[Bug c++/46097] Switch to warn of global variables in a C++ shared object

[noloader at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46097

--- Comment #2 from Jeffrey Walton <noloader at gmail dot com> 2010-10-20 17:33:43 UTC ---
(In reply to comment #1)
> (In reply to comment #0)
> > When a module meets the above compile and runtime requirements, a crash can
> > occur in global objects with destructors when more than one process loads and
> > subsequently unloads a shared object.
> Are you saying independent processes interfere with each other?
Yes and No :/

If each process loads the SO with RTLD_LOCAL, then No. If the processes each
load with RTLD_GLOBAL (so an exception can be caught) *AND* the SO has an
non-trivial global (such as an object with a destructor) then YES.

Crpyto++ has a test case demonstrating the RTLD_GLOBAL crash at [1]. [1] is
accompanied by an analysis under GDB at [2]. Unfortunately, the test case is
not minimal. It is based on the Crypto++ library and needs intermediate SOs to
load the SO of interest. So the final executable never directly loads the
Crypto++ shared object.

Based on the demonstartion, Wei Dai modified global objects so that only PODs
were global. Non-trivial objects were hidden in a GetGlobalXxx() (some hand
waiving). A write up distribution packagers (from our understanding of the
moving parts) is available at [3,4].

[1] http://www.cryptopp.com/w/images/8/89/Cryptopp-SO-Test-1.zip
[2]
http://groups.google.com/group/cryptopp-users/browse_thread/thread/7eae009a4e02e726
[3] http://www.cryptopp.com/wiki/Linux#Note_for_Shared_Object_Callers
[4] http://www.cryptopp.com/wiki/Linux#Note_for_Distribution_Packagers