[safehook] Alignment for WvSafeHookDefaultDummyIds

A future call to WvDummyAdd should have an aligned ExtraDataOffset
argument, so calculate it ahead of time.

src/winvblock/safehook/probe.c

@@ -58,12 +58,44 @@
   M_WV_SAFE_HOOK_VENDOR_ID M_WV_SAFE_HOOK_HARDWARE_ID
 #define M_WV_SAFE_HOOK_DEVICE_TEXT_DESC L"Safe INT 0x13 Hook Bus"
 
+/** Default dummy IDs for a safe hook PDO */
+WV_M_DUMMY_ID_GEN(
+    static,
+    WvSafeHookDefaultDummyIds,
+    M_WV_SAFE_HOOK_HARDWARE_ID,
+    M_WV_SAFE_HOOK_INSTANCE_ID,
+    M_WV_SAFE_HOOK_VENDOR_ID,
+    M_WV_SAFE_HOOK_COMPAT_ID,
+    M_WV_SAFE_HOOK_DEVICE_TEXT_DESC,
+    FILE_DEVICE_CONTROLLER,
+    FILE_DEVICE_SECURE_OPEN
+  );
+
 /** Object types */
+
 typedef UCHAR
   A_WV_SAFE_HOOK_VENDOR_STRING[sizeof M_WV_SAFE_HOOK_SIGNATURE];
 typedef WCHAR
   A_WV_SAFE_HOOK_WIDE_VENDOR_STRING[sizeof M_WV_SAFE_HOOK_SIGNATURE];
 
+/** This type is used for an alignment calculation */
+typedef struct S_WV_SAFE_HOOK_DUMMY_WRAPPER {
+    /** The type of this member was produced by WV_M_DUMMY_ID_GEN */
+    struct WvSafeHookDefaultDummyIdsStruct_ DummyIdsWrapper[1];
+
+    /** The associated safe hook */
+    S_X86_SEG16OFF16 Whence[1];
+  } S_WV_SAFE_HOOK_DUMMY_WRAPPER;
+
+/** Constants */
+
+static const ULONG CvWvSafeHookDummyIdsSize =
+  sizeof (struct WvSafeHookDefaultDummyIdsStruct_);
+
+/** An alignment calculation */
+static const ULONG CvWvSafeHookDummyIdsExtraDataOffset =
+  FIELD_OFFSET(S_WV_SAFE_HOOK_DUMMY_WRAPPER, Whence);
+
 /** Public function declarations */
 DRIVER_INITIALIZE WvSafeHookDriverEntry;
 
@@ -379,19 +411,6 @@ static WV_S_DUMMY_IDS * WvSafeHookDummyIds(
     IN A_WV_SAFE_HOOK_VENDOR_STRING * vendor,
     IN S_X86_SEG16OFF16 * whence
   ) {
-    /* Default dummy IDs for a safe hook PDO */
-    WV_M_DUMMY_ID_GEN(
-        static,
-        safe_hook_dummy_ids,
-        M_WV_SAFE_HOOK_HARDWARE_ID,
-        M_WV_SAFE_HOOK_INSTANCE_ID,
-        M_WV_SAFE_HOOK_VENDOR_ID,
-        M_WV_SAFE_HOOK_COMPAT_ID,
-        M_WV_SAFE_HOOK_DEVICE_TEXT_DESC,
-        FILE_DEVICE_CONTROLLER,
-        FILE_DEVICE_SECURE_OPEN
-      );
-    SIZE_T dummy_ids_sz;
     UCHAR * ptr;
     WV_S_DUMMY_IDS * dummy_ids;
     WCHAR * dest;
@@ -401,15 +420,17 @@ static WV_S_DUMMY_IDS * WvSafeHookDummyIds(
     /* Generate the safe hook vendor string */
     WvSafeHookVendorString(&wide_vendor, vendor);
 
-    /* The struct type on the next line was generated by the macro above */
-    dummy_ids_sz = sizeof (struct safe_hook_dummy_idsStruct_);
-    ptr = wv_malloc(dummy_ids_sz);
+    ptr = wv_malloc(CvWvSafeHookDummyIdsSize);
     if (!ptr)
       goto err_dummy_ids;
 
     /* Populate with defaults */
     dummy_ids = (VOID *) ptr;
-    RtlCopyMemory(dummy_ids, safe_hook_dummy_ids, dummy_ids_sz);
+    RtlCopyMemory(
+        dummy_ids,
+        WvSafeHookDefaultDummyIds,
+        CvWvSafeHookDummyIdsSize
+      );
 
     /* Generate the specific details */
     ptr += dummy_ids->Offset;