Process virtual address space partition

Process virtual address space area division

Before we write a program in a language , There are two things ： Instructions and data . After we compile the link , Generate an executable file and store it on our disk , When you run this program , Will load the program into memory .
And in the process of loading , What contents of the executable file are loaded into memory ？ How is it stored when loaded into memory ？ Which areas are divided into ？ How to divide ？

Before that, we need to know , Programs cannot be loaded directly into physical memory ！
Let's say X86 32 position Linux Environment as an example .

When the program is executed ,Linux The system will assign a to the current process 2^32(4G) The size of a space , This space is the virtual address space of the process , It has all the resources for the process , All resources constitute the division of state .

This space is divided into two parts by default ： User space and kernel space , The user space is occupied by default 3G Size space , The default size of kernel space is 1G.

All processes in the system have an address space .

In user space , The system is not from 0 Address （0x00000000） Start storing resources , stay 0x00000000 To 0x08048000 This memory cannot be accessed , So when dereferencing a null pointer, the program will crash .

The next memory segment stores .text Paragraph and .rodata paragraph ..text The segment stores instructions ,.rodata The segment stores read-only data , For example, the string constant defined in the program char* str = "hello world";, The resources of these two paragraphs are read-only resources , When we try to modify the data of these two paragraphs , The program will collapse directly .

The next thing to store is .data Paragraph and .bss paragraph ,.data The segment store is initialized and the value is not 0 And static variables , and .bss The segment store is uninitialized or initialized to 0 And static variables .

What follows is .heap Heap memory segment , The space dynamically requested by the program is in this memory .

If the program is linked to a dynamic library , The memory behind the heap memory is used to load the shared library .

Next is the function operation 、 Or when opening threads stack Stack space , Different from other memory segments , The growth direction of stack space is opposite to that of other segments , From high address to low address .

The last memory segment stores command line parameters and environment variables .


Intercepted from 《 Learn more about computer systems 》.

The user space of each process is private , But kernel space is shared ！