C++ CGI报“资源访问错误”问题分析

灰太狼 2023-05-30 06:29 0阅读 0赞

一线上CGI偶发性会报“资源访问错误”，经过分析得出是因为CgiHost没有读取到CGI的任务输出，即CGI运行完成后连HTTP头都没有一点输出。

然而实际上，不可能没有任何输出，因为CGI至少有无条件的HTTP头部分输出，因此问题是输出丢失了。CGI和CgiHost间是通过重定向CGI的标准输出到Unix套接字进行交互的，如果这个套接字坏了，或者CGI的标准输出关闭了，自然不会有任何输出。但经测试，如果是关闭了套接字，报的错误不一样，因此直接排除这个可能。

经调查，该CGI的输出使用是C++库的std::cout，不是printf这套C库I/O，初步推断是std::cout对象的状态值不是goodbit。不是goodbit主要分三种情况：

1. 人为置为badbit等；
2. 程序有越界造成状态为badbit或failbit等；
3. 有类似“char\* str=NULL; std::cout << str”的调用出现，造成状态为badbit；
4. std::cout调用的basic\_streambuf<typename \_CharT, typename \_Traits>::**sputn**返回的大小不是期望值，造成状态为failbit。

从了解来看，第三种和第四种情况概率高出许多：

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 <td style="vertical-align:top;width:426.1pt;"> #include &lt;iosfwd&gt; namespace std { &nbsp;&nbsp;template&lt;typename _CharT, typename _Traits = char_traits&lt;_CharT&gt; &gt; &nbsp;&nbsp;class basic_ostream; &nbsp;&nbsp;typedef basic_ostream&lt;char&gt; ostream; } </td> 
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 <td style="vertical-align:top;width:426.1pt;"> #include &lt;iostream&gt; namespace std { &nbsp;&nbsp;extern istream cin; /// Linked to standard input &nbsp;&nbsp;extern ostream cout; /// Linked to standard output &nbsp;&nbsp;extern ostream cerr; /// Linked to standard error (unbuffered) &nbsp;&nbsp;extern ostream clog; /// Linked to standard error (buffered) } </td> 
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 <td style="vertical-align:top;width:426.1pt;"> #include &lt;ostream&gt; namespace std { &nbsp;&nbsp;// Partial specializations &nbsp;&nbsp;template&lt;class _Traits&gt; &nbsp;&nbsp;inline basic_ostream&lt;char, _Traits&gt;&amp; &nbsp;&nbsp;operator&lt;&lt;(basic_ostream&lt;char, _Traits&gt;&amp; __out, const char* __s)&nbsp;// 一个全局函数 &nbsp;&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;if (!__s) // 如果“__s”此时是NULL &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;__out.setstate(ios_base::badbit); // 其它一些情况，可查看源码文件ostream.tcc &nbsp;&nbsp;&nbsp;&nbsp;else &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;__ostream_insert(__out, __s, static_cast&lt;streamsize&gt;(_Traits::length(__s))); &nbsp;&nbsp;&nbsp;&nbsp;return __out; &nbsp;&nbsp;} &nbsp; &nbsp;&nbsp;// __ostream_write是一个位于名字空间std中的全局函数 &nbsp;&nbsp;// __ostream_write被兄弟函数__ostream_insert调用， &nbsp;&nbsp;// 而__ostream_insert又被函数全局函数operator&lt;&lt;调用 &nbsp;&nbsp;template&lt;typename _CharT, typename _Traits&gt; &nbsp;&nbsp;inline void &nbsp;&nbsp;__ostream_write(basic_ostream&lt;_CharT, _Traits&gt;&amp; __out, &nbsp;&nbsp;&nbsp;&nbsp;const _CharT* __s, streamsize __n) &nbsp;&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;typedef basic_ostream&lt;_CharT, _Traits&gt; __ostream_type; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;typedef typename __ostream_type::ios_base __ios_base; &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;// 类basic_streambuf的成员函数sputn实际调用的是兄弟函数xsputn &nbsp;&nbsp;&nbsp;&nbsp;// 而xsputn是一个虚拟函数。 &nbsp;&nbsp;&nbsp;&nbsp;// 虚类basic_streambuf有两个具体的子类：stringbuf和filebuf， &nbsp;&nbsp;&nbsp;&nbsp;// 对std::cout而言，对应的是filebuf，xsputn底层调用的实际是write函数。 &nbsp;&nbsp;&nbsp;&nbsp;// 注： &nbsp;&nbsp;&nbsp;&nbsp;// file版的xsputn实现在文件fstream.tcc中， &nbsp;&nbsp;&nbsp;&nbsp;// string版的xsputn实现在文件streambuf.tcc中。 &nbsp;&nbsp;&nbsp;&nbsp;const streamsize __put = __out.rdbuf()-&gt;sputn(__s, __n); &nbsp;&nbsp;&nbsp;&nbsp;if (__put != __n) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;__out.setstate(__ios_base::badbit); &nbsp;&nbsp;} &nbsp; &nbsp;&nbsp;template&lt;typename _CharT, typename _Traits&gt; &nbsp;&nbsp;class basic_streambuf&nbsp;{ // 虚拟基类 &nbsp;&nbsp;public: &nbsp;&nbsp;&nbsp;&nbsp;virtual streamsize xsputn(const char_type* __s, streamsize __n); &nbsp;&nbsp;}; &nbsp;&nbsp;class basic_stringbuf: public basic_streambuf; // 字符串子类 &nbsp;&nbsp;class basic_filebuf: public basic_streambuf; // 文件子类 } </td> 
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 <td style="vertical-align:top;width:426.1pt;"> typedef _Ios_Iostate iostate; enum _Ios_Iostate { &nbsp;&nbsp;_S_goodbit&nbsp; = 0, &nbsp;&nbsp;_S_badbit&nbsp; = 1L &lt;&lt; 0, // cout &lt;&lt; (char*)NULL &nbsp;&nbsp;_S_eofbit = 1L &lt;&lt; 1, &nbsp;&nbsp;_S_failbit = 1L &lt;&lt; 2, // write(buf,n) &lt; n &nbsp;&nbsp;_S_ios_iostate_end = 1L &lt;&lt; 16 }; &nbsp; // 注： // ios_base是一个普通类，并不是模板类 class ios_base { &nbsp;&nbsp;Iostate _M_streambuf_state; &nbsp;&nbsp;basic_streambuf&lt;_CharT, _Traits&gt;* _M_streambuf; // 对于fstream实际为basic_filebuf }; &nbsp; template&lt;typename _CharT, typename _Traits&gt; class basic_ios&nbsp;: public ios_base { }; &nbsp; // 这里用到了virtual继承， // 因为子类basic_iostream会同时继承basic_istream和basic_ostream， // 出现共享basic_ios，所以需要使用virtual继承 template&lt;typename _CharT, typename _Traits&gt; class basic_ostream&nbsp;: virtual public basic_ios&lt;_CharT, _Traits&gt; { }; </td> 
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 <td style="vertical-align:top;width:426.1pt;"> (gdb) ptype std::char_traits&lt;char&gt; type = struct std::char_traits&lt;char&gt; { &nbsp;&nbsp;public: &nbsp;&nbsp;&nbsp;&nbsp;static void assign(char_type &amp;, const char_type &amp;); &nbsp;&nbsp;&nbsp;&nbsp;static char_type * assign(char_type *, std::size_t, char_type); &nbsp;&nbsp;&nbsp;&nbsp;static bool eq(const char_type &amp;, const char_type &amp;); &nbsp;&nbsp;&nbsp;&nbsp;static bool lt(const char_type &amp;, const char_type &amp;); &nbsp;&nbsp;&nbsp;&nbsp;static int_type compare(const char_type *, const char_type *, std::size_t); &nbsp;&nbsp;&nbsp;&nbsp;static std::size_t length(const char_type *); &nbsp;&nbsp;&nbsp;&nbsp;static const char_type * find(const char_type *, std::size_t, const char_type &amp;); &nbsp;&nbsp;&nbsp;&nbsp;static char_type * move(char_type *, const char_type *, std::size_t); &nbsp;&nbsp;&nbsp;&nbsp;static char_type * copy(char_type *, const char_type *, std::size_t); &nbsp;&nbsp;&nbsp;&nbsp;static char_type to_char_type(const int_type &amp;); &nbsp;&nbsp;&nbsp;&nbsp;static int_type to_int_type(const char_type &amp;); &nbsp;&nbsp;&nbsp;&nbsp;static bool eq_int_type(const int_type &amp;, const int_type &amp;); &nbsp;&nbsp;&nbsp;&nbsp;static int_type eof(void); &nbsp;&nbsp;&nbsp;&nbsp;static int_type not_eof(const int_type &amp;); &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;typedef char char_type; &nbsp;&nbsp;&nbsp;&nbsp;typedef int int_type; } </td> 
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尝试使用GDB实地考察，遗憾的是无法对std::cout进行Debug，所以只有直接修改代码线上验证。但如果有办法取得std::cout的地址，然后根据对象的内存布局，找到成员**\_M\_streambuf\_state**的内存位置，也是可以查看和动态修改的。

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 <td style="vertical-align:top;width:426.1pt;"> (gdb) p std::cout No symbol "cout" in namespace "std". &nbsp; (gdb) p &amp;std::cout No symbol "cout" in namespace "std". &nbsp; 找到std::cout在进程中的位置，以便找到其成员_M_streambuf_state在进程中的位置 (gdb) p _ZSt4cout $1 = -144214548 &nbsp; (gdb) call write(1,"1234567890",10) $6 = -1 &nbsp; (gdb) p *__errno_location() $4 = 5 &nbsp; (gdb) whatis std::cout type = std::ostream &nbsp; (gdb) ptype std::cout type = std::ostream &nbsp; (gdb) p &amp;std::cout $1 = (std::ostream *) 0x7ffff7dd8700 &lt;std::cout&gt; &nbsp; (gdb) ptype std::ostream &nbsp;&nbsp; type = std::ostream &nbsp; (gdb) p std::cout $1 = &lt;incomplete type&gt; &nbsp; (gdb) p &amp;std::cout $3 = (std::ostream *) 0x7ffff7dd8700 &lt;std::cout&gt; (gdb) p *(std::ostream *)&amp;std::cout $4 = &lt;incomplete type&gt; &nbsp; (gdb) info symbol&nbsp;0x7ffff7dd8700 std::cout in section .bss of /lib64/libstdc++.so.6 &nbsp; (gdb) info address&nbsp;std::cout Symbol "std::cout" is static storage at address 0x7ffff7dd8700. &nbsp; (gdb) set solib-search-path /lib64 (gdb) info share 或 info sharedlibrary From &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;To &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Syms Read &nbsp;&nbsp;Shared Object Library 0x00007ffff7ddbb10 &nbsp;0x00007ffff7df6460 &nbsp;Yes (*) &nbsp;&nbsp;&nbsp;&nbsp;/lib64/ld-linux-x86-64.so.2 0x00007ffff7ef4060 &nbsp;0x00007ffff7ef54f8 &nbsp;Yes &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/lib64/libonion.so 0x00007ffff7b2e510 &nbsp;0x00007ffff7b9559a &nbsp;Yes (*) &nbsp;&nbsp;&nbsp;&nbsp;/lib64/libstdc++.so.6 0x00007ffff77d6370 &nbsp;0x00007ffff7841278 &nbsp;Yes (*) &nbsp;&nbsp;&nbsp;&nbsp;/lib64/libm.so.6 0x00007ffff75bdaf0 &nbsp;0x00007ffff75cd298 &nbsp;Yes (*) &nbsp;&nbsp;&nbsp;&nbsp;/lib64/libgcc_s.so.1 0x00007ffff7216480 &nbsp;0x00007ffff735cc00 &nbsp;Yes (*) &nbsp;&nbsp;&nbsp;&nbsp;/lib64/libc.so.6 0x00007ffff6ff3e60 &nbsp;0x00007ffff6ff4960 &nbsp;Yes (*) &nbsp;&nbsp;&nbsp;&nbsp;/lib64/libdl.so.2 (*): Shared library is missing debugging information. (gdb) sharedlibrary libstdc Symbols already loaded for /lib64/libstdc++.so.6 (gdb) sharedlibrary libstdc++ Symbols already loaded for /lib64/libstdc++.so.6 </td> 
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 <td style="vertical-align:top;width:426.1pt;"> # lsof -p 4442 cgihost &nbsp;4442 root &nbsp;&nbsp;&nbsp;0r &nbsp;&nbsp;CHR &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1,3 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;0t0 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1028 /dev/null cgihost &nbsp;4442 root &nbsp;&nbsp;&nbsp;1u &nbsp;&nbsp;CHR &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;136,2 &nbsp;&nbsp;&nbsp;0t0 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5 /dev/pts/2 (deleted) cgihost &nbsp;4442 root &nbsp;&nbsp;&nbsp;2u &nbsp;&nbsp;CHR &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;136,2 &nbsp;&nbsp;&nbsp;0t0 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5 /dev/pts/2 (deleted) cgihost &nbsp;4442 root &nbsp;&nbsp;&nbsp;3u &nbsp;&nbsp;REG &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;253,17 &nbsp;&nbsp;1144245 &nbsp;&nbsp;2097190 /data/cgi/log/httpserver/cgi_test.log cgihost &nbsp;4442 root &nbsp;&nbsp;&nbsp;4u &nbsp;0000 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;0,9 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;0 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6842 anon_inode cgihost &nbsp;4442 root &nbsp;&nbsp;&nbsp;7u &nbsp;&nbsp;REG &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;253,1 &nbsp;&nbsp;&nbsp;144 &nbsp;&nbsp;1360125 /usr/local/httpserver/bin/map/mem-cgi-bin-test cgihost &nbsp;4442 root &nbsp;&nbsp;&nbsp;8u &nbsp;unix&nbsp;0xffff880006933b80 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;0t0 831550706 socket # pmap 4442 </td> 
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 <td style="vertical-align:top;width:426.1pt;"> # objdump -t test|grep _ZSt4cout 0000000000601080&nbsp;g &nbsp;&nbsp;&nbsp;&nbsp;O .bss &nbsp;&nbsp;0000000000000110 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;_ZSt4cout@@GLIBCXX_3.4 # readelf -s /usr/lib/libstdc++.so.6|grep cout &nbsp;&nbsp;&nbsp;Num: &nbsp;&nbsp;&nbsp;Value &nbsp;Size Type &nbsp;&nbsp;&nbsp;Bind &nbsp;&nbsp;Vis &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Ndx Name &nbsp;&nbsp;&nbsp;884: 000e3ec0 &nbsp;&nbsp;140 OBJECT &nbsp;GLOBAL DEFAULT &nbsp;&nbsp;27 _ZSt4cout@@GLIBCXX_3.4 &nbsp;&nbsp;&nbsp;902: 000e4140 &nbsp;&nbsp;144 OBJECT &nbsp;GLOBAL DEFAULT &nbsp;&nbsp;27 _ZSt5wcout@@GLIBCXX_3.4 # readelf -r&nbsp;/usr/lib/libstdc++.so.6|grep cout Offset &nbsp;&nbsp;&nbsp;&nbsp;Info &nbsp;&nbsp;&nbsp;Type &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Sym.Value &nbsp;Sym. Name 000e2b64 &nbsp;00038606 R_386_GLOB_DAT &nbsp;&nbsp;&nbsp;000e4140 &nbsp;&nbsp;_ZSt5wcout 000e2ea0 &nbsp;00037406 R_386_GLOB_DAT &nbsp;&nbsp;&nbsp;000e3ec0 &nbsp;&nbsp;_ZSt4cout </td> 
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如果希望能够Debug标准库中的设施，可在编译时加上开关“**-D\_GLIBCXX\_DEBUG**”。

实际上，即使不能GDB中直接得到std::cout的地址，特别是其成员\_M\_streambuf\_state的地址，但可采取变通的办法取得。

先编写如下一小段代码，然后执行这一小段代码，取得成员\_M\_streambuf\_state和std::cout间的偏移Offset，以方便得到std::cout地址时取得成员\_M\_streambuf\_state的地址，以达到修改成员\_M\_streambuf\_state值的目的。

注意，编译之前需要修改标准库头文件ios\_base.h，将\_M\_streambuf\_state的类型由protected改成public。不然，应当修改小段代码成如下：

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 <td style="vertical-align:top;width:426.1pt;"> #include &lt;stdio.h&gt; #include &lt;iostream&gt; class X: public std::ostream { public: &nbsp;&nbsp;using std::ostream::_M_streambuf_state; }; int main() { &nbsp;&nbsp;X x; &nbsp;&nbsp;const int n = (unsigned long)&amp;x._M_streambuf_state - (unsigned long)&amp;x; &nbsp;&nbsp;printf("offset: %d\n", n); &nbsp;&nbsp;return 0; } </td> 
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当前的多数环境上，offset值一般为**40**。

如果是可执行程序文件，找cout的地址简单多（“0000000000**601280**”即为cout的内存地址）：

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 <td style="vertical-align:top;width:426.1pt;"> # file xxx xxx: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.18, not stripped # objdump -t&nbsp;xxx|grep cout 0000000000601280 g &nbsp;&nbsp;&nbsp;&nbsp;O .bss &nbsp;&nbsp;0000000000000110 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;_ZSt4cout@@GLIBCXX_3.4 </td> 
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这里介绍一种通用的取std::cout地址，及std::cout的\_M\_streambuf\_state成员偏移方式。得到std::cout的地址和成员\_M\_streambuf\_state的偏移，实际也就得到了成员\_M\_streambuf\_state的地址，有了地址就可以控制它了。

首先，编写如下这样的一小段Hook代码：

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 <td style="vertical-align:top;width:426.1pt;"> // hooker.cpp #include &lt;iostream&gt; #include &lt;stdio.h&gt; class Hooker { public: &nbsp;&nbsp;Hooker() &nbsp;&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;// 得到std::cout的成员_M_streambuf_state偏移 &nbsp;&nbsp;&nbsp;&nbsp;const int offset = (unsigned long)&amp;std::cout._M_streambuf_state&nbsp;- (unsigned long)&amp;std::cout; &nbsp;&nbsp;&nbsp;&nbsp;FILE* fp = fopen("/tmp/hooker.txt", "w+"); &nbsp;&nbsp;&nbsp;&nbsp;fprintf(fp, "&amp;std::cout: %p, offset: %d, _M_streambuf_state: %p\n", &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&amp;std::cout, offset, &amp;std::cout+offset); &nbsp;&nbsp;&nbsp;&nbsp;fclose(fp); &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;} }; static Hooker __hooker; </td> 
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这小段代码的目的是为得到std::cout成员\_M\_streambuf\_state的内存地址，以方便在GDB中控制它。将Hook代码编译成共享库：

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 <td style="vertical-align:top;width:426.1pt;"> g++ -g -o libhooker.so -fPIC -shared hooker.cpp </td> 
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如果是64位系统，需要编译成32位的共享库，则编译命令为：

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 <td style="vertical-align:top;width:426.1pt;"> g++ -m32&nbsp;-g -o libhooker.so -fPIC -shared hooker.cpp </td> 
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假设将libhooker.so放在/tmp目录下，先使用GDB进入目标进程，假设目标进程ID为2019，则：

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 <td style="vertical-align:top;width:426.1pt;"> # gdb -p 2019 在GDB中加载共享库，这样共享库中的全局变量的构造函数将执行，从而可从文件/tmp/hooker.txt中得到想要的信息 (gdb) call dlopen("/tmp/libhooker.so",258) (gdb) c &nbsp; 假设/tmp/hooker.txt中std::cout的地址为0xf76f9ec0，成员_M_streambuf_state的偏移为24，则在GDB中可如下查看_M_streambuf_state的值： (gdb) p *(int*)(0xf76f9ec0+24) &nbsp; 也可在GDB中执行如下命令确认： (gdb) info symbol (0xf76f9ec0+24) &nbsp; 可在GDB中执行如下命令修改_M_streambuf_state的值： (gdb) set *(int*)(0xf76f9ec0+24)=1 </td> 
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掌握了Hook方法后，查明原因就十分简单了。这个方法有一个前提，目标进程有链接**libdl.so**，因为它提供了加载共享库函数dlopen的。确认是否链接了libdl.so方法，使用ldd即可：

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 <td style="vertical-align:top;width:426.1pt;"> $ ldd z &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;linux-vdso.so.1 =&gt; &nbsp;(0x00007ffde7822000) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/$LIB/libonion.so =&gt; /lib64/libonion.so (0x00007f4872630000) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;libstdc++.so.6 =&gt; /lib64/libstdc++.so.6 (0x00007f487220f000) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;libm.so.6 =&gt; /lib64/libm.so.6 (0x00007f4871f0d000) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;libgcc_s.so.1 =&gt; /lib64/libgcc_s.so.1 (0x00007f4871cf7000) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;libc.so.6 =&gt; /lib64/libc.so.6 (0x00007f4871933000) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;libdl.so.2 =&gt; /lib64/libdl.so.2 (0x00007f487172f000) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/lib64/ld-linux-x86-64.so.2 (0x00007f4872517000) </td> 
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