When is static relocation appropriate?

The timing of static relocation is before the program is loaded into memory. In the operating system, when an executable file is loaded into memory, the address reference in the program needs to be modified to the actual memory address based on the relocation information contained in the executable file. This process is static relocation.

Static relocation is to solve the problem of address space. When an executable file is executed, the operating system loads it into a location in memory. However, the address reference in the executable file is relative to the file itself. If the address is not relocated, the program's location in memory will be inconsistent with the address reference in the file, and it will not be executed correctly.

The following is a simple sample code to demonstrate the process of static relocation:

#include <stdio.h>

int global_var = 10;

int main() {
    int local_var = 20;

    printf("global_var address: %p
", &global_var);
    printf("local_var address: %p
", &local_var);

    return 0;
}

In this example, we declare a global variable global_var and a Local variables local_var. In the main function, we use the & operator to get the addresses of these two variables and print them out through the printf function.

If we run this code without static relocation, the output address may not be consistent with what we expect. Because in the executable file, the address reference of the variable is relative to the file itself, while in memory, the address of the variable is the actual physical address.

In order to solve this problem, the operating system will perform a static relocation process when loading the executable file. The specific relocation method depends on the target file format and operating system support, but the basic principle is the same, which is to modify the reference in the program to the actual memory address.

It should be noted that the timing of static relocation is when the executable file is loaded, not at runtime. Once a program is loaded into memory and relocated, its address never changes.

Through static relocation, we can ensure that the running address of the program in memory is consistent with the address reference in the file, so that the program can be executed correctly.

To sum up, the time for static relocation is before the program is loaded into memory. It modifies the address reference in the program so that the program's address in the memory is consistent with the address reference in the file, thereby achieving correct execution. The relocation method of each executable file may be different, but the basic principle is the same.

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