Red Hat: using <atomic> compiles fine but linker can't find __atomic_store_16; what library?

Question

I'm using atomic<> for the first time, and just as using <thread> requires you to link a thread library, it seems like using <atomic> wants you to do... something. What?

> uname -a
Linux sdclxd00239 3.10.0-693.11.6.el7.x86_64 #1 SMP Thu Dec 28 14:23:39 EST 2017 x86_64 x86_64 x86_64 GNU/Linu

> g++ Foo.cxx -g -o MsgQueueNoLock -pthread
/tmp/ccnGOKUG.o: In function `std::atomic<Ptr_T>::store(Ptr_T, std::memory_order)':
/opt/rh/devtoolset-7/root/usr/include/c++/7/atomic:239: undefined reference to `__atomic_store_16'
/tmp/ccnGOKUG.o: In function `std::atomic<Ptr_T>::load(std::memory_order) const':
/opt/rh/devtoolset-7/root/usr/include/c++/7/atomic:250: undefined reference to `__atomic_load_16'
collect2: error: ld returned 1 exit status>

g++ Foo.cxx -g -o Foo -pthread
/tmp/ccnGOKUG.o: In function `std::atomic<Ptr_T>::store(Ptr_T, std::memory_order)':
/opt/rh/devtoolset-7/root/usr/include/c++/7/atomic:239: undefined reference to `__atomic_store_16'
/tmp/ccnGOKUG.o: In function `std::atomic<Ptr_T>::load(std::memory_order) const':
/opt/rh/devtoolset-7/root/usr/include/c++/7/atomic:250: undefined reference to `__atomic_load_16'
collect2: error: ld returned 1 exit status

UPDATE: I need to use -latomic . Fair enough! However I can't find one I can actually use.

First I look under /usr/lib, and I see I have a simlink under gcc/.../4.8.2 pointing to gcc/.../4.8.5 ?!!? I've never in my life seen an old version depend on a new version though the timestamp causes me to suspect either manual intervention by someone in the past, or a complicated history.

> l `find /usr/lib -name '*atomic*'`
-rw-r--r--. 2 root root 1379 Jul 13  2017 /usr/lib/python2.7/site-packages/sos/plugins/atomichost.pyo
-rw-r--r--. 2 root root 1379 Jul 13  2017 /usr/lib/python2.7/site-packages/sos/plugins/atomichost.pyc
-rw-r--r--. 1 root root 1672 Jul 13  2017 /usr/lib/python2.7/site-packages/sos/plugins/atomichost.py
-rw-r--r--  1 root root   40 Sep 22  2017 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/libatomic.so
-rw-r--r--  1 root root   38 Sep 22  2017 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/32/libatomic.so
lrwxrwxrwx  1 root root   44 Jul  3  2018 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/32/libatomic.a -> ../../../i686-redhat-linux/4.8.5/libatomic.a

Something on the 'net suggested I might find joy under /usr/local/lib but in fact joy is not to be found:

> find /usr/local/lib -name '*atomic*'
>

The gcc actually installed is old (4.8.5) and I'm running 7.2.1 via the scl utility, which puts /opt/rh/devtoolset-7/root/usr/bin/gcc into the path. Anticipating that the requisite lib was probably delivered with the gcc, I look at /opt/rh/devtoolset-7 ... and like a bad dream the libatomic.a again is a symlink to a non-existent file.

> l `find /opt/rh/devtoolset-7/ -name '*atomic*'`
    :
    (headers elided)
    :
-rw-r--r-- 1 root root 40975 Aug 31  2017 /opt/rh/devtoolset-7/root/usr/include/c++/7/atomic
-rw-r--r-- 1 root root    80 Aug 31  2017 /opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/32/libatomic.so
-rw-r--r-- 1 root root  1553 Oct  6  2017 /opt/rh/devtoolset-7/root/usr/share/systemtap/tapset/linux/atomic.stp
lrwxrwxrwx 1 root root    40 Jul  3  2018 /opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/32/libatomic.a -> ../../../i686-redhat-linux/7/libatomic.a

So using -L options with every path I can think of based on what find found, here's all the errors:

> g++ MsgQueueNoLock.cxx -g -o MsgQueueNoLock -pthread -latomic
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/ld: cannot find -latomic
collect2: error: ld returned 1 exit status
> g++ MsgQueueNoLock.cxx -g -o MsgQueueNoLock -pthread -L/usr/lib/gcc/x86_64-redhat-linux/4.8.2 -latomic
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/ld: cannot find /usr/lib64/libatomic.so.1.0.0
collect2: error: ld returned 1 exit status
> g++ MsgQueueNoLock.cxx -g -o MsgQueueNoLock -pthread -L/usr/lib/gcc/x86_64-redhat-linux/4.8.2/32 -latomic
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/ld: cannot find /usr/lib/libatomic.so.1.0.0
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/ld: skipping incompatible /usr/lib/gcc/x86_64-redhat-linux/4.8.2/32/libstdc++.so when searching for -lstdc++
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/ld: skipping incompatible /usr/lib/gcc/x86_64-redhat-linux/4.8.2/32/libgcc_s.so when searching for -lgcc_s
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/ld: skipping incompatible /usr/lib/gcc/x86_64-redhat-linux/4.8.2/32/libgcc.a when searching for libgcc.a
collect2: error: ld returned 1 exit status
> g++ MsgQueueNoLock.cxx -g -o MsgQueueNoLock -pthread -L/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/32 -latomic
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/ld: skipping incompatible /opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/32/libatomic.so when searching for -latomic
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/ld: cannot find -latomic
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/ld: skipping incompatible /opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/32/libstdc++.so when searching for -lstdc++
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/ld: skipping incompatible /opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/32/libgcc_s.so when searching for -lgcc_s
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/ld: skipping incompatible /opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/32/libgcc.a when searching for libgcc.a
collect2: error: ld returned 1 exit status

Answer 1

Someone that is building 64bit code in CentOS and needs atomic might stumble upon this article, so I just want to add that I actually had to install it as follows,

sudo yum install devtoolset-7-libatomic-devel

I do not know much about the library. I was just trying to compile ponyc, and I first needed to run the following commands,

yum install llvm-toolset-7
echo "source scl_source enable devtoolset-7 llvm-toolset-7" >> ~/.bashrc

There were some more modifications that I had to make to the CMakeLists.txt files but that would now be off-topic.