Re: [PATCH v2 1/1] target/riscv: misa to ISA string conversion fix

[Frédéric Pétrot]

Hello,

Le 28/03/2022 à 15:11, Tsukasa OI a écrit :
> Some bits in RISC-V `misa' CSR should not be reflected in the ISA
> string.  For instance, `S' and `U' (represents existence of supervisor
> and user mode, respectively) in `misa' CSR must not be copied since
> neither `S' nor `U' are valid single-letter extensions.
>
> This commit also removes all reserved/dropped single-letter "extensions"
> from the list.
>
> -   "B": Not going to be a single-letter extension (misa.B is reserved).
> -   "J": Not going to be a single-letter extension (misa.J is reserved).
> -   "K": Not going to be a single-letter extension (misa.K is reserved).
> -   "L": Dropped.
> -   "N": Dropped.
> -   "T": Dropped.
>
> It also clarifies that the variable `riscv_single_letter_exts' is a
> single-letter extension order list.
>
> Signed-off-by: Tsukasa OI <research_trasio@irq.a4lg.com>
> ---
>   target/riscv/cpu.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index ddda4906ff..1f68c696eb 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -34,7 +34,7 @@
>   
>   /* RISC-V CPU definitions */
>   
> -static const char riscv_exts[26] = "IEMAFDQCLBJTPVNSUHKORWXYZG";
> +static const char riscv_single_letter_exts[] = "IEMAFDQCPVH";
>   
>   const char * const riscv_int_regnames[] = {
>     "x0/zero", "x1/ra",  "x2/sp",  "x3/gp",  "x4/tp",  "x5/t0",   "x6/t1",
> @@ -901,12 +901,12 @@ static void riscv_cpu_class_init(ObjectClass *c, void 
> *data)
>   char *riscv_isa_string(RISCVCPU *cpu)
>   {
>       int i;
> -    const size_t maxlen = sizeof("rv128") + sizeof(riscv_exts) + 1;
> +    const size_t maxlen = sizeof("rv128") + sizeof(riscv_single_letter_exts);
>       char *isa_str = g_new(char, maxlen);
>       char *p = isa_str + snprintf(isa_str, maxlen, "rv%d", TARGET_LONG_BITS);

To avoid one dependency on TARGET_LONG_BITS that is not necessary now that we
have mxl, I would suggest to replace the previous line with:
     char *p = isa_str + snprintf(isa_str, maxlen, "rv%d",
                                  1 << (4 + cpu->env.misa_mxl_max));

Frédéric