linux-kernel - [PATCH v3 0/4] exec: unify native/compat code

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Date:	Wed, 2 Mar 2011 17:26:50 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, pageexec@...email.hu,
	Solar Designer <solar@...nwall.com>,
	Eugene Teo <eteo@...hat.com>,
	Brad Spengler <spender@...ecurity.net>,
	Roland McGrath <roland@...hat.com>,
	Milton Miller <miltonm@....com>
Subject: [PATCH v3 0/4] exec: unify native/compat code

On 03/01, Linus Torvalds wrote:
>
> So I'm ok with your alternative
>
> >        typedef union {
> >                const char __user *const __user *native;
> >                compat_uptr_t __user *compat;
> >        } conditional_user_ptr_t;
>
> model instead, which moves the pointer into the union.
>
> However, if you do this, then I have one more suggestion: just move
> the "compat" flag in there too!
>
> Every time you pass the union, you're going to pass the compat flag to
> distinguish the cases. So do it like this:
>
>   struct conditional_ptr {
>     int is_compat;
>     union {
>       const char __user *const __user *native;
>       compat_uptr_t __user *compat;
>     };
>   };
>
> and it will all look much cleaner, I bet.

Heh. I knew. I swear, I knew you would suggest this ;)

OK, please find v3. I had to deanonymize the union though, otherwise
the initializer in do_execve() becomes nontrivial.



But I don't think this is right. Not only this adds 200 bytes to exec.o.
To me, is_compat is not the private property of argv/envp. Yes, currently
nobody except get_arg_ptr() needs to know the difference. But who knows,
it is possible that we will need more "if (compat)" code in future. IOW,
I think that the explicit argument is a win.

Never mind. I agree with everything as long as we can remove this c-a-p
compat_do_execve().

Oleg.

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