Debugging Symbols

Debugging symbols

If you ever need to install packages with debugging symbols, you need to modify your /etc/apt/sources.lists.d/<ppa>-<dist>.list to contain main/debug component in addition to main:

Example for ppa:ondrej/php for Ubuntu 14.04 Trusty Tahr:

# cat /etc/apt/sources.list.d/ondrej-php-trusty.list
deb http://ppa.launchpad.net/ondrej/php/ubuntu trusty main
deb http://ppa.launchpad.net/ondrej/php/ubuntu trusty main/debug
# deb-src http://ppa.launchpad.net/ondrej/php/ubuntu trusty main

After apt-get update you can apt-get install <phpX.Y-foo>-dbgsym, f.e.: apt-get install php-mongodb-dbgsym php7.0-fpm-dbgsym php7.0-common-dbgsym.

Please note that while dbgsym packages are supported in Ubuntu, there are some packages that use older way of putting all debug symbols into '-dbg' package. Always use apt-cache search <package> dbg to lookup whether there is a manual debug symbol package or not.

That would allow you together with libc6-dbg and cyrus-sasl2-dbg packages to create much nicer bt full backtrace:

# apt-get install php-mongodb-dbgsym php7.0-fpm-dbgsym php7.0-common-dbgsym libc6-dbg cyrus-sasl2-dbg
# [...]
# gdb /usr/sbin/php-fpm7.0
(gdb) run -t
Starting program: /usr/sbin/php-fpm7.0 -t
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[15-Mar-2016 15:07:01] NOTICE: configuration file /etc/php/7.0/fpm/php-fpm.conf test is successful


Program received signal SIGSEGV, Segmentation fault.
zend_mm_free_heap (ptr=<optimized out>, heap=<optimized out>) at /build/php7.0-CpkoVe/php7.0-7.0.4/Zend/zend_alloc.c:1400
1400	/build/php7.0-CpkoVe/php7.0-7.0.4/Zend/zend_alloc.c: No such file or directory.
(gdb) bt full
#0  zend_mm_free_heap (ptr=<optimized out>, heap=<optimized out>) at /build/php7.0-CpkoVe/php7.0-7.0.4/Zend/zend_alloc.c:1400
        chunk = 0x555555a00000
        info = 1438578080
        page_offset = 495
#1  _efree (ptr=0x555555bef3f0) at /build/php7.0-CpkoVe/php7.0-7.0.4/Zend/zend_alloc.c:2458
No locals.
#2  0x00007ffff32ccc85 in sasl_common_done () at ../../lib/common.c:686
No locals.
#3  0x00007ffff32c9d41 in sasl_client_done () at ../../lib/client.c:101
        result = 0
#4  0x00007ffff3519bbe in _mongoc_do_cleanup () at /build/php-mongodb-xrFNrX/php-mongodb-1.1.4/mongodb-1.1.4/src/libmongoc/src/mongoc/mongoc-init.c:130
No locals.
#5  0x00007ffff5e1aa90 in pthread_once () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_once.S:103
No locals.
#6  0x00007ffff7dea73a in _dl_fini () at dl-fini.c:252
        array = 0x7ffff3757df0
        i = 1
        nmaps = 56
        nloaded = <optimized out>
        i = 18
        l = 0x555555bce920
        ns = 0
        maps = 0x7fffffffde50
        maps_size = 448
        do_audit = 0
        __PRETTY_FUNCTION__ = "_dl_fini"
#7  0x00007ffff5a84259 in __run_exit_handlers (status=status@entry=0, listp=0x7ffff5e066c8 <__exit_funcs>, run_list_atexit=run_list_atexit@entry=true) at exit.c:82
        atfct = <optimized out>
        onfct = <optimized out>
        cxafct = <optimized out>
        f = <optimized out>
#8  0x00007ffff5a842a5 in __GI_exit (status=status@entry=0) at exit.c:104
No locals.
#9  0x0000555555824922 in fpm_init (argc=<optimized out>, argv=<optimized out>, config=<optimized out>, prefix=<optimized out>, pid=<optimized out>, test_conf=1, run_as_root=0, force_daemon=-1, force_stderr=0)
    at /build/php7.0-CpkoVe/php7.0-7.0.4/sapi/fpm/fpm/fpm.c:72
        __func__ = "fpm_init"
#10 0x0000555555632546 in main (argc=2, argv=0x7fffffffe578) at /build/php7.0-CpkoVe/php7.0-7.0.4/sapi/fpm/fpm/fpm_main.c:1863
        exit_status = 0
        c = -1
        use_extended_info = 0
        file_handle = {handle = {fd = 1, fp = 0x1, stream = {handle = 0x1, isatty = -134252512, mmap = {len = 140737354101960, pos = 140737351928209, map = 0x0, buf = 0x7ffff7fecab8 "\271[\275\367\377\177", old_handle = 0x1, 
                old_closer = 0x0}, reader = 0x1, fsizer = 0x7ffff7ff74c8, closer = 0x0}}, filename = 0x555555b81020 "", opened_path = 0x555555b81028, type = 1438126104, free_filename = 85 'U'}
        orig_optind = 1
        orig_optarg = 0x0
        ini_entries_len = 0
        max_requests = 500
        requests = 0
        fcgi_fd = 0
        fpm_config = 0x0
        fpm_prefix = 0x0
        fpm_pid = 0x0
        test_conf = 1
        force_daemon = -1
        force_stderr = 0
        php_information = 0
        php_allow_to_run_as_root = 0
        __func__ = "main"

This is example of php-mongodb segfault after the libsasl2 library call.