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Example of Registry Redirection on WOW64

The following example code demonstrates the separate views of the registry provided by the registry redirector on 64-bit Windows. It also demonstrates how the values of keys are set depending on whether a key is shared or redirected. For more information, see Registry Keys Affected by WOW64.

Compile the following code separately for both 32-bit and 64-bit Windows. Run each resulting executable file on 64-bit Windows and compare the output. Sample output for both versions is listed below the source code.


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

#pragma comment(lib, "advapi32.lib")

// Define application constants.
#if defined(_WIN64)

#define VIEW_DATA L"Hello! 64-bit World"
#define ALT_VIEW_DATA L"Hello! 32-bit World"
#define CROSS_ACCESS KEY_WOW64_32KEY

#else

#define VIEW_DATA L"Hello! 32-bit World"
#define ALT_VIEW_DATA L"Hello! 64-bit World"
#define CROSS_ACCESS KEY_WOW64_64KEY

#endif

// Create a registry key and set its value.
// Return TRUE if the function succeeds, FALSE if it fails.
BOOL
    CreateRegistryKeyValue(
        HKEY hKeyParent,
        PWCHAR KeyName,
        REGSAM rsAccessMask,
        REGSAM rsSamViewFlag,
        PBYTE pValue,
        DWORD dwValueSize
        )
{
    DWORD dwDisposition;
    HKEY  hKey;
    DWORD dwRet;

    dwRet = 
        RegCreateKeyEx(
            hKeyParent,
            KeyName,
            0,
            NULL,
            REG_OPTION_NON_VOLATILE,
            rsAccessMask | rsSamViewFlag,
            NULL,
            &hKey,
            &dwDisposition);

    if (dwRet != ERROR_SUCCESS)
    {
        printf("Error opening or creating key.\n");
        return FALSE;
    }

    // Attempt to set the value of the key.
    // If the call fails, close the key and return.
    if (ERROR_SUCCESS !=
            RegSetValueEx(
                hKey,
                NULL,
                0,
                REG_SZ,
                pValue,
                dwValueSize))
    {
        printf("Could not set registry value.\n");
        RegCloseKey(hKey);
        return FALSE;
    }

    RegCloseKey(hKey);
    return TRUE;
}

// Access a registry key and print its value.
// Return TRUE if the function succeeds, FALSE if it fails.
BOOL
    AccessRegistryKeyValue(
        HKEY hKeyParent,
        PWCHAR KeyName,
        REGSAM rsAccessMask,
        REGSAM rsSamViewFlag
        )
{
    HKEY hKey;
    WCHAR Buffer[MAX_PATH];
    DWORD dwSize = sizeof(Buffer);
    DWORD dwType;
    DWORD dwRet;

    dwRet =
        RegOpenKeyEx(
            hKeyParent,
            KeyName,
            0,
            rsAccessMask | rsSamViewFlag,
            &hKey);

    if (dwRet != ERROR_SUCCESS)
    {
        printf("Error opening key!\n");
        return FALSE;
    }

    if (ERROR_SUCCESS !=
            RegQueryValueEx(
                hKey,
                NULL,
                0,
                &dwType,
                (PBYTE)Buffer,
                &dwSize))
    {
        printf("Could not read registry value.\n");
        RegCloseKey(hKey);
        return FALSE;
    }

    if (rsSamViewFlag != 0)
    {
        printf("Alternate view:   %S\n", Buffer);
    }
    else
    {
        printf("Default view:     %S\n", Buffer);
    }

    RegCloseKey(hKey);
    return TRUE;
}

int
main()
{
    BOOL Res;

    // Define the list of keys to work with.
    typedef struct {
        HKEY hkRoot;
        LPWSTR szRootName;
        LPWSTR szName;
    }KEYDATA;

    KEYDATA Keys[] =
    {
        { HKEY_LOCAL_MACHINE, L"HKLM", L"Software\\Hello World" },
        { HKEY_CLASSES_ROOT,  L"HKCR", L"Hello" },
        { HKEY_CLASSES_ROOT,  L"HKCR", L"CLSID\\{00000000-0000-0000-0000-ABCD00000000}" },
        { HKEY_CLASSES_ROOT,  L"HKCR", L"CLSID\\{00000000-0000-0000-0000-ABCD00000000}\\InprocServer32" },
        { HKEY_CLASSES_ROOT,  L"HKCR", L"CLSID\\{00000000-0000-0000-0000-ABCD00000000}\\LocalServer32" }
    };

    // Now create the keys.
    for (int i = 0; i < _countof(Keys); i++)
    {
        // Create the keys in the alternate view of the registry.
        Res = 
            CreateRegistryKeyValue(
                Keys[i].hkRoot,
                Keys[i].szName,
                KEY_READ | KEY_WRITE,
                CROSS_ACCESS,
                (PBYTE)ALT_VIEW_DATA,
                sizeof(ALT_VIEW_DATA));
        if (Res == FALSE)
        {
            printf("Could not create keys in alternate view of the registry.\n");
            return 1; 
       }

        // Create the keys in the default view of the registry.
        Res = 
            CreateRegistryKeyValue(
                Keys[i].hkRoot,
                Keys[i].szName,
                KEY_READ | KEY_WRITE,
                0,
                (PBYTE)VIEW_DATA,
                sizeof(VIEW_DATA));
        if (Res == FALSE)
        {
            printf("Could not create keys in default view of the registry.\n");
            return 1;
        }
    }

    // Access the registry and print key values.
    printf("Application string: %S\n", VIEW_DATA);

    for (int i = 0; i < _countof(Keys); i++)
    {
        printf("%S\\%S\n", Keys[i].szRootName, Keys[i].szName);
        Res = 
            AccessRegistryKeyValue(
                Keys[i].hkRoot,
                Keys[i].szName,
                KEY_READ, 
                0);
        if (Res == FALSE)
        {
            printf("Unable to access default view of registry.\n");
            return 1;
        }

        // Calls with CROSS_ACCESS explicitly access the alternate registry view.
        Res =
            AccessRegistryKeyValue(
                Keys[i].hkRoot,
                Keys[i].szName,
                KEY_READ,
                CROSS_ACCESS);
        if (Res == FALSE)
        {
            printf("Unable to access alternate view of registry.\n");
            return 1;
        }
    }
    return 0;
}


When the 64-bit version of the example is run, it produces the following output. The values of both the default and alternate views of HKCR\Hello are the same because this key is shared. The values of the other keys differ because they are redirected.

Windows Server 2008, Windows Vista, Windows Server 2003, and Windows XP:  When this example is run on these operating systems, the default and alternate views of the LocalServer32 key have the same value. This is because the LocalServer32 key is redirected and reflected, which causes its value to be synchronized between the 64-bit and 32-bit views of the registry as soon as the handle to the key is closed. Registry reflection was removed starting with Windows 7. For more information, see Registry Reflection.

Application string: Hello! 64-bit World
HKLM\Software\Hello World
Default view:     Hello! 64-bit World
Alternate view:   Hello! 32-bit World
HKCR\Hello
Default view:     Hello! 64-bit World
Alternate view:   Hello! 64-bit World
HKCR\CLSID\{00000000-0000-0000-0000-ABCD00000000}
Default view:     Hello! 64-bit World
Alternate view:   Hello! 32-bit World
HKCR\CLSID\{00000000-0000-0000-0000-ABCD00000000}\InprocServer32
Default view:     Hello! 64-bit World
Alternate view:   Hello! 32-bit World
HKCR\CLSID\{00000000-0000-0000-0000-ABCD00000000}\LocalServer32
Default view:     Hello! 64-bit World
Alternate view:   Hello! 32-bit World


When the 32-bit version of the example is run, it produces the following output. For a 32-bit application, the 64-bit view of the registry is the alternate view so the values are reversed, except for HKCR\Hello, which is a shared key.

Application string: Hello! 32-bit World
HKLM\Software\Hello World
Default view:     Hello! 32-bit World
Alternate view:   Hello! 64-bit World
HKCR\Hello
Default view:     Hello! 32-bit World
Alternate view:   Hello! 32-bit World
HKCR\CLSID\{00000000-0000-0000-0000-ABCD00000000}
Default view:     Hello! 32-bit World
Alternate view:   Hello! 64-bit World
HKCR\CLSID\{00000000-0000-0000-0000-ABCD00000000}\InprocServer32
Default view:     Hello! 32-bit World
Alternate view:   Hello! 64-bit World
HKCR\CLSID\{00000000-0000-0000-0000-ABCD00000000}\LocalServer32
Default view:     Hello! 32-bit World
Alternate view:   Hello! 64-bit World


To examine the effect of running this example with regedit, inspect the values of the following keys. Note that applications should avoid using Wow6432Node in hard-coded registry paths.

HKLM\SOFTWARE\Hello World
HKLM\SOFTWARE\Wow6432Node\Hello World
HKCR\CLSID\{00000000-0000-0000-0000-ABCD00000000}
HKCR\CLSID\{00000000-0000-0000-0000-ABCD00000000}\InprocServer32
HKCR\CLSID\{00000000-0000-0000-0000-ABCD00000000}\LocalServer32
HKCR\Hello HKCR\Wow6432Node\CLSID\{00000000-0000-0000-0000-ABCD00000000}
HKCR\Wow6432Node\CLSID\{00000000-0000-0000-0000-ABCD00000000}\InprocServer32
HKCR\Wow6432Node\CLSID\{00000000-0000-0000-0000-ABCD00000000}\LocalServer32
HKCR\Wow6432Node\Hello

Related topics

Registry Redirector
Registry Reflection

 

 

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