红帽:使用<atomic>编译很好，但是链接器找不到__atomic_store_16；什么库？

Question

我第一次使用atomic<>，正如使用<thread>要求您链接线程库一样，似乎使用<atomic>需要您这样做。某物。什么？

> 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

更新：我需要使用-latomic。当然可以!但是我找不到我能用的。

首先，我在/usr/lib下面查看，我看到gcc/.../4.8.2下面有一个simlink指向gcc/.../4.8.5？！？在我的一生中，我从未见过一个旧版本依赖于一个新版本，尽管时间戳让我怀疑过去有人手动干预，或者是复杂的历史。

> 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

网上的一些信息表明，我可能会在/usr/local/lib下找到joy，但实际上没有人能找到joy：

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

gcc的实际安装是旧的(4.8.5)，我通过scl实用程序运行7.2.1，它将/opt/rh/devtoolset-7/root/usr/bin/gcc放入路径中。由于预期所需的库可能与gcc一起交付，我看了/opt/rh/devtoolset-7 .和噩梦一样，libatomic.a也是一个指向一个不存在的文件的符号链接。

> 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

因此，将-L选项与我能想到的基于find发现的每一条路径一起使用，下面是所有的错误：

> 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

这里有一个示例libatomic.c实现：https://gcc.gnu.org/wiki/Atomic/GCCMM?action=AttachFile&do=view&target=libatomic.c --它的编译会产生几个警告，但最终会生成一个对象文件。

> gcc -c -o libatomic.o libatomic.c
libatomic.c:475:1: warning: conflicting types for built-in function '__atomic_compare_exchange_1' [-Wbuiltin-declaration-mismatch]
 __atomic_compare_exchange_ ## SIZE   (I ## SIZE *mem, I ## SIZE *expect, I ## SIZE desired, int success, int failure)    \
 ^
libatomic.c:524:1: note: in expansion of macro 'ATOMIC_COMPARE_EXCHANGE'
 ATOMIC_COMPARE_EXCHANGE (1)
 ^~~~~~~~~~~~~~~~~~~~~~~
libatomic.c:475:1: warning: conflicting types for built-in function '__atomic_compare_exchange_2' [-Wbuiltin-declaration-mismatch]
 __atomic_compare_exchange_ ## SIZE   (I ## SIZE *mem, I ## SIZE *expect, I ## SIZE desired, int success, int failure)    \
 ^
libatomic.c:537:1: note: in expansion of macro 'ATOMIC_COMPARE_EXCHANGE'
 ATOMIC_COMPARE_EXCHANGE (2)
 ^~~~~~~~~~~~~~~~~~~~~~~
libatomic.c:475:1: warning: conflicting types for built-in function '__atomic_compare_exchange_4' [-Wbuiltin-declaration-mismatch]
 __atomic_compare_exchange_ ## SIZE   (I ## SIZE *mem, I ## SIZE *expect, I ## SIZE desired, int success, int failure)    \
 ^
libatomic.c:551:1: note: in expansion of macro 'ATOMIC_COMPARE_EXCHANGE'
 ATOMIC_COMPARE_EXCHANGE (4)
 ^~~~~~~~~~~~~~~~~~~~~~~
libatomic.c:475:1: warning: conflicting types for built-in function '__atomic_compare_exchange_8' [-Wbuiltin-declaration-mismatch]
 __atomic_compare_exchange_ ## SIZE   (I ## SIZE *mem, I ## SIZE *expect, I ## SIZE desired, int success, int failure)    \
 ^
libatomic.c:565:1: note: in expansion of macro 'ATOMIC_COMPARE_EXCHANGE'
 ATOMIC_COMPARE_EXCHANGE (8)
 ^~~~~~~~~~~~~~~~~~~~~~~
libatomic.c:475:1: warning: conflicting types for built-in function '__atomic_compare_exchange_16' [-Wbuiltin-declaration-mismatch]
 __atomic_compare_exchange_ ## SIZE   (I ## SIZE *mem, I ## SIZE *expect, I ## SIZE desired, int success, int failure)    \
 ^
libatomic.c:579:1: note: in expansion of macro 'ATOMIC_COMPARE_EXCHANGE'
 ATOMIC_COMPARE_EXCHANGE (16)
 ^~~~~~~~~~~~~~~~~~~~~~~
> ar rcs libatomic.a libatomic.o

> g++ Foo.cxx -g -o Foo-pthread -L. -latomic

链接成功:二进制文件是无错误创建的。我的应用程序写得太少了，无法判断它是否真的有效。

即使这是可行的，它也是非常清楚的“不是你应该做什么才能让它起作用。”所以我不把它标记为“答案”，只是把它留给将来参考。

Answer 2

要与gcc一起使用16字节原子，您需要-latomic

Answer 3

在CentOS中构建64位代码并需要atomic的人可能会无意中发现本文，因此我只想补充说，我实际上必须按如下方式安装它，

sudo yum install devtoolset-7-libatomic-devel

我对图书馆知之甚少。我只是想编译ponyc，首先需要运行以下命令，

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

我还需要对CMakeLists.txt文件进行更多的修改，但这将是一个非主题的问题。