/proc/<pid>/stack文件的作用

/proc/<pid>/stack文件是Linux系统中的一个特殊文件，用于查看进程的堆栈信息。每个运行中的进程都有一个对应的/proc/<pid>/stack文件，其中的内容记录了该进程当前的函数调用栈信息。

通过读取/proc/<pid>/stack文件，你可以了解进程当前所执行的函数调用路径，即函数调用栈。这对于调试和分析进程的行为和性能问题非常有用。

/proc/<pid>/stack文件的内容通常以十六进制显示，每一行表示一个函数调用栈帧。每个栈帧包含了函数的返回地址和一些其他与函数调用相关的信息。

注意，/proc/<pid>/stack文件只显示进程当前的函数调用栈，因此在不同时间读取该文件可能会得到不同的结果。如果需要获取完整的函数调用栈信息，可以考虑使用其他调试工具，如gdb。

相关问题

/proc/PID/stat

The /proc/PID/stat file contains various statistics about the process with the specified PID. The file is a single line of text, with each field separated by a space.

The fields in the file are as follows:

1. pid - process ID
2. comm - name of the command that started the process
3. state - current state of the process (e.g. running, sleeping, etc.)
4. ppid - parent process ID
5. pgrp - process group ID
6. session - session ID
7. tty_nr - controlling terminal of the process
8. tpgid - ID of the foreground process group of the controlling terminal
9. flags - process flags (e.g. whether it is being traced, etc.)
10. minflt - number of minor faults (i.e. page faults that could be resolved without disk IO)
11. cminflt - number of minor faults of child processes
12. majflt - number of major faults (i.e. page faults that required disk IO)
13. cmajflt - number of major faults of child processes
14. utime - amount of time the process has spent in user mode
15. stime - amount of time the process has spent in kernel mode
16. cutime - amount of time waited-for children have been in user mode
17. cstime - amount of time waited-for children have been in kernel mode
18. priority - priority of the process
19. nice - nice value of the process
20. num_threads - number of threads in the process
21. starttime - time the process started, in jiffies (1/100th of a second)
22. vsize - virtual memory size of the process
23. rss - resident set size of the process (i.e. amount of physical memory it is using)
24. rsslim - current limit on the resident set size
25. startcode - address of the start of the code segment
26. endcode - address of the end of the code segment
27. startstack - address of the start of the stack
28. kstkesp - current value of the stack pointer
29. kstkeip - current value of the instruction pointer
30. signal - bitmap of pending signals for the process
31. blocked - bitmap of blocked signals for the process
32. sigignore - bitmap of ignored signals for the process
33. sigcatch - bitmap of caught signals for the process
34. wchan - address of the kernel function the process is currently waiting in
35. nswap - number of pages swapped to disk
36. cnswap - number of pages swapped to disk of child processes
37. exit_signal - signal to be sent to the parent process when the process exits
38. processor - CPU the process last ran on
39. rt_priority - real-time priority of the process
40. policy - scheduling policy of the process

Note: Some fields may be displayed as 0 if they are not applicable to the process or if they are not available. Also, the values for utime, stime, cutime, and cstime are given in clock ticks, which can be converted to seconds by dividing by the value of the system variable HZ (which is typically 100 on most systems).

通过运行代码mainProg，观察进程空间变化(/proc/$pid/maps)过程，用图示简要说明进程空间变化的内容，截图画出变量所在内存段；请给出解决思路以及示例代码。

解决思路：

1.编写一个简单的C程序，包含全局变量、局部变量和动态分配内存等。

2.在程序中使用一些系统调用，例如malloc、free、sleep等，使进程空间发生变化。

3.在程序中打印出进程ID，并在程序执行过程中使用ps和top命令查看进程的内存使用情况。

4.通过观察/proc/$pid/maps文件，可以了解进程空间的变化情况，并可以画出变量所在内存段的图示。

示例代码如下：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int global_var = 10; //全局变量
const int const_var = 20; //常量变量

int main()
{
    int local_var = 30; //局部变量
    int *dynamic_var = (int*)malloc(sizeof(int)); //动态分配内存

    printf("Process ID: %d\n", getpid()); //打印进程ID

    printf("Global variable: %p\n", &global_var); //打印全局变量地址
    printf("Constant variable: %p\n", &const_var); //打印常量变量地址
    printf("Local variable: %p\n", &local_var); //打印局部变量地址
    printf("Dynamic variable: %p\n", dynamic_var); //打印动态分配内存地址

    free(dynamic_var); //释放动态分配内存
    sleep(10); //等待10秒钟

    return 0;
}

上述代码中，获取进程ID使用了getpid函数，打印变量地址使用了&符号，动态分配内存使用了malloc函数，释放内存使用了free函数，等待10秒钟使用了sleep函数。在程序运行过程中，可以通过ps和top命令查看进程的内存使用情况，通过观察/proc/$pid/maps文件，可以了解进程空间的变化情况。

以下为变量所在内存段的图示示例：

Global variable: 0x6020a0
Constant variable: 0x6020ac
Local variable: 0x7ffd7c5d8b0c
Dynamic variable: 0x1576010

00400000-00401000 r-xp 00000000 08:01 3932173                            /home/user/mainProg
00600000-00601000 rw-p 00001000 08:01 3932173                            /home/user/mainProg
01576000-01578000 rw-p 00000000 00:00 0                                  [heap]
7f8e8c000000-7f8e8c021000 rw-p 00000000 00:00 0 
7f8e8c021000-7f8e90000000 ---p 00000000 00:00 0 
7f8e908f0000-7f8e908f4000 r--p 00000000 08:01 268440                      /lib/x86_64-linux-gnu/libc-2.27.so
7f8e908f4000-7f8e9090a000 r-xp 00004000 08:01 268440                      /lib/x86_64-linux-gnu/libc-2.27.so
7f8e9090a000-7f8e9094e000 r--p 0015a000 08:01 268440                      /lib/x86_64-linux-gnu/libc-2.27.so
7f8e9094e000-7f8e9094f000 ---p 0019e000 08:01 268440                      /lib/x86_64-linux-gnu/libc-2.27.so
7f8e9094f000-7f8e90951000 r--p 0019e000 08:01 268440                      /lib/x86_64-linux-gnu/libc-2.27.so
7f8e90951000-7f8e90954000 rw-p 001a0000 08:01 268440                      /lib/x86_64-linux-gnu/libc-2.27.so
7f8e90954000-7f8e90958000 rw-p 00000000 00:00 0 
7f8e9096e000-7f8e90971000 r--p 00000000 08:01 268408                      /lib/x86_64-linux-gnu/ld-2.27.so
7f8e90971000-7f8e9098f000 r-xp 00003000 08:01 268408                      /lib/x86_64-linux-gnu/ld-2.27.so
7f8e9098f000-7f8e90999000 r--p 00021000 08:01 268408                      /lib/x86_64-linux-gnu/ld-2.27.so
7f8e90999000-7f8e9099a000 rw-p 0002b000 08:01 268408                      /lib/x86_64-linux-gnu/ld-2.27.so
7f8e9099a000-7f8e9099b000 rw-p 00000000 00:00 0 
7ffcd1b0b000-7ffcd1b2c000 rw-p 00000000 00:00 0                          [stack]
7ffcd1b8d000-7ffcd1b8f000 r--p 00000000 00:00 0                          [vvar]
7ffcd1b8f000-7ffcd1b91000 r-xp 00000000 00:00 0                          [vdso]
ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0                  [vsyscall]