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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Hari Bathini <hbathini@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     kernel test robot <lkp@intel.com>, Pingfan Liu <piliu@redhat.com>,
        Kexec-ml <kexec@lists.infradead.org>,
        Mimi Zohar <zohar@linux.ibm.com>,
        Nayna Jain <nayna@linux.ibm.com>,
        Petr Tesarik <ptesarik@suse.cz>,
        Mahesh J Salgaonkar <mahesh@linux.ibm.com>,
        Sourabh Jain <sourabhjain@linux.ibm.com>,
        lkml <linux-kernel@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@ozlabs.org>,
        Eric Biederman <ebiederm@xmission.com>,
        Thiago Jung Bauermann <bauerman@linux.ibm.com>,
        Dave Young <dyoung@redhat.com>, Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [PATCH v4 07/12] ppc64/kexec_file: add support to relocate purgatory
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Date:   Wed, 22 Jul 2020 14:25:19 +1000
Message-ID: <871rl4rxao.fsf@mpe.ellerman.id.au>
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Hari Bathini <hbathini@linux.ibm.com> writes:
> Right now purgatory implementation is only minimal. But if purgatory
> code is to be enhanced to copy memory to the backup region and verify
> sha256 digest, relocations may have to be applied to the purgatory.
> So, add support to relocate purgatory in kexec_file_load system call
> by setting up TOC pointer and applying RELA relocations as needed.
>
> Reported-by: kernel test robot <lkp@intel.com>
> [lkp: In v1, 'struct mem_sym' was declared in parameter list]
> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
> ---
>
> * Michael, can you share your opinion on the below:
>     - https://lore.kernel.org/patchwork/patch/1272027/
>     - My intention in cover note.

It seems like a lot of complexity for little benefit.

AFAICS your final purgatory_64.c is only 36 lines, and all it does is a
single (open coded) memcpy().

It seems like we could write that in not many more lines of assembler
and avoid all this code.

What am I missing?

cheers