linux-kernel - Re: framebuffer corruption due to overlapping stp instructions on arm64

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Message-ID: <2d7cddbe-6523-f388-339b-382231514f6f@arm.com>
Date:   Fri, 3 Aug 2018 10:12:24 +0100
From:   Szabolcs Nagy <szabolcs.nagy@....com>
To:     Florian Weimer <fweimer@...hat.com>,
        Andrew Pinski <pinskia@...il.com>, mpatocka@...hat.com
Cc:     nd@....com, Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>, linux@...linux.org.uk,
        thomas.petazzoni@...e-electrons.com,
        linux-arm-kernel@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        GNU C Library <libc-alpha@...rceware.org>
Subject: Re: framebuffer corruption due to overlapping stp instructions on
 arm64

On 03/08/18 08:53, Florian Weimer wrote:
> On 08/03/2018 09:11 AM, Andrew Pinski wrote:
>> Yes fix Links not to use memcpy on the framebuffer.
>> It is undefined behavior to use device memory with memcpy.
> 
> Some (de facto) ABIs require that it is supported, though.  For example, the POWER string functions avoid unaligned loads and stores for this 
> reason because the platform has the same issue with device memory.  And yes, GCC will expand memcpy on POWER to something that is incompatible 
> with device memory. 8-(
> 

i think it's not reasonable to require libc memcpy to work on device memory.

i think if device memory is exposed to regular userspace applications that should be fixed.

> If we don't want people to use memcpy, we probably need to provide a credible alternative.
> 
> Thanks,
> Florian