Re: g++: -fno-rtti breaks polymorphic catch on dynamic library
Re: g++: -fno-rtti breaks polymorphic catch on dynamic library
- Subject: Re: g++: -fno-rtti breaks polymorphic catch on dynamic library
- From: Andrew Pinski <email@hidden>
- Date: Fri, 3 Sep 2010 11:54:17 -0700
On Sep 3, 2010, at 11:33 AM, "Pedro d'Aquino" <email@hidden> wrote:
Hello,
This is my first time posting on one of Apple's mailing lists, so
please forgive me if I'm in the wrong place. I did look for a gcc-
specific mailing list but could not find any.
I'm building a shared library with f-no-rtti. Internally, this
library throws 'std:invalid_argument' and catches 'std::exception',
but the catch clause is never entered.
Stop right there. Exceptions require rtti info to figure out what the
types are so compiling with -fno-rtti will break exceptions.
The following code reproduces the problem (g++ 4.2, Mac OS X 10.6):
// library.cpp: exports f(), compiled with -fno-rtti
#include <stdexcept>
#include <iostream>
extern "C" {
void f() {
try {
throw std::invalid_argument("std::exception handler");
} catch( std::exception& e) {
std::cout << e.what() << "\n";
} catch(...) {
std::cout << "... handler\n";
}
}
}
----------
// main.cpp: the main executable, dynamically loads the library
#include <dlfcn.h>
typedef void(*fPtr)();
int main() {
void* handle = dlopen( "./libexception_problem.dylib",
RTLD_LAZY );
fPtr p_f = reinterpret_cast<fPtr>( dlsym( handle, "f" ) );
p_f();
}
----------
Output:
MacBook-Pro:teste pfranco$ # works fine with rtti
MacBook-Pro:teste pfranco$ g++ -c library.cpp && g++ -shared -o
libexception_problem.dylib library.o && g++ main.cpp -o main && ./main
std::exception handler
MacBook-Pro:teste pfranco$ # breaks with -fno-rtti
MacBook-Pro:teste pfranco$ g++ -c -fno-rtti library.cpp && g++ -
shared -o libexception_problem.dylib library.o && g++ -fno-rtti
main.cpp -o main && ./main
... handler
MacBook-Pro:teste pfranco$ #-no_dead_strip_inits_and_terms
doesn't change anything
MacBook-Pro:teste pfranco$ g++ -c -no_dead_strip_inits_and_terms
-fno-rtti library.cpp && g++ -no_dead_strip_inits_and_terms -shared -
o libexception_problem.dylib library.o && g++ -fno-rtti -
no_dead_strip_inits_and_terms main.cpp -o main && ./main
... handler
MacBook-Pro:teste pfranco$ # linking against the shared library
works, but this isn't always an option
MacBook-Pro:teste pfranco$ g++ -c -fno-rtti library.cpp && g++ -
shared -o libexception_problem.dylib library.o && g++ -fno-rtti
main.cpp -o main -L. -lexception_problem && ./main
std::exception handler
----------
This only happens if the code that throws is in a shared library,
and only if the caught type is a base class of the actual exception
- catch(std::invalid_argument&) works fine, std::logic_error&
doesn't.
Interestingly, this doesn't happen on Linux (g++-4.4), even when
running the exact same commands.
Questions:
1. Is this a bug, undefined behavior or by design?
2. How could I make it work, short of linking against the library?
Thanks a lot.
Pedro d'Aquino
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