Hi Jeffrey, Thanks for your response. You are absolutely right regarding to -Wglobal-variable. I would prefer to get some kind of error (linking error?) about two global variables with the same name instead of dynamic loader/linker decision to "merge" them. Thanks, Alexey -----Original Message----- From: Jeffrey Walton [mailto:noloader@xxxxxxxxx] Sent: Thursday, October 21, 2010 5:00 PM To: Alexey Skidanov Cc: gcc-help@xxxxxxxxxxx; skidanovalexey@xxxxxxxxx Subject: Re: Global variable in static library - double free or corruption error Hi Alexey, I saw the same thing in Crypto++ when distributions began porting/packaging as shared object [1, 2]. The mailing list was getting 'double free' reports under obscure circumstances [3]. [2] was a test case to reproduce and looks exactly like your analysis :). Anyway, the fix is to hide the the global TestClass: OLD: TestClass test_var; NEW: TestClass& GetTestClass() { static TestClass test_var; return test_var; } I just opened a feature request for a -Wglobal-variable for this sort of thing: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46097. You might chime in on the issue since the GCC team is contemplating whether the feature is even worth while. I claim it is because this behavior has jumped up a bit a few people in the ass. I was thinking that -Wglobal-variable should be a part of -Wextra, and possibly -Wall. Jeff [1] http://www.cryptopp.com/wiki/Linux#Shared_Objects_and_Globals [2] RTLD_GLOBAL and libcryptopp.so crash, http://groups.google.com/group/cryptopp-users/browse_thread/thread/7eae0 09a4e02e726 [3] Errors with multiple loading cryptopp as shared lib on Linux, http://groups.google.com/group/cryptopp-users/browse_thread/thread/68fbc 22e8c6e2f48 On Thu, Oct 21, 2010 at 7:53 AM, Alexey Skidanov <Alexey.Skidanov@xxxxxxxxxxxx> wrote: > Hello, > We use the gcc 4.1.1 in our project. After some code refactoring > (creating new shared library) the application crashes at exit with > following error: > > *** glibc detected *** : double free or corruption (fasttop) *** > > In order to simulate our application, I created the test one, with two > shared libraries and one static library. The code is below: > > [SNIP] > > Static library defines some global variable (test_var), that during > library linking "injected" into the dynamic library bss segment. > Actually, static.o object file is linked with dynamic1.o and with > dynamic2.o files. > Please, pay attention that constructor and destructor of the SAME > INSTANCE (at address 0x60ca9c) of global variable were called twice - at > each dynamic library start up. Generally, it seems that this is partial > solution of double definition problem during main application linking: > Dynamic linker somehow merges two definition of the same global variable > - but each shared library start up code contains calls of this variable > constructor and destructor. > > I would expect that TWO different instances of the global variable would > be created in TWO different shared libraries - maybe with name mangling. > > > Is this a linker/loader bug? Can we cause (by linker/loader options) > linker/loader more consistent behavior? > > Thanks, > Alexey > >
