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Date:	Sun, 24 Jan 2010 12:24:20 +0000
From:	Dave Korn <dave DOT korn DOT cygwin AT googlemail DOT com>
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Subject:	Re: question on gdb
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On 24/01/2010 07:42, Marco Atzeri wrote:

> My question however is about the gdb backtrace, is the 
> "Cannot access memory at address 0x1a" at # 9 normal ?

  I wouldn't read too much into it.  Could indicate that there's some kind of
corruption at the top end of the stack, or it could just be gdb getting
confused about a value that was in a register at the start of execution but
has long since been lost.


> Program received signal SIGSEGV, Segmentation fault.
> 0x20f414d0 in ?? ()
> (gdb) backtrace
> #0  0x20f414d0 in ?? ()
> #1  0x6112e117 in __call_exitprocs () from /usr/bin/cygwin1.dll
> #2  0x6110b6da in exit () from /usr/bin/cygwin1.dll
> #3  0x61004e5a in cygwin_exit () from /usr/bin/cygwin1.dll
> #4  0x610b6838 in _sigfe () from /usr/bin/cygwin1.dll
> #5  0x0022bba8 in ?? ()
> #6  0x6c4e401e in cygstdc++-6!_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc ()
>    from /usr/bin/cygstdc++-6.dll
> #7  0x6e5c8c65 in _fu4930___ZSt4cerr () at ../../octave_clone/src/toplev.cc:625
> #8  0x6e58fd9c in _fu4441___ZN8file_ops14static_members8instanceE ()
>     at ../../octave_clone/src/octave.cc:876
> #9  0x00401167 in main (argc=Cannot access memory at address 0x1a
> ) at ../../octave_clone/src/main.c:35

  Looks like maybe an exception was thrown in ostream::operator<<(const
char*).  Looks also like somewhere up the stack is
file_ops::static_members::instance(), and it's quite possibly trying to print
something to std::cerr.  Possibly a NULL pointer?

  Also, you want to set breakpoints on __call_exitprocs and on atexit, and see
what functions are getting registered, whether there's a corrupt entry
pointing at 0x20f414d0 or whether one of the exitprocs is going astray and
jumping into space.

    cheers,
      DaveK

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