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From: Ard Biesheuvel <ardb@kernel.org>
Date: Mon, 5 Feb 2024 08:59:02 +0100
Message-ID: <CAMj1kXFTFjM3LjJk=M4ZcO7=vfFxSH2c_GPu3YpwByZkVknkcw@mail.gmail.com>
Subject: Re: Broken section alignment in 6.7 and 6.8rc EFI stub
To: Mike Beaton <mjsbeaton@gmail.com>
Cc: Bagas Sanjaya <bagasdotme@gmail.com>, Linux EFI <linux-efi@vger.kernel.org>, 
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Ivan Hu <ivan.hu@canonical.com>, 
	Jeremy Kerr <jk@ozlabs.org>, Peter Jones <pjones@redhat.com>
Content-Type: text/plain; charset="UTF-8"

On Mon, 5 Feb 2024 at 08:47, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Mon, 5 Feb 2024 at 08:37, Mike Beaton <mjsbeaton@gmail.com> wrote:
> >
> > On Mon, 5 Feb 2024 at 02:06, Bagas Sanjaya <bagasdotme@gmail.com> wrote:
> > >
> > > So v6.7 onwards misses .reloc section, right?
> > >
> > > Confused...
> >
> > Reloc info is still present as normal in data directories, e.g.
> > `llvm-objdump -p` shows NumberOfRvaAndSizes = 6. Reloc info is taken
> > from index 5 https://github.com/tianocore/edk2/blob/master/MdePkg/Include/IndustryStandard/PeImage.h#L128
> > . (I've been told a dummy .reloc section was dumped recently?)
> >
>
> So there are a couple of things going on here:
> - the .reloc section was indeed dropped because we could not find any
> evidence anywhere that the reason it was added is still valid;
> - the .compat section uses a non-1:1 RVA mapping, to avoid padding,
> but reading the PE/COFF spec again, I suppose this is not compliant.
>
> Note that objdump looks broken too, on an image I have locally, I get
>
> (llvm-readelf -a)
>
>   Section {
>     Number: 2
>     Name: .compat (2E 63 6F 6D 70 61 74 00)
>     VirtualSize: 0x8
>     VirtualAddress: 0xB82000
>     RawDataSize: 4096
>     PointerToRawData: 0x4000
>
> (objdump -h)
>
>   1 .compat       00000008  0000000000b82000  0000000000b82000  00004000  2**2
>                   CONTENTS, ALLOC, LOAD, READONLY, DATA
>
> So the .compat section is in the correct spot in the file view but not
> in the memory view.
>
> Given that the .setup section is not relevant to EFI boot anyway, we
> could try to use the same file mapping as the virtual mapping, and
> just split the content preceding .text across the .setup and .compat
> sections arbitrarily.
>
> Could you try the below?
>

OK, never mind - that violates the section alignment.