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

[Palmer Dabbelt]

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).

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.

Thanks!