backtrace shows ?? instead of function names in gdb

backtrace shows ?? instead of function names in gdb

[Saurabh Thukral]

Hi all,

While debugging a core file produced by a program, I found the
following backtrace:
#0  0x0000000000000000 in ?? ()
#1  0x000000010009e4c0 in stMesg ()
#2  0x000000010009e380 in stMhandler ()
#3  0x000000010088351c in stSchedule ()
#4  0x000000010087bd5c in stRun()
#5  0x000000010008c030 in main ()

I am unable to understand the reason for gdb displaying ??() in frame
#0 instead of a valid function name.

System: SunOS 5.10 64 bit
             gdb version 5.3. This problem is encountered in gdb
version 6.1 also.

I tried to find a post related to this problem and came across the
following post:
http://sourceware.org/ml/gdb/2007-03/msg00167.html. The reason that
was posted is reproduced below:

>Because GDB could not figure out what came next.  The library might be
>too optimized and stripped, or the stack might be corrupt, or GDB
>might have a bug, or some other operating system specific problem.

I have a few queries
1. What is the meaning of too optimized ? Should we avoid compiling
with highest level of optimisation - in that case we will be forgoing
performance ?
2. Please suggest a solution by which such backtraces can be avoided ?

Please help,
Thanks,
Saurabh

Re: backtrace shows ?? instead of function names in gdb

[Andreas Schwab]

"Saurabh Thukral" <saurabhth@gmail.com> writes:

> Hi all,
>
> While debugging a core file produced by a program, I found the
> following backtrace:
> #0  0x0000000000000000 in ?? ()

That looks like an indirect call through a NULL function pointer.  Never
a valid function, thus it never has a name.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: backtrace shows ?? instead of function names in gdb

[Saurabh Thukral]

>
> That looks like an indirect call through a NULL function pointer.  Never
> a valid function, thus it never has a name.
>
> Andreas.
>
> --
> Andreas Schwab, SuSE Labs, schwab@suse.de
> SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
> PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
> "And now for something completely different."
>

Hi Andreas,

Thanks for the prompt response.
I will investigate this matter by doing code review.

Whether this is the only reason that such a peculiar backtrace is
produced ? If you refer to the link given in my original post, the
answer posted states several reasons.

Saurabh