JPH04241032A - System call execution device - Google Patents

Abstract

PURPOSE:To improve a protecting function by judging whether or not a bank state is to be saved before the execution of a system call process, entering a privileged mode unconditionally for access to a vector address area, and approving only access based upon double indirect addresses for branching to a vector address table. CONSTITUTION:Address table specification 14 is inputted to an address table area decision part 7 by an interruption 3 with a system call instruction 2. It is judged whether privileged bank information is automatically saved in a specified address table area and the mode is automatically changed into privileged mode. The protecting function operates since normal operation is not performed without double indirect addressing when a specific address area called a address table is specified and a branch instruction 1 is issued. The privileged mode is entered without any software intervention, and high-speed processing becomes possible.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention does not uniformly perform automatic save processing to the stack area that occurs during branch processing, system call processing, and interrupt processing, but executes it only when necessary, and privileges the above processing. mode, it relates to the system call execution device that executes the transition to privileged mode.

0002

[Prior Art] Conventionally, tasks related to system management have controlled operations such as system control registers that determine the CPU state. To avoid executing instructions that determine configuration or CPU status, hardware protection was implemented for tasks that involved system management, improving system reliability. Interrupt acceptance processing, task scheduling processing, and IO driver startup are performed on the system task, but in systems configured with multi-banks, after the user task is started, processing occurs in the bank that was executing the privileged task. There are also systems that generate system calls or wait for interrupts to occur. In addition, when a system call or an interrupt occurs, the hardware saves the results of the CPU arithmetic unit of the bank that executes the privileged task, the instruction pointer of the privileged task, or the register that determines the state of the CPU, and saves the state of the bank. System call processing and interrupt processing were executed after the Therefore, even though the bank in the above-mentioned wait state does not require a save operation, the save process is executed.

On the other hand, there are systems that directly execute a privileged program by executing a branch instruction without using a system call instruction that is automatically set to a privileged mode by hardware at the time of a system call.

0004

However, in the above configuration, the user mode remains in the normal branch instruction, and it is impossible to switch from the user mode to the privileged mode. As a way to solve this problem, there are ways to change the flag indicating whether the user is in privileged mode or user mode from user mode, or to enter the privileged state by executing a so-called privileged instruction that can only be executed in privileged mode. However, such systems did not provide sufficient protection.

The present invention solves the above-mentioned conventional problems, and in the case of branch processing, system call processing, and interrupt processing,
The purpose of the present invention is to provide a system call execution device that allows the user to arbitrarily specify whether or not to automatically save the state on the bank that executes these processes, and that has a protection function when transitioning from the user state to the privileged state. It is something.

[0006]

[Means for Solving the Problems] In order to solve this problem, the system call execution device of the present invention saves the bank state before executing branch processing, system call processing, or interrupt processing using a table address of a vector address. Accesses to the vector address area are now unconditionally shifted to privileged mode, and branches to the vector address table by branch instructions are now protected by only allowing access with double indirect addresses. It is configured.

Furthermore, the system call device of the present invention is configured such that when branching to a specific area by a branch instruction, the bank state is not saved and the system is unconditionally shifted to a privileged mode.

Furthermore, the system call device of the present invention includes:
It is possible to arbitrarily decide whether to save the bank state using a flag, and the flag is reset when the user bank is started, and the system is configured so that basically no save operation is performed when transitioning from the user bank to the privileged bank. ing.

[0009]

[Effect] This configuration enables real-time processing, improves system throughput, and adds protection functions to the transition from user tasks to system tasks, achieving high system reliability. .

0010

【Example】

An embodiment of the present invention will be described below based on the drawings. FIG. 1 is a configuration diagram of a system call execution device according to an embodiment of the present invention, which determines whether or not to perform an automatic save operation to the stack based on an address table, and when transitioning from user task processing to privileged task processing. Shows the configuration to switch to privileged mode.

In FIG. 1, branch instruction 1 can specify double indirect addressing, and address table specification 14 is performed by the first indirect addressing, and an address in address table area 6 of memory space 4 is selected. be done. The data in the address table area 6 stores the start address of the program. Branch instruction 1 branches to the branch destination program by second indirect addressing, and the program is started. address table area 6
The start address of the program to be executed is stored in the address table area 6, and part of the address table area 6 includes an address table area 5 in which no automatic save processing by hardware occurs.

The address table area determination unit 7 determines whether or not the address table area 5 without automatic save processing of the address table area 6 is selected by the address table designation 14. The upper limit address 10 and lower limit address 11 of the address table area 6 and the upper limit address 8 and lower limit address 9 of the address table area 5 without automatic save processing are input to the address table area determination unit 7, and a comparison with the address table specification 14 is performed. It will be done. If the first indirect address specification of branch instruction 1 is an address between upper limit address 10 and lower limit address 11 of address table area 6, address table area determination unit 7
outputs the control signal 15 to the privileged/user mode manager 13 and outputs the CPU mode signal 16 without software intervention.
Switch to privileged mode. Furthermore, address table specification 14 is address table area 5 without automatic save processing.
If the addresses are upper limit address 8 and lower limit address 9, address table area determination section 7 outputs control signal 15 to μROM 12, and does not automatically save the program information on the privileged bank to the stack area.

System call instruction 2 is an instruction for calling a system task from a user task, has an address table specifier, uses an address in address table area 6 as a vector address, and starts a privileged program. Furthermore, for interrupt 3, an address in address table area 6 is used as a vector address depending on the cause of the interrupt occurrence. Similar to branch instruction 1, system call instruction 2 and interrupt 3
The address table designation 14 is input to the address table area determining section 7, and it is determined whether the privileged bank information is automatically saved based on the designated address table area, and the mode is automatically changed to the privileged mode.

The protection function works because a specific address area called an address table is designated and the branch instruction 1 cannot operate normally unless double indirect addressing is used. Further, the transition to the privileged mode does not involve software intervention, and it is possible to select whether or not to execute automatic saving processing of program information on the privileged bank to the stack area, allowing high-speed processing.

FIG. 2 is a block diagram of a system call execution device according to another embodiment of the present invention, showing a configuration for determining whether to switch to a privileged mode based on a branch destination address. In FIG. 2, a branch instruction 17 is an instruction to execute a program branch, and the branch address is the memory area determination unit 1.
8 is input. The upper limit address 21 and lower limit address 22 of the privileged program area 20 in the memory space 19 are input to the memory area determination unit 18, and the branch address of the branch instruction 17 is directed to a privileged program between the upper limit address 21 and the lower limit address 22. It is determined whether there is a branch. If the branch address of the branch instruction 17 is in the privileged program area 20, the memory area determination unit 18 outputs the privileged mode signal 23 to the privileged/user mode management unit 24. In response to this, the privilege/user mode management section 24 generates a CPU mode signal 25 and is automatically changed to the privilege mode.

[0016] At this time, the protection function is activated because the mode shifts to the privileged mode only when a specific address area is specified. In addition, the transition to privileged mode does not involve software intervention, and by using a branch instruction that performs a jump operation, no save processing occurs, and system tasks can be started at high speed.

FIG. 3 is a block diagram of a system call execution device according to yet another embodiment of the present invention, showing a configuration in which it can be arbitrarily determined whether or not to save the bank state based on a flag.

In FIG. 3, the register file group 30 has a plurality of banks a and b including a user bank and a privileged bank.
, c to n, and the bank management unit 29 selects which bank a task uses. At startup, when a system task is executed, the bank management unit 29 outputs a signal 36 indicating that the privileged bank is being executed. The stack automatic save flag 31, which indicates whether or not to save the bank state to the stack area, is set to an initial state of "1" so that the bank state is automatically saved.
It is input to the D circuit 35. The output of the AND circuit 35 is input to the μROM 37, and automatic saving is executed when the output of the AND circuit 35 is "1".

The stack automatic save flag 31 can be set by the setting 34 using a program or a terminal, and can be set to any state. It is always reset by the inverter circuit 32 to which the user task activation signal 33 is input. Therefore, branch processing 26, system call processing 2
Even if the user bank is activated from the user bank to the privileged bank by 7 or the interrupt processing 28, the output of the AND circuit 35 becomes "0", and automatic saving processing of the contents of the privileged bank is not performed in the transition to the privileged bank.

In this way, the stack automatic save flag 31
is reset when the user bank is started, and basically no save operation is performed when transferring from the user bank to the privileged bank, so the overhead until the start of processing of privileged tasks can be reduced and a real-time system can be realized. I can do it.

[0021]

As described above, according to the present invention, software does not intervene in the transition to the privileged mode, and it is possible to determine whether or not to execute automatic saving processing of program information on the privileged bank to the stack area. selection, real-time processing is possible, and system throughput can be improved. In addition, a protection function can be added to the transition from a user task to a system task, preventing destruction of the system environment due to user tasks, and achieving high system reliability.

[Brief explanation of the drawing]

FIG. 1 is a system call execution device according to an embodiment of the present invention that determines whether or not to perform an automatic save operation to the stack based on an address table, and switches to privileged mode when transitioning from user task processing to privileged task processing. FIG.

FIG. 2 is a configuration diagram showing a system call execution device that determines whether to switch to a privileged mode based on a branch destination address according to another embodiment of the present invention.

FIG. 3 is a configuration diagram showing a system call execution device that can arbitrarily determine whether or not to save the bank state based on a flag, according to still another embodiment of the present invention.

[Explanation of symbols]

1,17 Branch instruction 2 System call instruction 3
Interrupts 4, 19 Memory space 5 Address table area 6 without automatic save processing Address table area 7, 1
8 Address table area determination unit 8, 9
Upper limit address and lower limit address 10, 11 of address table area without automatic save processing Upper limit address and lower limit address 12, 37 of address table area 12, 37 μROM 13, 24 Privilege/user mode management unit 14
Address table specification 15
Control signals 16, 25 CPU mode signal 20 Privilege program area 21, 22
Upper limit address and lower limit address of privileged program area 23 Privileged mode 26 Branch processing 27 System call 28 Interrupt processing 29 Bank management section 30 Register file group 31
Stack automatic save flag 32
Inverter circuit 33 User task activation signal 34
Setting by program and terminal 35
AND circuit

Claims (3)

[Claims] Claim 1: When a task is composed of a privileged task that performs system management and a user task, and when transitioning from user task processing to privileged task processing, the CPU mode (operation result flag) and instruction pointer used by the privileged task. It is configured such that it is possible to switch between saving data in the memory area or register area, or transferring control to a privileged task without saving data at all, and furthermore, when issuing a system call on a user task, A first means for processing a system call by executing a system call instruction in which this system call issuance consists of a system call opcode and a value in an address table in which a start address of an execution instruction of a privileged bank is stored; When a branch instruction is executed on a task, this branch instruction can indirectly specify the start address of the instruction by specifying the branch instruction opcode and the address table in which the start address of the execution instruction of the privileged bank is stored. A second means for performing branch processing by executing a branch instruction consisting of double indirect addresses, and an address table storing interrupt processing start addresses specified for each interrupt processing factor when executing an interrupt. and a third means for processing an interrupt by using one of the three means, and when executed by any of the three means, it is determined based on the address of the address table itself whether to transfer to a privileged task and perform save processing, and the user task A system call execution device comprising means for switching a CPU to a privileged mode without software intervention when transitioning from processing to privileged task processing. Claim 2: A task consists of a privileged task that performs system management and a user task, and a branch instruction consisting of a branch instruction opcode and a start address of an execution instruction in a privileged bank is executed to switch from user task processing to privileged task processing. A system call execution system configured such that transition can be switched by executing a branch instruction on a user task, and further comprising means for switching a CPU to a privileged mode without software intervention when transitioning to privileged task processing. Device. [Claim 3] In a multi-register file configuration, at the time of branch processing, system call processing, or interrupt,
It is possible to set the CPU mode (operation result flag), instruction pointer, and whether to save data in the memory area or register area before executing the process, or to execute the process without saving the data at all. The flag can be set by a program or an external terminal, and when switching from a privileged bank to a user bank, the flag is reset, and when a system call instruction is used to transition from a user bank to a privileged bank, the above-mentioned save processing is basically performed. A system call execution device characterized by comprising means for not performing.