01 PrivateMemory內存

原創

2019-02-20 19:23

1、申請內存的兩種方式
<1>通過VirtualAlloc/VirtualAllocEx申請的：PrivateMemory(當前的線性地址獨享物理頁)
<2>通過CreateFileMapping映射的：Mapped Memory（線性地址對應的物理頁可能不是獨有的，可能與其他進程共享物理頁）

2、申請內存
LPVOID VirtualAlloc{
LPVOID lpAddress, // 要分配的內存區域的地址
DWORD dwSize, // 分配的大小,按頁的大小分，小於一個頁也按一個頁分
DWORD flAllocationType, // 分配的類型
DWORD flProtect // 該內存的初始保護屬性
};
實驗代碼：

#include <windows.h>
#include <stdio.h>

LPVOID lpAddress;

int main()
{
	printf("程序運行了，內存還沒有申請\n");
	getchar();
	//要申請的內存，申請內存的線性地址；大小，以頁爲單位；保留還是提交，MEM_RESERVER|MEM_COMMIT；訪問權限
	lpAddress = ::VirtualAlloc(NULL, 0x1000 * 2, MEM_COMMIT, PAGE_READWRITE);
	printf("申請的線性地址爲：%x\n", lpAddress);
	getchar();
	return 0;
}

步驟：
首先，我們先運行程序停下來，然後在WinDbg中查看該程序的內存分配情況

kd> !vad 0x8667a2c0 
VAD   Level     Start       End Commit
86699ed8  1        10        10      1 Private      READWRITE          
868ccd18  2        20        20      1 Private      READWRITE          
866f5288  3        30       12f      3 Private      READWRITE          
8672a210  4       130       132      0 Mapped       READONLY           Pagefile section, shared commit 0x3
8673dc48  5       140       23f      4 Private      READWRITE          
86a4e6e8  6       240       24f      6 Private      READWRITE          
86ab0488  7       250       25f      0 Mapped       READWRITE          Pagefile section, shared commit 0x3
86955c60  8       260       275      0 Mapped       READONLY           \WINDOWS\system32\unicode.nls
865fbd48  9       280       2c0      0 Mapped       READONLY           \WINDOWS\system32\locale.nls
8689b670 10       2d0       310      0 Mapped       READONLY           \WINDOWS\system32\sortkey.nls
868d7840 11       320       325      0 Mapped       READONLY           \WINDOWS\system32\sorttbls.nls
868c8b30 12       330       370      0 Mapped       READONLY           Pagefile section, shared commit 0x41
865fbc98 13       380       38f      8 Private      READWRITE          
86ad42f0 14       390       392      0 Mapped       READONLY           \WINDOWS\system32\ctype.nls
8667a2c0  0       400       426      4 Mapped  Exe  EXECUTE_WRITECOPY  \MSDev98\MyProjects\VirtualAlloc\Debug\VirtualAlloc.exe
86ab02c8  3       430       52f      8 Private      READWRITE          
868de588  2     7c800     7c91d      6 Mapped  Exe  EXECUTE_WRITECOPY  \WINDOWS\system32\kernel32.dll
867b26a8  1     7c920     7c9b5      5 Mapped  Exe  EXECUTE_WRITECOPY  \WINDOWS\system32\ntdll.dll
86a3fd90  3     7f6f0     7f7ef      0 Mapped       EXECUTE_READ       Pagefile section, shared commit 0x7
862184e8  2     7ffa0     7ffd2      0 Mapped       READONLY           Pagefile section, shared commit 0x33
86a48008  3     7ffda     7ffda      1 Private      READWRITE          
8667a3a8  4     7ffdf     7ffdf      1 Private      READWRITE          

Total VADs: 22, average level: 6, maximum depth: 14
Total private commit: 0x30 pages (192 KB)
Total shared commit:  0x81 pages (516 KB)

接着我們回到虛擬機繼續執行程序，然後回到WinDbg中查看內存分配情況

3、堆與棧
C中的堆是操作系統先用VirtualAlloc分配了很大一塊內存，當我們使用malloc是調用HeapAlloc，HeapAlloc分配內存是從操作系統中分好的內存直接拿來用，malloc函數使用的時候根本沒有進0環
棧也是操作系統已經分配好的內存
實驗代碼

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

int x = 0x1111;

int main()
{
	printf("申請內存前\n");
	getchar();

	int y = 0x2222;
	int *z = (int*)malloc(sizeof(int) * 128);
	printf("全局變量：%x\n", &x);
	printf("棧：%x\n", &y);
	printf("堆：%x\n", z);

	getchar();
	return 0;
}

首先，我們先運行代碼並用WinDbg查看內存分配狀況

然後繼續運行代碼，再回到WinDbg中查看內存

對比兩圖，發現全局變量是Mapped內存，其他兩個也是提前分配好的