Debugging C Program

[ghempton]

I am trying to compile vnc reflector, SourceForge.net: VNC Reflector, from source on Ubuntu 8.10. Everything compiles successfully, but after someone connects I get the following output:

Starting program: /usr/local/vnc_reflector/vncreflector -q -p pass -T 9 -f 3 -l 5900 hosts
/usr/local/vnc_reflector/vncreflector: error opening log file (ignoring this error)
29/03/09 22:22:44 + Starting VNC Reflector 1.2.4
29/03/09 22:22:44 + Listening for host connections on port 5580
29/03/09 22:22:59 + Accepted host connection from 192.168.1.25
29/03/09 22:22:59 * Protocol sub-version does not match (ignoring)
*** buffer overflow detected ***: /usr/local/vnc_reflector/vncreflector terminated
======= Backtrace: =========
/lib/libc.so.6(__fortify_fail+0x37)[0x7f220efa5887]
/lib/libc.so.6[0x7f220efa3750]
/lib/libc.so.6[0x7f220efa2af9]
/lib/libc.so.6(_IO_default_xsputn+0x96)[0x7f220ef1e236]
/lib/libc.so.6(_IO_vfprintf+0x63b)[0x7f220eeedceb]
/lib/libc.so.6(__vsprintf_chk+0x99)[0x7f220efa2b99]
/lib/libc.so.6(__sprintf_chk+0x80)[0x7f220efa2ae0]
/usr/local/vnc_reflector/vncreflector[0x403dc2]
/usr/local/vnc_reflector/vncreflector[0x405457]
/usr/local/vnc_reflector/vncreflector[0x402992]
/lib/libc.so.6(__libc_start_main+0xe6)[0x7f220eec4466]
/usr/local/vnc_reflector/vncreflector[0x401e29]
======= Memory map: ========
[snip]
7fff1785e000-7fff17873000 rw-p 7ffffffea000 00:00 0 [stack]
7fff179ff000-7fff17a00000 r-xp 7fff179ff000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]

This happens ONLY when it is compiled with the -O2 flag. Otherwise, it appears to work fine. What is the best practice for debugging this? I have compiled the source with the -g flag and started it up in gdb, but I am not sure where to proceed from there. I was hoping to see some line numbers or something.

Thanks in advance,
-Gordon

[gerard4143]

Try this GDB tutorial:

gdb Tutorial

Gerard4143