Cannot build on Ubuntu 18.04 with GCC 7.5.0

[juj]

Heya, reporting an apparently unsupported build configuration. Noticed this when attempting to update Emscripten to latest at Unity. Our CI gives at CMake time:

[15:06:45.499 Information] Cloning into '/home/bokken/build/output/Unity-Technologies/emscripten-builder/emsdk/binaryen/main'...
[15:06:53.652 Information] Submodule 'third_party/googletest' (https://github.com/google/googletest.git) registered for path 'third_party/googletest'
[15:06:53.656 Information] Cloning into '/home/bokken/build/output/Unity-Technologies/emscripten-builder/emsdk/binaryen/main/third_party/googletest'...
[15:07:00.712 Information] Submodule path 'third_party/googletest': checked out 'e2239ee6043f73722e7aa812a459f54a28552929'
[15:07:00.770 Information] -- The C compiler identification is GNU 7.5.0
[15:07:00.840 Information] -- The CXX compiler identification is GNU 7.5.0
[15:07:00.851 Information] -- Detecting C compiler ABI info
[15:07:00.915 Information] -- Detecting C compiler ABI info - done
[15:07:00.931 Information] -- Check for working C compiler: /usr/bin/cc - skipped
[15:07:00.932 Information] -- Detecting C compile features
-- Detecting C compile features - done
[15:07:00.939 Information] -- Detecting CXX compiler ABI info
[15:07:01.023 Information] -- Detecting CXX compiler ABI info - done
[15:07:01.040 Information] -- Check for working CXX compiler: /usr/bin/c++ - skipped
[15:07:01.041 Information] -- Detecting CXX compile features
[15:07:01.043 Information] -- Detecting CXX compile features - done
[15:07:01.054 Information] fatal: No names found, cannot describe anything.
[15:07:01.055 Information] CMake Warning at CMakeLists.txt:37 (message):
Error running git describe to determine version
[15:07:01.056 Information] -- Building with -DBUILD_LLVM_DWARF
[15:07:01.057 Information] -- Looking for pthread.h
[15:07:01.117 Information] -- Looking for pthread.h - found
[15:07:01.118 Information] -- Performing Test CMAKE_HAVE_LIBC_PTHREAD
[15:07:01.183 Information] -- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed
[15:07:01.184 Information] -- Check if compiler accepts -pthread
[15:07:01.254 Information] -- Check if compiler accepts -pthread - yes
[15:07:01.256 Information] -- Found Threads: TRUE
-- Building with -std=c++17
-- Building with -Wall
-- Building with -Werror
-- Building with -Wextra
-- Building with -Wno-unused-parameter
[15:07:01.257 Information] -- Building with -fno-omit-frame-pointer
-- Building with -fno-rtti
-- Building with -Wno-implicit-int-float-conversion
-- Building with -Wno-unknown-warning-option
-- Building with -Wswitch
-- Building with -Wimplicit-fallthrough
-- Building with -Wnon-virtual-dtor
-- Building with -fPIC
-- Building with -O2
-- Building with -UNDEBUG
[15:07:01.508 Information] -- Building libbinaryen as shared library.
[15:07:01.509 Information] -- Configuring done

and then at build time:

for (auto& [Target, _] : Invalidatee->BranchesOut) {
^
[15:07:04.697 Information] /home/bokken/build/output/Unity-Technologies/emscripten-builder/emsdk/binaryen/main/src/cfg/Relooper.cpp: In member function ‘void CFG::Relooper::Calculate(CFG::Block*)::Analyzer::FindIndependentGroups(CFG::BlockSet&, CFG::BlockBlockSetMap&, CFG::BlockSet*)’:
/home/bokken/build/output/Unity-Technologies/emscripten-builder/emsdk/binaryen/main/src/cfg/Relooper.cpp:1319:27: error: unused variable ‘_’ [-Werror=unused-variable]
for (auto& [New, _] : Curr->BranchesOut) {
^
[15:07:04.700 Information] /home/bokken/build/output/Unity-Technologies/emscripten-builder/emsdk/binaryen/main/src/cfg/Relooper.cpp: In member function ‘CFG::Shape* CFG::Relooper::Calculate(CFG::Block*)::Analyzer::Process(CFG::BlockSet&, CFG::BlockSet&)’:
/home/bokken/build/output/Unity-Technologies/emscripten-builder/emsdk/binaryen/main/src/cfg/Relooper.cpp:1549:38: error: unused variable ‘_’ [-Werror=unused-variable]
for (auto& [Target, _] : Curr->BranchesOut) {
^
[15:07:04.997 Information] [ 5%] Building CXX object third_party/llvm-project/CMakeFiles/llvm_dwarf.dir/dwarf2yaml.cpp.o
[15:07:07.253 Information] [ 5%] Building CXX object src/ir/CMakeFiles/ir.dir/eh-utils.cpp.o
[15:07:08.016 Information] [ 5%] Building CXX object third_party/llvm-project/CMakeFiles/llvm_dwarf.dir/DWARFAbbreviationDeclaration.cpp.o
[15:07:08.092 Information] At global scope:
cc1plus: error: unrecognized command line option ‘-Wno-unknown-warning-option’ [-Werror]
cc1plus: error: unrecognized command line option ‘-Wno-implicit-int-float-conversion’ [-Werror]
cc1plus: all warnings being treated as errors
[15:07:08.105 Information] src/cfg/CMakeFiles/cfg.dir/build.make:75: recipe for target 'src/cfg/CMakeFiles/cfg.dir/Relooper.cpp.o' failed
[15:07:08.105 Information] make[2]: *** [src/cfg/CMakeFiles/cfg.dir/Relooper.cpp.o] Error 1
[15:07:08.105 Information] CMakeFiles/Makefile2:418: recipe for target 'src/cfg/CMakeFiles/cfg.dir/all' failed
[15:07:08.105 Information] make[1]: *** [src/cfg/CMakeFiles/cfg.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
[15:07:08.108 Information] [ 6%] Building CXX object src/ir/CMakeFiles/ir.dir/intrinsics.cpp.o
[15:07:09.305 Information] [ 6%] Building CXX object src/ir/CMakeFiles/ir.dir/lubs.cpp.o
[15:07:09.429 Information] [ 6%] Building CXX object third_party/llvm-project/CMakeFiles/llvm_dwarf.dir/DWARFAcceleratorTable.cpp.o
[15:07:10.418 Information] [ 7%] Building CXX object third_party/llvm-project/CMakeFiles/llvm_dwarf.dir/DWARFAddressRange.cpp.o
[15:07:11.168 Information] [ 8%] Building CXX object src/ir/CMakeFiles/ir.dir/memory-utils.cpp.o

Do you know what is the minimum required Ubuntu and/or GCC version and/or Clang/LLVM version to build? Building section only requires a C++17 compiler, which GCC 7.5.0 says it would be.

[kripken]

Hmm, the first one looks like that version of gcc warns more than others for some reason.. To it I think we just need to use the WASM_UNUSED macro on that _ variable to suppress that warning.

The other warning I'm not sure, but maybe there's a gcc flag to not error on unrecognized warning flags?

Another option is for you to disable warnings-as-errors on that build.

This is odd though that you see it happen when updating emscripten, as that code (Relooper) is extremely old... did you change gcc version perhaps?

[juj]

To my knowledge there should not be any change in the CI config.. I am using the identical VM image to build as before. I observed this change when updating the CI from Emscripten 2.0.19 to building 3.1.8.

Passing -DENABLE_WERROR=0 to Binaryen CMake does get through the warnings and I got a green CI run.