MEMORY_BASIC_INFORMATION结构中的BaseAddress和AllocationBase有什么区别？

Question

在MSDN中,我发现以下`

BaseAddress - 指向页面区域的基址的指针.

AllocationBase - 指向VirtualAlloc函数分配的一系列页面的基址的指针.BaseAddress成员指向的页面包含在此分配范围内.

但我真的不明白有什么区别.谁能告诉我区别？(不像在MSDN :))

Answer 1

Windows上的虚拟内存分配的粒度为64千字节,即SYSTEM_INFO.dwAllocationGranularity的值.但虚拟内存页面为4096字节,SYSTEM_INFO.dwPageSize的值.

使用VirtualAlloc分配虚拟内存时,您将始终获得一个BaseAddress等于AllocationBase的块.但是,如果您随后更改了此块中一个或多个页面的页面保护,那么您可以观察到此块被细分为不同的BaseAddress.使用示例程序最佳显示,在MSVC++上运行:

#include "stdafx.h"
#include <Windows.h>
#include <stdio.h>
#include <conio.h>

void showmem(void* mem) {
    MEMORY_BASIC_INFORMATION info = {};
    VirtualQuery(mem, &info, sizeof info);
    printf("Alloc = %p, base = %p, size = %d, protect = %d\n",
           info.AllocationBase, info.BaseAddress, info.RegionSize, info.Protect);
}


int main() {
    BYTE* mem = (BYTE*)VirtualAlloc(0, 65536, MEM_COMMIT, PAGE_READWRITE);
    printf("%s", "Initial allocation:\n");
    showmem(mem);

    DWORD oldprotect;
    BOOL ok = VirtualProtect(mem + 4096, 4096, PAGE_NOACCESS, &oldprotect);
    printf("%s", "\nAfter protection changes:\n");
    showmem(mem);
    showmem(mem + 4096);
    showmem(mem + 4096 + 4096);

    _getch();
    return 0;
}

该程序的示例输出:

Initial allocation:
Alloc = 00ED0000, base = 00ED0000, size = 65536, protect = 4

After protection changes:
Alloc = 00ED0000, base = 00ED0000, size = 4096, protect = 4
Alloc = 00ED0000, base = 00ED1000, size = 4096, protect = 1
Alloc = 00ED0000, base = 00ED2000, size = 57344, protect = 4

并注意VirtualProtect()调用如何要求原始块在具有不同BaseAddress但具有相同AllocationBase的3个区域中分割.