts the control to a subroutine if a relative address is not identical with O (step 2). An instruction included in the subroutine transfers the value to a program counter from a stack and shifts the control to the instruction (step 4) following an instruction 5 (step 3). The instruction 3 shifts the control to the instruction 5 if the relative address is identical with O (step 6). Then the instruction 5 transfers the value to the program counter from a stack and shifts the control to the next instruction (step 8) in a step 7 respectively.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subroutine call control system in an information processing apparatus in which relative addresses are used in control transfer instructions.

0002

[Background Art] Conventionally, in a module composed of multiple compilation units intended for general use, a user of the module wishes to execute the functions of some of the compilation units. If not, it was necessary to either replace the compilation unit that you do not want to run with a dedicated one that does not process anything, or modify the side that uses it so that it does not use the compilation unit function.

[0003] Furthermore, if a load module is created without linking unnecessary compilation units, the address of the call destination is not resolved in a control transfer instruction that calls a subroutine in the compilation unit that was not linked, so the relative address is 0, and the immediately following command was executed.

That is, when a normal compiler converts an instruction that calls a subroutine in a source program into an object, it creates an instruction having a function like instruction 1 shown in FIG. 3. When a subroutine is compiled, an instruction having a function such as instruction 2 in FIG. 3 is attached to the end of the object. Therefore, when linking, instruction 1
When the relative address is resolved, control is transferred to the subroutine using instruction 1, and control is returned to immediately after instruction 1 using instruction 2. However, in this case, if the relative address of instruction 1 is not resolved at the time of linking and remains 0, control will not be transferred to the destination of the subroutine, and the instruction at address 0, that is, immediately after instruction 1, will be executed.

[0005]

[Problem to be solved by the invention] Conventionally, even if a module is used for general purposes, if you do not want to execute some functions, a dedicated compilation unit is required as described above, and creating it requires a lot of man-hours. This has the drawback that the management of compilation units is complicated. Additionally, if a load module is created without linking unnecessary compilation units, the call destination address will not be resolved in a control transfer instruction that calls a subroutine in a compilation unit that was not linked, so the relative address will be 0. Therefore, when that instruction is executed, control is not transferred and the next instruction is executed, which poses a risk of the program running out of control.

[0006]

[Means for Solving the Problems] A first invention provides a subroutine in an information processing device in which the relative address of a call destination in a transfer control instruction that calls a subroutine in a compilation unit that is not linked when creating a load module is 0. In the call control method, a first means stores a restart address obtained by decrementing a value of a stack pointer and adding a predetermined value to a value of a program counter in a stack indicated by the stack pointer; If the relative address of the called destination is 0, the subroutine is started by adding the relative address to the value of the program counter, and if the relative address of the called destination is 0, the subroutine is executed next to the value of the program counter. a second means for activating an address, and a second means activated by the second means when the relative address of the call destination is 0, decrements the value of the stack pointer, sets the restart address in the program counter, and starts from the restart address. The present invention is characterized by having a third means for executing the program.

[0007]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing the types and structure of instructions according to an embodiment of the present invention.

The present invention uses instructions having the functions shown in instructions 3 to 5. Also, the last instruction 2 of the subroutine
The command will continue to be used as before. In the present invention, instruction 4
By combining this with instruction 3, the same function as the conventional instruction 1 is realized. However, the return address saved by instruction 4 is "program counter value + number of bytes of instruction 3 + number of bytes of instruction 5." FIG. 2(a) shows a case where the relative address of instruction 3 is resolved at the time of linking, and the relative address of instruction 4 (
instruction 1) by step 1) and instruction 3 (step 2)
Control is transferred to the subroutine under the same conditions as , and control is returned to the instruction following instruction 5 (step 4) at instruction 2 (step 3). FIG. 2(b) shows a case where the relative address of instruction 3 is not resolved and remains 0, and after execution of instruction 4 (step 5) and instruction 3 (step 6), control does not proceed to the subroutine and instruction 5
(Step 7) is executed, but since this instruction sets the address next to instruction 5 in the program counter, instruction 5
The next instruction (step 8) will be executed. In other words, since the processing corresponding to instruction 2 has been taken by instruction 5, the processing continues normally thereafter.

0010

[Effects of the Invention] According to the present invention, when a compilation unit with a function that is not to be executed in a commonly used module is not specified at the time of linking, a transfer control instruction that calls a subroutine in a compilation unit that is not linked. This has the effect of preventing the risk of program runaway due to execution.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing types and configurations of instructions showing an embodiment of a subroutine call control method of the present invention.

FIG. 2(a) is a flowchart showing an example of the operation when the linked subroutine of this embodiment is called;
b) is a flowchart showing an example of the operation when an unlinked subroutine of this embodiment is called.

FIG. 3 shows the types and configuration of instructions used in a conventional subroutine call.

[Explanation of symbols]

Step 1 Instruction 4 Step 2 Instruction 3 Step 3 Instruction 2 Step 4 Next command Step 5 Instruction 4 Step 6 Instruction 3 Step 7 Instruction 5 Step 8 Next command

Claims (1)

[Claims] Claim 1: In a subroutine call control method in an information processing device in which the relative address of the call destination in a transfer control instruction that calls a subroutine in a compilation unit that was not linked when creating a load module is 0, the value of the stack pointer is a first means for saving a restart address obtained by decrementing the value of the program counter and adding a predetermined value to the stack indicated by the stack pointer; If not, a second means for activating the subroutine by adding the relative address to the value of the program counter, and activating an address next to the value of the program counter if the relative address of the called destination is 0; Third means is activated by the second means when the relative address of the call destination is 0, decrements the value of the stack pointer, sets the restart address in the program counter, and causes the program to be executed from the restart address. A subroutine call control method characterized by: