cmd/internal/obj: instructions and registers for RISC-V

Start implementing an assembler for RISC-V - this provides register
definitions and instruction mnemonics as defined in the RISC-V
Instruction Set Manual, along with instruction encoding.

The instruction encoding is generated by the parse_opcodes script with
the "opcodes" and "opcodes-pseudo" files from (`make inst.go`):

  https://github.com/riscv/riscv-opcodes

This is based on the riscv-go port:

  https://github.com/riscv/riscv-go

Contributors to the riscv-go port are:

  Amol Bhave <ammubhave@gmail.com>
  Benjamin Barenblat <bbaren@google.com>
  Josh Bleecher Snyder <josharian@gmail.com>
  Michael Pratt <michael@pratt.im>
  Michael Yenik <myenik@google.com>
  Ronald G. Minnich <rminnich@gmail.com>
  Stefan O'Rear <sorear2@gmail.com>

This port has been updated to Go 1.13:

  https://github.com/4a6f656c/riscv-go

Updates #27532

Change-Id: I257b6de87e9864df61a2b0ce9be15968c1227b49
Reviewed-on: https://go-review.googlesource.com/c/go/+/193677
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/cmd/internal/obj/util.go b/src/cmd/internal/obj/util.go
index f1517d3d5d..46d662c6c8 100644
--- a/src/cmd/internal/obj/util.go
+++ b/src/cmd/internal/obj/util.go
@@ -457,6 +457,7 @@ const (
 	RBaseARM64 = 8 * 1024  // range [8k, 13k)
 	RBaseMIPS  = 13 * 1024 // range [13k, 14k)
 	RBaseS390X = 14 * 1024 // range [14k, 15k)
+	RBaseRISCV = 15 * 1024 // range [15k, 16k)
 	RBaseWasm  = 16 * 1024
 )