linux-kernel - Re: [PATCH v2 3/3] openrisc: Fix issue with get

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Message-ID: <20200905213408.GI3562056@lianli.shorne-pla.net>
Date:   Sun, 6 Sep 2020 06:34:08 +0900
From:   Stafford Horne <shorne@...il.com>
To:     Luc Van Oostenryck <luc.vanoostenryck@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Greentime Hu <green.hu@...il.com>,
        openrisc@...ts.librecores.org
Subject: Re: [PATCH v2 3/3] openrisc: Fix issue with get_user for 64-bit
 values

On Sat, Sep 05, 2020 at 03:57:14PM +0200, Luc Van Oostenryck wrote:
> On Sat, Sep 05, 2020 at 10:19:35PM +0900, Stafford Horne wrote:
> 
> Hi,
> 
> The change for 64-bit get_user() looks good to me.
> But I wonder, given that openrisc is big-endian, what will happen
> you have the opposite situation:
> 	u32 *ptr;
> 	u64 val;
> 	...
> 	get_user(val, ptr);
> 
> Won't you end with the value in the most significant part of
> the register pair?

Hi Luc,

The get_user function uses the size of the ptr to determine how to do the load ,
so this case would not use the 64-bit pair register logic.  I think it should be
ok, the end result would be the same as c code:

  var = *ptr;

-Stafford