Dark Souls III: Crash when entering game world / during character creation (muvm+FEX, Steam, Asahi Arch Linux)

[anemptyinkwell]

What Game
Dark Souls III.
Steam: https://store.steampowered.com/agecheck/app/374320/

Describe the bug
Dark Souls III consistently crashes when attempting to load into the game world when running through Steam using the muvm+FEX stack on Asahi Arch Linux (Apple M1 Pro). The game launches successfully, menus work, and character creation is sometimes functional. However, the game

• always crashes when transitioning from menus into actual gameplay
• occasionally crashes when entering character creation.

Proton log shows

wine: Unhandled exception 0xc0000093 in thread ... at address ...

with the particular thread and address changing based on when the crash occurs.

To Reproduce
Steps to reproduce the behavior:

1. Install Dark Souls III via Steam.
2. Launch Steam using muvm and FEX.
3. Start Dark Souls III.
4. Either start a new game and proceed through character creation or attempt to load into a previous save.
5. Observe crash either (a) sometimes at character creation or (b) always during loading screen before entering game world.

Expected behavior
The game should complete character creation and load into the game world without crashing.

Screenshots and Video
N/A (can provide further logs if needed)

System information:

• OS: Arch Linux (Asahi Linux / Apple Silicon)
• CPU/SoC: Apple M1 Pro
• Video driver version: DXVK v2.7.1-505-g6f3a758f7982fc5, Mesa 25.3.6-4
• RootFS used: Arch Linux (from Asashi ALARM)
• FEX version: FEX-2603
• Thunks Enabled: Yes

Additional context

• Is this an x86 or x86-64 game: x86-64
• Does this reproduce on AArch64 with Radeon/Intel/Nvidia: Untested
• Is this a Vulkan game: Yes
  • If Yes, What is your Vulkan driver: Honeykrisp 25.3.6

Additional notes:

• The crash also occurs with the same behavior when using WINED3D instead of DXVK
• The crash does not occur when running the game through Steam with muvm and CrossOver Preview 20260304

[Sonicadvance1]

This is definitely a weird crash. It looks like the game is using expf on a value and its generating some sort of denormal, which it then is manually checking inside of its static compiled cmath library. Once a denormal is detected it raises an exception which turns in to a crash. this is why it is exception 0xc0000093 instead of the typical 0xc0000005.

At first I thought this was an issue with hardware that doesn't support AFP, as we don't emulate DAZ on hardware without AFP (it's prohibitively expensive otherwise!), but I was able to reproduce the crash on hardware that doesn't support AFP and also hardware that does. So it's still generating a denormal /somehow/.

This will take a bit of time to instrument and work out what exactly it's doing here.

[anemptyinkwell]

Thanks for looking into this! I understood that this would probably take some time when I posted the issue, but if I can provide anything at all to help facilitate the process I am perfectly willing to do so. Since this is reproducible on other hardware I imagine this is less of a need, but regardless.