使用g++和clang编译opengauss相关问题

环境：
opengauss版本：5.0.0
openeuler版本：20.03LTS

我们这边尝试修改makefile来支持clang编译，对configure流程生成的opengauss-server/src/Makefile.global做了修改使编译启动：
1. "CC_VERSION = 7.3.0"注释掉
2. configure_args中的gcc_version相关信息删除，把CC=g++改为CC=clang++
3. CC = g++改CC = clang++，GCC = yes 改为GCC = no，C = gcc改为C = clang
4. 删除CFLAGS中的-fno-aggressive-loop-optimizations和-freg-struct-return，因为clang不支持这两个flag
5. CFLAGS中加入 -std=c11
再次进行编译，error过多导致编译停止，error形式均是：

```
 In file included from gs_thread.cpp:53:
 In file included from ../../../src/include/gs_policy/policy_common.h:30:
 ../../../src/include/gs_policy/gs_map.h:217:9: error: static_cast from 'const char *' to 'char *' is not
       allowed
         securec_check(rc, "\0", "\0");
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 ../../../src/include/utils/elog.h:301:35: note: expanded from macro 'securec_check'
             freeSecurityFuncSpace(static_cast<char*>(charList), ##__VA_ARGS__)...
```

这里涉及多个文件文件的编译，均报出该error

我们提取了gs_thread.cpp文件的编译命令作为例子：

```
clang++  -std=c++11 -D_GLIBCXX_USE_CXX11_ABI=0 -fsigned-char -DSTREAMPLAN -DPGXC -mcx16 -msse4.2 -O2 -g3 -Wall -Wpointer-arith -Wno-write-strings -fnon-call-exceptions -fno-common -pipe -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -DENABLE_GSTRACE -Wno-attributes -fno-omit-frame-pointer -fno-expensive-optimizations -Wno-unused-but-set-variable -fPIC -fstack-protector-all  -I../../../src/common/port  -I../../../src/include -I../../../src/lib/gstrace -I/home/sda/binarylibs/kernel/dependency/libxml2/comm/include/libxml2 -D_GNU_SOURCE -I/home/sda/binarylibs/kernel/dependency/libxml2/comm/include/libxml2 -I/home/sda/binarylibs/kernel/dependency/unixodbc/include -I/home/sda/binarylibs/kernel/dependency/libobs/comm/include -I/home/sda/binarylibs/kernel/dependency/libcgroup/comm/include -I/home/sda/binarylibs/kernel/dependency/openssl/comm/include -I/home/sda/binarylibs/kernel/dependency/boost/comm/include -I/home/sda/binarylibs/kernel/dependency/llvm/comm/include -I/home/sda/binarylibs/kernel/dependency/kerberos/comm/include -I/home/sda/binarylibs/kernel/dependency/cjson/comm/include -I/home/sda/binarylibs/kernel/dependency/numactl/comm/include -I/home/sda/binarylibs/kernel/dependency/zlib1.2.11/comm/include -I/home/sda/binarylibs/kernel/dependency/lz4/comm/include -I/home/sda/binarylibs/kernel/dependency/zstd/include -I/home/sda/binarylibs/kernel/dependency/libcurl/comm/include -I/home/sda/binarylibs/kernel/component/dcf/include -msse4.2 -fPIC -fstack-protector-all -c gs_thread.cpp -o gs_thread_srv.o
```

尝试单独使用clang++进行编译，依然报出static cast的error：

```
In file included from gs_thread.cpp:53:
In file included from ../../../src/include/gs_policy/policy_common.h:31:
../../../src/include/gs_policy/gs_vector.h:133:25: error: static_cast from 'const char *' to 'char *' is
      not allowed
                        securec_check(rc, "\0", "\0");
                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../../src/include/utils/elog.h:301:35: note: expanded from macro 'securec_check'
            freeSecurityFuncSpace(static_cast<char*>(charList), ##__VA_ARGS__)...
                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
fatal error: too many errors emitted, stopping now [-ferror-limit=]
8 warnings and 20 errors generated.
```
我的clang信息：

```
[root@localhost port]# clang++ -v
clang version 7.0.0 (openEuler 7.0.0-6.oe1)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.3.0
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7.3.0
Candidate multilib: .;@m64
Selected multilib: .;@m64
```

尝试使用系统原生的g++编译，发现不能通过：
系统原生g++：
```
[root@localhost port]# /usr/bin/g++ -v
Using built-in specs.
COLLECT_GCC=/usr/bin/g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-linux-gnu/7.3.0/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-linker-hash-style=gnu --enable-languages=c,c++,objc,obj-c++,fortran,lto --enable-plugin --enable-initfini-array --disable-libgcj --with-isl=/home/abuild/rpmbuild/BUILD/gcc-7.3.0/obj-x86_64-linux-gnu/isl-install --without-cloog --enable-gnu-indirect-function --build=x86_64-linux-gnu --with-stage1-ldflags=' -Wl,-z,relro,-z,now' --with-boot-ldflags=' -Wl,-z,relro,-z,now' --with-tune=generic --with-arch_32=x86-64 --disable-multilib
Thread model: posix
gcc version 7.3.0 (GCC) 
```
报错：

```
[root@localhost port]# /usr/bin/g++ -std=c++11 -D_GLIBCXX_USE_CXX11_ABI=0 -fsigned-char -DSTREAMPLAN -DPGXC -mcx16 -msse4.2 -O2 -g3 -Wall -Wpointer-arith -Wno-write-strings -fnon-call-exceptions -fno-common -pipe -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -DENABLE_GSTRACE -Wno-attributes -fno-omit-frame-pointer -fno-expensive-optimizations -Wno-unused-but-set-variable -fPIC -fstack-protector-all  -I../../../src/common/port  -I../../../src/include -I../../../src/lib/gstrace -I/home/sda/binarylibs/kernel/dependency/libxml2/comm/include/libxml2 -D_GNU_SOURCE -I/home/sda/binarylibs/kernel/dependency/libxml2/comm/include/libxml2 -I/home/sda/binarylibs/kernel/dependency/unixodbc/include -I/home/sda/binarylibs/kernel/dependency/libobs/comm/include -I/home/sda/binarylibs/kernel/dependency/libcgroup/comm/include -I/home/sda/binarylibs/kernel/dependency/openssl/comm/include -I/home/sda/binarylibs/kernel/dependency/boost/comm/include -I/home/sda/binarylibs/kernel/dependency/llvm/comm/include -I/home/sda/binarylibs/kernel/dependency/kerberos/comm/include -I/home/sda/binarylibs/kernel/dependency/cjson/comm/include -I/home/sda/binarylibs/kernel/dependency/numactl/comm/include -I/home/sda/binarylibs/kernel/dependency/zlib1.2.11/comm/include -I/home/sda/binarylibs/kernel/dependency/lz4/comm/include -I/home/sda/binarylibs/kernel/dependency/zstd/include -I/home/sda/binarylibs/kernel/dependency/libcurl/comm/include -I/home/sda/binarylibs/kernel/component/dcf/include -msse4.2 -fPIC -fstack-protector-all -c gs_thread.cpp -o gs_thread_srv.o
In file included from ../../../src/include/knl/knl_instance.h:43:0,
                 from ../../../src/include/knl/knl_variable.h:28,
                 from gs_thread.cpp:26:
../../../src/include/utils/knl_globalsysdbcache.h:123:9: internal compiler error: Illegal instruction
         SAFETY_GSC_MEMORY_SPACE = (uint64)(REAL_GSC_MEMORY_SPACE * 0.8);
         ^~~~~~~~~~~~~~~~~~~~~~~
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://gcc.gnu.org/bugs/> for instructions.
```

使用opengauss提供的第三方包中的gcc7.3.0则可以通过编译：
第三方包g++：

```
[root@localhost port]# g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/home/sda/binarylibs/buildtools/gcc7.3/gcc/bin/../libexec/gcc/x86_64-pc-linux-gnu/7.3.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ./configure CFLAGS='-fstack-protector -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now -s ' CXXFLAGS='-fstack-protector -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now -s ' --disable-multilib --prefix=/data/gcc2/target/gcc7.3
Thread model: posix
gcc version 7.3.0 (GCC) 
```
编译通过：
```
[root@localhost port]# g++ -std=c++11 -D_GLIBCXX_USE_CXX11_ABI=0 -fsigned-char -DSTREAMPLAN -DPGXC -mcx16 -msse4.2 -O2 -g3 -Wall -Wpointer-arith -Wno-write-strings -fnon-call-exceptions -fno-common -pipe -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -DENABLE_GSTRACE -Wno-attributes -fno-omit-frame-pointer -fno-expensive-optimizations -Wno-unused-but-set-variable -fPIC -fstack-protector-all  -I../../../src/common/port  -I../../../src/include -I../../../src/lib/gstrace -I/home/sda/binarylibs/kernel/dependency/libxml2/comm/include/libxml2 -D_GNU_SOURCE -I/home/sda/binarylibs/kernel/dependency/libxml2/comm/include/libxml2 -I/home/sda/binarylibs/kernel/dependency/unixodbc/include -I/home/sda/binarylibs/kernel/dependency/libobs/comm/include -I/home/sda/binarylibs/kernel/dependency/libcgroup/comm/include -I/home/sda/binarylibs/kernel/dependency/openssl/comm/include -I/home/sda/binarylibs/kernel/dependency/boost/comm/include -I/home/sda/binarylibs/kernel/dependency/llvm/comm/include -I/home/sda/binarylibs/kernel/dependency/kerberos/comm/include -I/home/sda/binarylibs/kernel/dependency/cjson/comm/include -I/home/sda/binarylibs/kernel/dependency/numactl/comm/include -I/home/sda/binarylibs/kernel/dependency/zlib1.2.11/comm/include -I/home/sda/binarylibs/kernel/dependency/lz4/comm/include -I/home/sda/binarylibs/kernel/dependency/zstd/include -I/home/sda/binarylibs/kernel/dependency/libcurl/comm/include -I/home/sda/binarylibs/kernel/component/dcf/include -msse4.2 -fPIC -fstack-protector-all -c gs_thread.cpp -o gs_thread_srv.o
```

因此我们猜想opengauss使用了某些不被标准c++11标准支持的语法（比如static_cast from 'const char *' to 'char *'），因此定制了相应的gcc7.3.0包用于版本编译，但是这会对通用程序分析造成麻烦，是否有相应的解决方法。

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