Re: [PATCH] binfmt: Don't consider riscv{32, 64} part of the same family

[Andrea Bolognani]

On Tue, Dec 03, 2024 at 10:59:24AM +0100, Philippe Mathieu-Daudé wrote:
> On 3/12/24 10:47, Andrea Bolognani wrote:
> > Currently the script won't generate a configuration file that
> > sets up qemu-user-riscv32 on riscv64, likely under the
> > assumption that 64-bit RISC-V machines can natively run 32-bit
>
> I'm confused by the "machines" description used for user emulation.

I meant it in the sense of physical machines. I can use the word
"hosts" instead if you think that's less ambiguous.

> > However this functionality, while theoretically possible, in
> > practice is missing from most commonly available RISC-V hardware
> > and not enabled at the distro level. So qemu-user-riscv32 really
> > is the only option to run riscv32 binaries on riscv64.
>
> We have definitions such ELF_ARCH/ELF_PLATFORM/ELF_MACHINE to
> parse ELF header and select the best CPU / flags. Maybe RISC-V
> lacks them?
>
> BTW we should expose that for linux-user as target_arch_elf.h,
> like bsd-user does, that would reduce all these #ifdef'ry in
> linux-user/elfload.c...

All of this is flying way over my head, sorry :)

qemu-user-riscv32 already works great on riscv64 as far as I can
tell. I tested it by chrooting into a riscv32 Gentoo rootfs from a
riscv64 Fedora installation. We just need the configuration file to
be generated.

> > Make riscv32 and riscv64 each its own family, so that the
> > configuration file we need to make 32-on-64 userspace emulation
> > work gets generated.
>
> Does this patch aim for 9.2? Otherwise FYI  I'm working on unifying
> 32/64-bit targets, maybe for 10.0...

Having this in 9.2 would be great.

-- 
Andrea Bolognani / Red Hat / Virtualization