Hi, a colleague and I are facing a problem with unhandled exceptions in our C++ programs in Cygwin. The C++ standard guarantees, that std::terminate() shall be called for thrown exceptions, that are not caught [0]. Unfortunately for C++ applications compiled for Cygwin64 running on recent Windows systems, std::terminate_handler is never executed.
A minimal example for showing the non-standard conform behaviour can be found
here [1]:
```
#include <cstdlib>
#include <exception>
#include <iostream>
int main()
{
std::set_terminate([]()
{
std::cout << "Unhandled exception\n" << std::flush;
std::abort();
});
throw 1;
}
```
In Cygwin64 on Windows 11, Windows Server 2022 and Windows Server 2025 the
above program doesn't print anything to stdout and exits with status code 0.
The expected behaviour would be a non-zero exit code and the above error
message on stdout.
Windows 10 and Windows Server 2019 are not affected. As another data point,
Cygwin 32bit on Windows Server 2022 works as well. We actually found this
behaviour, while migrating some programs from Cygwin 32bit to 64bit.
I also disabled SEHOP, which had no effect.
My colleague started an investigation and traced the error back to a change in
behaviour in RtlRaiseException() from ntdll.dll, that's where our investigation
hit a wall.
Here is a thread [2], discussing a possibly related problem for some Windows
applications, which apparently can be traced back to a change of behaviour in
the SetUnhandledExceptionFilter API in Windows Server 2022.
That's all we know. It would be great, if this could be fixed on the Cygwin
side. While some Windows programs seem to be affected as well, under Cygwin all
C++ programs with unhandled exceptions are currently affected.
Best regards
Markus Jörg
[0] : https://en.cppreference.com/w/cpp/error/terminate
[1] : https://en.cppreference.com/w/cpp/error/set_terminate
[2] :
https://learn.microsoft.com/en-us/answers/questions/2046601/filter-from-setunhandledexceptionfilter-not-captur
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