Getting sensible information from gdb

From	"Morten W. Petersen" <morphex@gmail.com>
Newsgroups	comp.lang.c
Subject	Getting sensible information from gdb
Date	2015-10-11 21:21 +0200
Organization	Aioe.org NNTP Server
Message-ID	<mvecqu$b25$1@speranza.aioe.org> (permalink)

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Hi.

I'm encountering a segmentation violation in my code, and running
gdb on it doesn't help much, as I can't seem to find out what's
wrong anyway.

The gdb session goes like this:

"""
(gdb) watch count
Hardware watchpoint 2: count
(gdb) break decode_xml.c:934 if count == 5
Breakpoint 3 at 0x804a089: file decode_xml.c, line 934.
(gdb) cont
Continuing.
                 <print_unicode: bfafed50
entry  65,6e,74,72,79,
end print_unicode
 >
print_tree, 2, bfafed7c, 3
                 <print_unicode: bf9fecf0
entry  65,6e,74,72,79,
end print_unicode
 >
print_tree, 2, bf9fed1c, 4
                 <print_unicode: bf8fec90
entry  65,6e,74,72,79,
end print_unicode
 >
print_tree, 2, bf8fecbc, 5

Breakpoint 3, print_tree (start=0x80509c0, level=2, count=5)
     at decode_xml.c:935
935         print_tree(start->next, level, count+1);
(gdb) step

Program received signal SIGSEGV, Segmentation fault.
0x08049ec5 in print_tree (
     start=<error reading variable: Cannot access memory at address 
0xbf7fec5c>, level=2, count=6) at decode_xml.c:914
914     void print_tree(struct xml_element* start, int level, int count) {
(gdb)
"""

And when poking around in gdb after that, I can't see anything
that can be the cause of this error.

The version of the project that gives this error is here:

https://github.com/morphex/smash_xml/tree/25221c21d163ec106abca704b0619e1375e5409c

Is there something I can do to get information of what's going on?

-Morten

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Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-11 21:21 +0200
  Re: Getting sensible information from gdb Geoff <geoff@invalid.invalid> - 2015-10-11 14:47 -0700
    Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 00:07 +0200
      Re: Getting sensible information from gdb Geoff <geoff@invalid.invalid> - 2015-10-11 16:15 -0700
        Re: Getting sensible information from gdb James Kuyper <jameskuyper@verizon.net> - 2015-10-11 21:02 -0400
          Re: Getting sensible information from gdb Geoff <geoff@invalid.invalid> - 2015-10-11 18:55 -0700
            Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 04:04 +0200
              Re: Getting sensible information from gdb Geoff <geoff@invalid.invalid> - 2015-10-11 19:37 -0700
                Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 05:16 +0200
            Re: Getting sensible information from gdb James Kuyper <jameskuyper@verizon.net> - 2015-10-12 00:01 -0400
              Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 06:06 +0200
                Re: Getting sensible information from gdb James Kuyper <jameskuyper@verizon.net> - 2015-10-12 00:48 -0400
                Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 07:08 +0200
          Re: Getting sensible information from gdb Keith Thompson <kst-u@mib.org> - 2015-10-11 18:56 -0700
    Re: Getting sensible information from gdb Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-11 18:14 -0400
      Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 00:20 +0200
        Re: Getting sensible information from gdb James Kuyper <jameskuyper@verizon.net> - 2015-10-11 21:07 -0400
          Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 03:59 +0200
            Re: Getting sensible information from gdb Geoff <geoff@invalid.invalid> - 2015-10-11 23:21 -0700
              Re: Getting sensible information from gdb Geoff <geoff@invalid.invalid> - 2015-10-11 23:32 -0700
                Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 08:42 +0200
                Re: Getting sensible information from gdb Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-12 17:13 +0100
                Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 23:50 +0200
                Re: Getting sensible information from gdb Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-13 01:39 +0100
                Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-13 03:04 +0200
                Re: Getting sensible information from gdb Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-13 14:13 +0100
                Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-13 16:26 +0200
                Re: Getting sensible information from gdb Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-13 17:16 +0100
                Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-13 18:27 +0200
                Re: Getting sensible information from gdb Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-14 00:17 +0100
                Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-14 02:26 +0200
                Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-14 03:59 +0200
                Re: Getting sensible information from gdb Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-14 13:04 +0100
                Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-15 12:48 +0200
              Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 08:41 +0200
      Re: Getting sensible information from gdb Geoff <geoff@invalid.invalid> - 2015-10-11 16:18 -0700
        Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 01:22 +0200
          Re: Getting sensible information from gdb Geoff <geoff@invalid.invalid> - 2015-10-11 16:42 -0700
            Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 02:16 +0200
  Getting sensible information from gdb "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-10-11 18:59 -0700
    Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 04:09 +0200
      Re: Getting sensible information from gdb "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-10-11 19:28 -0700
        Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 04:59 +0200
          Re: Getting sensible information from gdb "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-10-12 07:10 -0700
            Re: Getting sensible information from gdb Rosario19 <Ros@invalid.invalid> - 2015-10-12 19:41 +0200
  Re: Getting sensible information from gdb Ian Collins <ian-news@hotmail.com> - 2015-10-12 17:59 +1300
    Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 07:36 +0200
      Re: Getting sensible information from gdb Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-11 22:59 -0700
        Re: Getting sensible information from gdb "Morten W. Petersen" <morphex@gmail.com> - 2015-10-12 08:27 +0200
          Re: Getting sensible information from gdb Johann Klammer <klammerj@NOSPAM.a1.net> - 2015-10-12 10:55 +0200
          Re: Getting sensible information from gdb Keith Thompson <kst-u@mib.org> - 2015-10-12 08:04 -0700
          Re: Getting sensible information from gdb Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-12 17:35 +0100
      Re: Getting sensible information from gdb Keith Thompson <kst-u@mib.org> - 2015-10-12 08:00 -0700
      Re: Getting sensible information from gdb James Kuyper <jameskuyper@verizon.net> - 2015-10-12 12:25 -0400

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