[PATCH v3 1/4] RISC-V: Update the CSR to privilege spec 1.12.

[Andrew Waterman]

On Fri, Jan 31, 2020 at 4:19 PM Jim Wilson <jimw@sifive.com> wrote:
>
> On Sun, Dec 15, 2019 at 9:22 PM Nelson Chu <nelson.chu@sifive.com> wrote:
> >         gas/
> >         * testsuite/gas/riscv/priv-reg.s: Rename to priv-reg-all.s  Update
> >         the CSR to privilege spec 1.12.
> >         * testsuite/gas/riscv/priv-reg.d: Likewise.
> >         * testsuite/gas/riscv/bad-csr.s: Rename to priv-reg-fail-nonexistent.
> >         * testsuite/gas/riscv/bad-csr.d: Likewise.
> >         * testsuite/gas/riscv/bad-csr.l: Likewise.
> >         * testsuite/gas/riscv/satp.s: Deleted.  Duplicate of priv-reg-all.s
> >         * testsuite/gas/riscv/satp.d: Likewise.
> >         * testsuite/gas/riscv/csr-dw-regnums.s: Updated.
> >         * testsuite/gas/riscv/csr-dw-regnums.d: Likewise.
> >
> >         include/
> >         * opcode/riscv-opc.h: Update the CSR to privilege spec 1.12.
> >
> >         gdb/
> >         * features/riscv/32bit-csr.xml: Regenerated.
> >         * features/riscv/64bit-csr.xml: Regenerated.
>
> Privilege spec 1.11 is ratified, and spec 1.12 is in draft form.  Do
> we want to implement a draft?

It seems inadvisable to incorporate draft standards into the FSF
binutils port.  In particular, the hypervisor ISA is virtually certain
to change in backwards-incompatible ways prior to being frozen.  It
seems to me that pushing this stuff upstream at this time will cause
more problems than it solves.

We could consider maintaining these patches on branches in the RISC-V
github repositories, and push them to the FSF tree at the appropriate
time.  That way, we can support software development against these
draft standards while reducing the scope of backwards
incompatibilities.

>
>
> I see some hypervisor registers missing, e.g. hgeie and hgeip which
> were added to the 1.12 draft on November 20.  Hie was added Oct 29,
> and is listed as dropped in your patch.  It isn't clear to me which
> version of the 1.12 draft you are using, but it seems to be an old
> one.  If we are implementing
> 1.12 draft we should probably implement the current one.
>
> Overall it looks reasonable, but we need to be clear which spec we are
> implementing, so we can verify that the patch matches the spec.
>
> I see that the csr-dw-regnums.s test doesn't have any of the csr
> aliases, but that seems OK.  priv-reg-all.s is the important one and
> does have all of them.
>
> You are modifying gdb xml files.  These need to be sent to gdb-patches
> for approval instead of the binutils list, and I don't have gdb patch
> approval permission.  These are shared with qemu, and ideally should
> be kept in sync.  As a practical matter though, gdb doesn't use the
> csr xml files as yet.  And updating qemu means adding priv spec 1.12
> draft support to qemu which is probably non-trivial, unless we can
> ignore the as yet unsupported registers in the gdb stub which should
> work.  I believe WDC is working on the qemu hypervisor support, so it
> might actually be tracking the 1.12 draft already.  It is probably OK
> to submit the gdb xml changes, and then file a bug somewhere asking
> for gdb and qemu xml support to be synchronized.
>
> Jim