windows-gnu: Failed to load codegen backend: LoadLibraryExw failed: The specified procedure could not be found. (os error 127)

[Algorhythm-sxv]

Expected Behaviour

Build script using spirv-builder runs without errors

Example & Steps To Reproduce

1. Copy rust-toolchain.toml to use rustc nightly-2025-06-23
2. build-dependency spirv-builder = { git = "https://github.com/Rust-GPU/rust-gpu" }
3. cargo build

The build fails with the full error:

    error: couldn't load codegen backend \\?\C:\Users\****\Downloads\fvm2d\target\debug\deps\rustc_codegen_spirv.dll: LoadLibraryExW failed: The specified procedure could not be found. (os error 127) (The specified procedure could not be found. (os error 127)) (retried 5 times)

rustc_codegen_spirv.dll does exist in that location, but the error suggests that some symbol is missing that is attempting to be loaded. I don't know how to get the name of the procedure it wants.

System Info

• Rust: rustc 1.89.0-nightly (be19eda0d 2025-06-22) (the date on this value always seems to be 1 day behind the version specified in rust-toolchain.toml)
• OS: Win11
• GPU: NVIDIA GeForce MX450
• SPIR-V: SPIRV-Tools v2025.2 unknown hash, 2025-05-06T12:14:19+00:00

[Firestar99]

I've never seen it fail like that on windows. I can only suggest cargo clean and hope it goes away?

If you've specified a rust-toolchain-toml next to your workspace / root Cargo.toml, it will take precedence over your global rustc version.

[Algorhythm-sxv]

Unfortunately no luck. I tried both cargo clean as well as removing Cargo.lock but the same error always happens. Perhaps of interest is that the error occurs only once trying to build the top-level application crate. The build of all the dependencies including spirv-builder happens without errors

[Algorhythm-sxv]

After further investigation I finally found this stackoverflow post linking to this rustc issue which indicates that the issue lies in certain GCC versions from MinGW simply not working with custom codegen backends.

The version this build was failing on is gcc.exe (Rev6, Built by MSYS2 project) 15.1.0. I upgraded the MinGW GCC version to 15.2.0 but the issue persists. Running ldd on the rustc_codegen_spirv.dll gives this output:

ldd .\target\debug\rustc_codegen_spirv.dll
        ntdll.dll => /c/WINDOWS/SYSTEM32/ntdll.dll (0x7ffed76b0000)
        KERNEL32.DLL => /c/WINDOWS/System32/KERNEL32.DLL (0x7ffed69e0000)
        KERNELBASE.dll => /c/WINDOWS/System32/KERNELBASE.dll (0x7ffed4d20000)
        msvcrt.dll => /c/WINDOWS/System32/msvcrt.dll (0x7ffed7510000)
        umppc19907.dll => /c/WINDOWS/System32/umppc19907.dll (0xb40000)
        umppc19907.dll => /c/WINDOWS/System32/umppc19907.dll (0xb40000)
        rustc_codegen_spirv.dll => /c/Users/****/Downloads/fvm2d/target/debug/rustc_codegen_spirv.dll (0x7ffdf27a0000)
        bcryptprimitives.dll => /c/Windows/System32/bcryptprimitives.dll (0x7ffed47a0000)
        libgcc_s_seh-1.dll => /mingw64/bin/libgcc_s_seh-1.dll (0x7ffeafa30000)
        libstdc++-6.dll => /mingw64/bin/libstdc++-6.dll (0x7ffe04fd0000)
        rustc_driver-81202c118dde1aff.dll => not found
        std-653c984df7ca0d22.dll => not found

I am not sure if the 'not found' rustc_driver and std dlls are the cause of this issue

[Firestar99]

I don't think we have anyone using rust-gpu with mingw, our CI also only tests msvc. So I can't really tell you what a suitable solution would be, please let us know if you find something!