On Thu, 2016-07-21 at 20:38 +0200, Jiri Kosina wrote:
> On Thu, 21 Jul 2016, David Woodhouse wrote:
> 
> > Apart from resolutely not wanting to implement variable length arrays on 
> > the stack, the LLVM folks actually seem quite keen to make things work. 
> > I'm interested in the problem you report above.. and note the absence of 
> > a bug number. Can you provide it?
> 
> I am currently on vacation and on super-lousy internet connection, so 
> looking through my archives is a bit complicated ... I *think* it started 
> in "[PATCH] usbhid: Fix lockdep unannotated irqs-off warning" thread on 
> lkml.
> 
> In case you're not able to find it from there, I'll do my homework 
> mid-next week when I am back properly online.

OK, thanks. So it looks like that's acknowledged to have been a bug,
there's a patch to fix it at https://reviews.llvm.org/D6629 which may
even have been committed already.

The main sticking point for LLVM seems to be the variable length arrays
on the stack (VLAIS), which is a GCC'ism that the LLVM/clang folks
*really* don't want to support, and the fact that
__builtin_constant_p() is basically always false under LLVM because it
doesn't look very hard.

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation