Re: [tip:x86/mm] x86, mm: Use a bitfield to mask nuisance get_user()warnings

From: H. Peter Anvin
Date: Tue Feb 12 2013 - 13:58:56 EST

On 02/12/2013 10:46 AM, Linus Torvalds wrote:
On Tue, Feb 12, 2013 at 10:25 AM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
I just thought up this variant, I'm about to test it, but H.J., do you
see any problems with it?

Looks good to me. And we already use __builtin_choose_expr(), so it's
"portable". And it should avoid all the potential issues with
bitfields (rmk already pointed out how bitfields don't work well with
the ARM model, who knows what other pitfalls bitfield code generation
could have)

I wonder if we could/should eventually do some of the sizeof() in
generic code - not have these magic things duplicated in all the
architectures, just have the architectures specify the raw typed
details (__copy_to_user_4() etc). So cross-platform portability could
be a good thing. That's a separate discussion, though, and possibly
not worth it.

I'm getting rid of the switch statement in the variant that I'm currently testing, so that would probably be undesirable.


H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.

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