linux-kernel - Re: [PATCH repost 12/16] parisc/uaccess: fix sparse errors

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Message-ID: <1420057406.2085.7.camel@HansenPartnership.com>
Date:	Wed, 31 Dec 2014 12:23:26 -0800
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Helge Deller <deller@....de>, linux-kernel@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	linux-parisc@...r.kernel.org
Subject: Re: [PATCH repost 12/16] parisc/uaccess: fix sparse errors

On Wed, 2014-12-31 at 20:38 +0200, Michael S. Tsirkin wrote:
> On Wed, Dec 31, 2014 at 09:17:20AM -0800, James Bottomley wrote:
[...]
> > OK, parisc developers still being dense, but this does look like an
> > abuse of the bitwise type.
> 
> To give you another example:
> 
> 	__le16 __user *p;
> 	__le16 foo;
> 	int rc = get_user(v, p);
> 
> really should be fine, ATM this gives a warning.

OK, I think I've figured it out.  You're saying that casting __gu_val to
a bitwise annotated type is an automatic sparse failure because it has
to be a long in our assembly code to receive the load/store as a
register.  However, this is required for sparse to do the correct lvalue
type = rvalue type check in the assignment to x.  We were all thinking
the __force just killed these sparse type checks.

In that case, I think parisc is fine with this.

James


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