[PATCH 0/2] riscv: support ELF format binaries in nommu mode

[Damien Le Moal]

On 3/15/23 12:58, Palmer Dabbelt wrote:
> On Tue, 28 Feb 2023 16:20:35 PST (-0800), gerg at 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 at kernel.org wrote:
>>>> The following changes add the ability to run ELF format binaries when
>>>> 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-bit
>>>> ELF files.
>>>>
>>>> Secondly some changes are required to enable and compile the ELF-FDPIC
>>>> 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/gregungerer/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 at kernel.org>
>>>> ---
>>>>
>>>>  arch/riscv/include/asm/elf.h         |   11 +++++++++-
>>>>  arch/riscv/include/asm/mmu.h         |    4 +++
>>>>  arch/riscv/include/uapi/asm/ptrace.h |    5 ++++
>>>>  fs/Kconfig.binfmt                    |    2 -
>>>>  fs/binfmt_elf_fdpic.c                |   38 +++++++++++++++++------------------
>>>>  include/linux/elf-fdpic.h            |   14 +++++++++++-
>>>>  include/uapi/linux/elf-fdpic.h       |   15 +++++++++++++
>>>>  7 files changed, 67 insertions(+), 22 deletions(-)
>>>
>>> Adding Damien, as IIRC he's had some hacked up userspace bits for the K210.  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 doing builds now).
>>
>> This is a simple script I user to generate a working QEMU example:
>>
>>    https://raw.githubusercontent.com/gregungerer/simple-linux/master/build-riscvnommu-linux-uclibc-elf.sh
>>
>> It does reference some configs here https://github.com/gregungerer/simple-linux/tree/master/configs
>> and this posted patchset as https://github.com/gregungerer/simple-linux/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 bunch of new uABI it seems best to hold off until the next cycle.  I poked around and don't see anything wrong, but I'll try and take a more detailed look after the merge window.
>>
>> Oh, yeah, no hurry.
> 
> Maciej and Damien: I'm fine taking this, but not in any rush.  I'd 
> rather get the uABI right if things are still in flight, but if we're 
> all just waiting for something to get merged first then I'm fine with 
> 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.

> 
>>
>> Regards
>> Greg

-- 
Damien Le Moal
Western Digital Research