linux-kernel - Re: [tip:x86/mm] x86, mm: Use a bitfield to mask nuisance get

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Message-ID: <CA+55aFwMr8pDfj+wuv=-tUFqZQOhnqkwC7tVq-S=4MGGWiqz1A@mail.gmail.com>
Date:	Tue, 12 Feb 2013 09:00:30 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"H.J. Lu" <hjl.tools@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jamie Lokier <jamie@...reable.org>,
	ville.syrjala@...ux.intel.com, Borislav Petkov <bp@...en8.de>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/mm] x86, mm: Use a bitfield to mask nuisance get_user() warnings

On Tue, Feb 12, 2013 at 8:38 AM, H.J. Lu <hjl.tools@...il.com> wrote:
>
> Can you do something similar to what we did in glibc:

No. Because we use macros to be type-independent (i e"get_user()"
works *regardless* of type), so casting to "uintptr_t" doesn't work.
It throws away the type information, and truncates 64-bit values on
32-bit architectures.

The whole point of the bitmask thing is that it doesn't have that
issue, and gets the size correct automatically. It's not pretty, but
it allows the rest of the sources to be readable.

                Linus
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