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

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Date:	Tue, 2 Feb 2010 15:36:51 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Christoph Hellwig <hch@....de>
Cc:	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 Monday 01 February 2010, Christoph Hellwig wrote:
> +/*
> + * Get/set the personality.
> + *
> + * Note that we simply return PER_LINUX even if we actually have a 32-bit
> + * task (PER_LINUX32) as this is expected by 32-bit userland.
> + */
>  SYSCALL_DEFINE1(personality, u_long, personality)
>  {
>         u_long old = current->personality;
>  
>         if (personality != 0xffffffff) {
> +               if (personality(old) == PER_LINUX32 &&
> +                   personality == PER_LINUX)
> +                       personality = PER_LINUX32;
>                 set_personality(personality);
>                 if (current->personality != personality)
>                         return -EINVAL;
>         }
>  
> -       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.

	Arnd
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