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

[Philippe Mathieu-Daudé]

Hi Andrea,

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.

> RISC-V code.
>
> 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...

> 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...

> Link: https://src.fedoraproject.org/rpms/qemu/pull-request/72
> Thanks: David Abdurachmanov <davidlt@rivosinc.com>
> Thanks: Daniel P. Berrangé <berrange@redhat.com>
> Signed-off-by: Andrea Bolognani <abologna@redhat.com>
> ---
>   scripts/qemu-binfmt-conf.sh | 7 ++-----
>   1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/scripts/qemu-binfmt-conf.sh b/scripts/qemu-binfmt-conf.sh
> index 6ef9f118d9..e38b767c24 100755
> --- a/scripts/qemu-binfmt-conf.sh
> +++ b/scripts/qemu-binfmt-conf.sh
> @@ -110,11 +110,11 @@ hppa_family=hppa
>   
>   riscv32_magic='\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xf3\x00'
>   
> riscv32_mask='\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff'
> -riscv32_family=riscv
> +riscv32_family=riscv32
>   
>   riscv64_magic='\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xf3\x00'
>   
> riscv64_mask='\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff'
> -riscv64_family=riscv
> +riscv64_family=riscv64
>   
>   xtensa_magic='\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x5e\x00'
>   
> xtensa_mask='\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff'
> @@ -168,9 +168,6 @@ qemu_get_family() {
>       sparc*)
>           echo "sparc"
>           ;;
> -    riscv*)
> -        echo "riscv"
> -        ;;
>       loongarch*)
>           echo "loongarch"
>           ;;