linux-kernel - Re: [PATCH] ARM: add a private asm/unaligned.h

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Date:   Wed, 1 Nov 2017 15:57:36 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Gregory CLEMENT <gregory.clement@...e-electrons.com>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        Petr Cvek <petrcvekcz@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrea Adami <andrea.adami@...il.com>,
        Romain Izard <romain.izard.pro@...il.com>,
        Sven Schmidt <4sschmid@...ormatik.uni-hamburg.de>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: add a private asm/unaligned.h

On 31 October 2017 at 13:22, Gregory CLEMENT
<gregory.clement@...e-electrons.com> wrote:
> Hi Ard,
>
>  On mar., oct. 31 2017, Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:
>
>> On 31 October 2017 at 12:47, Russell King - ARM Linux
>> <linux@...linux.org.uk> wrote:
>>> On Mon, Oct 30, 2017 at 04:38:17PM +0000, Russell King - ARM Linux wrote:
>>>> On Mon, Oct 30, 2017 at 05:24:34PM +0100, Gregory CLEMENT wrote:
>>>> > Hi Russell King,
>>>> >
>>>> > Here you will find all the objects included the vmlinux:
>>>> >
>>>> > http://free-electrons.com/~gregory/pub/compressed.tgz
>>>>
>>>> Thanks.  Unfortunately, nothing stands out, but I do see a difference
>>>> between the output of your linker from mine.
>>>>
>>>> Yours:
>>>>
>>>> Idx Name          Size      VMA       LMA       File off  Algn
>>>>   0 .text         00005ef8  00000000  00000000  00010000  2**5
>>>>                   CONTENTS, ALLOC, LOAD, READONLY, CODE
>>>>
>>>> Mine:
>>>>
>>>> Idx Name          Size      VMA       LMA       File off  Algn
>>>>   0 .text         00005f00  00000000  00000000  00010000  2**5
>>>>                   CONTENTS, ALLOC, LOAD, READONLY, CODE
>>>>
>>>> That has the effect of moving the addresses of the following
>>>> sections in your vmlinux down by 8 bytes.  However, I don't think
>>>> that's the cause of this - but it does hint at something being
>>>> different in binutils in the way sections are processed in the
>>>> linker.
>>>>
>>>> Please add to your linker script after the assignment of _edata:
>>>>
>>>>   .image_end (NOLOAD) : {
>>>>     _edata_foo = .;
>>>>   }
>>>>
>>>> relink the decompressor, and see what value _edata_foo ends up with
>>>> compared to _edata?  They should be the same, but I suspect using
>>>> your linker, they will be different.
>>>>
>>>> Also try adding
>>>>     BYTE(0);
>>>>
>>>> after the _edata_foo assignment as a separate test, and see whether
>>>> that makes any difference - with that you should end up with the
>>>> .image_end section in the output image.
>>>
>>> Gregory sent me has new url... for _both_ changes, which gives me:
>
> If needed I can provide this url.
>
>>>
>>> $ arm-linux-nm vmlinux |grep _edata
>>> 00491160 D _edata
>>> 00491160 D _edata_foo
>>>
>>> So there's no reason that ASSERT() should be failing!  However, as I
>>> don't have the intermediate step, I can't say whether the addition
>>> of the BYTE() affected it in some way - sorry, but I asked for _both_
>>> to be tested above because I wanted to speed up the process, and
>>> clearly that's backfired.
>>>
>>> Given how close we potentially are to 4.14, I don't think we're going
>>> to get to the bottom of this to make 4.14.  I'd want to get this
>>> sorted by Wednesday so linux-next (which is resuming this evening)
>>> can grab a copy of my tree with it in, and we have another day to
>>> sort out any remaining issues, but I'm basically out of time to do
>>> anything further with this as of now.
>>
>>> So, 4.14 will likely be released without any of this being fixed.
>>>
>>
>> IIUC, the current issue is limited to the ASSERT() itself, which is
>> there to prevent future regressions, while the other two patches deal
>> with severe and difficult to diagnose known issues.
>
> I confirm that whithout the last commit (adding the ASSERT()) in the
> fixes branch it worked well.
>
>>
>> So why can't we apply those two patches as fixes, and revisit the
>> patch that helps us prevent this from regressing in the future for
>> v4.15?
>
> I also agree with this.
>

Russell,

Please drop the EFI patch from your tree. I will forward it myself.

Thanks,
Ard.