C++ 11 undefined reference to `__atomic_store_16'

Question

The following code fails to link:

#include <atomic>                                                                                                                                                             
struct A
{
    unsigned long a;
    unsigned long b;
};                                                                                                                                                           
struct B
{
    void set(A tmp)
    {
        _a.store(tmp);
    }
    std::atomic<A> _a;
 };                                                                                                                                                           

 int main()
{
   B b;
   b.set(A());
   return  0;
}

With the following error:

/tmp/cc8gyaZM.o: In function `std::atomic<A>::store(A, std::memory_order)':
dryn.cpp:     (.text._ZNSt6atomicI1AE5storeES0_St12memory_order[_ZNSt6atomicI1AE5storeES0_St12memory_order]+0x3e): undefined reference to `__atomic_store_16'

If I replace the unsigned long-s with anything that is up-to int in size, this compiles just fine. Using g++ 4.7.2 . Do you have any idea why is that?

Compiled with command:

g++ dryn.cpp --std=c++11

Show your command line, what arch are you compiling for? Did you try `-latomic`? — Marc Glisse, Aug 20 '14 at 11:44
Fwiw, clang eats this up without issue (Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)) — WhozCraig, Aug 20 '14 at 11:51
On linux clang fails just as much, with undefined __atomic_store (libstdc++) or __sync_lock_test_and_set_16 (libc++). g++ accepts the code with -m32... — Marc Glisse, Aug 20 '14 at 11:56
I see, and probably not implemented in your linux clang version as well... — , Aug 20 '14 at 12:10

score 7 · Answer 1 · edited May 23 '17 at 12:24

As answered by Zeta:

Atomic API isn't complete in GCC 4.7:

When lock free instructions are not available (either through hardware or OS support) atomic operations are left as function calls to be resolved by a library. Due to time constraints and an API which is not finalized, there is no libatomic supplied with GCC 4.7. This is easily determined by encountering unsatisfied external symbols beginning with __atomic_*.

Since there is no libatomic shipped with GCC 4.7 you need to use another compiler which actually supports the features you want or provide the missing features (sample implementation).

comments: Install libatomic to fix it. (note that in GCC the dll named 'libatomic.so.1' , so using -l:libatomic.so.1 to linking) — vrqq, Mar 14 '23 at 15:20

C++ 11 undefined reference to `__atomic_store_16'

1 Answers1