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[RFC PATCH 1/1] RISC-V: Add privileged extensions without instructions/CSRs

Nelson Chu nelson@rivosinc.com
Thu Sep 22 08:48:22 GMT 2022 
On Thu, Sep 22, 2022 at 3:59 PM Tsukasa OI <research_trasio@irq.a4lg.com> wrote:
>
> Currently, GNU Binutils does not support following privileged extensions:
>
> -   'Smepmp'
> -   'Svnapot'
> -   'Svpbmt'
>
> as they do not provide new CSRs or new instructions ('Smepmp' extends the
> privileged architecture CSRs but does not define the CSR itself).  However,
> adding them might be useful as we no longer have to "filter" ISA strings
> just for toolchains (if full ISA string is given by a vendor, we can
> straightly use it).

OKay.

Nelson

> And there's a fact that supports this theory: there's already an
> (unprivileged) extension which does not provide CSRs or instructions (but
> only an architectural guarantee): 'Zkt' (constant timing guarantee for
> certain subset of RISC-V instructions).
>
> This simple patchset simply adds three privileged extensions listed above.
>
> bfd/ChangeLog:
>
>         * elfxx-riscv.c (riscv_supported_std_s_ext): Add 'Smepmp',
>         'Svnapot' and 'Svpbmt' extensions.
> ---
>  bfd/elfxx-riscv.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/bfd/elfxx-riscv.c b/bfd/elfxx-riscv.c
> index 7eda177bd6e..bbc30c9afc2 100644
> --- a/bfd/elfxx-riscv.c
> +++ b/bfd/elfxx-riscv.c
> @@ -1210,10 +1210,13 @@ static struct riscv_supported_ext riscv_supported_std_z_ext[] =
>
>  static struct riscv_supported_ext riscv_supported_std_s_ext[] =
>  {
> +  {"smepmp",           ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
>    {"smstateen",                ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
>    {"sscofpmf",         ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
>    {"sstc",             ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
>    {"svinval",          ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
> +  {"svnapot",          ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
> +  {"svpbmt",           ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
>    {NULL, 0, 0, 0, 0}
>  };
>
> --
> 2.34.1
>
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