Re: JIT compiling with LLVM v9.0 - Mailing list pgsql-hackers

On Thu, Feb 1, 2018 at 5:05 PM, Andres Freund <andres@anarazel.de> wrote:
> Just to understand: You're running in the issue with the header being
> included from within the extern "C" {}?  Hm, I've pushed a quick fix for
> that.
>
> Other than that, you can compile with both gcc or clang, but clang needs
> to be available. Will be guessed from PATH if clang clang-5.0 clang-4.0
> (in that order) exist, similar with llvm-config llvm-config-5.0 being
> guessed. LLVM_CONFIG/CLANG/CXX= as an argument to configure overrides
> both of that. E.g.
> ./configure --with-llvm LLVM_CONFIG=~/build/llvm/5/opt/install/bin/llvm-config
> is what I use, although I also add:
> LDFLAGS='-Wl,-rpath,/home/andres/build/llvm/5/opt/install/lib'
> so I don't have to install llvm anywhere the system knows about.


On Ubuntu 16.04
SHA1: 302b7a284
gcc (Ubuntu 5.4.0-6ubuntu1~16.04.6) 5.4.0 20160609

packages: llvm-5.0 llvm-5.0-dev llvm-5.0-runtime libllvm-5.0
clang-5.0 libclang-common-5.0-dev libclang1-5.0

./configure --with-llvm --prefix=/home/jdavis/install/pgsql-dev
...
checking for llvm-config... no
checking for llvm-config-5.0... llvm-config-5.0
checking for clang... no
checking for clang-5.0... clang-5.0
checking for LLVMOrcGetSymbolAddressIn... no
checking for LLVMGetHostCPUName... no
checking for LLVMOrcRegisterGDB... no
checking for LLVMOrcRegisterPerf... no
checking for LLVMOrcUnregisterPerf... no
...

That encounters errors like:

/usr/include/c++/5/bits/c++0x_warning.h:32:2: error: #error This file
requires compiler an
d library support for the ISO C++ 2011 standard. This support must be
enabled with the -st
d=c++11 or -std=gnu++11 compiler options.
...
/usr/include/c++/5/cmath:505:22: error: conflicting declaration of C
function ‘long double
...
/usr/include/c++/5/cmath:926:3: error: template with C linkage
...

So I reconfigure with:
CXXFLAGS="-std=c++11" ./configure --with-llvm
--prefix=/home/jdavis/install/pgsql-dev

I think that got rid of the first error, but the other errors remain.

I also tried installing libc++-dev and using CC=clang-5.0
CXX=clang++-5.0 and with CXXFLAGS="-std=c++11 -stdlib=libc++" but I am
not making much progress, I'm still getting:

/usr/include/c++/v1/cmath:316:1: error: templates must have C++ linkage

I suggest that you share your exact configuration so we can get past
this for now, and you can work on the build issues in the background.
We can't be the first ones with this problem; maybe you can just ask
on an LLVM channel what the right thing to do is that will work on a
variety of machines (or at least reliably detect the problem at
configure time)?

Regards,
    Jeff Davis