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POtypeinfo, shared libraries and dlopen() without RTLD_GLOBAL
 

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    <p>I'm having some trouble with exceptions not functioning correctly (or at least, as I would hope; I know there are issues with this) across shared libraries when loaded using <em>dlopen</em>. I include some simplified example code here. The actual situation is <em>myapp</em>=Matlab, <em>myext1</em>=mexglx matlab extension, <em>mylib</em> is a shared library of my code between the two extensions (<em>myext1</em>, <em>myext2</em>)</p> <p><strong>mylib.h</strong></p> <pre><code>struct Foo { Foo(int a); m_a; } void throwFoo(); </code></pre> <p><strong>mylib.cpp</strong></p> <pre><code>#include "mylib.h" Foo::Foo(int a): m_a(a) {} void throwFoo() { throw Foo(123); } </code></pre> <p><strong>myext1.cpp</strong></p> <pre><code>#include "mylib.h" #include &lt;iostream&gt; extern "C" void entrypoint() { try { throwFoo(); } catch (Foo &amp;e) { std::cout &lt;&lt; "Caught foo\n"; } } </code></pre> <p><strong>myext2.cpp</strong> Identical to myext1.cpp</p> <p><strong>myapp.cpp</strong></p> <pre><code>#include &lt;dlfcn.h&gt; int main() { void *fh1 = dlopen("./myext1.so",RTLD_LAZY); void *fh2 = dlopen("./myext2.so",RTLD_LAZY); void *f1 = dlsym(fh1,"entrypoint"); void *f2 = dlsym(fh2,"entrypoint"); ((void (*)())func1)(); // call myext1 (A) ((void (*)())func2)(); // call myext2 (B) } </code></pre> <p>Compiling this code:</p> <pre><code>g++ mylib.cpp -fPIC -o libmylib.so -shared g++ myext1.cpp -fPIC -o myext1.so -shared -L. -lmylib -Wl,-rpath=. g++ myext2.cpp -fPIC -o myext2.so -shared -L. -lmylib -Wl,-rpath=. g++ myapp.cpp -fPIC -o myapp -ldl </code></pre> <p>The call to <em>entrypoint()</em> at <strong>A</strong> works as expected, with <em>throwFoo()</em> throwing the exception and <em>entrypoint()</em> catching it. The call at <strong>B</strong> however fails to catch the exception. Adding more diagnostic code shows that the typeinfo for the <em>Foo</em> class differs in the two extensions. Changing the order of the two <em>dlopen</em> calls makes no difference, the second loaded extension fails. </p> <p>I know I can fix this by using <strong>RTLD_GLOBAL</strong> as an additional flag for <em>dlopen</em>, but the application (Matlab) using dlopen is out of my control. Is there anything I can do with <em>mylib</em> or <em>myext1</em>, <em>myext2</em> to fix this problem? </p> <p>I have to avoid using LD flags for runtime (since I cannot control the users running the Matlab binary). Any other suggestions?</p>
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