[Bug 2116086] Re: Build for RVA23U64 extension profile on RISC-V

[Heinrich Schuchardt]

The fencei instruction creates a synchronization fence for the whole
instruction cache. It is included in the RVA23S64 set of instructions
but not in RVA23U64.

I don't think that this is an instruction that a compiler would
generate. But you may see it as assembly instruction.

As the instruction may be issued in unprivileged mode it might be wiser
to include it in the -march= parameter to avoid touching packages
loading code into memory like JIT engines.

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Title:
  Build for RVA23U64 extension profile on RISC-V

Status in dpkg package in Ubuntu:
  Won't Fix
Status in gcc-14 package in Ubuntu:
  Incomplete
Status in gcc-15 package in Ubuntu:
  New
Status in llvm-toolchain-20 package in Ubuntu:
  New

Bug description:
  Up to now we have been building RISC-V packages for the RV64GC
  profile. With Ubuntu 25.10 we want to move to the RVA23U64 ISA
  extension profile.

  In scripts/Dpkg/Vendor/Ubuntu.pm we have to update CPPFLAGS, CFLAGS,
  OBJCFLAGS, CXXFLAGS, OBJCXXFLAGS and add a -march= value specifying
  the extensions.

  The mandatory RVA23U64 extensions are specified in

  RVA23 Profiles, Version 1.0, 2024-10-17:
  https://drive.google.com/file/d/12QKRm92cLcEk8-5J9NI91m0fAQOxqNAq/view

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