Re: Need help with a backtrace

[Fernando Nasser <fnasser@cygnus.com>]

Matt Schalit wrote:
> 
> In general, when a backtrace gives a really meager output
> like the following:
> 
> > > (gdb) file /usr/local/cgi-bin/convert
> > > (gdb) run
> > > Program received signal SIGSEGV, Segmentation fault.
> > > 0x80016d76 in ?? () from /usr/lib/libc.so.1
> > > (gdb) bt
> > > #0  0x80016d76 in ?? () from /usr/lib/libc.so.1
> > > #1  0x80016c5c in ?? () from /usr/lib/libc.so.1
> > > #2  0x8001826d in ?? () from /usr/lib/libc.so.1
> > > #3  0x8001932d in ?? () from /usr/lib/libc.so.1
> > > #4  0x80014b20 in ?? () from /usr/lib/libc.so.1
> 
> and that's all the lines it output, am I supposed to
> put breakpoints into my convert program to see when
> it makes a call to a libc function?  I can't understand
> why there's so little info nor why it left out the function
> values.
> 


These addresses are inside the libc.so that was probably compiled without debugging symbols.  That is why the debugger cannot give you more information.

Unless you are dealing with a bug in libc (very unlikely), just forget about these lines and check how your program called the library function.  Probably it called it with a bad argument and causes the crash.


-- 
Fernando Nasser
Red Hat - Toronto                       E-Mail:  fnasser@redhat.com
2323 Yonge Street, Suite #300
Toronto, Ontario   M4P 2C9