question about RISCV EFI stub support

[Kefeng Wang]

On 2021/2/25 7:35, Atish Patra wrote:
> On Wed, Feb 24, 2021 at 3:14 AM Kefeng Wang <wangkefeng.wang at huawei.com> wrote:
>> Hi Atish and Ard,
>>
>> The commit "cb7d2dd5612a RISC-V: Add PE/COFF header for EFI stub" use
>> c.li to
>>
>> add Magic "MZ" signature for PE/COFF header, which select RISCV_ISA_C,
>> but "C"
>>
>> to the ISA is optional,  and if "C" is not support ,  EFI boot is not
>> supported.
>>
>> Could we use ".word MZ_MAGIC" like x86 code or some other way to support
>> "MZ" signature?
>>
> .word won't work but .short will. With .word, you end up 0000 in the 2
> bytes which can be interpreted as illegal instruction.
Yes, should use ".short" in RV.
>
> I guess your larger objective is to make the C extension optional and
> not enabled by default for the Linux kernel.

"C" extension is optional, and the upstream kernel has the RISCV_ISA_C which

could be configurable.  and I think the EFI_STUB should not depend or 
select it,

and maybe we only want to support RV64G in some cases,  what's your option?

> Do you just want it for a custom kernel or the upstream kernel ?
>
>> Thanks,
>>
>> Kefeng
>>
>>
>> _______________________________________________
>> linux-riscv mailing list
>> linux-riscv at lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-riscv
>
>