Date: Sat, 26 Dec 2015 12:59:08 +0100 From: Ivan Radovanovic <radovanovic@gmail.com> To: freebsd-hackers@freebsd.org Subject: Unexpected behavior of dynamic linker Message-ID: <567E810C.3040809@gmail.com>
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Hello, While investigating possibility of building some module system on FreeBSD I stumbled upon unexpected (at least for me) behavior of dynamic linker. I have several (C++) modules organized like this: * main program (executable) * main library (shared object, loaded with RTLD_GLOBAL since it provides symbols for main program and other modules) * module 1 (shared object, loaded with RTLD_LOCAL) I put all private initializations for library and module in (static) global object constructors, but I gave to both classes same (original) name "PrivateClass" (so there is in fact PrivateClass in mainlib.so, and unrelated PrivateClass in module.so). What is happening is that when main program loads main library (via dlopen(3)) its _init calls correctly mainlib::PrivateClass constructor which performs initialization, but when main program later loads module (again via dlopen(3)) its _init doesn't call module::PrivateClass constructor, but rather mainlib::PrivateClass constructor. I understand this is happening because symbols with same name exist in both shared objects and dynamic linker is replacing reference to module::PrivateClass with reference to mainlib::PrivateClass, but I would expect symbol to be looked up outside of module only if it doesn't exist within it (ie, the inner-most definition to be used) - in this case PrivateClass exists within module? Further I am not sure what would be correct solution for this in my case - C++ has static modifier for objects and functions, but not for classes to make them unavailable from other modules and solution with same random namespace name doesn't sound elegant enough :-) Any thoughts regarding this (I can also supply source files to test this behavior)? Kind regards, Ivan
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