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c++segmentation-faultmariadbconnector

Segfault Occurs when using MariaDB c++ connector and regex

I'm building a simple utility program that queries a mysql database, and uses regex to isolate strings in the table data.

I'm using MariaDB c++/connector, and the latest versions of MariaDB. The code was copied from the MariaDB website. I have simplified the software to illustrate the problem. See below:

// g++ -o mariadb_connect mariadb_connect.cpp -lmariadbcpp
// From https://mariadb.com/docs/clients/connector-cpp/
// with three additional lines that cause segfault

#include <iostream>
#include <mariadb/conncpp.hpp>

#include <regex>    // <-- Added to the example

int main()
{
   try
   {
      // Instantiate Driver
      sql::Driver* driver = sql::mariadb::get_driver_instance();

      // Configure Connection
      // The URL or TCP connection string format is
      // ``jdbc:mariadb://host:port/database``.
      sql::SQLString url("jdbc:mariadb://localhost:3306/??????");

      // Use a properties map for the user name and password
      sql::Properties properties({
            {"user", "???????"},
            {"password", "????????"}
         });

      // Establish Connection
      // Use a smart pointer for extra safety
      std::unique_ptr<sql::Connection> conn(driver->connect(url, properties));

      // Use Connection
      std::cout << "Using the connection" << std::endl; // <-- Added

      std::regex regexp("(faststatic.com)(.*)");    // <-- Added (Causes segfault)

      // Close Connection
      conn->close();
   }

   // Catch Exceptions
   catch (sql::SQLException& e)
   {
      std::cout << "Error Connecting to MariaDB Platform: "
         << e.what() << std::endl;

      // Exit (Failed)
      return 1;
   }

   // Exit (Success)
   return 0;
}

(???? used for private data)

Compiled with g++ on an AWS EC2 instance running Amazon Linux 2 AMI.

Compiles fine and runs fine until I added the std::regex regexp(...) line. It still compiles fine with the addition, but on execution calls a segfault.

I have used gdb which provides the following output with breakpoint set to main.

(gdb) b main
Breakpoint 1 at 0x40404b: file mariadb_connect.cpp, line 15.
(gdb) run
Starting program: /home/msellers/proj/preload_images/spike/mariadb_connect
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Program received signal SIGSEGV, Segmentation fault.
0x000000000064a588 in ?? ()

Here is the output of the gdb bt command after the segfault:

(gdb) bt
#0  0x000000000064a588 in ?? ()
#1  0x0000000000409155 in std::__detail::_Scanner<char>::_M_scan_normal (this=0x7fffffffe018) at /usr/include/c++/7/bits/regex_scanner.tcc:119
#2  0x00000000004084a1 in std::__detail::_Scanner<char>::_M_advance (this=0x7fffffffe018) at /usr/include/c++/7/bits/regex_scanner.tcc:80
#3  0x00007ffff7c3e060 in std::__detail::_Compiler<std::regex_traits<char> >::_M_match_token (this=this@entry=0x7fffffffe000, token=std::__detail::_ScannerBase::_S_token_subexpr_begin) at /usr/local/include/c++/4.9.4/bits/regex_compiler.tcc:541
#4  0x00007ffff7c513a2 in std::__detail::_Compiler<std::regex_traits<char> >::_M_match_token (token=std::__detail::_ScannerBase::_S_token_subexpr_begin, this=0x7fffffffe000) at /usr/local/include/c++/4.9.4/bits/regex_compiler.tcc:316
#5  std::__detail::_Compiler<std::regex_traits<char> >::_M_atom (this=this@entry=0x7fffffffe000) at /usr/local/include/c++/4.9.4/bits/regex_compiler.tcc:326
#6  0x00007ffff7c515b0 in std::__detail::_Compiler<std::regex_traits<char> >::_M_term (this=0x7fffffffe000) at /usr/local/include/c++/4.9.4/bits/regex_compiler.tcc:136
#7  std::__detail::_Compiler<std::regex_traits<char> >::_M_alternative (this=0x7fffffffe000) at /usr/local/include/c++/4.9.4/bits/regex_compiler.tcc:118
#8  0x00007ffff7c51809 in std::__detail::_Compiler<std::regex_traits<char> >::_M_disjunction (this=this@entry=0x7fffffffe000) at /usr/local/include/c++/4.9.4/bits/regex_compiler.tcc:97
#9  0x00007ffff7c51e18 in std::__detail::_Compiler<std::regex_traits<char> >::_Compiler (this=0x7fffffffe000, __b=<optimized out>, __e=<optimized out>, __traits=..., __flags=<optimized out>)
    at /usr/local/include/c++/4.9.4/bits/regex_compiler.tcc:82
#10 0x00007ffff7c5222d in std::__detail::__compile_nfa<std::regex_traits<char> > (__first=<optimized out>, __last=<optimized out>, __traits=..., __flags=<optimized out>) at /usr/local/include/c++/4.9.4/bits/regex_compiler.h:158
#11 0x00007ffff7c524da in std::basic_regex<char, std::regex_traits<char> >::basic_regex<char const*> (__f=<optimized out>, __last=<optimized out>, __first=<optimized out>, this=0x7ffff7dc2a40 <sql::mariadb::UrlParser::URL_PARAMETER>)
    at /usr/local/include/c++/4.9.4/bits/regex.h:540
#12 std::basic_regex<char, std::regex_traits<char> >::basic_regex (this=0x7ffff7dc2a40 <sql::mariadb::UrlParser::URL_PARAMETER>, __p=<optimized out>, __f=<optimized out>) at /usr/local/include/c++/4.9.4/bits/regex.h:452
#13 0x00007ffff7c331ee in __static_initialization_and_destruction_0 (__initialize_p=1, __priority=65535) at /home/buildbot/src/src/UrlParser.cpp:34
#14 _GLOBAL__sub_I_UrlParser.cpp(void) () at /home/buildbot/src/src/UrlParser.cpp:444
#15 0x00007ffff7de7dc2 in call_init (l=<optimized out>, argc=argc@entry=1, argv=argv@entry=0x7fffffffe2b8, env=env@entry=0x7fffffffe2c8) at dl-init.c:72
#16 0x00007ffff7de7eb6 in call_init (env=0x7fffffffe2c8, argv=0x7fffffffe2b8, argc=1, l=<optimized out>) at dl-init.c:119
#17 _dl_init (main_map=0x7ffff7ffe130, argc=1, argv=0x7fffffffe2b8, env=0x7fffffffe2c8) at dl-init.c:120
#18 0x00007ffff7dd9f2a in _dl_start_user () from /lib64/ld-linux-x86-64.so.2
#19 0x0000000000000001 in ?? ()
#20 0x00007fffffffe520 in ?? ()
#21 0x0000000000000000 in ?? ()
(gdb)

Does this help?

Mark

Solution

  • GCC version 7.3.1

    In the backtrace, we see that the crash is happening in the GCC-7 regexp implementation:

    #1  0x0000000000409155 in std::__detail::_Scanner<char>::_M_scan_normal (this=0x7fffffffe018) at /usr/include/c++/7/bits/regex_scanner.tcc:119

    We also see that this crash is happening while some global inside (presumably1) MariaDB connector is being initialized, while using GCC-4.9.4 version of libstdc++:

    #12 std::basic_regex<char, std::regex_traits<char> >::basic_regex (this=0x7ffff7dc2a40 <sql::mariadb::UrlParser::URL_PARAMETER>, __p=<optimized out>, __f=<optimized out>) at /usr/local/include/c++/4.9.4/bits/regex.h:452
#13 0x00007ffff7c331ee in __static_initialization_and_destruction_0 (__initialize_p=1, __priority=65535) at /home/buildbot/src/src/UrlParser.cpp:34

    It is exceedingly likely that this 4.9.4 vs. 7.3.1 mismatch is the cause of the crash, and that either building the app with g++-4.9.4 or building the MariaDB with g++-7.3.1 will fix the problem.

    In theory GCC version of libstdc++ should be backwards compatible, but verifying ABI compatibility in C++ is quite hard, and many mistakes have been made. Also, g++4.9.4 is ancient.

    Another possible solution is to build the application with clang using libc++ -- this will avoid any possibility of symbol conflicts2.

    1 You can verify whether frame #13 is really coming from the MariaDB by executing these GDB commands: frame 13, info symbol $pc.

    2 To achieve this, you may need to explicitly tell clang to use libc++, as it may default to using libstdc++. Use clang++ -stdlib=libc++ ... to be sure. Documentation here.