CN111984411A - Application relocation method for resource-constrained platform - Google Patents

Abstract

The present invention provides an application relocation method for a resource-limited platform, which is used to solve the problems that the current application loads ELF files, occupies a lot of resources, and the system loads the application operation is complicated. Mainly include: TEXT unit; REL table unit; GOT table unit; DATA unit; There is no need to store redundant data for system relocation, thereby reducing the size of the application and achieving the purpose of reducing the occupation of system resources, so that embedded systems with the same resource conditions can run more applications at the same time.

Description

An application relocation method for resource-constrained platforms

technical field

The present disclosure relates to the field of embedded and real-time operating systems, and in particular, to an application relocation method for resource-constrained platforms.

Background technique

Traditional application relocation methods are based on parsing ELF files, installing them in a certain format, and loading them into memory by the system to run. To realize relocation in this way, it is necessary to ensure that enough information must be retained in the ELF, so that the system can find the required information, such as: program entry, data segment start address, etc. This means that the ELF file is bound to be much larger than the executable image file BIN, resulting in a waste of resources.

However, if we can move the relocation of the application address to the inside of the application in some way, so that the application can dynamically complete the relocation of its own data address according to its own location when it is started. Through this mechanism, the application will be allowed to be compiled into an executable image file BIN, because, through this mechanism, the system does not need to parse the application when loading the application, just jump to the application after allocating resources. . This reduces the difficulty of loading the application by the system, and in this way, the application file does not need to retain fields that should be included in the ELF file, which reduces the size of the application and achieves the purpose of reducing system resource occupation.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide an application relocation method for a resource-constrained platform, so as to solve the problem of using ELF files to realize application relocation in the existing embedded system and occupying high system resources.

An application relocation method for a resource-constrained platform provided by the present invention includes:

GOT table unit, which is a data table for storing global data address offsets;

REL table unit, which is used to store the offset of the data that needs to be relocated;

DATA unit, which is used to store all data including initial values.

TEXT unit, which is used to store all executable code.

Relocation unit, which is used to perform the work of real data address relocation.

Further, the GOT table unit belongs to the RW segment data, and will be copied to the RAM when the application is just started.

Further, the RAM space is pre-allocated before the system loads the application, and the starting address of the RAM space is passed to the application through a general-purpose register when the application is loaded.

Further, the REL table unit belongs to RO segment data, and the offset corresponding to the data to be relocated is stored therein. When the application is just started, the REL table unit itself will not be copied to RAM, but the data it points to that needs to be relocated will be moved to RAM.

Further, the DATA unit belongs to the RW segment data, which stores all the data including the initial value, including the data that needs to be relocated pointed to by the REL table unit.

Further, the TEXT unit belongs to RO segment data, stores all executable codes of the application, and will be copied to the Flash when the program is installed, and this unit is in the head of the spatial arrangement of the entire application.

Further, the relocation unit is the code for performing real relocation, which is included in the TEXT unit. After the application executes the code for copying the RW segment data, the code in this relocation unit will be executed.

Further, the actual running address of the application is obtained through the pseudo-instruction ADR after the application is loaded into the application running space and before the relocation unit is executed.

Further, when the described relocation unit begins to revise the data pointed to by the REL table unit in the GOT table unit and the DATA unit, it will be compared with the offset of the DATA unit, if less than the offset of the DATA unit, then the storage will be explained. The address itself is the data pointing to the TEXT unit, the offset of the TEXT unit will be subtracted and the actual running address of the code segment will be added to correct it; if it is greater than the offset of the DATA unit, it means that the stored address itself is the data pointing to the DATA unit , which will be corrected by subtracting the DATA unit offset and adding the pre-allocated RAM space start address.

Further, the offsets of the DATA unit, the TEXT unit, the GOT table unit, and the REL table unit are obtained according to the symbols defined in the link script when the application is linked.

Description of drawings

In order to illustrate the technical solutions of the present invention more clearly, the accompanying drawings required in the embodiments will be briefly introduced below. It should be understood that the following drawings only illustrate some embodiments of the present disclosure, and therefore should not be viewed as As a limitation of the present invention, those of ordinary skill in the art can also obtain drawings related to the prerequisites according to these drawings without any creative effort.

FIG. 1 is a frame diagram of an application relocation method for a resource-constrained platform according to a specific embodiment of the present invention.

FIG. 2 is a schematic diagram of a startup flow of an application to which the relocation method is applied according to a specific embodiment of the present invention.

FIG. 3 is a schematic diagram of a memory data arrangement and a relocation method of an application running process according to a specific embodiment of the present invention.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all of the embodiments. The embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but merely to represent selected embodiments of the invention. Based on the embodiments of the present invention, all the prerequisite embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present invention.

An embodiment of the present invention provides a description of an application relocation method for a resource-constrained platform. As shown in FIG. 1, the method consists of a TEXT unit 11, a REL table unit 12, a GOT table unit 13, a DATA unit 14, and a relocation unit. Unit 15 is composed.

TEXT unit 11, which is used to store the code data of the application;

REL table unit 12, which is used to store the offset of the data that needs to be relocated;

GOT table unit 13, which is used to store the offset of the global data address;

DATA unit 14, which is used to store all the data including the initial value;

The relocation unit 15 is used to perform real data address relocation.

FIG. 2 is a schematic diagram of a startup flow of an application to which the relocation method is applied according to a specific embodiment of the present invention. The process starts from step S201.

In step S201, before the application is loaded, the system allocates necessary RAM resources to the application for storing the data segment data after the application is started.

In step S202, the system will put the first address of the allocated RAM space into a general-purpose register for transfer to the application space.

In step S203, the system will jump to the first address of the application location according to the application storage location, and directly run the application.

In step S204, the application will read the first address of the allocated RAM space from the general-purpose register, so that the offset of the data address of the GOT table unit can be calculated later.

In step S205, the application obtains the actual running address of the current application code segment by using the ADR instruction, so as to facilitate the subsequent calculation of the offset of the data pointing to the TEXT unit.

In step S206, the application obtains the offsets of the TEXT unit, the GOT table unit, and the REL table unit according to the symbols defined in the link script at the time of linking, so as to locate the offset of the data address that needs to be relocated.

In step S207, the application will process the address stored in the GOT table unit, and compare it with the start address of the RW segment. If it is less than the start address of the RW segment, it means that the stored address itself is the data pointing to the TEXT unit, and will be subtracted from the start address of the RW segment. Go to the TEXT unit address offset and add the actual running address of the code segment to correct it. If it is greater than the starting address of the RW segment, it means that the stored address itself is the data pointing to the DATA unit, and the address of the DATA unit will be subtracted and the first address of the pre-allocated RAM space will be added to correct it.

In step S208, the application will process the data pointed to by the REL table, and also compare its stored address with the start address of the RW segment. If it is less than the start address of the RW segment, it means that the stored address itself is the data pointing to the TEXT unit, It will be corrected by subtracting the TEXT unit address offset and adding the actual running address of the code segment. If it is greater than the starting address of the RW segment, it means that the stored address itself is the data pointing to the DATA unit, and the address of the DATA unit will be subtracted and the first address of the pre-allocated RAM space will be added to correct it.

In step S209, the application has completed the relocation work at this time, and will jump to the application program entry to execute the application program.

FIG. 3 is a schematic diagram of a memory data arrangement and a relocation method of an application running process according to a specific embodiment of the present invention. The process starts from step S301.

In step S301, what is shown is the distribution of the code segment in the chip after the application is installed in the Flash, including executable code TEXT, read-only data RODATA, and relocation data table REL, etc.;

In step S302, the distribution of the data segment in the chip after the application is installed in the Flash is shown, including the global offset table GOT, the data area DATA with initial values, etc.; this part of data is displayed when the application is started. is copied to RAM space;

In step S303, the distribution in the memory after the data segment is transferred to the memory during the running process of the application is shown, from top to bottom are GOT, DATA, others, and BSS;

In step S304, the GOT table unit that needs to be relocated when the application is started is displayed, and the application will process the address stored in the GOT table unit and compare it with the start address of the RW segment shown in S302, such as If it is less than the starting address of the RW segment, it means that the stored address itself is the data pointing to the TEXT unit, which will be corrected by subtracting the TEXT unit address offset and adding the actual operating address of the code segment. If it is greater than the starting address of the RW segment, it means that the stored address itself is the data pointing to the DATA unit, and the address of the DATA unit will be subtracted and the first address of the pre-allocated RAM space will be added to correct it.

In step S305, the data area DATA with an initial value that is transferred to the memory by the application during the running process is shown, which contains the address data that the REL table unit points to to be relocated. When the application starts, it will process the address to be relocated stored in the DATA, and compare it with the start address of the RW segment shown in S302. If it is smaller than the start address of the RW segment, it means that the stored address itself points to the TEXT unit. data, it will be corrected by subtracting the TEXT unit address offset and adding the actual running address of the code segment. If it is greater than the starting address of the RW segment, it means that the stored address itself is the data pointing to the DATA unit, and the address of the DATA unit will be subtracted and the first address of the pre-allocated RAM space will be added to correct it.

Claims (7)

1. An application relocation method for a resource-constrained platform is characterized in that an actual pre-allocated RAM address space is transferred to an application through a general register, and then before the application is started to enter a program entry main, a relocation unit in a TEXT unit is used for correcting a GOT table unit and DATA pointed by a REL table unit in a DATA unit according to an actual RAM address and an actual running address of the application, so that the relocation of the application is completed.

2. The method of claim 1, wherein passing the actual pre-allocated RAM address space to the application through the general purpose registers is performed when the system loads the application.

3. The method of claim 1, wherein the actual running address of the application is obtained by the pseudo-instruction ADR after the application loading into the application running space is completed.

4. The application relocation method for resource-constrained platform according to claim 1, wherein the relocation unit is a code that really performs data address relocation, and is part of a TEXT unit.

5. The method of claim 1, wherein the relocation unit starts to modify the GOT table elements and the DATA pointed to by the REL table elements in the DATA elements after completing the application loading into the application runtime space and before the application enters the program entry main.

6. The application relocation method for resource-constrained platform as claimed in claim 1, wherein when correcting the DATA pointed to by the REL table element in the GOT table element and the DATA element, comparing them with the offset of the DATA element, if smaller than the offset of the DATA element, it means that the stored address itself is the DATA pointing to the TEXT element, and correcting it by subtracting the offset of the TEXT element and adding the actual running address of the code segment; if greater than the DATA element offset, indicating that the stored address is itself DATA pointing to the DATA element, the DATA element offset will be subtracted and corrected by adding the pre-allocated RAM space starting address.

7. The application relocation method for resource-constrained platform as claimed in claim 6, wherein the offsets of DATA units, TEXT units, GOT table units, REL table units are derived from symbols defined in the chaining script at the time of application chaining.

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