JPS6391740A - Stack control system - Google Patents

Abstract

PURPOSE:To always secure and release frames by a last-in first-out method by providing a frame pointer indicating the latest frame and plural stack pointers, which can be allocated to the frames next time, in the frame of each stack. CONSTITUTION:In using a stack (b) first time, the frame b1 is secured. The leading address of the next frame b2 is held in the stack pointer S24 in the frame b1, while the leading address of the frame c1 in a stack (c) is held in the stack pointer S31. In this time, the leading address of the frame b1 is held in the frame pointer (a). In using the stack (c) next time, the frame pointer (a) reads the stack pointer S31 in the frame b1, and according to the read-out value, the frame c1 is secured. The stack pointer S24 in the frame b1 is moved to the stack pointer S24 in the frame c1 as it is, and the leading address of the frame c2 is held in the stack pointer S31.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a stack control method used to save the contents of registers and the like when switching processing routines in an electronic computer system, and particularly relates to a method of controlling a stack used for saving the contents of registers etc. when switching processing routines. The present invention relates to a stack control method suitable for securing frames in an arbitrary order in a plurality of different stacks.

[Conventional technology]

In general, a stack consists of multiple frames (data storage area)
The frame that stores data primarily is indicated by a stack pointer. When there is one stack, once data for one frame is stored in the stack, the stack pointer can be updated by the number of frames, and stack control is simple. - On the other hand, if there are multiple stack pointers,
Traditionally, each stack was used completely independently, or each stack was chained; in other words, if one stack overflowed, it was switched to the next stack)
, either logically used as one stack, and stack control was basically the same as in the case of one stack.

Note that stack control using a stack pointer is described in, for example, Japanese Patent Laid-Open No. 74646/1983.

[Problem that the invention seeks to solve]

In recent years, computer systems have emerged that support multiple addressing modes, such as 24-bit and 31-bit addressing modes.

In this case, in order to make the user program unaware of addressing mode switching, prepare separate stacks for saving the contents of registers, etc. for each addressing mode, and then use these stacks in any order. However, within each stack, last-in, first-out is guaranteed, and even across multiple stacks, frames must always be allocated and released on a last-in, first-out basis. The prior art does not consider using multiple stacks in any order.

The purpose of the present invention is to address multiple stacks.

Although the order in which frames are allocated to individual stacks is arbitrary, last-in, first-out is guaranteed within each stack, and frames are always allocated on a last-in, first-out basis across multiple stacks. The object of the present invention is to provide a stack control method in which release is performed.

[Means for solving problems]

The present invention provides, in a computer system equipped with a plurality of stacks, one frame pointer common to all the plurality of stacks pointing to the start address of the latest frame, and a frame pointer that points to the start address of the latest frame. A plurality of stack pointers are provided that indicate addresses to which frames can be allocated next to other stacks.

[For production]

Let there be n stacks. In the claim pointed to by the frame pointer, the final end address of the n stacks used at the latest point in time is set, so if you can determine which stack to use next, you can place the next frame in any stack. can be ensured.

When securing the next frame in stack i, the following operations are performed.

(1) As the next frame pointer, the stack pointer i in the frame pointed to by the current frame pointer is used as is.

(2) Stack pointer i to stack pointer i-1 and stack pointer i+ held during the next frame
For stack pointers 1 to n, the value of the corresponding stack pointer in the current frame is used as is.

(3) For stack pointer 1 in the next frame, set the address of the current frame pointer plus the next frame length.

In this way, from the frame pointer at any point in time,
It becomes possible to allocate frames in any order in any stack.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows one embodiment of the present invention, showing two types of stacks corresponding to 24-bit and 31-bit addressing modes, and the relationship between the frame pointer and the stack pointer in the frame of each stack.

In FIG. 1, on general-purpose register 1 with a specific number, -
There is a frame pointer a that indicates the starting address of the incorrect frame. The frame indicated by frame pointer a is called the current frame. On memory 2, there are 2
There are two types of stacks: stack b corresponding to 4-bit address space and stack C corresponding to 31-bit address space.6 stacks B and C have memory that is allocated and released once, secured on a last-in, first-out basis. The frame in the stack b is defined as the unit of the area by the frame b (i=1.2
．． ), the frame in stack C is set to C4 (1=1-
+ 2 +...). In each frame of stacks b and C, there is a stack pointer S24 for the 24-bit address space indicating the address at which the next frame can be allocated in stack b, and a stack pointer S24 indicating the address at which the next frame can be allocated in stack C. It maintains two stack pointers: a stack pointer S31 for a 31-bit address space indicating possible addresses.

Figure 1 shows b □ → C engineering → b2 → c in stacks b and C.
This figure shows a state in which frames are secured in the order of 2.

That is, if stack b is used initially, frame b□
and secure the stack pointer S24 in the frame b1.
holds the start address of the next frame b2, and the stack pointer S31 holds the start address of frame C□ of the stack C. At this time, frame pointer a has
The start address of frame B is held. Next, when using stack C, read stack pointer 331 in frame b1 using frame pointer a, secure frame C1 using that value, and set stack pointer S24 in frame C to stack pointer 331 in frame b1. Move S24 as is and set stack pointer S31
holds the start address of the next frame c2. At this time, the start address of frame C□ is held in frame pointer a. Next, when stack b is to be used again, stack pointer S24 of frame C□ is read using frame pointer a, and frame b2 is secured using its 4jff. Then, the start address of the next frame b3 is entered into the stack pointer S24 in the frame b2, and the stack pointer S31 in the frame c1 is directly transferred to the stack pointer S31. At this time, the start address of frame b2 is held in frame pointer a.

Next, when using stack C, frame pointer a
Therefore, the stack pointer S! in frame b2 is set to S! 31 and secures frame c2 using that value.

Note that the path indicated by the dotted line in FIG. 1 is created by providing a backward chain between frames.
→The order to secure the frame c2 is bl, c, and T.
This shows that it is possible to match the calling order of the program corresponding to S21c.

FIG. 2 shows the state after frame b3Tb4 is allocated to stack b in the 24-bit address space after frame c2 in FIG. 1.

The stack allocation request is made after determining the storage size of the next frame to be allocated and whether the frame will be allocated to a 24-bit address space or a 31-bit address space.

Even if frame pointer a points to a frame in stack b for 24-bit address space (when allocated after C2), stack C for 31-bit address space
(b4 is allocated after b), the next time a frame is secured in stack b for 24-bit address space, the same operation described below can be performed.

(1) Stack pointer S for the 24-bit address space in the current frame as the value of the next frame pointer a
Use the value of 24 as is.

(When C2-+b3, 524 in C2 indicated by a=a
When b3→b4, a = 824 in the case indicated by a
) (2) Stack pointer S31 for the 31-bit address space in the current frame as the value of the stack pointer S31 for the 31-bit address space in the next frame.
Use the value of N as is.

(When C2-+b, b, 531=a indicates C
531b in 2, when -*b4 831 in b4=
831 in b3 indicated by a (3) 24 in the next frame
The value of the stack pointer S24 for the bit address space is the address obtained by adding the size of the storage area to be allocated as the next frame to the stack pointer S24 for the 24-bit address space in the current frame.

(When cz→b, the size of 834+b in C2 indicated by 524=a inside.

When b3→b4, 824=a in b4 indicates the size of S24+b4.Conversely, when allocating a frame to the frame pointer a at an arbitrary point in the stack C for the 31-bit address space, You can perform the same operation as above. However, in this case, S24 and 831 are replaced with the above and a lot is created.

By managing the stacks as described above, two types of stacks b and C within the 24-bit or 31-bit address space can be used at any time and in any order. Also, if we look at this from the perspective of program control, 24
It is possible to call programs that use a stack in a bit or 31-bit address space in any order.

〔Effect of the invention〕

As is clear from the above description, according to one aspect of the present invention, multiple stacks can be used in any order, while maintaining a last-in, first-out order within each stack and across multiple stacks.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a stack and the relationship between a frame pointer and a stack pointer according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating updating of the frame pointer and stack pointer according to the present invention. a...Frame pointer, b, c...Stack, S24. S34...Stack pointer. ;°−1 Figure 1

Claims (1)

[Claims] (1) In a stack control method that allocates frames in multiple stacks in any order, a frame pointer common to each stack pointing to the latest frame and a self-linked frame pointer in the already allocated frame of each stack are used. A stack and multiple stack pointers pointing to addresses where frames can be allocated next to other stacks are provided, and when a request to use a certain stack occurs, the frame indicated by the frame pointer is allocated to the stack corresponding to the request. A stack control method characterized by reading a stack pointer and securing a frame on the stack based on the value of the stack pointer.