x11: fix undefined behavior when copying the coordinates of ptr movements actions

Left shift of a negative integer. For some reason the protocol
representation here got really botched (in the spec it is just a nice
and simple INT16).

Signed-off-by: Ran Benita <ran234@gmail.com>

diff --git a/meson.build b/meson.build
index 9effe29..87193dd 100644 (file)
--- a/meson.build
+++ b/meson.build
@@ -31,6 +31,7 @@ foreach cflag: [
     '-Wdate-time',
     '-Wwrite-strings',
     '-Wno-documentation-deprecated-sync',
+    '-fsanitize-undefined-trap-on-error',
 ]
     if cc.has_argument(cflag)
         add_project_arguments(cflag, language: 'c')

diff --git a/src/x11/keymap.c b/src/x11/keymap.c
index 1642011..701b614 100644 (file)
--- a/src/x11/keymap.c
+++ b/src/x11/keymap.c
@@ -218,8 +218,8 @@ translate_action(union xkb_action *action, const xcb_xkb_action_t *wire)
     case XCB_XKB_SA_TYPE_MOVE_PTR:
         action->type = ACTION_TYPE_PTR_MOVE;
 
-        action->ptr.x = (wire->moveptr.xLow | (wire->moveptr.xHigh << 8));
-        action->ptr.y = (wire->moveptr.yLow | (wire->moveptr.yHigh << 8));
+        action->ptr.x = (int16_t) (wire->moveptr.xLow | ((uint16_t) wire->moveptr.xHigh << 8));
+        action->ptr.y = (int16_t) (wire->moveptr.yLow | ((uint16_t) wire->moveptr.yHigh << 8));
 
         if (!(wire->moveptr.flags & XCB_XKB_SA_MOVE_PTR_FLAG_NO_ACCELERATION))
             action->ptr.flags |= ACTION_ACCEL;