riscv_priv_ext_without_insn_or_csrs

RISC-V: Add privileged extensions without instructions/CSRs

• Status: Merged for Binutils 2.40
• Branch: riscv-priv-ext-without-insn-or-csrs
• Tracking PR: #48 (view Pull Request and Diff)
• Mailing List:
  • RFC PATCH v1 (2022-09-22)

Issue Solved

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, I started considering adding them to GNU Binutils' supported extension list.

One of the reason is simple: if we do that, 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).

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 I described above.