question about RISCV EFI stub support

[Atish Patra]

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 ?

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



-- 
Regards,
Atish