[PATCH 1/1] RISC-V: Change signature header field to use `.ascii` instead of opcode

[Atish Patra]

On Mon, Jan 17, 2022 at 11:00 AM Jessica Clarke <jrtc27 at jrtc27.com> wrote:
>
> On 17 Jan 2022, at 17:39, Florian Wagner <florian.wagner at nextsilicon.com> wrote:
> >
> > The `MZ` in the signature header field is now encoded via `.ascii` to make
> > the kernel compile without the `c` extension.
> >
> > Signed-off-by: Florian Wagner <florian.wagner at nextsilicon.com>
> > Signed-off-by: Yaron Dinkin <yaron.dinkin at nextsilicon.com>
> > ---
> > arch/riscv/kernel/head.S | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> > index f52f01ecbeea..931b63464b90 100644
> > --- a/arch/riscv/kernel/head.S
> > +++ b/arch/riscv/kernel/head.S
> > @@ -48,7 +48,7 @@ ENTRY(_start)
> >       /*
> >        * This instruction decodes to "MZ" ASCII required by UEFI.
> >        */
> > -     c.li s4,-13
> > +     .ascii "MZ"
> >       j _start_kernel
>
> CONFIG_EFI has select RISCV_ISA_C, so this doesn’t seem to achieve
> anything? If you then remove that select, well, you get an EFI binary
> that works, but if you jump to it directly as a non-EFI binary then
> you’ll trap on a non-RVC system as that won’t be a valid instruction.
> So I think this needs more explanation and discussion.
>

Here is the previous discussion regarding this.

http://lists.infradead.org/pipermail/linux-riscv/2021-March/004998.html

TLDR, there is no cleaner way to support both EFI & non-UEFI booting
on a platform
without C extension. Linux kernel anyways recommend rv64gc for platforms.

> Jess
>
>
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-- 
Regards,
Atish