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

Russell King - ARM Linux
2012-11-13T11:05:13Z

On Mon, Nov 12, 2012 at 06:31:50PM -0600, 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; \
> } \
>
> 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.

The problem with that is... big endian systems - where the 32-bit word we
want is the second one, so you can't just reduce that down to a 32-bit
access like that. You also need to add an offset to the pointer in the BE
case (which can be done.)

I'd suggest calling the 4-byte version in there __get_user_xb() and doing
the 4-byte offset for BE inside that (or aliasing it to __get_user_x for
LE systems).