`Building libc++` instructions fail on linux

[rconde01]

Following these directions using gcc 13.1 on Redhat EL9:
https://releases.llvm.org/19.1.0/projects/libcxx/docs/BuildingLibcxx.html#id4

ninja -C build runtimes gives:

CMake Error at /home/rconde/Documents/cn2/p/b/clang4e9cde48f94f6/b/libunwind/src/CMakeLists.txt:102 (message):
  Compiler doesn't support generation of unwind tables if exception support
  is disabled.  Building libunwind DSO with runtime dependency on C++ ABI
  library is not supported.

[philnik777]

What exactly were the commands you ran?

[rconde01]

cmake --version
gcc --version
ninja --version

wget https://github.com/llvm/llvm-project/releases/download/llvmorg-19.1.0/llvm-project-19.1.0.src.tar.xz

rm -rf llvm-project-19.1.0.src

tar -xJf llvm-project-19.1.0.src.tar.xz

cd llvm-project-19.1.0.src

mkdir build

cmake -G Ninja -S llvm -B build \
   -DCMAKE_BUILD_TYPE=Release \
   -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra" \
   -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \
   -DLLVM_RUNTIME_TARGETS="x86_64-unknown-linux-gnu"
ninja -C build runtimes

And the log is attached.

build.txt

[philnik777]

It looks like your Clang build is broken somehow. Could you check what happens when you try to build a simple test program with the just built Clang? The executable should be at build/bin/clang++. Something like int main() {} is probably enough of a test program.

[rconde01]

hmm:

/opt/rh/gcc-toolset-13/root/usr/bin/ld: cannot find crtbeginS.o: No such file or directory
/opt/rh/gcc-toolset-13/root/usr/bin/ld: cannot find -lstdc++: No such file or directory
clang++: error: linker command failed with exit code 1 (use -v to see invocation)

I used gcc-toolset-13 to compile

[philnik777]

Ok, that's out of my field of expertise. Moving to Clang.

[rconde01]

FYI I tried adding:

   -DLIBCXX_USE_COMPILER_RT=YES -DLIBCXXABI_USE_COMPILER_RT=YES

But it behaved the same

[zaryc89]

I'm seeing this probelm everywhere with no solution. Ok fine...few solutions.
One post I saw somewhere said to build libcxxabi on it's own, then build libcxx linking to that.
The same post said to build libcxxabi and libcxx a second time using the first? and then use those results to build your llvm-project? something like that, I have it bookmarked I think. I'll find it.
I'm having an extremely similar probelm too, if it wan't obvious.

[zaryc89]

I still have this plague even after rebuilding cxx and cxxabi with compiler-rt. anyway, here are the references

https://discourse.llvm.org/t/how-to-build-libc-libunwind-independent-of-libgcc-s-so-use-compiler-rt-builtins-atomics/63141
https://discourse.llvm.org/t/failed-to-replace-stdlibc-with-libc-linker-phase-error/51748

[zaryc89]

https://discourse.llvm.org/t/building-clang-llvm-without-libstdc-or-gplv3-tools-libraries/35226

[zaryc89]

this gentoo link says building entirely gcc-free on a glibc system is not currently possible . i wonder if that's gentoo specific?
https://wiki.gentoo.org/wiki/Clang/Bootstrapping