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easy-build flow: on linux, if both GCC and Clang are installed, build fails because CMake picks GCC #8515

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dneto0 opened this issue Mar 11, 2025 · 7 comments · May be fixed by #8522
Open

easy-build flow: on linux, if both GCC and Clang are installed, build fails because CMake picks GCC #8515

dneto0 opened this issue Mar 11, 2025 · 7 comments · May be fixed by #8522
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@poweifeng
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build Build & build system issues

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@dneto0
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dneto0 commented Mar 11, 2025

⚠️ Issues not using this template will be systematically closed.

Describe the bug
On Linux a default build will fail because CMake selects GCC instead of Clang

To Reproduce
Steps to reproduce the behavior:

  1. On linux, where both GCC and Clang are installed, run ./build.sh release

Expected behavior
When clang is available, Filament should be built.

Screenshots
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Logs
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use screenshots of logs, copy them as text, use gist or attach an uncompressed file.

$ ./build.sh release
Building release in out/cmake-release...
-- The C compiler identification is GNU 14.2.0
-- The CXX compiler identification is GNU 14.2.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Error at CMakeLists.txt:286 (message):
  Detected C compiler GNU is unsupported


-- Configuring incomplete, errors occurred!

Desktop (please complete the following information):

  • OS: Linux
  • GPU: n/a
  • Backend: n/a

Smartphone (please complete the following information):

  • Device: n/a
  • OS: n/a

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@show50726
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I think that is in expected, you need to tell Filament where is clang if your default compiler is not clang.
You can refer to here to see how to specify the compiler path:

CC=/usr/bin/clang CXX=/usr/bin/clang++ CXXFLAGS=-stdlib=libc++ ./build.sh release

@dneto0
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dneto0 commented Mar 11, 2025

I only got as far as using the "easy build" flow.
https://github.com/google/filament/blob/main/BUILDING.md#easy-build

@dneto0 dneto0 changed the title on linux, if both GCC and Clang are installed, build fails because CMake picks GCC easy-build flow: on linux, if both GCC and Clang are installed, build fails because CMake picks GCC Mar 11, 2025
@dneto0
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dneto0 commented Mar 11, 2025

I made a fresh docker image based on Ubuntu Noble 24.04, installed cmake, ninja-build, gcc, and clang.

Then specifying the CC and CXX and CXXFLAGS as suggested also fails:

# CC=/usr/bin/clang CXX=/usr/bin/clang++ CXXFLAGS=-stdlib=libc++ ./build.sh -c release
Cleaning build directories...
Building release in out/cmake-release...
-- The C compiler identification is Clang 18.1.3
-- The CXX compiler identification is Clang 18.1.3
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/clang - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - failed
-- Check for working CXX compiler: /usr/bin/clang++
-- Check for working CXX compiler: /usr/bin/clang++ - broken
CMake Error at /usr/share/cmake-3.28/Modules/CMakeTestCXXCompiler.cmake:60 (message):
  The C++ compiler

    "/usr/bin/clang++"

  is not able to compile a simple test program.

  It fails with the following output:

    Change Dir: '/src/filament/out/cmake-release/CMakeFiles/CMakeScratch/TryCompile-rZUKFq'
    
    Run Build Command(s): /usr/bin/ninja -v cmTC_13331
    [1/2] /usr/bin/clang++   -stdlib=libc++ -MD -MT CMakeFiles/cmTC_13331.dir/testCXXCompiler.cxx.o -MF CMakeFiles/cmTC_13331.dir/testCXXCompiler.cxx.o.d -o CMakeFiles/cmTC_13331.dir/testCXXCompiler.cxx.o -c /src/filament/out/cmake-release/CMakeFiles/CMakeScratch/TryCompile-rZUKFq/testCXXCompiler.cxx
    [2/2] : && /usr/bin/clang++ -stdlib=libc++  CMakeFiles/cmTC_13331.dir/testCXXCompiler.cxx.o -o cmTC_13331   && :
    FAILED: cmTC_13331 
    : && /usr/bin/clang++ -stdlib=libc++  CMakeFiles/cmTC_13331.dir/testCXXCompiler.cxx.o -o cmTC_13331   && :
    /usr/bin/ld: cannot find -lc++: No such file or directory
    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:17 (project)


-- Configuring incomplete, errors occurred!

This is probably just a documentation issue.

@dneto0
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dneto0 commented Mar 11, 2025

When I modify the command line to use -libstdc++ I get past configuration but fail compilation because it can't find the C++ headers.

CC=/usr/bin/clang CXX=/usr/bin/clang++ CXXFLAGS=-stdlib=libstdc++ ./build.sh -c release | tee build.log

I'm attaching the build.log file.

build.log

@poweifeng
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So in the BUILD instructions, there are some dependencies. Can you try installing them and try again? (You'll have to remove the out directory). Note that the instructions are based on clang-14. For your case, you'll want to replace all the 14 with 18.

Instead of export, can you also try update-alternatives instructions also on the same page. Either way should work.

@show50726
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I agree it should be the dependency issue since the specifying CC= method works in my docker env.
You can check out my CL for the Dockerfile I used: cl/735804622

dneto0 added a commit to dneto0/filament that referenced this issue Mar 13, 2025
@dneto0
build.sh: On Linux force use of latest Clang
a548f5f 
CMake will default to GCC if it's available.
Force use of the latest Clang instead.
This can be overridden with CC, CXX, and CXXFLAGS

Fixed: google#8515
dneto0 added a commit to dneto0/filament that referenced this issue Mar 13, 2025
@dneto0
build.sh: On Linux force use of latest Clang
6760e26 
CMake will default to GCC if it's available.
Force use of the latest Clang instead.
This can be overridden with CC, CXX, and CXXFLAGS

Fixed: google#8515
@dneto0 dneto0 linked a pull request Mar 13, 2025 that will close this issue
Draft
dneto0 added a commit to dneto0/filament that referenced this issue Mar 13, 2025
@dneto0
build.sh: On Linux force use of latest Clang
58481c8 
CMake will default to GCC if it's available.
Force use of the oldest installed Clang instead.
This can be overridden with CC, CXX, and CXXFLAGS

Fixed: google#8515
@pixelflinger pixelflinger added the build Build & build system issues label Mar 18, 2025
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build.sh: On Linux force use of latest Clang dneto0/filament
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