Compiling for RISC-V

[Richard Levitte]

On Mon, 09 Mar 2020 05:18:17 +0100,
Kristin Barber wrote:
> I've looked at the INSTALL docs, and it doesn't seem that RISC-V processors are supported
> currently as a platform. Is this correct?

That is correct.  No one has implemented that support yet.

> Is there a branch which enables configuring for a RISC-V machine that hasn't yet made it into a
> stable release?  

Not that I know of.  Although, this same question has also been raised
on github (I forget the issue number).

> Any advice on where to look for information or changes to the build process in order to compile
> for RISC-V?

The first thing to attempt is a generic build with no assembler.
There are some really simply config targets that could be a first
step, one of:

    ./Configure cc

    ./Configure gcc

A (pretty big) step up from that, at least if Linux is your target,
would be one of these:

    ./Configure linux-generic32

    ./Configure linux-generic64

Note that in either case, you may have to add C flags and ld flags,
which you can do in one of two ways:

1)  directly on the configuration command line, like this (Configure
    makes an educated guess on what flags go where):

    ./Configure linux-generic64 -m64 -DWHATEVER=value -Wl,-something

2)  via "make variable" assignment:

    ./Configure linux-generic64 \
                CPPFLAGS='-DWHATEVER=value' \
                CFLAGS='-m64' \
                LDFLAGS='-Wl,-something'

At some point, you might find a combination that works for you.  We
would definitely like to know what you figure out, and it may be that
the result makes it into our database of config targets (which, if
you're curious, are the files Configurations/*.conf).

Now, configuration is the easy bit when it comes to new CPUs,
relatively speaking.  I assume that part of your question is whether
there is assembler support.  This is the hard part in terms of
effort.  We currently have no such thing at all for RISC-V, and I
haven't seen any attempts to start such an effort...  PRs would
certainly be welcome, but anyone who tries this will have to be
prepared for it to take a while to get into the main source.

Cheers,
Richard

-- 
Richard Levitte         levitte at openssl.org
OpenSSL Project         http://www.openssl.org/~levitte/