Question about POSIX libgcj signals / exception handling

Sat Mar 11 13:08:00 GMT 2006

Hi David,
>> Are the signal handlers in POSIX libgcj set up
>> such that the application is bulletproof and
>> immune from core dumps?
>>Certainly. With java and especially libgcj it is impossible to write 
>buggy code. I have not had a single bug in over three years!

:) This was meant to be read as "bulletproof from core
dumps and immune from core dumps" - i.e. anything that would
normally cause a core dump is properly converted to a Java
exception.
>That is a little out of date. i386 MAKE_THROW_FRAME is a nop. Stack 
>unwinding through the signal frame is handled by the DWARF based 
>exception unwinder in libgcc.

Thanks. Hadn't realized this.
>SIGSEGV gets converted to NullPointerException. This is unconditional 
>it happens even if the faulting location is far away from address zero. 
> Native code is not treated any differently than the java code. 
>Any SIGSEGV is converted to NPE.

>SIGFPE likewise is converted to ArithmaticException, but on the x86 some 
>analysis of the faulting code is done first as x86 sometimes generates 
>the SIGFPE when the JLS requires it not to throw the exception. In this 
>case things are fixed up and control returned to the faulting code.

>The GC uses two signals that are not related to machine faults. The 
>Thread.Interrupt facility also uses a signal (I forget which ones), 
>java.lang.Process uses SIGCHLD.

>SIGBUS and SIGILL are not handled by libgcj. If you get one of them, 
>your program will be terminated unless you explicitly install your own 
>handler for them. But they usually indicate that something is seriously 
>screwed up, so bailing out is probably for the best.

This is all very informative. Thanks for this.
>One thing that you need to remember if you are using native code is to 
>have GCC generate exception data for all your non-java code so that 
>faults in native code can be gracefully handled.

Can you explain what you mean by this? Doesn't this happen automatically
in C++?
Thanks again for your detailed answer.
-- Mohan
http://www.thisiscool.com/
http://www.animalsong.org/