Re: [PATCH] target/riscv: Restore the predicate() NULL check behavior

[LIU Zhiwei <zhiwei_liu@linux.alibaba.com>]

On 2023/4/11 17:02, Bin Meng wrote:
> When reading a non-existent CSR QEMU should raise illegal instruction
> exception, but currently it just exits due to the g_assert() check.
>
> This actually reverts commit 0ee342256af9205e7388efdf193a6d8f1ba1a617,
> Some comments are also added to indicate that predicate() must be
> provided for an implemented CSR.
>
> Reported-by: Fei Wu <fei2.wu@intel.com>
> Signed-off-by: Bin Meng <bmeng@tinylab.org>

Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>

Zhiwei

> ---
>
>   target/riscv/csr.c | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index d522efc0b6..736ab64275 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -3797,6 +3797,11 @@ static inline RISCVException riscv_csrrw_check(CPURISCVState *env,
>           return RISCV_EXCP_ILLEGAL_INST;
>       }
>   
> +    /* ensure CSR is implemented by checking predicate */
> +    if (!csr_ops[csrno].predicate) {
> +        return RISCV_EXCP_ILLEGAL_INST;
> +    }
> +
>       /* privileged spec version check */
>       if (env->priv_ver < csr_min_priv) {
>           return RISCV_EXCP_ILLEGAL_INST;
> @@ -3814,7 +3819,6 @@ static inline RISCVException riscv_csrrw_check(CPURISCVState *env,
>        * illegal instruction exception should be triggered instead of virtual
>        * instruction exception. Hence this comes after the read / write check.
>        */
> -    g_assert(csr_ops[csrno].predicate != NULL);
>       RISCVException ret = csr_ops[csrno].predicate(env, csrno);
>       if (ret != RISCV_EXCP_NONE) {
>           return ret;
> @@ -3991,7 +3995,10 @@ RISCVException riscv_csrrw_debug(CPURISCVState *env, int csrno,
>       return ret;
>   }
>   
> -/* Control and Status Register function table */
> +/*
> + * Control and Status Register function table
> + * riscv_csr_operations::predicate() must be provided for an implemented CSR
> + */
>   riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
>       /* User Floating-Point CSRs */
>       [CSR_FFLAGS]   = { "fflags",   fs,     read_fflags,  write_fflags },