From: Christoph Hellwig <hch@lst.de>
To: Greg Ungerer <gerg@linux-m68k.org>
Cc: linux-m68k@vger.kernel.org, hch@lst.de, geert@linux-m68k.org,
arnd@arndb.de, kernel test robot <lkp@intel.com>
Subject: Re: [PATCH] m68knommu: switch to using asm-generic/uaccess.h
Date: Wed, 9 Sep 2020 08:56:39 +0200 [thread overview]
Message-ID: <20200909065639.GB9618@lst.de> (raw)
In-Reply-To: <20200909021831.1881990-1-gerg@linux-m68k.org>
On Wed, Sep 09, 2020 at 12:18:31PM +1000, Greg Ungerer wrote:
> Switch to using the asm-generic/uaccess functions for non-MMU builds.
> Remove all the m68knommu local specific uaccess defines and macros.
>
> There is nothing so special about the m68knommu targets that they cannot
> use all of the asm-generic uaccess support. Using the asm-generic
> uaccess definitions also resolves some of the existing problems with
> missing __user annotations in the m68knommu specific functions.
>
> The elimination of all of the contents of uaccess_no.h means we can fold
> the uaccess_mm.h back into uaccess.h - and just have the single file
> now.
>
> The resulting generated code ends up being slightly smaller (by a few
> hundred bytes) due to the compilers ability to better optimize load
> and stores without forcing its hand with asm statements.
>
> Specifically trivial cases like this contrived example:
>
> get_user(x, ptr);
> x++;
> put_user(x, ptr);
>
> end up now being optimized to a single instruction on m68k. More
> generally the compiler can avoid using a temporary register in many
> cases as well.
This looks great!
Reviewed-by: Christoph Hellwig <hch@lst.de>
next prev parent reply other threads:[~2020-09-09 6:56 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-09 2:18 [PATCH] m68knommu: switch to using asm-generic/uaccess.h Greg Ungerer
2020-09-09 6:55 ` Geert Uytterhoeven
2020-09-09 7:54 ` Greg Ungerer
2020-09-09 6:56 ` Christoph Hellwig [this message]
2020-09-09 7:58 ` Greg Ungerer
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