Effect-Compiler (FXC) fails to run with error C0000139

[davidebeatrici]

AppVeyor is used to build official Windows releases of Mumble and the latest one is from May.

After triggering a new build this week it was discovered that fxc.exe fails to run and the exit code is -1073741511, which corresponds to C0000139 (entry point not found?).

The issue is reproduced with both the Visual Studio 2019 and Visual Studio 2022 images.

[davidebeatrici]

After spending a few hours debugging this, in particular checking all DLLs dependencies and the required symbols, I came to the realization I could connect through RDP and see if the GUI would show a useful hint. Turns out it does:

SHA256 hash of d3dcompiler_47.dll: 2c5cd9f942c33f892edac4d109ba7bcda679d8c62efa325d9dc574f753ef3823

The reported version is 10.0.26100.1.

[davidebeatrici]

Forcing the executable to load the DLL that is shipped with Windows by deleting the file in the SDK directory makes the tool work again.

For reference, here's the operating system version:

Updating to the latest SDK (10.0.26100.1742) doesn't fix the issue.