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PostgreSQL 源码解读(227)- Linux Kernel(进程虚拟内存#2)

翻译 PostgreSQL 作者:husthxd 时间:2019-09-17 15:47:50 0 删除 编辑

PostgreSQL使用进程架构,每个连接对应一个后台进程,为了更好的理解这种架构,有必要深入理解进程的相关知识.本节主要介绍了Linux下的进程虚拟内存结构,并以使用C语言样例程序进行说明.

一、虚拟内存

进程虚拟内存的详细结构如下图所示:

C样例程序如下:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
/**                                                                                                      
 * f - print locations of various elements                                                               
 *                                                                                                       
 * Returns: nothing                                                                                      
 */
void f(void)//子函数
{
     int a;
     int b;
     int c;
     a = 98;
     b = 1024;
     c = a * b;
     printf("[f] a = %d, b = %d, c = a * b = %d\n", a, b, c);
     printf("[f] Adresses of a: %p, b = %p, c = %p\n", (void *)&a, (void *)&b, (void *)&c);
}
/**                                                                                                      
 * main - print locations of various elements                                                            
 *                                                                                                       
 * Return: EXIT_FAILURE if something failed. Otherwise EXIT_SUCCESS                                      
 */
int main(int ac, char **av, char **env)
{
     int a;//本地变量,位于栈中
     void *p;//指针,在堆中分配内存
     int i;
     int size;
     printf("Address of a: %p\n", (void *)&a);
     p = malloc(98);//在堆中分配内存
     if (p == NULL)
     {
          fprintf(stderr, "Can't malloc\n");
          return (EXIT_FAILURE);
     }
     printf("Allocated space in the heap: %p\n", p);
     printf("Address of function main: %p\n", (void *)main);//main函数所在的内存地址
     printf("First bytes of the main function:\n\t");
     for (i = 0; i < 15; i++)
     {
          printf("%02x ", ((unsigned char *)main)[i]);//首16个字节
     }
     printf("\n");
     printf("Address of the array of arguments: %p\n", (void *)av);//输入参数数组地址
     printf("Addresses of the arguments:\n\t");//
     for (i = 0; i < ac; i++)
     {
          printf("[%s]:%p ", av[i], av[i]);//打印输入参数
     }
     printf("\n");
     printf("Address of the array of environment variables: %p\n", (void *)env);//环境变量地址
     printf("Address of the first environment variables:\n");//环境变量信息
     for (i = 0; i < 3; i++)
     {
          printf("\t[%p]:\"%s\"\n", env[i], env[i]);
     }
     /* size of the env array */
     i = 0;
     while (env[i] != NULL)//以NULL作为终结
     {
          i++;
     }
     i++; /* the NULL pointer */
     size = i * sizeof(char *);
     printf("Size of the array env: %d elements -> %d bytes (0x%x)\n", i, size, size);//计算环境变量数组大小
     f();//调用函数
     getchar();//接受输入,进程不退出
     return (EXIT_SUCCESS);
}

编译并执行

[root@localhost hacker]# gcc -Wall -Wextra -Werror main-7.c -o 7
[root@localhost hacker]# ./7 Hello Hacker Jack!
Address of a: 0x7fff5b327bb8 --> 位于栈中
Allocated space in the heap: 0x9b6010 --> 位于堆中
Address of function main: 0x400729 --> 可执行文件
First bytes of the main function:
    55 48 89 e5 48 83 ec 40 89 7d dc 48 89 75 d0 
Address of the array of arguments: 0x7fff5b327cb8 -->参数数组地址
Addresses of the arguments:
    [./7]:0x7fff5b329808 [Hello]:0x7fff5b32980c [Hacker]:0x7fff5b329812 [Jack!]:0x7fff5b329819 --> 输入参数
Address of the array of environment variables: 0x7fff5b327ce0 --> 环境变量数组
Address of the first environment variables:
    [0x7fff5b32981f]:"XDG_SESSION_ID=1"
    [0x7fff5b329830]:"HOSTNAME=localhost.localdomain"
    [0x7fff5b32984f]:"SELINUX_ROLE_REQUESTED="
Size of the array env: 27 elements -> 216 bytes (0xd8)
[f] a = 98, b = 1024, c = a * b = 100352 
[f] Adresses of a: 0x7fff5b327b7c, b = 0x7fff5b327b78, c = 0x7fff5b327b74 --> 函数f中的变量地址

通过udis86可反编译,得到汇编代码

[root@localhost install]#  echo "55 48 89 e5 48 83 ec 10 48 8d 45 f0 48 89 c6" | udcli -64 -x -o 400729
0000000000400729 55               push rbp                
000000000040072a 4889e5           mov rbp, rsp            
000000000040072d 4883ec10         sub rsp, 0x10           
0000000000400731 488d45f0         lea rax, [rbp-0x10]     
0000000000400735 4889c6           mov rsi, rax            
[root@localhost install]#

查看该进程的内存映射信息

[root@localhost install]# ps aux | grep "./7" | grep -v grep
root      6471  0.0  0.0   4348   348 pts/0    S+   15:24   0:00 ./7 Hello Hacker Jack!
[root@localhost install]# cat /proc/6471/maps
00400000-00401000 r-xp 00000000 fd:00 134287606                          /data/source/hacker/7
00600000-00601000 r--p 00000000 fd:00 134287606                          /data/source/hacker/7
00601000-00602000 rw-p 00001000 fd:00 134287606                          /data/source/hacker/7
009b6000-009d7000 rw-p 00000000 00:00 0                                  [heap]
7f95b5d16000-7f95b5ed8000 r-xp 00000000 fd:00 151914                     /usr/lib64/libc-2.17.so
7f95b5ed8000-7f95b60d8000 ---p 001c2000 fd:00 151914                     /usr/lib64/libc-2.17.so
7f95b60d8000-7f95b60dc000 r--p 001c2000 fd:00 151914                     /usr/lib64/libc-2.17.so
7f95b60dc000-7f95b60de000 rw-p 001c6000 fd:00 151914                     /usr/lib64/libc-2.17.so
7f95b60de000-7f95b60e3000 rw-p 00000000 00:00 0 
7f95b60e3000-7f95b6105000 r-xp 00000000 fd:00 151907                     /usr/lib64/ld-2.17.so
7f95b62f8000-7f95b62fb000 rw-p 00000000 00:00 0 
7f95b6301000-7f95b6304000 rw-p 00000000 00:00 0 
7f95b6304000-7f95b6305000 r--p 00021000 fd:00 151907                     /usr/lib64/ld-2.17.so
7f95b6305000-7f95b6306000 rw-p 00022000 fd:00 151907                     /usr/lib64/ld-2.17.so
7f95b6306000-7f95b6307000 rw-p 00000000 00:00 0 
7fff5b309000-7fff5b32a000 rw-p 00000000 00:00 0                          [stack]
7fff5b3f1000-7fff5b3f3000 r-xp 00000000 00:00 0                          [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]
[root@localhost install]#

二、参考资料

Virtual memory
Hack the Virtual Memory: drawing the VM diagram
Udis86

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