[PATCH 5/7] RISC-V: fix auipc-jalr addresses in patched alternatives

[Lad, Prabhakar]

Hi Heiko,

Thank you for the patch.

On Thu, Nov 10, 2022 at 4:50 PM Heiko Stuebner <heiko at sntech.de> wrote:
>
> From: Heiko Stuebner <heiko.stuebner at vrull.eu>
>
> Alternatives live in a different section, so addresses used by call
> functions will point to wrong locations after the patch got applied.
>
> Similar to arm64, adjust the location to consider that offset.
>
> Signed-off-by: Heiko Stuebner <heiko.stuebner at vrull.eu>
> ---
>  arch/riscv/kernel/cpufeature.c | 79 +++++++++++++++++++++++++++++++++-
>  1 file changed, 77 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 694267d1fe81..026512ca9c4c 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -298,6 +298,74 @@ static u32 __init_or_module cpufeature_probe(unsigned int stage)
>         return cpu_req_feature;
>  }
>
> +#include <asm/parse_asm.h>
> +
> +DECLARE_INSN(jalr, MATCH_JALR, MASK_JALR)
> +DECLARE_INSN(auipc, MATCH_AUIPC, MASK_AUIPC)
> +
> +static inline bool is_auipc_jalr_pair(long insn1, long insn2)
> +{
> +       return is_auipc_insn(insn1) && is_jalr_insn(insn2);
> +}
> +
> +#define JALR_SIGN_MASK         BIT(I_IMM_SIGN_OPOFF - I_IMM_11_0_OPOFF)
> +#define JALR_OFFSET_MASK       I_IMM_11_0_MASK
> +#define AUIPC_OFFSET_MASK      U_IMM_31_12_MASK
> +#define AUIPC_PAD              (0x00001000)
> +#define JALR_SHIFT             I_IMM_11_0_OPOFF
> +
> +#define to_jalr_imm(offset)                                            \
> +       ((offset & I_IMM_11_0_MASK) << I_IMM_11_0_OPOFF)
> +
> +#define to_auipc_imm(offset)                                           \
> +       ((offset & JALR_SIGN_MASK) ?                                    \
> +       ((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) :    \
> +       (offset & AUIPC_OFFSET_MASK))
> +
> +static void riscv_alternative_fix_auipc_jalr(unsigned int *alt_ptr,
> +                                            unsigned int len, int patch_offset)
> +{

I am yet to test this with my ASM code yet, but maybe can we move this
to [0] so that other erratas can make use of it too?

[0] arch/riscv/kernel/patch.c

Cheers,
Prabhakar