When exactly does a static relocation occur?

The specific moment when static relocation occurs is when the program is loaded. Static relocation refers to the process of converting absolute reference addresses in the program to actual physical memory addresses before the program is run. In modern operating systems, static relocation is completed by the linker when the program is loaded.

The specific code examples are as follows:

#include <stdio.h>

// 全局变量，需要进行静态重定位
int global_var = 10;

// 静态函数，也需要进行静态重定位
static void static_func()
{
    printf("This is a static function.
");
}

int main()
{
    printf("Before relocation:
");
    printf("Global variable: %p
", &global_var);
    printf("Static function: %p
", &static_func);

    // 程序加载后进行静态重定位
    // 在这里进行具体的重定位操作

    printf("
After relocation:
");
    printf("Global variable: %p
", &global_var);
    printf("Static function: %p
", &static_func);

    return 0;
}

In the above code, both the global variable global_var and the static function static_func need to be statically relocated. In the main function, we first print the addresses of these two variables and functions, then perform specific static relocation operations after the program is loaded, and finally print the addresses of these two variables and functions again.

The specific process of static relocation will vary depending on the operating system, but it usually includes the following steps:

1. Determine the base address (Base Address) of program loading.
2. Traverse the executable file of the program and find all absolute references.
3. Convert absolute references to actual physical memory addresses, that is, relocation.
4. Update the program's memory mapping table and replace the absolute reference address with the actual physical memory address.

After completing the above steps, the absolute references in the program are successfully converted into actual physical memory addresses, and the program can run normally.

It should be noted that static relocation is done when the program is loaded, so it will only happen once when the program starts. During the running of the program, if dynamic loading and linking operations are involved, the concept of dynamic relocation may be involved.

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