[PATCH] RISC-V: errata: Use medany for relocatable builds

[Alexandre Ghiti]

On 26/03/2025 23:45, Palmer Dabbelt wrote:
> We're trying to mix non-PIC/PIE objects into the otherwise-PIE
> relocatable kernels, to avoid GOT/PLT references during early boot
> alternative resolution (which happens before the GOT/PLT are set up).
>
> riscv64-unknown-linux-gnu-ld: arch/riscv/errata/sifive/errata.o: relocation R_RISCV_HI20 against `tlb_flush_all_threshold' can not be used when making a shared object; recompile with -fPIC
> riscv64-unknown-linux-gnu-ld: arch/riscv/errata/thead/errata.o: relocation R_RISCV_HI20 against `riscv_cbom_block_size' can not be used when making a shared object; recompile with -fPIC


thead erratas are already compiled with medany if 
CONFIG_RISCV_ALTERNATIVE_EARLY is set 
(https://elixir.bootlin.com/linux/v6.14-rc6/source/arch/riscv/errata/thead/Makefile#L2) 
so why isn't it enough?


>
> Fixes: 8dc2a7e8027f ("riscv: Fix relocatable kernels with early alternatives using -fno-pie")
> Signed-off-by: Palmer Dabbelt <palmer at rivosinc.com>
> ---
> I'm not 100% sure it's possible to expose this without Samuel's NOMMU
> relocatable builds, see
> <https://lore.kernel.org/all/mhng-517c0318-c8fb-4c4a-aa0e-0d08f8d34d78@palmer-ri-x1c9/>
> ---
>   arch/riscv/errata/Makefile | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/errata/Makefile b/arch/riscv/errata/Makefile
> index f0da9d7b39c3..bc6c77ba837d 100644
> --- a/arch/riscv/errata/Makefile
> +++ b/arch/riscv/errata/Makefile
> @@ -1,5 +1,9 @@
>   ifdef CONFIG_RELOCATABLE
> -KBUILD_CFLAGS += -fno-pie
> +# We can't use PIC/PIE when handling early-boot errata parsing, as the kernel
> +# doesn't have a GOT setup at that point.  So instead just use medany: it's
> +# usually position-independent, so it should be good enough for the errata
> +# handling.
> +KBUILD_CFLAGS += -fno-pie -mcmodel=medany
>   endif
>   
>   ifdef CONFIG_RISCV_ALTERNATIVE_EARLY