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5.8.1.5 Using a Stack Trace

On some operating systems, the error log contains a stack trace ifmysqld dies unexpectedly. You can use this to find out where (and maybe why)mysqld died. SeeSection 5.4.2, “The Error Log”. To get a stack trace, you must not compilemysqld with the-fomit-frame-pointer option to gcc. SeeSection 5.8.1.1, “Compiling MySQL for Debugging”.

A stack trace in the error log looks something like this:

mysqld got signal 11;Attempting backtrace. You can use the following informationto find out where mysqld died. If you see no messages afterthis, something went terribly wrong...stack_bottom = 0x41fd0110 thread_stack 0x40000mysqld(my_print_stacktrace+0x32)[0x9da402]mysqld(handle_segfault+0x28a)[0x6648e9]/lib/libpthread.so.0[0x7f1a5af000f0]/lib/libc.so.6(strcmp+0x2)[0x7f1a5a10f0f2]mysqld(_Z21check_change_passwordP3THDPKcS2_Pcj+0x7c)[0x7412cb]mysqld(_ZN16set_var_password5checkEP3THD+0xd0)[0x688354]mysqld(_Z17sql_set_variablesP3THDP4ListI12set_var_baseE+0x68)[0x688494]mysqld(_Z21mysql_execute_commandP3THD+0x41a0)[0x67a170]mysqld(_Z11mysql_parseP3THDPKcjPS2_+0x282)[0x67f0ad]mysqld(_Z16dispatch_command19enum_server_commandP3THDPcj+0xbb7[0x67fdf8]mysqld(_Z10do_commandP3THD+0x24d)[0x6811b6]mysqld(handle_one_connection+0x11c)[0x66e05e]

If resolution of function names for the trace fails, the trace contains less information:

mysqld got signal 11;Attempting backtrace. You can use the following informationto find out where mysqld died. If you see no messages afterthis, something went terribly wrong...stack_bottom = 0x41fd0110 thread_stack 0x40000[0x9da402][0x6648e9][0x7f1a5af000f0][0x7f1a5a10f0f2][0x7412cb][0x688354][0x688494][0x67a170][0x67f0ad][0x67fdf8][0x6811b6][0x66e05e]

In the latter case, you can use theresolve_stack_dump utility to determine wheremysqld died by using the following procedure:

  1. Copy the numbers from the stack trace to a file, for examplemysqld.stack. The numbers should not include the surrounding square brackets:

    0x9da4020x6648e90x7f1a5af000f00x7f1a5a10f0f20x7412cb0x6883540x6884940x67a1700x67f0ad0x67fdf80x6811b60x66e05e

  2. Make a symbol file for themysqld server:

    $> nm -n libexec/mysqld > /tmp/mysqld.sym

    Ifmysqld is not linked statically, use the following command instead:

    $> nm -D -n libexec/mysqld > /tmp/mysqld.sym

    If you want to decode C++ symbols, use the--demangle, if available, tonm. If your version ofnm does not have this option, you must use thec++filt command after the stack dump has been produced to demangle the C++ names.

  3. Execute the following command:

    $> resolve_stack_dump -s /tmp/mysqld.sym -n mysqld.stack

    If you were not able to include demangled C++ names in your symbol file, process theresolve_stack_dump output usingc++filt:

    $> resolve_stack_dump -s /tmp/mysqld.sym -n mysqld.stack | c++filt

    This prints out wheremysqld died. If that does not help you find out whymysqld died, you should create a bug report and include the output from the preceding command with the bug report.

    However, in most cases it does not help us to have just a stack trace to find the reason for the problem. To be able to locate the bug or provide a workaround, in most cases we need to know the statement that killedmysqld and preferably a test case so that we can repeat the problem! SeeSection 1.5, “How to Report Bugs or Problems”.

Newer versions ofglibc stack trace functions also print the address as relative to the object. Onglibc-based systems (Linux), the trace for an unexpected exit within a plugin looks something like:

plugin/auth/auth_test_plugin.so(+0x9a6)[0x7ff4d11c29a6]

To translate the relative address (+0x9a6) into a file name and line number, use this command:

$> addr2line -fie auth_test_plugin.so 0x9a6auth_test_pluginmysql-trunk/plugin/auth/test_plugin.c:65

Theaddr2line utility is part of thebinutils package on Linux.

On Solaris, the procedure is similar. The Solarisprintstack() already prints relative addresses:

plugin/auth/auth_test_plugin.so:0x1510

To translate, use this command:

$> gaddr2line -fie auth_test_plugin.so 0x1510mysql-trunk/plugin/auth/test_plugin.c:88

Windows already prints the address, function name and line:

000007FEF07E10A4 auth_test_plugin.dll!auth_test_plugin()[test_plugin.c:72]