[llvm-dev] Link statically against libc++ on Cray XC 40

[C Bergström via llvm-dev]

On Wed, Sep 30, 2015 at 1:12 PM, Schlottke-Lakemper, Michael via
llvm-dev <llvm-dev at lists.llvm.org> wrote:
> Hi folks,
>
> In our scientific simulation tool, we set up our build system to link
> against LLVMSupport to print stack traces for debugging purposes, also from
> other compilers. This works very well on most hosts, but we fail to make it
> work with gcc on a Cray XC 40 cluster. They have a very restrictive
> toolchain setup (everything is controlled by the “module” command; you never
> get to see any real paths or commands but just use “CC” as the compiler and
> everything is included/linked to automagically).
>
> I already could solve some of the problems but now I am stuck at the linking
> stage. Specifically, their CC tool tries to link everything statically, but
> since we built LLVM using libc++, we also need to link against libc++, which
> fails with the error
>
> /usr/bin/ld: attempted static link of dynamic object
> `/zhome/academic/HLRS/xac/xacmicha/.pool/llvm/cur/lib/libc++.so’
>
> Does anyone have a suggestion what I can do to make this work (link)?
>
> Regards,
>
> Michael
>
> P.S.: This is the full linker command minus some (many) object files and
> -Wl,-rpath,library/paths:
>
> /opt/cray/craype/2.4.1/bin/CC   -O0 -g3 -fno-inline -std=c++11 -pedantic
> -fdiagnostics-color=auto
> -L/zhome/academic/HLRS/xac/xacmicha/.pool/llvm/cur/lib
> <many_object_files_go_here> CMakeFiles/zfs.dir/main.cpp.o  -o zfs -rdynamic
> /zhome/academic/HLRS/xac/xacmicha/.pool/llvm/cur/lib/libLLVMSupport.a -ldl
> -lpthread /zhome/academic/HLRS/xac/xacmicha/.pool/llvm/cur/lib/libc++.so
> /zhome/academic/HLRS/xac/xacmicha/.pool/llvm/cur/lib/libc++abi.a

I don't recommend to use shared libs, but if you add CC -shared it
will do shared linking. Also if you add -v to compilation you can see
the collect2 line (which is basically the linker line). That info
would give you enough to manually figure out your -L and -rpath. From
there you can do a simple clang wrapper script to work-around modules.

The problem isn't going to be resolving static compilation, but making
mpiCC work. The modified mpich which Cray uses links *everything*
against GNU C++ STL and runtime. That will out-of-the-box conflict
with libc++. So you can get clang to work using the gnu
stl/runtime/libunwind, but libc++ is no-go.

If you *really* want to test libc++ and clang there's 2 options
1) Get Cray to build mpi with clang and libc++ (I suspect they will
pushback and not do this)
2) Email me off list and I'll share more of my work (which partially
overlaps with this)

side note: Why are you trying to pull in libLLVMSupport.a (I suspect
this may not be correct unless you're trying to build clang itself)