Understand when static relocation occurs

Understanding the moment when static relocation occurs requires specific code examples

Abstract: Static relocation is a process that a computer program performs based on the actual memory address during the compilation process. operate. This article will use specific code examples to introduce when static relocation occurs and how to implement it.

Introduction:
In the process of writing computer programs, the code segments and data segments of the program are usually determined during compilation, which can ensure the reliability and stability of the program. However, when a program needs to run in a different memory address space, static relocation is required. Static relocation is a basic computer technology. This article will use specific code examples to explain when static relocation occurs and how it is implemented.

1. The time when static relocation occurs
Static relocation is performed during the compilation process, and the specific time it occurs is during the target file generation phase. During the object file generation process, the compiler will correct and relocate the addresses involved in the program based on the actual memory addresses of the code segment and data segment. There are usually two specific processing methods: one is to directly modify the addresses of the code segment and data segment in the target file, and the other is to perform address mapping through the symbol table during the link stage.

2. How to implement static relocation
In order to better understand how to implement static relocation, a specific code example will be used to illustrate it below.

#include <stdio.h>

int main() {
    int a = 10;
    int b = 20;
    int c;

    c = a + b;
    printf("The sum is: %d
", c);

    return 0;
}

In the above code example, variables a and b are assigned values ​​of 10 and 20 respectively, and their sum is stored in a variable c. When the program is running, we need to ensure that these variables are correctly located in memory.

In the compilation phase, the compiler will convert the source code into an object file, and the generated object file contains code segments and data segments. For code segments, the compiler assigns each instruction an offset based on its actual memory address. For the data segment, the location of the variable in memory needs to be statically relocated.

In the link phase, the connector will read the relocation information in the target file, and then perform address mapping through the symbol table. The symbol table stores the correspondence between variable names and addresses. The connector can relocate variables in memory by looking up corresponding relationships in the symbol table. After the linking phase is completed, we have an executable file that can run in memory.

We can view the contents of the target file by using the objdump command. The specific command is as follows:

$ objdump -D example.o

Through the output of the objdump command, we can see the specific addresses of the code segment and data segment. , as well as relocation information, etc. This information plays a key role in the actual static relocation process.

Conclusion:
Static relocation is an operation performed by the computer program based on the actual memory address during the compilation process. With specific code examples, we can better understand when static relocation occurs and how it is implemented. During the compilation phase, the actual memory addresses of the code segment and data segment are corrected and relocated to ensure that the program can run correctly in memory. Static relocation is a very important link in computer programming and is very helpful for understanding and mastering the underlying principles of computers.

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