Is the world coming to an end?

[Iain Buclaw]

== Quote from Nick Sabalausky (a at a.a)'s article
> "Don" <nospam at nospam.com> wrote in message
> news:inf4hj$3mg$1 at digitalmars.com...
> > Nick Sabalausky wrote:
> >> "spir" <denis.spir at gmail.com> wrote in message
> >> news:mailman.3141.1301915290.4748.digitalmars-d at puremagic.com...
> >>> On 04/04/2011 07:26 AM, Nick Sabalausky wrote:
> >>>> As far as LDC2, LLVM's uselessness on windows is a bit of a showstopper
> >>>> for
> >>>> many people. And the LLVM project doesn't appear to be interested in
> >>>> doing
> >>>> much about it. (Note I didn't say they *aren't* interested in getting
> >>>> it
> >>>> working. That's not something I could even pretend to know. I'm just
> >>>> saying
> >>>> that, at the very least, it *looks* like they don't care. And, for
> >>>> better or
> >>>> worse, perception does count for a lot.)
> >>> Yop, too bad. Else, LLVM could be the one target of choice for many PL's
> >>> "reference" implementation. I'd like to know rationales.
> >>>
> >>
> >> AIUI, the standard explanation is that exception support on Windows
> >> requires SEH which is covered by a patent owned by Borland/Microsoft. But
> >> I have a hard time buying that explanation because non-MS compilers like
> >> GCC and DMC support exceptions on windows just fine - so why not LLVM,
> >> too?
> >
> > AFAICT, that explanation is absolute bollocks.
> >
> > SEH is *not* covered by a patent. The Borland patent that people talk
> > about refers to a particular implementation detail which is a workaround
> > for an absolutely horrific Microsoft bug.
> > The idea is to use the exception handler pointer (which is in thread-local
> > storage(TLS)) to track which exception table to use.
> > Instead of pointing to your exception handler, it points to a thunk (one
> > for each try block) which sets a pointer to the try block table, then the
> > exception handler.
> > The reason for doing this, is that you need a TLS slot to store which try
> > block you're in.
> > Unfortunately, Windows' thread local storage is hopelessly broken for
> > DLLs. The exception handler pointer is just about the only TLS slot
> > guaranteed to be available, so it allows you to escape the bug.
> >
> Interesting. (And could be another reason we need to get the DDL project up
> and running again :) )
> > Now since the idea is just a straightforward application of thunks, I
> > wonder if it really satisfies the patent requirement for non-obviousness.
> >
> > But regardless, for D, Rainer has put code into druntime which fixes the
> > bug! So actually a D implementation can use any thread-local slot.
> > <g>
> Does that mean LLVM doesn't need exception support on Windows in order for
> LDC to support exceptions on windows?

I would have thought it would still need to implement the EH tables in the same
way that the runtime code in Druntime/Phobos expects it to be. But I wouldn't know
just how tied to the LLVM backend LDC is with exceptions.