[RFC PATCH 1/1] RISC-V: Add privileged extensions without instructions/CSRs

[Tsukasa OI]

On 2022/09/22 17:48, Nelson Chu wrote:
> On Thu, Sep 22, 2022 at 3:59 PM Tsukasa OI <research_trasio@irq.a4lg.com> wrote:
>>
>> Currently, GNU Binutils does not support following privileged extensions:
>>
>> -   'Smepmp'
>> -   'Svnapot'
>> -   'Svpbmt'
>>
>> as they do not provide new CSRs or new instructions ('Smepmp' extends the
>> privileged architecture CSRs but does not define the CSR itself).  However,
>> adding them might be useful as we no longer have to "filter" ISA strings
>> just for toolchains (if full ISA string is given by a vendor, we can
>> straightly use it).
> 
> OKay.
> 
> Nelson

Understood.  I'm going to push this patch in a week if there's no other
comments.  But until then, I'll wait for other opinions.

Thanks,
Tsukasa

> 
>> And there's a fact that supports this theory: there's already an
>> (unprivileged) extension which does not provide CSRs or instructions (but
>> only an architectural guarantee): 'Zkt' (constant timing guarantee for
>> certain subset of RISC-V instructions).
>>
>> This simple patchset simply adds three privileged extensions listed above.
>>
>> bfd/ChangeLog:
>>
>>         * elfxx-riscv.c (riscv_supported_std_s_ext): Add 'Smepmp',
>>         'Svnapot' and 'Svpbmt' extensions.
>> ---
>>  bfd/elfxx-riscv.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/bfd/elfxx-riscv.c b/bfd/elfxx-riscv.c
>> index 7eda177bd6e..bbc30c9afc2 100644
>> --- a/bfd/elfxx-riscv.c
>> +++ b/bfd/elfxx-riscv.c
>> @@ -1210,10 +1210,13 @@ static struct riscv_supported_ext riscv_supported_std_z_ext[] =
>>
>>  static struct riscv_supported_ext riscv_supported_std_s_ext[] =
>>  {
>> +  {"smepmp",           ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
>>    {"smstateen",                ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
>>    {"sscofpmf",         ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
>>    {"sstc",             ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
>>    {"svinval",          ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
>> +  {"svnapot",          ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
>> +  {"svpbmt",           ISA_SPEC_CLASS_DRAFT,           1, 0, 0 },
>>    {NULL, 0, 0, 0, 0}
>>  };
>>
>> --
>> 2.34.1
>>
>