Re: [PATCH v3] RISC-V: Add CONFIG_{NON,}PORTABLE

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Palmer,

On Sat, May 21, 2022 at 10:49 PM Palmer Dabbelt <palmer@rivosinc.com> wrote:
> From: Palmer Dabbelt <palmer@rivosinc.com>
>
> The RISC-V port has collected a handful of options that are
> fundamentally non-portable.  To prevent users from shooting themselves
> in the foot, hide them all behind a config entry that explicitly calls
> out that non-portable binaries may be produced.
>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Reviewed-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Thanks for your patch, which is now commit 44c1e84a38a03175 ("RISC-V:
Add CONFIG_{NON,}PORTABLE") in riscv/for-next

> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -222,6 +222,21 @@ source "arch/riscv/Kconfig.erratas"
>
>  menu "Platform type"
>
> +config NONPORTABLE
> +       bool "Allow configurations that result in non-portable kernels"
> +       help
> +         RISC-V kernel binaries are compatible between all known systems
> +         whenever possible, but there are some use cases that can only be
> +         satisfied by configurations that result in kernel binaries that are
> +         not portable between systems.
> +
> +         Selecting N does not guarantee kernels will be portable to all known
> +         systems.  Selecting any of the options guarded by NONPORTABLE will
> +         result in kernel binaries that are unlikely to be portable between
> +         systems.
> +
> +         If unsure, say N.

Doing it this way means allmodconfig will enable NONPORTABLE, which
may not be what we want?

> +
>  choice
>         prompt "Base ISA"
>         default ARCH_RV64I

> @@ -554,7 +571,7 @@ config PHYS_RAM_BASE
>
>  config XIP_KERNEL
>         bool "Kernel Execute-In-Place from ROM"
> -       depends on MMU && SPARSEMEM
> +       depends on MMU && SPARSEMEM && NONPORTABLE

Nice! Would we get something like this on arm32 past rmk?

>         # This prevents XIP from being enabled by all{yes,mod}config, which
>         # fail to build since XIP doesn't support large kernels.
>         depends on !COMPILE_TEST
> @@ -594,9 +611,16 @@ endmenu
>
>  config BUILTIN_DTB
>         bool
> -       depends on OF
> +       depends on OF && NONPORTABLE
>         default y if XIP_KERNEL
>
> +config PORTABLE
> +       bool
> +       default !NONPORTABLE
> +       select EFI
> +       select OF
> +       select MMU
> +
>  menu "Power management options"
>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds