JP2677458B2 - System call execution device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention does not uniformly perform automatic save processing to a stack area that occurs during branch processing, system call processing, and interrupt processing, but executes it only when necessary, and the above processing is privileged. The present invention relates to a system call execution device that executes a shift to privileged mode when performed in the mode.

[0002]

2. Description of the Related Art Conventionally, tasks related to system management control operations such as system control registers that determine the CPU state. Due to factors such as runaway of user tasks configured by user application programs, errors in the above registers may occur. In order to avoid execution of instructions that determine settings and the state of the CPU, the protection function is operated by hardware for tasks that handle system management to improve system reliability. Although interrupt acceptance processing, task scheduling processing, and IO driver startup are performed on system tasks, in a system configured with multiple banks, processing is performed in the bank that was executing privileged tasks after user tasks are started. However, there are systems that have a system call and are waiting for an interrupt. When a system call or an interrupt occurs, the hardware saves the state of the bank by saving the result of the CPU operation 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. Since then, system call processing and interrupt processing have been executed. Therefore, although the bank in the waiting state does not need the save operation, the save process is executed.

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

[0004]

However, in the above configuration, the normal branch instruction remains in the user mode state, and it is impossible to switch from the user mode state to the privileged mode state. As a means of solving this problem, there is a method of changing the flag indicating the privilege mode state or the user mode state also from the user mode, or shifting to the privilege state by executing a so-called privileged instruction that can be executed only in the privilege mode. However, such a system could not provide sufficient protection.

The present invention solves the above-mentioned conventional problems. In the case of branch processing, system call processing and interrupt processing, the user arbitrarily specifies whether or not to automatically save the state on the bank that executes those processing. It is an object of the present invention to provide a system call execution device that can perform a protection function at the time of transition from a user state to a privileged state.

[0006]

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 by the table address of the vector address. It is determined whether access to the vector address area is unconditionally switched to the privilege mode, and only the double indirect address access is allowed and protected for branching to the vector address table by a branch instruction. It is configured.

[0007]

[0008]

[0009]

With this configuration, real-time processing becomes possible, the throughput of the system can be improved, and a protection function can be added to the transition from the user task to the system task, so that the high reliability of the system can be realized. .

[0010]

【Example】

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a system call execution unit according to an embodiment of the present invention. When it is determined whether to perform an automatic save operation to a stack by an address table and when the user task process shifts to a privileged task process. The structure which switches to the privilege mode is shown.

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

The address table area determining unit 7 determines whether or not the address table area 5 which is not subject to the automatic save processing of the address table area 6 is selected by the address table designation 14. The upper limit address 10 and the lower limit address 11 of the address table region 6 and the upper limit address 8 and the lower limit address 9 of the address table region 5 without automatic save processing are input to the address table region determination unit 7 and are compared with the address table designation 14. Done. The first indirect addressing of the branch instruction 1 is the address table area 6
If the address is between the upper limit address 10 and the lower limit address 11, the address table area determination unit 7 outputs the control signal 15 to the privilege / user mode management unit 13 and the CPU mode signal 16 is privileged without software intervention. Switch to mode. Further, when the address table designation 14 is the address of the upper limit address 8 and the lower limit address 9 of the address table area 5 without automatic save processing, the address table area determination unit 7 outputs the control signal 15 to the μROM 12 and Do not automatically save the program information on the bank to the stack area.

The system call instruction 2 is an instruction for calling a system task from a user task, has an address table specifier, and uses an address in the address table area 6 as a vector address to activate a privileged program. Further, the interrupt 3 uses an address in the address table area 6 as a vector address due to an interrupt generation factor.
Similar to branch instruction 1, system call instruction 2 and interrupt 3
The address table designation 14 is input to the address table area determination unit 7, and it is determined whether or not the privileged bank information is automatically saved by the designated address table area, and the privileged mode is automatically changed.

The protection function works from the specification of a specific address area called the address table and the fact that the branch instruction 1 does not operate normally unless double indirect addressing is performed. Further, the software does not intervene in the shift to the privileged mode, and it is possible to select whether or not to execute the automatic save processing execution to the stack area of the program information on the privileged bank, and the processing can be performed at high speed.

[0015]

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

As described above, according to the present invention, the software does not intervene in the transition to the privileged mode, and whether or not to execute the automatic save processing execution to the stack area of the program information on the privileged bank is executed. It can be selected, real-time processing becomes possible, and the throughput of the system can be improved. Also, a protection function can be added to the transition from the user task to the system task, the destruction of the system environment due to the user task can be avoided, and high reliability of the system can be realized.

[Brief description of the drawings]

FIG. 1 is a system call execution device according to an embodiment of the present invention, which determines whether or not an automatic save operation to a stack is performed by an address table, and switches to a privileged mode when transitioning from user task processing to privileged task processing. It is a block diagram which shows.

[Explanation of symbols]

1,17 Branch instruction 2 System call instruction 3 Interrupt 4,19 Memory space 5 Address table area without automatic save processing 6 Address table area 7,18 Address table area determination unit 8, 9 Upper limit of address table area without automatic save processing Address and lower limit address 10, 11 Upper and lower address of address table area 12, 37 μROM 13, 24 Privilege / user mode management section 14 Address table designation 15 Control signal 16, 25 CPU mode signal 20 Privileged program area 21, 22 Privilege Upper and lower address of 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 start signal 34 Setting by program and pin 35 AND circuit 36 privilege van Running signal

Claims (1)

(57) [Claims] 1. A CPU mode (calculation result flag) and an instruction pointer used by a privileged task when the task is composed of a privileged task and a user task for system management, and the transition from the user task process to the privileged task process is performed. It is configured to be able to switch between saving data in the memory area or register area, or transferring control to a privileged task without saving the data at all, and when issuing a system call on the user task, This system call issuance executes a system call instruction consisting of a system call opcode and a value in an address table in which the start address of the execution instruction of the privilege bank is executed, and a first means for processing the system call and a user. Branch on task When the instruction is executed, this branch instruction indirectly specifies the start address of the instruction by specifying the address table in which the branch instruction opcode and the start address of the privileged bank execution instruction are stored. Second branch processing is executed by executing a branch instruction composed of
Means and a third means for performing interrupt processing by an address table that stores an interrupt processing start address specified for each interrupt processing factor when the interrupt is executed, and is executed by any one of the three means. Sometimes, a means for switching to a privileged task and determining whether or not to perform a save process based on the address of the address table itself, and for switching the CPU to a privileged mode without software intervention when a transition is made from the user task process to the privileged task process. A system call execution device comprising: