Using WASI SDK in CMake build on Windows

[arrisde]

I'm trying to use the Windows release of WASI SDK to build a WASI module using CMake, but I'm not quite able to wrap my head around this. Maybe someone can point out what I'm doing wrong here.

I have a simple CMakeLists.txt:

cmake_minimum_required(VERSION 3.10.0)
project(demo)
add_executable(MyDemo "demo.c")

And try to build as follows:

$ cmake .. -DCMAKE_TOOLCHAIN_FILE="C://wasi-sdk-12.0//share//cmake//wasi-sdk.cmake" -DWASI_SDK_PREFIX="C://wasi-sdk-12.0" -G "Ninja"

Which fails:

-- The C compiler identification is Clang 11.0.0
-- The CXX compiler identification is Clang 11.0.0
System is unknown to cmake, create:
Platform/WASI to use this system, please post your config file on discourse.cmake.org so it can be added to cmake
-- Detecting C compiler ABI info
System is unknown to cmake, create:
Platform/WASI to use this system, please post your config file on discourse.cmake.org so it can be added to cmake
-- Detecting C compiler ABI info - failed
-- Check for working C compiler: C://wasi-sdk-12.0/bin/clang.exe
System is unknown to cmake, create:
Platform/WASI to use this system, please post your config file on discourse.cmake.org so it can be added to cmake
-- Check for working C compiler: C://wasi-sdk-12.0/bin/clang.exe - broken
CMake Error at C:/Program Files/CMake/share/cmake-3.19/Modules/CMakeTestCCompiler.cmake:66 (message):
  The C compiler

    "C://wasi-sdk-12.0/bin/clang.exe"

  is not able to compile a simple test program.

  It fails with the following output:

    Change Dir: C:/demo/build/CMakeFiles/CMakeTmp

    Run Build Command(s):C:/ninja.exe cmTC_ba490 && [1/2] Building C object CMakeFiles/cmTC_ba490.dir/testCCompiler.c.obj
    [2/2] Linking C executable cmTC_ba490
    FAILED: cmTC_ba490
    cmd.exe /C "cd . && C:\\wasi-sdk-12.0\bin\clang.exe --target=wasm32-wasi   CMakeFiles/cmTC_ba490.dir/testCCompiler.c.obj -o cmTC_ba490   && cd ."
    wasm-ld: error: cannot open crt1.o: no such file or directory
    wasm-ld: error: unable to find library -lc
    clang: error: linker command failed with exit code 1 (use -v to see invocation)
    ninja: build stopped: subcommand failed.





  CMake will not be able to correctly generate this project.
Call Stack (most recent call first):
  CMakeLists.txt:2 (project)


-- Configuring incomplete, errors occurred!
See also "C:/demo/build/CMakeFiles/CMakeOutput.log".
See also "C:/demo/build/CMakeFiles/CMakeError.log".

So it seems clang isn't picking up the sysroot. I dug around a bit and found these settings in an older version of wasi-sdk.cmake:

set(CMAKE_C_COMPILER_WORKS ON)
set(CMAKE_CXX_COMPILER_WORKS ON)
set(CMAKE_SYSROOT ${WASI_SDK_PREFIX}/share/wasi-sysroot)

Adding these to my share\cmake\wasi-sdk.cmake makes the build succeed. But these settings were removed in #161, so presumably they shouldn't be necessary anymore?

[arrisde]

Btw, is there a reason why the Windows release still has mingw in its name? If I understand #164 correctly, it is now built by MSVC instead of GCC.

[sbc100]

Indeed, it looks like it was mistake to remove the CMAKE_SYSROOT from the version of wasi-sdk.cmake that is shipped.

Interestingly enough the very latest change should remove the need for explicit sysroot: 14d7b78. If we wan't for that change then we would need to add it back, but since 14d7b78 landed, the next release won't need it.

[arrisde]

Just tried 14d7b78 and indeed it fixes the issue. So I'm closing and hoping for a new release soon 😄

[rajsite]

Do we know when a new release might have these changes @sbc100 ? Alternatively are there any docs / hints for making a windows build?

[sbc100]

A new llvm due to out tomorrow (Sept 21) so we should probably do wasi-sdk release as soon as that happens.

In them an time I think you should be able to add set(CMAKE_SYSROOT ${WASI_SDK_PREFIX}/share/wasi-sysroot) to the end of share/cmake/wasi-sdk.cmake as a workaround.