Exceptions in native code

[Maurizio Cimadamore]

Hi,
We have explored the topic of exceptions, mostly from the point of view 
of a Java exception while executing an upcall from native code. At the 
time being the Linker doesn't handle native exceptions (as you have 
seen).  What you want to happen here is to unwind the stack in the same 
way as the C code would have done it (e.g. by letting other handlers, if 
present, to execute) -- then, when back to Java, rethrow as some kind of 
Java exception. What you don't want to happen is to stop native 
execution "there and then" and jump back to Java (e.g. pop all native 
frame) -- as that might leave the native library in an inconsistent state.

While it's not impossible to better support for native exceptions in 
downcalls/upcalls (API-wise, this is rather trivial to do, e.g. with a 
linker option), such support would have to wrestle with wild platform 
inconsistencies. For instance, Windows supports so called structured 
exceptions [1], which provides a standard API for doing stack unwinding. 
On Linux there's unfortunately no "standard" way for doing this. 
Libunwind [2] is probably the most portable effort in this direction, 
but creating adding a dependency between it and the JVM made us nervous 
back then (and still does).

Maurizio

[1] - 
https://learn.microsoft.com/en-us/cpp/cpp/structured-exception-handling-c-cpp?view=msvc-170
[2] - https://github.com/libunwind/libunwind

On 28/04/2025 13:11, White_145 wrote:
> Whenever C code uses exceptions (in my case raised by `RaiseException` 
> (windows) or `_Unwind_RaiseException` (linux)) and java takes control 
> of the execution, it crashes the VM with an "Internal Error" message.
> I'm using bindings for LuaJIT, and it raises exceptions quite a lot 
> for the purpose of stack unwinding. Most of them are easy to avoid: 
> errors and yields can be simply wrapped by a C function so that java 
> doesn't see it, but others, signaling for Out Of Memory, are not so 
> straightforward.
> Is there a way to handle (perhaps, convert to a Java Exception?) these 
> native exceptions before Java crashes the VM, given that the error 
> code is known? If not, is it planned/possible in the future?
> I have little experience in this kind of problem: in fact, my only 
> experience is trying to deal with it, so be free to call out the wrong 
> terminology and/or approach. I have been searching for a solution 
> [what seems to be] everywhere, but I haven't found anyone with the 
> same problem.
>