The test suite contains a large number of instances of things like:
fd = open(path, O_RDWR | O_CREAT);
When O_CREAT is specified, the third, variadic argument is
required as the permission. If on is not passed, then depending
on the ABI, either the contents of the third argument register
or some arbitrary stuff on the stack will be used as the permission.
(On some out-of-tree ABIs, accessing nonexistant variadic arguments
leads to a fault and a failed test.)