[user] segfault w/ error 4

[U.Mutlu]

Ian Lance Taylor wrote, On 09/11/2012 07:34 AM:
> On Mon, Sep 10, 2012 at 10:06 PM, U.Mutlu <for-gmane@mutluit.com> wrote:
>
>> recently a server daemon program suddenly started repeatedly crashing.
>> syslog says:
>>   segfault at 7f6d003d5453 ip 00007f6d49c9dd6d sp 00007f6d469c1b60 error 4 in
>> libstdc++.so.6.0.17[7f6d49bff000+e8000]
>>
>> What does "error 4" mean? Is this documented somewhere?
>>
>> Is this an application error or rather an error in libstdc++.so ?
>>
>> The error is not always repeatable, ie. happens occasionally, reason unknown
>> yet.
>>
>> What's the easiest method to locate the bug in this server daemon pgm?
>
> That message does not come from libstdc++.  You neglected to mention
> anything about the system, but that looks like the log from an x86
> Linux kernel when a program crashes.  For the Linux kernel, error 4
> means that this is a user-mode access.
>
> You can get this kind of thing if you pass a NULL pointer to a
> libstdc++ routine that is not expecting one, so this may be a bug in
> your program.  Or it may be a bug in libstdc++.

System is debian 7 (wheezy) w/ latest updates from the debian repository.
The error happens only with the 64-bit version of the system library on multicore systems (amd64).
On 32bit-multicore-systems the error doesn't happen. That's the weird thing.
Any suggestions for locating and fixing the bug are welcome as the program crashes every half hour or so :-(