question about RISCV EFI stub support

[Kefeng Wang]

+ Palmer, sorry forget add to cc list...

On 2021/2/25 10:00, Atish Patra wrote:
> On Wed, Feb 24, 2021 at 5:29 PM Kefeng Wang <wangkefeng.wang at huawei.com> wrote:
>>
>> 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?
>>
> I think RISCV_ISA_C was enabled by default just to generate a smaller
> binary size.
> @palmer : was there any other reason ?

Any comment about the too issue,

1)  directly use .shout MZ_MAGIC to decouple EFI_STUB and RISCV_ISA_C.

2)  don't set RISCV_ISA_C  to default y

>>> Do you just want it for a custom kernel or the upstream kernel ?
>>>
>>>> Thanks,
>>>>
>>>> Kefeng
>>>>
>>>>
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>>>
>
>