From: barabba <igor.sarzisartori@...>
Date: 2007-04-11T04:25:11+09:00
Subject: Re: Ruby C extension crash: how to create a stack trace?

On Apr 9, 11:44 pm, Ryan Davis <ryand-r...@zenspider.com> wrote:
> On Apr 6, 2007, at 11:20 , barabba wrote:
>
> > Hi,
>
> > I am using ruby to test and develop  my legacy C code. I packed it
> > inside  a ruby extension as dll under windows. I am using visual
> > studio 6 to debug my extension.
> > The process works very well, but when I make a mistake in my C code
> > ruby abort  without stack trace and it is difficult for me to find the
> > reason.
>
> I haven't done any MS development in over a decade (happily), so
> maybe I'm just missing something. This is how I get a BT on OSX/
> FreeBSD when I'm debugging my extensions:
>
> % gdb ruby
>  > r my_script.rb my_args
> ... go boom
>  > bt
> .. backtrace with hopefully useful information
>
> Can you not do that from the MS debugger???

Yes it is fast the same. MSVC start and run ruby using my_script.rb as
argument. The problem is the "backtrace", it is only one line, because
ruby don't crash, just exit.
I have solved my problem directly in the C part using Structured
Exception Handling(SEH) of win32.
Now my extension looks like:
void foo_thread_handler()
{
 __try{
    while(1)
    {
         //  a thread task
         mystruct* pCrash = 0; // null pointer usage
         pCrash->len = 555;     // BOOM
         do_realstuff(); // do real stuff
         // call a function inside ruby to get back to the scheduler
         rb_something()
    }
   }
   __except ( EXCEPTION_EXECUTE_HANDLER )
   {
      printf("Boom recognized\n");
   }

}

This solution works only under MSVC compiler, but it is ok for me.

It is still not clear  why
trap("SEGV"){"my seg fault handler";exit}
doesn't work on my system. It seam that the exception is caught, but
the C code is recalled at the same place where the error is generated
causing an infinite loop (may be an EXCEPTION_CONTINUE_EXECUTION is
used in the trap handler?).