On Wed, Jul 27, 2016 at 12:39:13AM +0000, Allen Samuels wrote:
> I don't think is the problem that John and Kefu described.
>
> Seems that the problem is that there are two dynamic libraries that think each one of them is responsible for static run-time initialization of the same global variable. This violates the "One Definition Rule".
I agree, I believe this is a violation of the ODR as well.
>
> I'm guessing that the source of the problem is that the AsyncMessager.cc file is included twice, one in each library. If so, then the solution is to break out the offending *.cc file into a separate third library that's linked in the right combination with the others so that there's no duplication.
>
I believe the problem can also be solved with a static member function or a
wrapper function for the static variable. I tried this and it appears to
resolve the issue.
It would be possible to audit use of such variables using nm or objdump but
this might be a bit difficult to maintain?
Since this is easy to reproduce it would also be simple to write a test to
check for this specific issue along the lines of the following.
$ g++ -O2 -x c++ - -Wl,--rpath=./lib -L./lib -lrados -lcephfs<<EOF
int main(int, char**)
{
return 0;
}
EOF
./a.out
*** Error in `./a.out': double free or corruption (fasttop): 0x0000000000ad45c0 ***
...
Aborted (core dumped)
I'd be happy to create a test that covers this case if we think it is worthwhile?
> I have no idea why this appears to work with autotools.
>
>
> Allen Samuels
> SanDisk |a Western Digital brand
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> allen.samuels@xxxxxxxxxxx
>
> > -----Original Message-----
> > From: ceph-devel-owner@xxxxxxxxxxxxxxx [mailto:ceph-devel-
> > owner@xxxxxxxxxxxxxxx] On Behalf Of Jesse Williamson
> > Sent: Tuesday, July 26, 2016 5:12 PM
> > To: kefu chai <tchaikov@xxxxxxxxx>
> > Cc: John Spray <jspray@xxxxxxxxxx>; ceph-devel@xxxxxxxxxxxxxxx
> > Subject: Re: static member variable in libcommon and double free
> >
> >
> > Folks,
> >
> > I hope this will help.
> >
> > Three are some issues that you need to know about when you're writing
> > computer programs in C++. Before you decide to change away from the
> > whole
> > structure, consider what it is currently accomplishing.
> >
> > Here is one of them. It may be exactly what you're running in to:
> > https://isocpp.org/wiki/faq/ctors#static-init-order
> >
> > Please feel free to ask questions.
> >
> > -Jesse
> >
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--
Cheers,
Brad
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