Re: [PATCH v2] target/riscv: raise an exception when CSRRS/CSRRC writes a read-only CSR

[Richard Henderson]

On 3/10/24 17:08, Yu-Ming Chang via wrote:
> Both CSRRS and CSRRC always read the addressed CSR and cause any read side
> effects regardless of rs1 and rd fields. Note that if rs1 specifies a register
> holding a zero value other than x0, the instruction will still attempt to write
> the unmodified value back to the CSR and will cause any attendant side effects.
>
> So if CSRRS or CSRRC tries to write a read-only CSR with rs1 which specifies
> a register holding a zero value, an illegal instruction exception should be
> raised.
>
> Signed-off-by: Yu-Ming Chang<yumin686@andestech.com>
> ---
> This incorporated the comments from Richard. Thank you.
>
>   target/riscv/cpu.h       |  2 ++
>   target/riscv/csr.c       | 17 ++++++++++++++---
>   target/riscv/op_helper.c |  2 +-
>   3 files changed, 17 insertions(+), 4 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~