linux-kernel - Re: [PATCH] ARM: Fix zImage file size not aligned with CONFIG_EFI

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Date:   Tue, 24 Oct 2017 11:03:05 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Chris Zhong <chris.zhong@...k-chips.com>,
        jeffy <jeffy.chen@...k-chips.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] ARM: Fix zImage file size not aligned with
 CONFIG_EFI_STUB enabled

On 24 October 2017 at 10:54, Russell King - ARM Linux
<linux@...linux.org.uk> wrote:
> On Tue, Oct 24, 2017 at 10:44:00AM +0100, Ard Biesheuvel wrote:
>> On 24 October 2017 at 10:38, Russell King - ARM Linux
>> <linux@...linux.org.uk> wrote:
>> > Do you have any preference - I'd prefer one that I can merge along with
>> > these changes?  One way forward would be to temporarily add the /DISCARD/
>> > for the ksym sections, which can then be removed once your sort() removal
>> > gets added to the EFI trees.
>> >
>>
>> Well, I can respin that patch to only discard the ksymtab/kcrctab
>> sections (and drop the alignment of piggydata), but I'd prefer to make
>> it permanent if you don't mind. I still intend to remove the sort()
>> call, given that ARM doesn't need it, but it seems more future proof
>> to me to always discard those sections, and if we end up incorporating
>> more core kernel code into the EFI stub, we won't need to revisit this
>> (although I am not aware of any reasons why we would be doing that in
>> the near future)
>
> I don't think it's future-proof.  The decompressor is a particularly
> special environment due to its runtime relocation support, where we
> (eg) don't really support initialised pointers in the .data section.
> Stuffing code from other parts of the kernel into the decompressor
> isn't going to work reliably, and I'd much rather discourage the
> practice.
>

Fair enough.

> Hence, there's really no reason to keep that discard, and I'd much
> rather have the build fail if the sections re-appear as a pointer
> towards something not being correct.
>

OK. You're welcome to take that sort() removal patch through the ARM
tree if you want to keep these patches together. Or I could respin the
/discard/ one. Whichever you prefer (although I am leaning towards the
former, so we can merge them and be done with it)

> A solution to this would be to link the decompressor ELF with -r
> and wrap that up in a mini-linker, but I suspect that will need
> quite a re-write because of the self-relocation that the image
> does if it detects overlap between itself and the destination for
> the decompressed kernel image.
>

It was already quite tricky to get the hybrid PE-COFF/bare metal image
working, especially because the stub code is shared between x86, arm64
and ARM, all of which have their own quirks when it comes to the early
environment this code executes in.