Re: [Boost-users] How to build Boost with Clang/libc++ and NOT link against libstdc++?

Subject: Re: [Boost-users] How to build Boost with Clang/libc++ and NOT link against libstdc++?
From: Jürgen Hunold (jhunold_at_[hidden])
Date: 2017-01-20 06:40:48

Hi Deniz, 

Am Freitag, 20. Januar 2017, 10:13:56 CET schrieb Deniz Bahadir:
> Hi guys,
> I am able to build the Boost libraries using Clang and flags "-std=c++14
> -stdlib=libc++", however, I noticed that several libraries are still
> linked against GCC's standard-library "libstdc++".

This works for me for quite a while. Please make sure you rebuild all 
libraries. Hint: b2 does not cache compiler flags. Add "-a" to your command 
line to force a full rebuild.
 

> Does anyone know how and why this link-dependency gets added and how to
> get rid of them? Does it come in through some other link-dependencies?
> At least none of them seem to link to "libstdc++"?

Most probably a not clean rebuild.

>      dll-path==/opt/BENOCS/clang38/lib/x86_64-linux-gnu  \
>      toolset=clang-3.8  \

The toolset "clang-3.8" is configured where and how?

>      cflags="$CFLAGS" CXXFLAGS="$CXXFLAGS" \

cxxflags="$CXXFLAGS" 

>      linkflags="-Wl,--as-needed $LINK_LIBCXXABI"

I'd put the extra flags into user-/project-/site-config.jam.

> For the environment-variable LINK_LIBCXXABI I tried "-lc++abi" as well
> and also tried providing it only in the cxxflags or the linkflags or
> both (as above).

linkflags should contain "-stdlib=libc++", too
 
> I would be happy, if anyone could explain that behavior or could even
> provide a workaround/fix for me, so that "libstdc++" is no longer linked.

from my user-config.jam:

# Clang trunk
using clang : # version
            : # compiler
              $(HOME)/local/bin/clang++
             : # options
                <cxxflags>-stdlib=libc++
                <cxxflags>-I$(HOME)/local/include/c++/v1
                <linkflags>-stdlib=libc++
                <linkflags>-L$(HOME)/local/lib
           ;

with custom clang trunk installed to $(HOME)/local

> PS: BTW, does anyone know if it is correct, that shared libraries (in
> general) that are linked against "libc++abi" do always also link to
> "libgcc_s"? (What is it for?)

The basic compiler runtime AFAIK. Might be replaced by clang's compiler-rt, I 
guess. But that is off-topic

Yours,

Jürgen
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