linux-kernel - Re: RISC-V nommu support v2

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Message-ID: <20190624131633.GB10746@lst.de>
Date:   Mon, 24 Jun 2019 15:16:33 +0200
From:   Christoph Hellwig <hch@....de>
To:     Vladimir Murzin <vladimir.murzin@....com>
Cc:     Christoph Hellwig <hch@....de>, Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Damien Le Moal <damien.lemoal@....com>,
        linux-riscv@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: RISC-V nommu support v2

On Mon, Jun 24, 2019 at 02:08:50PM +0100, Vladimir Murzin wrote:
> True, yet my observation was that elf2flt utility assumes that address
> space cannot exceed 32-bit (for header and absolute relocations). So,
> from my limited point of view straightforward way to guarantee that would
> be to build incoming elf in 32-bit mode (it is why I mentioned COMPAT/ILP32).
> 
> Also one of your patches expressed somewhat related idea
> 
> "binfmt_flat isn't the right binary format for huge executables to
> start with"
> 
> Since you said there is no support for compat/ilp32, probably I'm missing some
> toolchain magic?

There is no magic except for the tiny elf2flt patch, which for
now is just in the buildroot repo pointed to in the cover letter
(and which I plan to upstream once the kernel support has landed
in Linus' tree).  We only support 32-bit code and data address spaces,
but we otherwise use the normal RISC-V ABI, that is 64-bit longs and
pointers.