快哭了，为什么物理地址要除以256啊？

limingjing1986

快哭了，为什么物理地址要除以256啊？ [复制链接]

研究了一整天，查遍了所有资料，问遍了所以同事，还是没一点头绪，不是很难解决的问题我也不会来麻烦大家了，拜托了：
aViruAddr1 = AllocPhysMem(size, PAGE_READWRITE, 0, 0, &aPhysAddr1);
aViruAddr2 = VirtualAlloc(0, size, MEM_RESERVE, PAGE_NOACCESS )
VirtualCopy(aViruAddr2, (LPVOID)(aPhysAddr1/256), size, PAGE_PHYSICAL | PAGE_EXECUTE_READWRITE | PAGE_NOCACHE)
这里是把虚拟地址aViruAddr2映射到物理空间aPhysAddr1上是吧，但是为什么物理地址aPhysAddr1要除以256呢，头疼啊，先谢过了！

missingwind

  我同事跟我说，反正你遇到物理地址就把它除以256就得了。我晕，咱可是做学问的，怎么能这样子就成了呢，总要知道一下原因是不。
  楼下的哥们加油啊！

jiessiesun

确实是这样，物理地址（只要有page_physical标识的），就需要右移8位，也就是除以256。这个是微软文档里说的。

guangtonggg

Used to map a physical memory region. When using this flag, divide the physical address — that is, lpvSrc — by 256.

tsz

但这是为什么呢？
有谁知道理由的吗？

情场探花

因为VirtualCopy的原因,你看看VirtualCopy对你传的物理地址做了什么就明白了.

0400240116

大哥，virtualcopy的源代码能看到吗？在哪个文件里啊？

wangll

如果加了PAGE_PHYSICAL 这个标志，那么就说明是物理地址，必须右移8位，因为在VirtualCopy的源代码里，如果检测到有PAGE_PHYSICAL标志，会讲传入的地址左移8位的。如果你没有加PAGE_PHYSICAL这个标志，则不用这么做。

yangyali314

1.MSDN:
BOOL VirtualCopy(
  LPVOID lpvDest,
  LPVOID lpvSrc,
  DWORD cbSize,
  DWORD fdwProtect
);
Parameters
lpvDest
[out] Pointer to the destination memory, which must be reserved.
lpvSrc
[out] Pointer to committed memory.
.....
PAGE_PHYSICAL Used to map a physical memory region. When using this flag, divide the physical address — that is, lpvSrc — by 256.

Remarks
The following code example shows how VirtualCopy is called to map a 128-KB region at physical address 0x64000000.

VirtualCopy(
  pvDest, (void *)(0x64000000/256), 128*1024,   
  PAGE_READWRITE | PAGE_PHYSICAL | PAGE_NOCACHE);
Drivers or applications that run in user mode must use this function, because user-mode threads do not have permission to access physical memory directly.


printf(TEXT("VirtualAlloc reservation @%8.8lx\r\n"), lpv);
bRet = VirtualCopy(lpv, PHYSADDR>>8, SIZE, PAGE_READWRITE | PAGE_NOCACHE | PAGE_PHYSICAL);
// The lpv parameter is the virtual address returned
// by VirtualAlloc().
// Always use PAGE_NOCACHE */

// Check the return value: bRet ==0 is an error */
printf(TEXT("VirtualCopy returned: %d\r\n"), bRet);


2.I think this need  the  Page (512 Bytes) assign

liujiang200612

may be this is  usable:

VirtualCopy also supports the PAGE_PHYSICAL flag. You must set this flag when you are mapping physical memory that resides beyond 512 MB, that is, physical memory with an address above 0x1FFFFFFF.

xulei1008

多谢各位，结贴了