Alex S reported that Proton (which is Wine distribution integrated with Steam) depends on functionality mentioned at https://github.com/freebsd/freebsd/blob/8989bc4581101acb0dda31d9c4f9b6ec4732c5cf/sys/i386/linux/linux_machdep.c#L582:
* Semantics of Linux version: every thread in the system has array of
* 3 tls descriptors. 1st is GLIBC TLS, 2nd is WINE, 3rd unknown. This
* syscall loads one of the selected tls decriptors with a value and
* also loads GDT descriptors 6, 7 and 8 with the content of the
* per-thread descriptors.
* Semantics of FreeBSD version: I think we can ignore that Linux has 3
* per-thread descriptors and use just the 1st one. The tls_array
* is used only in set/get-thread_area() syscalls and for loading the
* GDT descriptors. In FreeBSD we use just one GDT descriptor for TLS
* so we will load just one.
* XXX: this doesn't work when a user space process tries to use more
* than 1 TLS segment. Comment in the Linux sources says wine might do