Re: + futex-runtime-enable-pi-and-robust-functionality.patch addedto -mm tree

[Heiko Carstens]

On Sat, Feb 16, 2008 at 02:48:17PM +0100, Thomas Gleixner wrote:
> On Sat, 16 Feb 2008, Heiko Carstens wrote:
> 
> > > Well, NULL pointer dereferencing is supposed to fail, isn't it ?
> >
> > I wasn't sure that this is true for all architectures, but...
> 
> It's an requirement for futex support.

To be more precise: dereferencing alone won't cause an exception for
NULL pointers on s390. Only writes will do so.
That is very architecture specific since we cannot unmap page 0,
it contains per-cpu data -- like exception pointers and all such stuff
that the cpu needs.
Just in case there is any code that relies on the fact that also reads
via a NULL pointer are supposed to failed.
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