Re: RISC-V support

[Jim Wilson <jimw@sifive.com>]

On Tue, Jan 8, 2019 at 5:52 AM Mark Wielaard <mark@klomp.org> wrote:
> The _start one seems to be:
> https://sourceware.org/bugzilla/show_bug.cgi?id=23125
> So that is fixed with glibc 2.29.
>
> Do you have a bug for the second issue with __thread_start?

https://sourceware.org/bugzilla/show_bug.cgi?id=24040

I plan to write a patch for it, if Andreas Schwab doesn't get to it
first, but the Fedora koji package server was down for a few weeks
which prevented me from installing the packages I needed to do this
work.  It is back up and I am looking at this now.

> It would be nice to have some riscv setup for our buildbot. Do you
> happen to have recommendations for something like that? Any distro that
> gets regular toolchain updates? Is a libvirt/qemu setup reliable enough
> or would you recommend trying to get real hardware?

I've been using Fedora, but Debian and OpenSuse are both usable too.
Fedora is just a little more convenient for me as they have images I
can download and boot, and a git tree for building a kernel with NBD
support which makes the HiFive Unleashed much more stable than when
using the SDcard for the root file system.  Plus I used to work for
Cygnus/Red Hat so maybe I am a little biased.

QEMU works too.  There are some known bugs in the RISC-V qemu FP
support, I wouldn't use it for numerical work.  If you stress the
system you might find some bugs, but overall it is certainly usable.
I used qemu for my gdb work, because it was easier to try kernel
patches that way, and I didn't want to risk trying untested kernel
patches on my main RISC-V development system.  The linux distro folks
are using qemu for builds also, to supplement the builds on hardware,
as they have limited numbers of boards at present.

There is only one ASIC option for running linux that I know of at this
time, and that is the SiFive HiFive Unleashed.  It is faster than qemu
running on a fast x86_64 machine.  It is stable if you don't use the
SDcard for anything other than booting.  I've hit 60 days of uptime on
my board, running a patched 4.15 kernel.  There are also FPGA options,
but these are more complicated and probably more expensive than using
the HiFive Unleashed.  I expect that more hardware options will be
available in the future.

Jim