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Difference between revisions of "Debugging"

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(Created page with "== Reporting bugs == Steps to do when you think you found a bug: * verify the bug exists in the latest version [https://github.com/znc/znc (Git)] * report it at [https://git...")
 
(Tracing crash bugs)
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<pre>
 
<pre>
 
gdb ./znc
 
gdb ./znc
run
+
handle SIGPIPE nostop
 +
run -D
 
</pre>
 
</pre>
  

Revision as of 17:29, 29 December 2011

Reporting bugs

Steps to do when you think you found a bug:

  • verify the bug exists in the latest version (Git)
  • report it at Github


Tracing crash bugs

Configure your ZNC version with --enable-debug.

./configure --enable-debug --enable-other-things-you-may-want
make

Then you can run ZNC under gdb:

gdb ./znc
handle SIGPIPE nostop
run -D

Now you use ZNC as you would always do and try to make it crash. Once it crashed, gdb will show you something like this:

Program received signal SIGSEGV, Segmentation fault.

Now we can get the useful info. This info, together with an explanation how the bug happened are then very useful to the developers.

bt full

Why use --enable-debug?

With this flag ZNC is compiled with some special flag: -ggdb So where's the difference?

Lets assume the code has a bug and does segfault. First we compile it without -ggdb and run it in GDB


Starting program: /znc/znc

Program received signal SIGSEGV, Segmentation fault.
0x0812d9a6 in CZNC::ParseConfig ()
(gdb) bt full
#0  0x0812d9a6 in CZNC::ParseConfig ()
	__ioinit = {static _S_refcount = <optimized out>, static _S_synced_with_stdio = <optimized out>}
	std::string::_Rep::_S_terminal = 0 '\0'
	std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::id = {_M_index = 5, 
  static _S_refcount = <optimized out>}
	std::string::_Rep::_S_empty_rep_storage = {0, 0, 0, 0}
	std::num_get<char, std::istreambuf_iterator<char, std::char_traits<char> > >::id = {_M_index = 4, 
  static _S_refcount = <optimized out>}
	std::numpunct<char>::id = {_M_index = 3, static _S_refcount = <optimized out>}
#1  0x0811ba35 in main ()
	__ioinit = {static _S_refcount = <optimized out>, static _S_synced_with_stdio = <optimized out>}
	std::string::_Rep::_S_empty_rep_storage = {0, 0, 0, 0}
	std::string::_Rep::_S_terminal = 0 '\0'
	std::numpunct<char>::id = {_M_index = 3, static _S_refcount = <optimized out>}

And now again with -ggdb

Starting program: /znc/znc

Program received signal SIGSEGV, Segmentation fault.
0x0813cbae in CZNC::ParseConfig (this=0x8256930, sConfig=@0xbf88f710) at znc.cpp:846
846		*i = 42;
(gdb) bt full
#0  0x0813cbae in CZNC::ParseConfig (this=0x8256930, sConfig=@0xbf88f710) at znc.cpp:846
	s = {<std::basic_string<char,std::char_traits<char>,std::allocator<char> >> = {static npos = 4294967295, 
    _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, 
      _M_p = 0x824c94c ""}}, _vptr.CString = 0x8249a78}
	i = (int *) 0x0
#1  0x08125945 in main (argc=1, argv=0xbf88f884) at main.cpp:190
	sConfig = {<std::basic_string<char,std::char_traits<char>,std::allocator<char> >> = {static npos = 4294967295, 
    _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, 
      _M_p = 0x825691c "znc.conf"}}, _vptr.CString = 0x8249a78}
	sDataDir = {<std::basic_string<char,std::char_traits<char>,std::allocator<char> >> = {static npos = 4294967295, 
    _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, 
      _M_p = 0x824c94c ""}}, _vptr.CString = 0x8249a78}
	iArg = -1
	iOptIndex = -1
	bMakeConf = false
	bMakePass = false
	bMakePem = false
	bEncPem = false
	pZNC = (class CZNC *) 0x8256930
	iPid = 136338569
	sa = {__sigaction_handler = {sa_handler = 0x1, sa_sigaction = 0x1}, sa_mask = {__val = {815, 3083576408, 3083575368, 134723832, 
      3082340416, 134607268, 1, 3086254020, 3086256136, 3213424396, 3213424424, 3086182628, 134607268, 3213424396, 3086256044, 7, 
      3083576408, 1, 0, 1, 1300, 3083576840, 3083575368, 3084744097, 3213424408, 3086181320, 3082362303, 3213424464, 3086255696, 
      134723832, 725871085, 0}}, sa_flags = -1208713276, sa_restorer = 0xb7b83c60}
	iRet = -1209189020

As you notice the second attempt shows the source of the problem better than the first one. The first one only mentions 0 and <optimized out>. In this example you can even see exactly why the crash happened, without looking at the source code!