Subject: Re: linux-next: build failure after merge of the aio tree

From: Russell King - ARM Linux <[email-masked]>
Date: Thu, 4 Feb 2016 16:17:42 +0000

On Thu, Feb 04, 2016 at 11:01:01AM -0500, Benjamin LaHaise wrote:
> On Thu, Feb 04, 2016 at 02:39:07PM +0000, Russell King - ARM Linux wrote:
> > However, this one should warn:
> > 
> > int test_wrong(char **v, const char **p)
> > { return __get_user(*v, p); }
> > 
> > Good luck (I think you'll need lots of it to get a working solution)! :)
> 
> This works with your test cases on x86-32.  Note that it's only compile + 
> link tested at present.

That's the easy bit!

The problem you're going to run into is here:

#define __get_user_nocheck(x, ptr, size)                                \
({                                                                      \
        int __gu_err;                                                   \
        unsigned long __gu_val;                                         \
        __uaccess_begin();                                              \
        __get_user_size(__gu_val, (ptr), (size), __gu_err, -EFAULT);    \
        __uaccess_end();                                                \
        (x) = (__force __typeof__(*(ptr)))__gu_val;                     \

__gu_val will be 32-bit, even when you're wanting a 64-bit quantity.
That's where the fun and games start...

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