win32u: Use user message packing for LB_GETSELITEMS.

dlls/user32/winproc.c

@@ -875,9 +875,7 @@ BOOL unpack_message( HWND hwnd, UINT message, WPARAM *wparam, LPARAM *lparam,
     case LB_SELECTSTRING:
     case CB_GETLBTEXT:
     case LB_GETTEXT:
-        break;
     case LB_GETSELITEMS:
-        if (!get_buffer_space( buffer, *wparam * sizeof(UINT), size )) return FALSE;
         break;
     case WM_NEXTMENU:
     {
@@ -1063,6 +1061,7 @@ BOOL WINAPI User32CallWindowProc( struct win_proc_params *params, ULONG size )
         case LB_SELECTSTRING:
         case CB_GETLBTEXT:
         case LB_GETTEXT:
+        case LB_GETSELITEMS:
         {
             LRESULT *result_ptr = (LRESULT *)buffer - 1;
             *result_ptr = result;

dlls/win32u/message.c

@@ -631,6 +631,9 @@ static BOOL unpack_message( HWND hwnd, UINT message, WPARAM *wparam, LPARAM *lpa
         if (!get_buffer_space( buffer, size, prev_size )) return FALSE;
         break;
     }
+    case LB_GETSELITEMS:
+        if (!get_buffer_space( buffer, *wparam * sizeof(UINT), size )) return FALSE;
+        break;
     case WM_WINE_SETWINDOWPOS:
     {
         WINDOWPOS wp;
@@ -1470,6 +1473,9 @@ size_t user_message_size( HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam,
         size = send_message_timeout( hwnd, LB_GETTEXTLEN, wparam, 0, SMTO_NORMAL, 0, ansi );
         size = (size + 1) * char_size( ansi );
         break;
+    case LB_GETSELITEMS:
+        size = wparam * sizeof(UINT);
+        break;
     }
 
     return size;
@@ -1640,6 +1646,9 @@ static void copy_user_result( void *buffer, size_t size, LRESULT result, UINT me
     case EM_GETLINE:
         copy_size = string_size( buffer, ansi );
         break;
+    case LB_GETSELITEMS:
+        copy_size = wparam * sizeof(UINT);
+        break;
     default:
         return;
     }
@@ -1667,9 +1676,6 @@ static void copy_reply( LRESULT result, HWND hwnd, UINT message, WPARAM wparam,
     case WM_MOVING:
         copy_size = sizeof(RECT);
         break;
-    case LB_GETSELITEMS:
-        copy_size = wparam * sizeof(UINT);
-        break;
     case WM_MDIGETACTIVE:
         if (lparam) copy_size = sizeof(BOOL);
         break;

dlls/win32u/tests/win32u.c

@@ -1681,6 +1681,7 @@ static void test_wndproc_hook(void)
     static const SCROLLBARINFO sbi_out = { .xyThumbTop = 60 };
     static const DWORD dw_in = 1, dw_out = 2;
     static const UINT32 tabstops_in[2] = { 3, 4 };
+    static const UINT32 items_out[2] = { 1, 2 };
 
     static const struct lparam_hook_test lparam_hook_tests[] =
     {
@@ -1891,6 +1892,11 @@ static void test_wndproc_hook(void)
             .lparam_size = sizeof(tabstops_in), .lparam = &tabstops_in, .poison_lparam = TRUE,
             .check_size = sizeof(tabstops_in),
         },
+        {
+            "LB_GETSELITEMS", LB_GETSELITEMS,
+            .wparam = ARRAYSIZE(items_out), .msg_result = ARRAYSIZE(items_out),
+            .lparam_size = sizeof(items_out), .change_lparam = items_out,
+        },
         /* messages that don't change lparam */
         { "WM_USER", WM_USER },
         { "WM_NOTIFY", WM_NOTIFY },

dlls/wow64win/user.c

@@ -846,6 +846,7 @@ static size_t packed_result_32to64( UINT message, WPARAM wparam, const void *par
     case EM_GETLINE:
     case CB_GETLBTEXT:
     case LB_GETTEXT:
+    case LB_GETSELITEMS:
         break;
 
     default: