Re: [RFC] gdb/riscv: Add target description support

[John Baldwin <jhb at FreeBSD dot org>]

On 11/8/18 11:32 AM, Palmer Dabbelt wrote:
> On Thu, 08 Nov 2018 10:32:57 PST (-0800), jhb@FreeBSD.org wrote:
>> On 11/8/18 8:07 AM, Andrew Burgess wrote:
>>> This commit adds target description support for riscv.
>>>
>>> I've used the split feature approach for specifying the architectural
>>> features, and the CSR feature is auto-generated from the riscv-opc.h
>>> header file.
>>
>> In general this looks fine to me (as far as I am familiar with the
>> target descriptions).  The only possible question/comment I have is if
>> you considered describing fields of specific registers such as the FP
>> status registers or MSTATUS, etc. as fields in the XML to replace the
>> current special cases in riscv_print_one_register_info().  I think the
>> XML can't handle enum values as riscv_print_one_register_info() uses for
>> some cases, but I think it would be able to handle many of the special
>> cases in that function.
>>
>> Some related-ish questions (though not about this patch): I wonder if we
>> can do things with pseudo registers to automatically derive FFLAGS and
>> FRM if a target provides FCSR.
>>
>> One more note: AFAIU, 1.10 of the privilege spec removed hypervisor mode
>> with the intention of implementing virtualization support differently.
>> We might want to remove the references to hypervisor mode from riscv-tdep.c
>> as a result?
> 
> The only reference I see is in the PRV decoding, which I think is OK: while the 
> spec doesn't mention hypervisor mode any more, the bit pattern is still there 
> and an upcoming spec will add it back in.  I believe the official name is now 
> "hypervisor-extended supervisor mode" but since that's a bit of a mouthfull I 
> still call it hypervisor mode :)

Ah, ok.  There are also HIE, etc. bits in the MSTATUS decoding that would
also be related, but if they are going to be reused then leaving them as-is
is probably fine.

-- 
John Baldwin