Re: [PATCH] ARM: add get_user() support for 8 byte types

Arnd Bergmann
2012-11-13T09:11:21Z

On Tuesday 13 November 2012, Rob Clark wrote:
> right, that is what I was worried about.. but what about something
> along the lines of:
>
> case 8: { \
> if (sizeof(x) < 8) \
> __get_user_x(__r2, __p, __e, __l, 4); \
> else \
> __get_user_x(__r2, __p, __e, __l, 8); \
> break; \
> } \

I guess that's still broken if x is 8 or 16 bits wide.

> maybe we need a special variant of __get_user_8() instead to get the
> right 32bits on big vs little endian systems, but I think something
> roughly along these lines could work.
>
> Or maybe in sizeof(x)<8 case, we just __get_user_bad().. I'm not 100%
> sure on whether this is supposed to be treated as an error case at
> compile time or not.

We know that nobody is using that at the moment, so we could define
it to be a compile-time error.

But I still think this is a pointless exercise, a number of people have
concluded independently that it's not worth trying to come up with a
solution, whether one exists or not. Why can't you just use copy_from_user()
anyway?

Arnd