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Message-ID: <9521f4da-1451-293e-ce0a-08b9edad2298@opensource.wdc.com>
Date:   Wed, 15 Mar 2023 13:12:50 +0900
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User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
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Subject: Re: [PATCH 0/2] riscv: support ELF format binaries in nommu mode
Content-Language: en-US
To:     Palmer Dabbelt <palmer@dabbelt.com>, gerg@kernel.org,
        macro@orcam.me.uk
Cc:     linux-riscv@lists.infradead.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <mhng-a62a57b8-4268-4c51-b79e-f5f6bd0c13a2@palmer-ri-x1c9a>
From:   Damien Le Moal <damien.lemoal@opensource.wdc.com>
Organization: Western Digital Research
In-Reply-To: <mhng-a62a57b8-4268-4c51-b79e-f5f6bd0c13a2@palmer-ri-x1c9a>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On 3/15/23 12:58, Palmer Dabbelt wrote:
> On Tue, 28 Feb 2023 16:20:35 PST (-0800), gerg@kernel.org wrote:
>> Hi Palmer,
>>
>> On 1/3/23 07:52, Palmer Dabbelt wrote:
>>> On Tue, 28 Feb 2023 05:51:24 PST (-0800), gerg@kernel.org wrote:
>>>> The following changes add the ability to run ELF format binaries whe=
n
>>>> running RISC-V in nommu mode. That support is actually part of the
>>>> ELF-FDPIC loader, so these changes are all about making that work on
>>>> RISC-V.
>>>>
>>>> The first issue to deal with is making the ELF-FDPIC loader capable =
of
>>>> handling 64-bit ELF files. As coded right now it only supports 32-bi=
t
>>>> ELF files.
>>>>
>>>> Secondly some changes are required to enable and compile the ELF-FDP=
IC
>>>> loader on RISC-V and to pass the ELF-FDPIC mapping addresses through=
 to
>>>> user space when execing the new program.
>>>>
>>>> These changes have not been used to run actual ELF-FDPIC binaries.
>>>> It is used to load and run normal ELF - compiled -pie format. Though=
 the
>>>> underlying changes are expected to work with full ELF-FDPIC binaries=
 if
>>>> or when that is supported on RISC-V in gcc.
>>>>
>>>> To avoid needing changes to the C-library (tested with uClibc-ng
>>>> currently) there is a simple runtime dynamic loader (interpreter)
>>>> available to do the final relocations, https://github.com/gregungere=
r/uldso.
>>>> The nice thing about doing it this way is that the same program
>>>> binary can also be loaded with the usual ELF loader in MMU linux.
>>>>
>>>> The motivation here is to provide an easy to use alternative to the
>>>> flat format binaries normally used for RISC-V nommu based systems.
>>>>
>>>> Signed-off-by: Greg Ungerer <gerg@kernel.org>
>>>> ---
>>>>
>>>> =C2=A0arch/riscv/include/asm/elf.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0 |=C2=A0=C2=A0 11 +++++++++-
>>>> =C2=A0arch/riscv/include/asm/mmu.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0 |=C2=A0=C2=A0=C2=A0 4 +++
>>>> =C2=A0arch/riscv/include/uapi/asm/ptrace.h |=C2=A0=C2=A0=C2=A0 5 +++=
+
>>>> =C2=A0fs/Kconfig.binfmt=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=
=A0=C2=A0=C2=A0 2 -
>>>> =C2=A0fs/binfmt_elf_fdpic.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0=C2=A0 38 +++++++=
++++++++++------------------
>>>> =C2=A0include/linux/elf-fdpic.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0=C2=A0 14 +++++++++++-
>>>> =C2=A0include/uapi/linux/elf-fdpic.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0 |=C2=A0=C2=A0 15 +++++++++++++
>>>> =C2=A07 files changed, 67 insertions(+), 22 deletions(-)
>>>
>>> Adding Damien, as IIRC he's had some hacked up userspace bits for the=
 K210.=C2=A0 I'm yet to get anything running, but it'd be great if we get=
 this to a point where I can actually boot test this on QEMU (I'm just do=
ing builds now).
>>
>> This is a simple script I user to generate a working QEMU example:
>>
>>    https://raw.githubusercontent.com/gregungerer/simple-linux/master/b=
uild-riscvnommu-linux-uclibc-elf.sh
>>
>> It does reference some configs here https://github.com/gregungerer/sim=
ple-linux/tree/master/configs
>> and this posted patchset as https://github.com/gregungerer/simple-linu=
x/tree/master/patches (this is
>> just these 2 patches combined as a single patch).
>>
>>
>>> Given that it's the second week of the merge window and this is a bun=
ch of new uABI it seems best to hold off until the next cycle.=C2=A0 I po=
ked around and don't see anything wrong, but I'll try and take a more det=
ailed look after the merge window.
>>
>> Oh, yeah, no hurry.
>=20
> Maciej and Damien: I'm fine taking this, but not in any rush.  I'd=20
> rather get the uABI right if things are still in flight, but if we're=20
> all just waiting for something to get merged first then I'm fine with=20
> that being Linux.

I did not try Gerg script with the k210. No time right now.
But if it works with QEMU, should be fine.

>=20
>>
>> Regards
>> Greg

--=20
Damien Le Moal
Western Digital Research