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

[Tsukasa OI]

On 2022/03/30 1:29, Frédéric Pétrot wrote:
> 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));

LGTM except... that won't be a part of my patch (you are trying to fix
separate issue).  You can submit separate patch for this.

To comment, I like
        16 << cpu->env.misa_mxl_max
rather than
        1 << (4 + cpu->env.misa_mxl_max)
for consistency with target/riscv/gdbstub.c:
        int bitsize = 16 << env->misa_mxl_max;

Tsukasa

> 
> Frédéric
>