[cfe-dev] [Driver][OpenMP] -L for build/install dir is after system dirs

[Jonas Hahnfeld via cfe-dev]

Hi Joel,

I started a discussion about this on cfe-dev a while ago: 
http://lists.llvm.org/pipermail/cfe-dev/2017-January/052499.html
The short answer is that there are / might be more libraries than just 
the OpenMP runtime (or libunwind in my case), so changing the default 
might break on some systems.

I had a patch in https://reviews.llvm.org/D26244 that added a CMake flag 
to change the behaviour, but I lost interest after some time. Feel free 
to revive it if it's important for you.

Cheers,
Jonas

On 2018-08-02 18:10, Joel E. Denny via cfe-dev wrote:
> Hi,
> 
> I'm trying to understand clang's ordering of -L flags, which, on my
> system, leads to linking against a system libomp rather than the
> clang/LLVM libomp.
> 
> Specifically, on my system, running with -v shows that it specifies
> -L/usr/lib/x86_64-linux-gnu before the -L for my llvm/clang
> build/install directory.  The effect is that it finds the system
> libomp.so.5 as libomp.  When the executable loads, it then looks for
> libomp.so.5 instead of the libomp.so built for llvm, so even
> LD_LIBRARY_PATH doesn't help it find the latter.
> 
> Is this intended behavior for some reason?  Shouldn't clang prefer its
> own libraries before system libraries?
> A fix for my use case is to, in lib/Driver/ToolChains/Linux.cpp, move
> the following lines from near the end of the Linux constructor to
> earlier, right after the declaration of the Paths variable:
> 
> if (StringRef(D.Dir).startswith(SysRoot))
>   addPathIfExists(D, D.Dir + "/../lib", Paths);
> 
> By the way, in case it helps, the ToolChain constructor also tries to
> insert the following subdirectories of the build/install directory,
> but they don't exist on my system:
> 
> lib/clang/7.0.0/x86_64-unknown-linux-gnu/lib
> lib/clang/7.0.0/lib/linux/x86_64
> 
> Thanks.
> 
> Joel
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