The following Linux-specific options [..] can also, since Linux 4.7, be used with waitid():
__WCLONE [...] This option is ignored if __WALL is also specified.
__WALL
So to trigger this:
* You have to call a deprecated function
* With a flag that was at that time illegal (linux < 4.7)
* And a second illegal flag that is cancelled out by the first illegal flag.
This is something any userspace process can do, but no sane process should ever do.
wait4's man page points to waitpid for details, and notes wait4 is deprecated in favor of waitpid.
So see the linux notes of this: https://man7.org/linux/man-pages/man2/waitpid.2.html
So to trigger this:* You have to call a deprecated function
* With a flag that was at that time illegal (linux < 4.7)
* And a second illegal flag that is cancelled out by the first illegal flag.
This is something any userspace process can do, but no sane process should ever do.