Starting build on ROOT-performance-centos7-multicore/default, ROOT-fedora27/noimt, ROOT-fedora29/python3, ROOT-fedora30/cxx14, ROOT-ubuntu16/nortcxxmod, ROOT-ubuntu18.04-i386/cxx14, mac1014/cxx17, windows10/cxx14
How to customize builds

Build failed on ROOT-performance-centos7-multicore/default.
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Build failed on ROOT-fedora29/python3.
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Errors:

• FAILED: tutorials/hsimple.root

Build failed on ROOT-fedora30/cxx14.
See console output.

Errors:

• FAILED: tutorials/hsimple.root

Build failed on ROOT-fedora27/noimt.
See console output.

Errors:

• FAILED: tutorials/hsimple.root

Build failed on ROOT-ubuntu16/nortcxxmod.
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Errors:

• FAILED: cd /mnt/build/workspace/root-pullrequests-build/build/tutorials && LD_LIBRARY_PATH=/mnt/build/workspace/root-pullrequests-build/build/lib: ROOTIGNOREPREFIX=1 ROOT_HIST=0 /mnt/build/workspace/root-pullrequests-build/build/bin/root.exe -l -q -b -n -x hsimple.C -e return

Starting build on ROOT-performance-centos7-multicore/default, ROOT-fedora27/noimt, ROOT-fedora29/python3, ROOT-fedora30/cxx14, ROOT-ubuntu16/nortcxxmod, ROOT-ubuntu18.04-i386/cxx14, mac1014/cxx17, windows10/cxx14
How to customize builds

@davidrohr let me know whether this fixes also your case.

@Axel-Naumann : I think this patch is correct in any case, since the symbols should be hidden.
Unfortunately, it is not enough to solve our problem. My test case from #4668 still yields:

Error in <UnknownClass::InitInterpreter()>: LLVM SYMBOLS ARE EXPOSED TO CLING! This will cause problems; please hide them or dlopen() them after the call to TROOT::InitInterpreter()!
: CommandLine Error: Option 'version' registered more than once!
LLVM ERROR: inconsistency in registered CommandLine options

• The first line LLVM SYMBOLS ARE EXPOSED.... is because the check in core/base/src/TROOT.cxx is not disabled, so this this is irrelevant. In fact, if your patch would work, this check should be removed.
• The second error ... inconsistency in registered.... however is the same problem we saw before, with the 2 LLVM instances clashing.

@davidrohr :

The second error ... inconsistency in registered.... however is the same problem we saw before, with the 2 LLVM instances clashing.

Damn. I tried with LD_PRELOADing libllvm and that worked with this PR, and failed without this PR. Can you come up with a reproducer for what you see?

I'll merge this nonetheless.

Can you come up with a reproducer for what you see?

@Axel-Naumann : The following simple test case

#include <TROOT.h>
int main(int argc, char** argv) {
  gROOT->GetInterpreter();
  return 0;
}

compiled via
c++ -o test -O0 -ggdb root-config --libs -Iroot-config --incdir -std=c++17 test.cpp /usr/lib64/libgandiva.so
yields the error for me. I have a system installation of arrow with gandiva. If I remove the libgandiva.so from the command line, it works fine.

Damn. I tried with LD_PRELOADing libllvm and that worked with this PR, and failed without this PR.

Damn, that is weird. Should be the same as linking to libgandiva. I'll try that on my setup to double-check.

@Axel-Naumann : I have rebuilt ROOT from scratch and attempted my above test case with

LD_PRELOAD=/usr/lib64/libgandiva.so ./test

which still gives me the same error:

Error in <UnknownClass::InitInterpreter()>: LLVM SYMBOLS ARE EXPOSED TO CLING! This will cause problems; please hide them or dlopen() them after the call to TROOT::InitInterpreter()!
: CommandLine Error: Option 'version' registered more than once!
LLVM ERROR: inconsistency in registered CommandLine options

Perhaps preloading individual LLVM libraries works, but with gandiva it certainly doesn't.
So unfortunately this patch is insufficient to solve my problem.

@Axel-Naumann : Did you have a chance to attempt the namespace hack we discussed, perhaps it has a better chance of solving the issue.

@Axel-Naumann : I have to admit I have been stupid and my last posts have been wrong.
I did built root without builtin_llvm, so this could not have worked by designed.
I have rebuilt now with builtin_llvm and with your patch, and now I am only getting the warning message

Error in <UnknownClass::InitInterpreter()>: LLVM SYMBOLS ARE EXPOSED TO CLING! This will cause problems; please hide them or dlopen() them after the call to TROOT::InitInterpreter()!

But this is clear, since ROOT just checks for the presence of the LLVM symbols.
I am now rebuilding the ALICE software with this ROOT and checking whether the segfaults are gone.

@Axel-Naumann : This patch is fully working for us. Thx a lot and sorry for the false information before.
Could you cherry-pick this to 6.18.00-patches?
In addition, the warning in https://github.com/root-project/root/blob/master/core/base/src/TROOT.cxx#2052 should be disabled, when ROOT is compiled with -DBUILTIN_LLVM. Otherwise it is misleading.

ACK on the warning, will take care after Jan 6.

Warning removal is in #4736 - I don't care too much about non-builtin llvm, people are on their own then.