gcc - 用clang编译时无法查看std::string

Question

g++(GCC)5.2.0

clang版本3.7.1(标签/ RELEASE_371 / final)

GNU gdb(GDB)7.12

使用clang编译时，由于某种原因，Gdb无法找到std::string的定义。我已自定义编译并构建gcc和clang，因为Centos 6.5随附了较早版本的gcc。

范例程式码

#include <string>

int main()
{
    std::string s("This is a string");

    return 0;
}

使用g++进行编译和调试-工作正常

[~]$ g++ -ggdb3 -std=c++14 stl.cpp 
[~]$ gdb a.out
GNU gdb (GDB) 7.12
Reading symbols from a.out...done.
(gdb) break main
Breakpoint 1 at 0x400841: file stl.cpp, line 5.
(gdb) r
Starting program: /home/vagrant/a.out 

Breakpoint 1, main () at stl.cpp:5
5       std::string s("This is a string");
(gdb) n
7       return 0;
(gdb) p s
$1 = {static npos = <optimized out>, 
  _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, _M_p = 0x612c20 "This is a string"}, _M_string_length = 16, {
    _M_local_buf = "\020\000\000\000\000\000\000\000\300\b@\000\000\000\000", _M_allocated_capacity = 16}}
(gdb) 

检查它是否与我的libstdc++的rpm构建版本链接，而不是系统链接

[~]$ ldd a.out
    linux-vdso.so.1 =>  (0x00007ffd709e0000)
    libstdc++.so.6 => /opt/spotx-gcc/lib64/libstdc++.so.6 (0x00007f29318fa000)
    libm.so.6 => /lib64/libm.so.6 (0x00007f2931676000)
    libgcc_s.so.1 => /opt/spotx-gcc/lib64/libgcc_s.so.1 (0x00007f293145f000)
    libc.so.6 => /lib64/libc.so.6 (0x00007f29310cb000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f2931c93000)

[~]$ objdump -T -C a.out
a.out:     file format elf64-x86-64
DYNAMIC SYMBOL TABLE:
0000000000000000  w   D  *UND*  0000000000000000              __gmon_start__
0000000000000000  w   D  *UND*  0000000000000000              _Jv_RegisterClasses
0000000000000000      DF *UND*  0000000000000000  GLIBC_2.2.5 __libc_start_main
0000000000000000  w   D  *UND*  0000000000000000              _ITM_deregisterTMCloneTable
0000000000000000  w   D  *UND*  0000000000000000              _ITM_registerTMCloneTable
0000000000000000      DF *UND*  0000000000000000  GLIBCXX_3.4.21 std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string()
0000000000000000      DF *UND*  0000000000000000  GLIBCXX_3.4 std::allocator<char>::~allocator()
0000000000000000      DF *UND*  0000000000000000  GLIBCXX_3.4.21 std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, std::allocator<char> const&)
0000000000000000      DF *UND*  0000000000000000  GLIBCXX_3.4 std::allocator<char>::allocator()
0000000000000000      DF *UND*  0000000000000000  GCC_3.0     _Unwind_Resume
0000000000400700      DF *UND*  0000000000000000  CXXABI_1.3  __gxx_personality_v0

如果我尝试使用clang，现在一切看起来都不错

[~]$ clang++ -std=c++14 -g stl.cpp
[~]$ gdb a.out
GNU gdb (GDB) 7.12
Reading symbols from a.out...done.
(gdb) break  main
Breakpoint 1 at 0x400853: file stl.cpp, line 5.
(gdb) r
Starting program: /home/vagrant/a.out 

Breakpoint 1, main () at stl.cpp:5
5       std::string s("This is a string");
(gdb) n
7       return 0;
(gdb) p s
$1 = <incomplete type>
(gdb) 

现在我得到了一个不完整的类型-但是正在使用相同的库

[~]$ ldd a.out
    linux-vdso.so.1 =>  (0x00007fff5352d000)
    libstdc++.so.6 => /opt/spotx-gcc/lib64/libstdc++.so.6 (0x00007f76b4023000)
    libm.so.6 => /lib64/libm.so.6 (0x00007f76b3d9f000)
    libgcc_s.so.1 => /opt/spotx-gcc/lib64/libgcc_s.so.1 (0x00007f76b3b88000)
    libc.so.6 => /lib64/libc.so.6 (0x00007f76b37f4000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f76b43bc000)


[~]$ objdump -T -C a.out
a.out:     file format elf64-x86-64
DYNAMIC SYMBOL TABLE:
0000000000000000  w   D  *UND*  0000000000000000              __gmon_start__
0000000000000000  w   D  *UND*  0000000000000000              _Jv_RegisterClasses
0000000000000000      DF *UND*  0000000000000000  GLIBC_2.2.5 __libc_start_main
0000000000000000  w   D  *UND*  0000000000000000              _ITM_deregisterTMCloneTable
0000000000000000  w   D  *UND*  0000000000000000              _ITM_registerTMCloneTable
0000000000000000      DF *UND*  0000000000000000  GLIBCXX_3.4.21 std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string()
0000000000000000      DF *UND*  0000000000000000  GLIBCXX_3.4 std::allocator<char>::~allocator()
0000000000000000      DF *UND*  0000000000000000  GLIBCXX_3.4.21 std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, std::allocator<char> const&)
0000000000000000      DF *UND*  0000000000000000  GLIBCXX_3.4 std::allocator<char>::allocator()
0000000000000000      DF *UND*  0000000000000000  GCC_3.0     _Unwind_Resume
0000000000400700      DF *UND*  0000000000000000  CXXABI_1.3  __gxx_personality_v0

有人对我在哪里寻找或我错过的东西有任何建议吗？编译它们时，两个编译器都被引导了-一切似乎都很好-使用clang时似乎没有定义std::string。

Answer 1

如ks1322所述，这是因为clang决定不为libstc++发出调试信息。

您可以通过提供以下标志来强制clang这样做:
-D_GLIBCXX_DEBUG
我只提供调试版本的标志，但是如果debug是默认的，发布版本是一个特殊的目标，则应将其删除:

release: CXXFLAGS := $(filter-out -D_GLIBCXX_DEBUG,$(CXXFLAGS)) -O2

这为我解决了相同的问题。