On Tue, Mar 16, 2021 at 5:28 PM Richard W.M. Jones <rjo...@redhat.com> wrote:
>
> On Mon, Mar 15, 2021 at 11:24:47AM +0100, Florian Weimer wrote:
> > * Takayuki Nagata:
> >
> > > I think "--with-arch=" should be "rv64g" for gcc without compressed
> > > instruction support, because the default is RV64GC[0].
> >
> > As far as I understand it, there is no glibc port for RISC-V without
> > compressed instruction support.  Presumably the GCC default reflects
> > this.
>
> Oh ah, is this so?  If so that's a problem for Billa because
> he's trying to rebuild Fedora for the SHAKTI chip that lacks
> compressed instructions.
>
> But I had a look through all the RISC-V asm files in current glibc and
> I can't see any compressed instructions there, nor any directives to
> turn on the rvc option.
>
>   $ egrep -i '(\bc\.|rvc)' `find sysdeps/riscv/ 
> sysdeps/unix/sysv/linux/riscv/ -name '*.S' `
>
> Do you know why glibc wouldn't understand the C extension?
>

Note, that Linux kinda requires C too now (since EFI was merged). See:
https://lists.infradead.org/pipermail/linux-riscv/2021-March/004961.html

Quote from Palmer's reply:
"""
So the dependency here is actually a bit odd: platforms without C _can_ use
EFI, the EFI images just can't be booted on non-EFI systems (because the flat
binaries need to execute the PE/COFF header).  The issue is really that we
can't support all three of non-C, EFI, and non-EFI in the Image format.

The reason we coupled C and EFI is really to avoid the existence of EFI-only
kernels, which are a headache these days because EFI isn't widely supported or
used on RISC-V.  The general assumption is that, since we recommend rv64gc for
portable systems and EFI is mostly of interest to portable systems, we won't
end up with non-C EFI systems and therefor don't need to worry about having
incompatible kernels.  That said, if there's one thing I've learned from the
whole RISC-V thing it's that whenever I say "we don't think hardware that does
X will show up" it does.  Assuming that's the case and we end up with non-C
systems that people want to run EFI on, we'll figure out a way to do that -- if
someone has real hardware I'm inclined to support it, otherwise we just end up
with a mess of vendor-specific forks.
"""
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