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cuda-manual-windows-build.md

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Manual CUDA Build on Windows

Building the CUDA-enabled gominer on a Windows platform is tricky, requires several GB worth of downloads and the automatic builder script that is called when running go generate -tags cuda is not guaranteed to work on every combination of setups.

The main difficulties when building the CUDA version on windows are:

  • The installers for CUDA Toolkit and MSVC do not put their respective binaries in the user's $PATH environment variable.
  • A default installation of MSYS2 ignores the global and user's $PATH anyway.
  • Having files in c:\Program Files\ (path with a space) causes all sorts of issues in all layers of the compilation stack. In particular, cgo directives do not work with such paths.
  • An outdated CUDA package currently used by gominer has wrong cgo include paths in any case.
  • CUDA requires cl.exe (MSVC compiler) to build its binary kernels, but Go does not accept it as a possible cgo compiler.

All of these must be resolved in other to correctly build the CUDA version of gominer on Windows. The automatic builder script uses a few tricks and some reasonable assumptions to attempt to solve building for the most common install scenarios. But for the cases where that is not sufficient, the following document lists a general procedure for setting the required Windows environment.

Install the Required Tools

Restart the computer and ensure Windows can recognize the NVIDIA GPU as such.

Setup MSYS2

While it may be possible to build on PowerShell or even cmd.exe, going through MSYS2 means the changes are more explicit and generally don't require clicking through GUIs to find settings.

  • Download and install MSYS2
    • Make sure you uncheck Run MSYS2 now.
  • Launch the MSYS2 MINGW64 shell from the start menu
    • NOTE: The MSYS2 installer will launch the UCRT64 shell by default if you didn't uncheck Run MSYS2 now as instructed. That shell will not work, so close it if you forgot to uncheck it in the installer.
  • From within the MSYS2 MINGW64 shell enter the following commands to install gcc, git, go, unzip:
    • pacman -S mingw-w64-x86_64-gcc mingw-w64-x86_64-tools mingw-w64-x86_64-go git unzip
    • git clone https://github.com/decred/gominer
  • Close the MSYS2 MINGW64 shell and relaunch it
    • NOTE: This is necessary to ensure all of the new environment variables are set properly

Create junction to NVIDIA Toolkit

Now comes the tricky bit. cgo flags don't currently support paths with spaces in them. Therefore, we'll create a junction to the NVIDIA Toolkit install path in order to be able to specify it.

  • Determine the NVIDIA Toolkit install path.
    • This is generally c:\Program Files\NVIDIA GPU Toolkit\CUDA\vXX.Y
  • Create a junction for the target directory from within MSYS2:
    • cd gominer
    • cmd.exe //c mklink //J nvidia "c:\Program Files\NVIDIA GPU Toolkit\CUDA\vXX.Y"
    • Replace vXX.Y with the version of the toolkit actually installed
  • Copy the file bin/cudart64_xx.dll to gominer's dir
    • This file will be needed by gominer once built
    • Replace XX with the major CUDA toolkit version
    • cp nvidia/bin/cudart64_*.dll .

If the toolkit is ever updated to a newer version, repeat this process. To remove the junction after it is no longer needed, execute rm nvidia

Determine the MSVC cl.exe location

Visual Studio versions after 2017 support multiple installs on the same machine, each with different sets of components and features installed. Determine which version contains the "Desktop Development with C++" component you wish to use and locate the path to its cl.exe compiler.

For example, for Visual Studio 2022 Community edition, building x64 targets in x64 host computers (the most common case), the path to cl.exe is C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.37.32822\bin\Hostx64\x64.

The important bit is that this dir MUST contain the cl.exe compiler. Modify the various versions as applicable to your specific computer. Note down this dir, as it will be used in the next step.

Setup the Environment Variables

Edit MSYS2's .bash_profile file to add the required environment variables. Any text editor may be used, as long as it supports Unix style line endings:

  • Edit ~/.bash_profile
    • If using a native Windows editor, the file is generally located at C:\msys64\home\[username]
  • Add the following lines at the end of the file:
export CL_PATH="<path-to-cl.exe-found-in-previous-step>"
export CGO_CFLAGS="$CGO_CFLAGS -Invidia/include"
export CGO_LDFLAGS="$CGO_CFLAGS -Lnvidia/lib"
export PATH="$CL_PATH:$PATH"

Restart the MSYS2 shell after editing the file. To know whether the values are being used, issue echo commands (for example, echo $CGO_CFLAGS).

Build blake3.dll using nvcc

Now with the environment fully setup, the Blake3 CUDA kernel may be built:

$ nvcc --shared --optimize=3 --compiler-options=-GS-,-MD -I. blake3.cu -o blake3.dll

The end result is that a blake3.dll shared library should be created in gominer's root dir.

Several warnings may be displayed, (specially regarding use of deprecated calls) but those may be safely ignored.

Build gominer.exe

Finally, with blake3.dll created, gominer may be buit in the standard way:

$ go build -tags cuda .
$ ./gominer -l

Continue with the standard configure and run procedure.

Troubleshooting gominer.exe does not run

If after building gominer.exe, it exists in the dir but executing (with -l or -h) does not display anything in the terminal, this is usually a sign of missing dlls.

Run the following command:

$ ldd gominer.exe

And search the output for any DLLs listed as "not found". Install any missing dependency or copy the DLL directly to gominers dir.