Message in CLI or PowerShell: ANOMALY: meaningless REX prefix used

Symptoms

When running Powershell, the following message is emitted:

Code
C:\WINDOWS\system32>powershell
Windows PowerShell
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[0x7FFD8EE423D0] ANOMALY: meaningless REX prefix used


Investigation

Code
C:\WINDOWS\system32>for /r "C:\Program Files (x86)" %F in (.) do @findstr /i /m /c:"ANOMALY: meaningless REX prefix used" "%F" >nul 2>&1 && echo %F
C:\Program Files (x86)\ASUS\GPU TweakII\GTII-OSD\Win7\x64\GTII-OSD64-GL.dll
C:\Program Files (x86)\ASUS\GPU TweakII\GTII-OSD\Win7\x64\GTII-OSD64-VK.dll
C:\Program Files (x86)\ASUS\GPU TweakII\GTII-OSD\Win7\x64\GTII-OSD64.dll
C:\Program Files (x86)\ASUS\GPU TweakII\GTII-OSD\Win7\x86\GTII-OSD-GL.dll
C:\Program Files (x86)\ASUS\GPU TweakII\GTII-OSD\Win7\x86\GTII-OSD-VK.dll
C:\Program Files (x86)\ASUS\GPU TweakII\GTII-OSD\Win7\x86\GTII-OSD.dll
C:\Program Files (x86)\ASUS\GPU TweakII\GTII-OSD\x64\GTII-OSD64-GL.dll
C:\Program Files (x86)\ASUS\GPU TweakII\GTII-OSD\x64\GTII-OSD64-VK.dll
C:\Program Files (x86)\ASUS\GPU TweakII\GTII-OSD\x64\GTII-OSD64.dll
C:\Program Files (x86)\ASUS\GPU TweakII\GTII-OSD\x86\GTII-OSD-GL.dll
C:\Program Files (x86)\ASUS\GPU TweakII\GTII-OSD\x86\GTII-OSD-VK.dll
C:\Program Files (x86)\ASUS\GPU TweakII\GTII-OSD\x86\GTII-OSD.dll


What’s really happening

The culprit is clearly this DLL:

GTII-OSD64‑VK.dll - and its siblings from the same suite:

GTII-OSD64.dll, GTII-OSD64-GL.dll, etc.

These belong to ASUS GPU Tweak II’s On‑Screen Display (OSD) module.

That module hooks into any process that creates a DirectX, Vulkan, or OpenGL context, so it can inject its frame‑rate counter, temperature readout, etc.

Unfortunately, its method of hooking involves runtime code patches that use invalid or redundant x86‑64 instruction prefixes—precisely what triggers: ANOMALY: meaningless REX prefix used

Every time a 64‑bit process loads, it may momentarily hit that malformed injected code region.

Resolution

11/13/2025 - This is the option I used and it worked for me.

Disable the OSD component:
  • Open GPU Tweak II.
  • On the monitor panel, turn OSD to Off.
  • Close GPU Tweak II entirely.
  • Restart GPU Tweak II.


Last edited by Russ; 11/13/25 03:44 PM.
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