Re: [PATCH 4/6] improve sys_personality for compat architectures

[Christoph Hellwig <hch@lst.de>]

On Tue, Feb 02, 2010 at 03:36:51PM +0100, Arnd Bergmann wrote:
> > -       return (long)old;
> > +       return (long)(old == PER_LINUX32 ? PER_LINUX : old);
> >  }
> 
> What does this do for a native 64 bit process setting PER_LINUX32?
> It looks to me like it could never set it back to the original
> value, or am I missing something here?
> 
> It's what the arch specific code does already, but it seems a bit
> strange anyway.

Indeed, this prevents a process from going back to 64bit.  And while
the setarch tool in util-linux also allows going back to 64-bit the
typical use case seems to be going into 32-bit mode.

But if the consensus is that we should fix this properly I can
replace the patch with one introducing a compat_sys_personality
which only gets used for compat tasks.