missing some c++11 support for clang in FreeBSD

[Dimitry Andric]

On May 14, 2013, at 02:35, Alexander K. Beros <alex at 154cm.com> wrote:
> I have just started using clang (on FreeBSD 9.1 AMD64) and encountered a
> couple problems.  I have worked around these points, but in case they
> represent something unintentional (as opposed to some error on my part while
> building from the port) I would like to mention them.  I am using
> 
> FreeBSD clang version 3.1 (branches/release_31 156863) 20120523
> Target: x86_64-unknown-freebsd9.0
> Thread model: posix
> 
> A key element in solving both problems was the installation of gcc47.  That
> was unexpected since I initially installed clang under the assumption that
> FBSD is moving from gcc to clang and since gcc42 doesn't support c++11.

On FreeBSD 9.1, you first need to build libc++, which provides C++11
support. (On 10.0-CURRENT, it is enabled and installed by default, but
not on previous releases.)

To build and install libc++ on 9.1, add the following lines to
/etc/src.conf:

  CC=clang
  CXX=clang++
  CPP=clang-cpp
  WITH_LIBCPLUSPLUS=foo

Then build and install world in the usual manner.  If you prefer to only
build libc++ (and its support library, libcxxrt) manually, you can do
the following:

  cd /usr/src/lib/libcxxrt
  make obj && make depend && make
  sudo make install
  cd /usr/src/lib/libc++
  make obj && make depend && make
  sudo make install

After libc++ is installed, you still need to tell clang to use it
instead of GNU libstdc++; see below.


> 1.. 
> Symptom:
> 
> 	%>  clang++ -std=c++11 -stdlib=libstdc++ refparms.c++
> 	initListTest.cpp:43:10: fatal error: 'initializer_list' file not
> found
> 	#include <initializer_list>
> 
> I had included initializer_list.

To enable libc++, you must add the flag -stdlib=libc++ instead.  If you
use -stdlib=libstdc++, or no -stdlib option, it will use the base system
version of GNU libstdc++, which is the version that comes with gcc 4.2,
and does not support C++11.


> Temporary Solution:
> 	I built gcc47 from the port and then added the following to my
> .cshrc file
> 	alias clang11 'clang++ -std=c++11 -I/usr/local/lib/gcc47/include/c++
> -I/usr/local/lib/gcc47/include/c++/x86_64-portbld-	freebsd9.1'
> 
> Alternate solution, compile using g++47.

This will only work partially, since you still need to make sure to add
the proper flags during linking, so clang can find the libstdc++
libraries installed by the gcc47 port.


> 2..
> Symptom:
> 	/usr/lib/libstdc++.so.6: version GLIBCXX_3.4.14 required by
> /usr/home/../binaries/a.out  not found

Yes, this is a problem with the gcc ports.  They are basically unusable
for C++ as-is.  Please complain to the maintainer. :-)


> Solution:
> 	I added the following line to /etc/libmap.conf
> 	libstdc++.so.6  gcc47/libstdc++.so.6
> 
> 	again compiling with g++47 had no such problem.

This is a rather brute-force solution, but it should work, since newer
versions of libstdc++ are backwards compatible.

-Dimitry