Understanding static relocation: when does it happen?

Understand static relocation: when it occurs, specific code examples are needed

Static relocation (static relocation) is a concept in computer systems, used To solve the address problem when the program is executed. When writing a program, it is impossible to know in advance where in the memory the program will be loaded for execution, so relocation is required to map the address in the program with the actual loaded memory address.

Static relocation occurs before the program is loaded and executed. When the operating system loads a program into memory, it allocates a contiguous memory space for the program and copies the program's instructions and data into this memory space. The starting address of this memory space is the base address of the program.

The purpose of static relocation is to solve the problem of the absolute address of the program in memory. In a program, the address used is relative to the address of the program itself, but in actual memory, the address of the program is relative to the base address. Therefore, it is necessary to convert the relative addresses in the program into absolute addresses so that the program can correctly access the instructions and data in the memory during execution.

The following is a specific code example, showing the process of static relocation:

#include <stdio.h>

int main() {
    char* str = "Hello, World!";
    printf("%s
", str);
    return 0;
}

The above code is a simple C language program that outputs the string "Hello, World!". In the program, a string pointer str is used to store the address of the string.

Before static relocation, the address of the program is relative to the address space at compile time. When the compiler compiles a program into machine code, it converts the relative addresses in the program into symbolic addresses, which are the addresses at compile time. Therefore, the address used in the code is actually an offset relative to the address at compile time.

When a program is executed, the operating system loads the program into memory and allocates a continuous memory space for it. The starting address of this memory space is the base address of the program. Therefore, after static relocation, relative addresses in the program need to be converted to absolute addresses, that is, offsets relative to the base address.

In the above code, the string is output through the printf function. At compile time, the compiler stores the string "Hello, World!" in the program's data segment and generates a pointer to the string. After static relocation, relative addresses pointing to strings in the program need to be converted to absolute addresses.

The static relocation process is completed by the linker. The linker converts relative addresses in the program to absolute addresses and populates the program's instructions and data with the correct addresses before the program is loaded into memory.

Summary:
Static relocation occurs before the program is loaded and executed to solve the program address problem. It enables the program to correctly access instructions and data in memory by converting relative addresses in the program into absolute addresses.

Through the above code examples, we understand the basic concepts and processes of static relocation. In actual development, static relocation is an important function of tools such as operating systems and compilers to ensure that programs can run correctly on different memory addresses.

The above is the detailed content of Understanding static relocation: when does it happen?. For more information, please follow other related articles on the PHP Chinese website!