I recently bought a HP Stream 11 laptop for my portable operations. It’s a reasonable priced 11.6” laptop with a net weight of 1 kg and only the most important features, like USB ports, headphone jack and a microSD card reader. It has a 64 GB eMMC storage device and comes with Windows 10 Home in S mode. Because I banned Windows from my shack long time ago, I directly installed Xubuntu 20.04 LTS on it and also the Wine runtime environment with all kind of ham radio software, which is only available for Windows, like 4NEC2, VOACAP, Ham Cap, IonoProbe and of course the Win-Test contest logger für contest operations.

The Win-Test integrated DX Telnet Cluster (wtDxTelnet.exe) ran fine out of the box, but the main Win-Test application (wt.exe) crashed immediately after the start with an almost endless error log.

Unhandled exception: page fault on read access to 0xffffffff in 32-bit code (0x008d156c).
Register dump:
 CS:0023 SS:002b DS:002b ES:002b FS:0063 GS:006b
 EIP:008d156c ESP:0031ff12 EBP:f894f014 EFLAGS:00010246(  R- --  I  Z- -P- )
 EAX:564d5868 EBX:8685d465 ECX:00000000 EDX:00006258
 ESI:008ce234 EDI:7b60b540
=>0 0x008d156c EntryPoint+0xffffffff() in wt (0xf894f014)
0x008d156c EntryPoint+0xffffffff in wt: sldt	0x0(%esp)

After trying different Wine versions and even a new installation of the older Xubuntu 18.04 LTS, the problem with wt.exe remained. So I filed a bug on the Wine website. Quick answer by one of the Wine developers: This problem is related to a rather new x86 security feature called User-Mode Instruction Prevention (UMIP). The execution of UMIP instructions like SLDT causes problems with the Linux 5.4 LTS kernel, which comes with Xubuntu 20.04. A quick solution is to update the Linux kernel to a version 5.10 or later, where UMIP instructions are supported. In my case Win-Test worked fine after I did that update.

All flavours of Ubuntu 21.04, coming out in April 2021, should have a Linux kernel 5.10 or newer on board.