protonscr

.NET 9 Runtime and SDK fails to load System.Runtime.dll

protonopen
ValveSoftware/Proton#9173 · opened 2025-11-02 by GBDonets · updated 2025-11-02 · 0 comments · github
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GGBDonets 2025-11-02 github

Proton version: Hotfix, Experimental, Proton GE fork, Wine 10
Linux version: Ubuntu 25.10

Repro steps:

  • create a 64bit prefix (add a non-steam game, for example)
  • install .NET 9 SDK (seem to be similar with .NET 8)
  • run any dotnet command

Result:
A failure to load System.Runtime.dll

Attached are the logs when I tried strace -f -e openat -o /tmp/strace-dotnet.log /home/gleb/.steam/steam/compatibilitytools.d/GE-Proton10-24/files/bin/wine64 "C:\\windows\\system32\\dotnet.exe" . Proton Experimental had similar results.
Apparently there are 3 issues:

  • symbol resolution in icuuc68 lib
  • failed to create L"C:\windows\system32\ucrtbase.dll" (is it even supposed to create this lib?)
  • missing quite a few Windows system dlls for unknown reason.

It started around begin October, was working fine before with GE, Experimental and Hotfix. It is unclear what has changed in my Ubuntu installation at that time. Nothing has been explicitly changed at least, but there were Proton and Ubuntu updates of course. Ubuntu also has native .NET 9 SDK installation.

Image

icu-loaddll.log
strace-dotnet.log
wine-dotnet.log

Proton versions

DLLs