linux-kernel - Re: [PATCH v2 4/8] KVM: arm64: Generate hyp relocation data

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Date:   Sat, 30 Jan 2021 12:16:40 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     David Brazdil <dbrazdil@...gle.com>, kvmarm@...ts.cs.columbia.edu,
        Mark Rutland <mark.rutland@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-kernel@...r.kernel.org, James Morse <james.morse@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Julien Thierry <julien.thierry.kdev@...il.com>
Subject: Re: [PATCH v2 4/8] KVM: arm64: Generate hyp relocation data

Hi Guenter,

Thanks a lot for the heads up.

On 2021-01-29 21:43, Guenter Roeck wrote:
> Hi,
> 
> On Tue, Jan 05, 2021 at 06:05:37PM +0000, David Brazdil wrote:
>> Add a post-processing step to compilation of KVM nVHE hyp code which
>> calls a custom host tool (gen-hyprel) on the partially linked object
>> file (hyp sections' names prefixed).
>> 
>> The tool lists all R_AARCH64_ABS64 data relocations targeting hyp
>> sections and generates an assembly file that will form a new section
>> .hyp.reloc in the kernel binary. The new section contains an array of
>> 32-bit offsets to the positions targeted by these relocations.
>> 
>> Since these addresses of those positions will not be determined until
>> linking of `vmlinux`, each 32-bit entry carries a R_AARCH64_PREL32
>> relocation with addend <section_base_sym> + <r_offset>. The linker of
>> `vmlinux` will therefore fill the slot accordingly.
>> 
>> This relocation data will be used at runtime to convert the kernel VAs
>> at those positions to hyp VAs.
>> 
>> Signed-off-by: David Brazdil <dbrazdil@...gle.com>
> 
> This patch results in the following error for me.
> 
> error: arch/arm64/kvm/hyp/nvhe/kvm_nvhe.tmp.o: assertion
> elf.ehdr->e_ident[5] == 1 failed (lhs=2, rhs=1, line=250)
> 
> The problem is seen when trying to build aarch64 images in big endian
> mode.

Ah, big-endian. of course, the ELF header is in native endianness,
and the sanity checks explode (still much better than generating crap).

I'll have a look shortly. It shouldn't too hard to fix, just a
bit invasive...

Thanks again,

         M.
-- 
Jazz is not dead. It just smells funny...