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

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Date:	Tue, 2 Feb 2010 17:31:45 +0100
From:	Christoph Hellwig <hch@....de>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Christoph Hellwig <hch@....de>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	tony.luck@...el.com, ralf@...ux-mips.org, kyle@...artin.ca,
	benh@...nel.crashing.org, schwidefsky@...ibm.com,
	heiko.carstens@...ibm.com, davem@...emloft.net, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, viro@...iv.linux.org.uk
Subject: Re: [PATCH 4/6] improve sys_personality for compat architectures

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.

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