Re: after upgrade: glibc detected *** /usr/bin/perl: double free or corruption

Peter Daum wrote:
> I recently upgraded a system (as far as perl is concerned from 5.8.8 to 
> 5.10.0). Afterwards I ran into a mysterious problem. I could eventually
 > find a  workaround, but still don't really understand, what is going on.
> 
> After the upgrade, a perl program wouldn't run anymore - it crashed with 
> a message:"*** glibc detected *** /usr/bin/perl: double free or corruption 
> (fasttop): ..." and a memory map suggesting some problem on the heap.
> The crash can be reproduced by the following code:
> 
> 
> use Net::LDAP;
> my $self=Net::LDAP->new("127.0.0.1");
> ($self->{prog_name}= $0) =~ s|^.*/([^/]+)$|$1|;
> 
> # when I put an intermediate variable into the statement:
> 
> $self->{prog_name}= (my $_p= $0) =~ s|^.*/([^/]+)$|$1|;
> 
> the program works again.
> 
> Technically, my problem is solved, but maybe somebody here can shed some 
> light on some questions:
> 
  > - I tried to run the program under the debugger hoping to find, where
>    exactly the error occurs - unfortunately the same program suddenly worked
 >    just  fine, so I ended up putting print statements into the code until I
 >    eventually  found the problematic line. Why can't the crash be reproduced
 >    under the debugger? Would there be an easier way to find the problem?
> 
> - Generally, I still don't understand what's wrong with the original 
>   program code.I didn't try it but I don't think it is anything specific to 
>   Net::LDAP. However, when $self is just some hash reverence ("my $self={}"),
 >   the code also works without any problem.

Actually, it seems like the problem is indeed specific to Net::LDAP; furthermore,
the crash only occurs, if there is a LDAP server running at the specified address.

I still would love to know where exactly the problem is.
Is there a bug somewhere in Perl or in Net::LDAP?
Am I doing something wrong? (well, some might argue that it's a bad to
rely on Net::LDAP::new returning a hash reference and isn't using a key named
"prog_name" ...)

Regards,
                      Peter Daum


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