linux-kernel - Re: [PATCH 00/18] uaccess: fix sparse warning on get

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Message-ID: <1418604052.19970.6.camel@ellerman.id.au>
Date:	Mon, 15 Dec 2014 11:40:52 +1100
From:	Michael Ellerman <mpe@...erman.id.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 00/18] uaccess: fix sparse warning on get_user for
 bitwise types

On Sun, 2014-12-14 at 18:51 +0200, Michael S. Tsirkin wrote:
> At the moment, if p and x are both tagged as bitwise types,
> get_user(x, p) produces a sparse warning on many architectures.
> This is because *p on these architectures is loaded into long
> (typically using asm), then cast back to typeof(*p).
> 
> When typeof(*p) is a bitwise type (which is uncommon), such a cast needs
> __force, otherwise sparse produces a warning.

What does __force actually mean? Force the cast even though it's a bitfield? Or
does it mean more than that?

ie. are we loosing the ability to detect any actual errors by adding force?

cheers


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