> As per:
> <https://github.com/riscv/riscv-code-size-reduction/issues/221>,
> the 'Zcf' extension does not exist on RV64.  This is reflected on the
> version 1.0.4-1 of the code size reduction specification:
> <https://github.com/riscv/riscv-code-size-reduction/releases/tag/v1.0.4-1>.
> 
> This commit prohibits the combination: RV64 (or any ISA with XLEN > 32)
> and the 'Zcf' extension.
> 
> bfd/ChangeLog:
> 
> * elfxx-riscv.c (riscv_parse_check_conflicts): Prohibit
> combination of RV64 and 'Zcf'.
> 
> gas/ChangeLog:
> 
> * testsuite/gas/riscv/march-fail-rv64i_zcf.d: New test.
> * testsuite/gas/riscv/march-fail-rv64i_zcf.l: Likewise.
> ---
>  bfd/elfxx-riscv.c                              | 7 +++++++
>  gas/testsuite/gas/riscv/march-fail-rv64i_zcf.d | 3 +++
>  gas/testsuite/gas/riscv/march-fail-rv64i_zcf.l | 2 ++
>  3 files changed, 12 insertions(+)
>  create mode 100644 gas/testsuite/gas/riscv/march-fail-rv64i_zcf.d
>  create mode 100644 gas/testsuite/gas/riscv/march-fail-rv64i_zcf.l
> 
> diff --git a/bfd/elfxx-riscv.c b/bfd/elfxx-riscv.c
> index ee96608358e8..eaf496649db1 100644
> --- a/bfd/elfxx-riscv.c
> +++ b/bfd/elfxx-riscv.c
> @@ -1946,6 +1946,13 @@ riscv_parse_check_conflicts (riscv_parse_subset_t *rps)
>        rps->error_handler (_("rv%d does not support the `q' extension"), xlen);
>        no_conflict = false;
>      }
> +  if (riscv_lookup_subset (rps->subset_list, "zcf", &subset)
> +      && xlen > 32)
> +    {
> +      rps->error_handler
> + (_("rv%d does not support the `zcf' extension"), xlen);
> +      no_conflict = false;
> +    }
>    if (riscv_lookup_subset (rps->subset_list, "zfinx", &subset)
>        && riscv_lookup_subset (rps->subset_list, "f", &subset))
>      {
> diff --git a/gas/testsuite/gas/riscv/march-fail-rv64i_zcf.d b/gas/testsuite/gas/riscv/march-fail-rv64i_zcf.d
> new file mode 100644
> index 000000000000..1b70a9e280f0
> --- /dev/null
> +++ b/gas/testsuite/gas/riscv/march-fail-rv64i_zcf.d
> @@ -0,0 +1,3 @@
> +#as: -march=rv64i_zcf
> +#source: empty.s
> +#error_output: march-fail-rv64i_zcf.l
> diff --git a/gas/testsuite/gas/riscv/march-fail-rv64i_zcf.l b/gas/testsuite/gas/riscv/march-fail-rv64i_zcf.l
> new file mode 100644
> index 000000000000..b9e07c64d52f
> --- /dev/null
> +++ b/gas/testsuite/gas/riscv/march-fail-rv64i_zcf.l
> @@ -0,0 +1,2 @@
> +.*Assembler messages:
> +.*Error: .*rv64 does not support the `zcf' extension
> -- 


> 2.41.0




LGTM, thanks for your work!