emscripten lacks standards-conforming C++ exceptions #2531
Comments
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I suspect our personality routine might be having issues with polymorphic exceptions. Other possibly helpful documents: |
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Ok, I plan on compiling libc++abi from source with debug symbols and linking against that. Then stepping through the above example while stepping through emscripten's build and seeing where they diverge. Suspect code. Also, cc @waywardmonkeys in case anything stands out. |
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Not sure we handle virtual inheritance here. |
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An exception that has virtual inheritance gets corrupted. This is demonstrated in the following test program; mangled_exception.cc: #include <cerrno>
#include <cstring>
#include <iostream>
#include <stdexcept>
#include <string>
//============================================================================
// :: Helpers
namespace
{
// A straight up derivation from std::runtime_error.
struct exception1: public std::runtime_error
{
// Construct with an errno value. The what() string will contain the
// std::strerror() string associated with the given error value.
explicit exception1(const int error)
: std::runtime_error(std::string("exception1: ")
+ std::strerror(error)),
m_error(error)
{}
// Access to our stored error value.
int error() const
{ return m_error; }
private:
// The errno value.
const int m_error;
};
// A virtual derivation from std::runtime_error.
struct exception2: public virtual std::runtime_error
{
// Construct with an errno value. The what() string will contain the
// std::strerror() string associated with the given error value.
explicit exception2(const int error)
: std::runtime_error(std::string("exception2: ")
+ std::strerror(error)),
m_error(error)
{}
// Access to our stored error value.
int error() const
{ return m_error; }
private:
// The errno value.
const int m_error;
};
void printException2(const exception2& ex)
{
std::cout
<< "exception2 with errno=" << ex.error() << " and what="
<< ex.what() << std::endl;
}
}
//============================================================================
// :: Entry Point
int main()
{
try {
throw exception1(EIO);
}
catch (const exception1& ex) {
std::cout
<< "Caught exception: " << ex.what() << " with error="
<< ex.error() << std::endl;
}
try {
const exception2 test(EIO);
printException2(test);
throw exception2(EIO);
}
catch (const exception2& ex) {
std::cout << "Caught exception: " << ex.error() << std::endl;
printException2(ex);
}
}To build use the following command: When the generated JavaScript is run through node, the following output is observed: Currently using a recent version of the incoming branches of emscripten: |
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This looks like a duplicate of #1546. |
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Yes, different testcases in them though, so let's keep both open so we don't forget one. |
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I believe I have managed to hook our exceptions catching decision code to use libcxxabi's |
…ust the pointer as an out param; fixes #2531; 1.21.9
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Those last commits make use use libcxxabi's |
It seems the specific issue of catching std::exception has been fixed (in the incoming branch), but in general, C++ exceptions still aren't working.
Below is a small program that is based on one set of real, essential C++ exceptions from a real program. It exercises exception polymorphism, including in cases with virtual and multiple inheritence. Here are a few examples of the expected (g++) and actual (emscripten) output:
I can't really exercise most of the polymorphism cases because everything is falling into the "first catch" still.
By no means is this program an exhaustive test of all C++ exceptions, but it does demonstrate some of what is missing.
toolchain and emscripten (on the incoming branches):
test.cc
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