Allocating memory using AWE

Question

I'm using 32bit Windows XP SP3 with PAE enabled and 8GB physical memory.

All i want is to use AWE to allocate memory from the dark side - ie the hidden 4GB - so i wrote i gave my user Lock pages in memory right then i wrote the following code:

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

BOOL EnableAWE();

int main()
{
    if(!EnableAWE())
    {
        printf("Can not enable AWE on this system.\n");
        return 1;
    }

    HANDLE hProcess = GetCurrentProcess();
    SIZE_T byts = ~0u >> 1;
    LPVOID ptr = VirtualAllocEx(hProcess, NULL, byts, MEM_PHYSICAL | MEM_RESERVE, PAGE_READWRITE);

    if (ptr == NULL)
    {
        printf("Allocation failed for requested memory size.\n");
        return 1;
    }

    VirtualFreeEx(hProcess, ptr, 0, MEM_RELEASE);

    return 0;
}

BOOL EnableAWE()
{
    HANDLE hToken = NULL;

    TOKEN_PRIVILEGES tp;
    tp.PrivilegeCount = 1;
    tp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;

    if(!OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY | TOKEN_ADJUST_PRIVILEGES, &hToken)) return FALSE;
    if (!LookupPrivilegeValue(NULL, SE_LOCK_MEMORY_NAME, &(tp.Privileges[0].Luid))) return FALSE;
    if (!AdjustTokenPrivileges(hToken, FALSE, &tp, sizeof(TOKEN_PRIVILEGES), NULL, NULL)) return FALSE;

    return TRUE;
}

the function EnableAWE always return true, but when i try to allocate the 2GB using VirtualProtect it fails with error code 87 which means The parameter is incorrect.

i don't know which parameter is incorrect.

thanks.

Answer 1

Um, VirtualAlloc does not allocate AWE memory. ( AllocateUserPhysicalPages actually allocates the memory.) It reserves virtual address space into which AWE memory can be mapped. And your process does not have 2GB of available virtual address space.

Answer 2

There's no call to VirtualProtect in the code that you posted. Also, did you compile with /LARGEADDRESSAWARE?

In any case, I suspect that you cannot get 2GB of contiguous address space on Win32, even with PAE. Try reducing byts and see if that helps.