Implement Zcb extension

This adds an implementation of the Zcb code size extension.

Co-authored-by: Martin Berger <martinberger@users.noreply.github.com>

11 files changed, 237 insertions, 1 deletions

diff --git a/LICENCE b/LICENCE
index 9dddf34..432b78d 100644
--- a/LICENCE
+++ b/LICENCE
@@ -16,7 +16,7 @@ Copyright (c) 2017-2024
    Brian Campbell
    Chris Casinghino
    Christopher Pulte
-   Codasip, for contributions by Tim Hutt
+   Codasip, for contributions by Tim Hutt, Martin Berger and Ben Fletcher
    dylux
    eroom1966
    Google LLC, for contributions by its employees
diff --git a/Makefile b/Makefile
index deaad55..7068968 100644
--- a/Makefile
+++ b/Makefile
@@ -32,6 +32,8 @@ SAIL_DEFAULT_INST += riscv_insts_zbb.sail
 SAIL_DEFAULT_INST += riscv_insts_zbc.sail
 SAIL_DEFAULT_INST += riscv_insts_zbs.sail
 
+SAIL_DEFAULT_INST += riscv_insts_zcb.sail
+
 SAIL_DEFAULT_INST += riscv_insts_zfh.sail
 # Zfa needs to be added after fext, dext and Zfh (as it needs
 # definitions from those)
diff --git a/c_emulator/riscv_platform.c b/c_emulator/riscv_platform.c
index 253da35..6544de6 100644
--- a/c_emulator/riscv_platform.c
+++ b/c_emulator/riscv_platform.c
@@ -32,6 +32,11 @@ bool sys_enable_fdext(unit u)
   return rv_enable_fdext;
 }
 
+bool sys_enable_zcb(unit u)
+{
+  return rv_enable_zcb;
+}
+
 bool sys_enable_zfinx(unit u)
 {
   return rv_enable_zfinx;
diff --git a/c_emulator/riscv_platform.h b/c_emulator/riscv_platform.h
index 38fac2f..4a53d12 100644
--- a/c_emulator/riscv_platform.h
+++ b/c_emulator/riscv_platform.h
@@ -4,6 +4,7 @@
 bool sys_enable_rvc(unit);
 bool sys_enable_next(unit);
 bool sys_enable_fdext(unit);
+bool sys_enable_zcb(unit);
 bool sys_enable_zfinx(unit);
 bool sys_enable_writable_misa(unit);
 bool sys_enable_writable_fiom(unit);
diff --git a/c_emulator/riscv_platform_impl.c b/c_emulator/riscv_platform_impl.c
index c2ae256..449bb1d 100644
--- a/c_emulator/riscv_platform_impl.c
+++ b/c_emulator/riscv_platform_impl.c
@@ -6,6 +6,7 @@
 uint64_t rv_pmp_count = 0;
 uint64_t rv_pmp_grain = 0;
 
+bool rv_enable_zcb = false;
 bool rv_enable_zfinx = false;
 bool rv_enable_rvc = true;
 bool rv_enable_next = false;
diff --git a/c_emulator/riscv_platform_impl.h b/c_emulator/riscv_platform_impl.h
index e3e4a96..d377c9c 100644
--- a/c_emulator/riscv_platform_impl.h
+++ b/c_emulator/riscv_platform_impl.h
@@ -11,6 +11,7 @@
 extern uint64_t rv_pmp_count;
 extern uint64_t rv_pmp_grain;
 
+extern bool rv_enable_zcb;
 extern bool rv_enable_zfinx;
 extern bool rv_enable_rvc;
 extern bool rv_enable_next;
diff --git a/c_emulator/riscv_sim.c b/c_emulator/riscv_sim.c
index 0094e9a..bf68da2 100644
--- a/c_emulator/riscv_sim.c
+++ b/c_emulator/riscv_sim.c
@@ -53,6 +53,7 @@ const char *RV32ISA = "RV32IMAC";
 #define OPT_ENABLE_WRITABLE_FIOM 1001
 #define OPT_PMP_COUNT 1002
 #define OPT_PMP_GRAIN 1003
+#define OPT_ENABLE_ZCB 10014
 
 static bool do_dump_dts = false;
 static bool do_show_times = false;
@@ -145,6 +146,7 @@ static struct option options[] = {
     {"inst-limit",                  required_argument, 0, 'l'                     },
     {"enable-zfinx",                no_argument,       0, 'x'                     },
     {"enable-writable-fiom",        no_argument,       0, OPT_ENABLE_WRITABLE_FIOM},
+    {"enable-zcb",                  no_argument,       0, OPT_ENABLE_ZCB          },
 #ifdef SAILCOV
     {"sailcov-file",                required_argument, 0, 'c'                     },
 #endif
@@ -386,6 +388,10 @@ static int process_args(int argc, char **argv)
     case 'l':
       insn_limit = atoi(optarg);
       break;
+    case OPT_ENABLE_ZCB:
+      fprintf(stderr, "enabling Zcb extension.\n");
+      rv_enable_zcb = true;
+      break;
     case 'x':
       fprintf(stderr, "enabling Zfinx support.\n");
       rv_enable_zfinx = true;
diff --git a/model/riscv_insts_zcb.sail b/model/riscv_insts_zcb.sail
new file mode 100644
index 0000000..1320736
--- /dev/null
+++ b/model/riscv_insts_zcb.sail
@@ -0,0 +1,210 @@
+/*=======================================================================================*/
+/*  This Sail RISC-V architecture model, comprising all files and                        */
+/*  directories except where otherwise noted is subject the BSD                          */
+/*  two-clause license in the LICENSE file.                                              */
+/*                                                                                       */
+/*  SPDX-License-Identifier: BSD-2-Clause                                                */
+/*=======================================================================================*/
+
+union clause ast = C_LBU : (bits(2), cregidx, cregidx)
+
+mapping clause encdec_compressed =
+      C_LBU(uimm1 @ uimm0, rdc, rs1c)                                                           if haveZcb()
+  <-> 0b100 @ 0b000 @ rs1c : cregidx @ uimm0 : bits(1) @ uimm1 : bits(1) @ rdc : cregidx @ 0b00 if haveZcb()
+
+mapping clause assembly = C_LBU(uimm, rdc, rs1c) <->
+  "c.lbu" ^ spc() ^ creg_name(rdc) ^ sep() ^ hex_bits_2(uimm) ^ opt_spc() ^ "(" ^ opt_spc() ^ creg_name(rs1c) ^ opt_spc() ^ ")"
+
+function clause execute C_LBU(uimm, rdc, rs1c) = {
+  let imm : bits(12) = zero_extend(uimm);
+  let rd = creg2reg_idx(rdc);
+  let rs1 = creg2reg_idx(rs1c);
+  execute(LOAD(imm, rs1, rd, true, BYTE, false, false))
+}
+
+/* ****************************************************************** */
+
+union clause ast = C_LHU : (bits(2), cregidx, cregidx)
+
+mapping clause encdec_compressed =
+      C_LHU(uimm1 @ 0b0, rdc, rs1c)                                                 if haveZcb()
+  <-> 0b100 @ 0b001 @ rs1c : cregidx @ 0b0 @ uimm1 : bits(1) @ rdc : cregidx @ 0b00 if haveZcb()
+
+mapping clause assembly = C_LHU(uimm, rdc, rs1c) <->
+  "c.lhu" ^ spc() ^ creg_name(rdc) ^ sep() ^ hex_bits_2(uimm) ^ opt_spc() ^ "(" ^ opt_spc() ^ creg_name(rs1c) ^ opt_spc() ^ ")"
+
+function clause execute C_LHU(uimm, rdc, rs1c) = {
+  let imm : bits(12) = zero_extend(uimm);
+  let rd = creg2reg_idx(rdc);
+  let rs1 = creg2reg_idx(rs1c);
+  execute(LOAD(imm, rs1, rd, true, HALF, false, false))
+}
+
+/* ****************************************************************** */
+
+union clause ast = C_LH : (bits(2), cregidx, cregidx)
+
+mapping clause encdec_compressed =
+      C_LH(uimm1 @ 0b0, rdc, rs1c)                                                  if haveZcb()
+  <-> 0b100 @ 0b001 @ rs1c : cregidx @ 0b1 @ uimm1 : bits(1) @ rdc : cregidx @ 0b00 if haveZcb()
+
+mapping clause assembly = C_LH(uimm, rdc, rs1c) <->
+  "c.lh" ^ spc() ^ creg_name(rdc) ^ sep() ^ hex_bits_2(uimm) ^ opt_spc() ^ "(" ^ opt_spc() ^ creg_name(rs1c) ^ opt_spc() ^ ")"
+
+function clause execute C_LH(uimm, rdc, rs1c) = {
+  let imm : bits(12) = zero_extend(uimm);
+  let rd = creg2reg_idx(rdc);
+  let rs1 = creg2reg_idx(rs1c);
+  execute(LOAD(imm, rs1, rd, false, HALF, false, false))
+}
+
+/* ****************************************************************** */
+
+union clause ast = C_SB : (bits(2), cregidx, cregidx)
+
+mapping clause encdec_compressed =
+      C_SB(uimm1 @ uimm0, rs1c, rs2c)                                                  if haveZcb()
+  <-> 0b100 @ 0b010 @ rs1c : cregidx @ uimm0 : bits(1) @ uimm1 : bits(1) @ rs2c @ 0b00 if haveZcb()
+
+mapping clause assembly = C_SB(uimm, rs1c, rs2c) <->
+  "c.sb" ^ spc() ^ creg_name(rs2c) ^ sep() ^ hex_bits_2(uimm) ^ opt_spc() ^ "(" ^ opt_spc() ^ creg_name(rs1c) ^ opt_spc() ^ ")"
+
+function clause execute C_SB(uimm, rs1c, rs2c) = {
+  let imm : bits(12) = zero_extend(uimm);
+  let rs1 = creg2reg_idx(rs1c);
+  let rs2 = creg2reg_idx(rs2c);
+  execute(STORE(imm, rs2, rs1, BYTE, false, false))
+}
+
+/* ****************************************************************** */
+
+union clause ast = C_SH : (bits(2), cregidx, cregidx)
+
+mapping clause encdec_compressed =
+      C_SH(uimm1 @ 0b0, rs1c, rs2c)                                                  if haveZcb()
+  <-> 0b100 @ 0b011 @ rs1c : cregidx @ 0b0 @ uimm1 : bits(1) @ rs2c : cregidx @ 0b00 if haveZcb()
+
+mapping clause assembly = C_SH(uimm, rs1c, rs2c) <->
+  "c.sh" ^ spc() ^ creg_name(rs1c) ^ sep() ^ hex_bits_2(uimm) ^ opt_spc() ^ "(" ^ opt_spc() ^ creg_name(rs2c) ^ opt_spc() ^ ")"
+
+function clause execute C_SH(uimm, rs1c, rs2c) = {
+  let imm : bits(12) = zero_extend(uimm);
+  let rs1 = creg2reg_idx(rs1c);
+  let rs2 = creg2reg_idx(rs2c);
+  execute(STORE(imm, rs2, rs1, HALF, false, false))
+}
+
+/* ****************************************************************** */
+
+union clause ast = C_ZEXT_B : (cregidx)
+
+mapping clause encdec_compressed =
+      C_ZEXT_B(rsdc)                                       if haveZcb()
+  <-> 0b100 @ 0b111 @ rsdc : cregidx @ 0b11 @ 0b000 @ 0b01 if haveZcb()
+
+mapping clause assembly = C_ZEXT_B(rsdc) <->
+  "c.zext.b" ^ spc() ^ creg_name(rsdc)
+
+function clause execute C_ZEXT_B(rsdc) = {
+  let rsd = creg2reg_idx(rsdc);
+  X(rsd) = zero_extend(X(rsd)[7..0]);
+  RETIRE_SUCCESS
+}
+
+/* ****************************************************************** */
+
+union clause ast = C_SEXT_B : (cregidx)
+
+mapping clause encdec_compressed =
+      C_SEXT_B(rsdc)                                       if haveZcb() & haveZbb()
+  <-> 0b100 @ 0b111 @ rsdc : cregidx @ 0b11 @ 0b001 @ 0b01 if haveZcb() & haveZbb()
+
+mapping clause assembly = C_SEXT_B(rsdc) <->
+  "c.sext.b" ^ spc() ^ creg_name(rsdc)
+
+function clause execute C_SEXT_B(rsdc) = {
+  let rsd = creg2reg_idx(rsdc);
+  execute(ZBB_EXTOP(rsd, rsd, RISCV_SEXTB))
+}
+
+/* ****************************************************************** */
+
+union clause ast = C_ZEXT_H : (cregidx)
+
+mapping clause encdec_compressed =
+      C_ZEXT_H(rsdc)                                       if haveZcb() & haveZbb()
+  <-> 0b100 @ 0b111 @ rsdc : cregidx @ 0b11 @ 0b010 @ 0b01 if haveZcb() & haveZbb()
+
+mapping clause assembly = C_ZEXT_H(rsdc) <->
+  "c.zext.h" ^ spc() ^ creg_name(rsdc)
+
+function clause execute C_ZEXT_H(rsdc) = {
+  let rsd = creg2reg_idx(rsdc);
+  execute(ZBB_EXTOP(rsd, rsd, RISCV_ZEXTH))
+}
+
+/* ****************************************************************** */
+
+union clause ast = C_SEXT_H : (cregidx)
+
+mapping clause encdec_compressed =
+      C_SEXT_H(rsdc)                                       if haveZcb() & haveZbb()
+  <-> 0b100 @ 0b111 @ rsdc : cregidx @ 0b11 @ 0b011 @ 0b01 if haveZcb() & haveZbb()
+
+mapping clause assembly = C_SEXT_H(rsdc) <->
+  "c.sext.h" ^ spc() ^ creg_name(rsdc)
+
+function clause execute C_SEXT_H(rsdc) = {
+  let rsd = creg2reg_idx(rsdc);
+  execute(ZBB_EXTOP(rsd, rsd,  RISCV_SEXTH))
+}
+
+/* ****************************************************************** */
+
+union clause ast = C_ZEXT_W : (cregidx)
+
+mapping clause encdec_compressed =
+      C_ZEXT_W(rsdc)                                       if haveZcb() & haveZba() & sizeof(xlen) == 64
+  <-> 0b100 @ 0b111 @ rsdc : cregidx @ 0b11 @ 0b100 @ 0b01 if haveZcb() & haveZba() & sizeof(xlen) == 64
+
+mapping clause assembly = C_ZEXT_W(rsdc) <->
+  "c.zext.w" ^ spc() ^ creg_name(rsdc)
+
+function clause execute C_ZEXT_W(rsdc) = {
+  let rsd = creg2reg_idx(rsdc);
+  execute (ZBA_RTYPEUW(0b00000, rsd, rsd, RISCV_ADDUW)) // Note 0b00000 is the regidx of the zero register
+}
+
+/* ****************************************************************** */
+
+union clause ast = C_NOT : (cregidx)
+
+mapping clause encdec_compressed =
+      C_NOT(rsdc)                                          if haveZcb()
+  <-> 0b100 @ 0b111 @ rsdc : cregidx @ 0b11 @ 0b101 @ 0b01 if haveZcb()
+
+mapping clause assembly = C_NOT(rsdc) <->
+  "c.not" ^ spc() ^ creg_name(rsdc)
+
+function clause execute C_NOT(rsdc) = {
+  let r = creg2reg_idx(rsdc);
+  X(r) = ~(X(r));
+  RETIRE_SUCCESS
+}
+
+/* ****************************************************************** */
+
+union clause ast = C_MUL : (cregidx, cregidx)
+
+mapping clause encdec_compressed =
+      C_MUL(rsdc, rs2c)                                             if haveZcb() & (haveMulDiv() | haveZmmul())
+  <-> 0b100 @ 0b111 @ rsdc : cregidx @ 0b10 @ rs2c : cregidx @ 0b01 if haveZcb() & (haveMulDiv() | haveZmmul())
+
+mapping clause assembly = C_MUL(rsdc, rs2c) <->
+  "c.mul" ^ spc() ^ creg_name(rsdc) ^ sep() ^ creg_name(rs2c)
+
+function clause execute C_MUL(rsdc, rs2c) = {
+  let rd = creg2reg_idx(rsdc);
+  let rs = creg2reg_idx(rs2c);
+  execute(MUL(rs, rd, rd, false, true, true))
+}
diff --git a/model/riscv_sys_regs.sail b/model/riscv_sys_regs.sail
index d8309ec..3e198b4 100644
--- a/model/riscv_sys_regs.sail
+++ b/model/riscv_sys_regs.sail
@@ -84,6 +84,8 @@ val sys_enable_writable_misa = {c: "sys_enable_writable_misa", ocaml: "Platform.
 val sys_enable_rvc = {c: "sys_enable_rvc", ocaml: "Platform.enable_rvc", _: "sys_enable_rvc"} : unit -> bool
 /* whether misa.{f,d} were enabled at boot */
 val sys_enable_fdext = {c: "sys_enable_fdext", ocaml: "Platform.enable_fdext", _: "sys_enable_fdext"} : unit -> bool
+/* whether Zcb was enabled at boot */
+val sys_enable_zcb = {c: "sys_enable_zcb", ocaml: "Platform.enable_zcb", _: "sys_enable_zcb"} : unit -> bool
 /* whether zfinx was enabled at boot */
 val sys_enable_zfinx = {c: "sys_enable_zfinx", ocaml: "Platform.enable_zfinx", _: "sys_enable_zfinx"} : unit -> bool
 /* whether the N extension was enabled at boot */
@@ -309,6 +311,9 @@ function haveZfh()     -> bool = (misa[F] == 0b1) & (mstatus[FS] != 0b00)
 /* V extension has to enable both via misa.V as well as mstatus.VS */
 function haveVExt()    -> bool = (misa[V] == 0b1) & (mstatus[VS] != 0b00)
 
+/* Zcb has simple code-size saving instructions. (The Zcb extension depends on the Zca extension.) */
+function haveZcb()     -> bool = sys_enable_zcb()
+
 /* Zhinx, Zfinx and Zdinx extensions (TODO: gate FCSR access on [mhs]stateen0 bit 1 when implemented) */
 function haveZhinx()   -> bool = sys_enable_zfinx()
 function haveZfinx()   -> bool = sys_enable_zfinx()
diff --git a/ocaml_emulator/platform.ml b/ocaml_emulator/platform.ml
index a8bde44..2f0aaaf 100644
--- a/ocaml_emulator/platform.ml
+++ b/ocaml_emulator/platform.ml
@@ -10,6 +10,7 @@ let config_enable_writable_misa        = ref true
 let config_enable_dirty_update         = ref false
 let config_enable_misaligned_access    = ref false
 let config_mtval_has_illegal_inst_bits = ref false
+let config_enable_zcb                  = ref false
 let config_enable_writable_fiom        = ref true
 let config_enable_vext                 = ref true
 let config_pmp_count                   = ref Big_int.zero
@@ -88,6 +89,7 @@ let enable_vext ()                   = !config_enable_vext
 let enable_dirty_update ()           = !config_enable_dirty_update
 let enable_misaligned_access ()      = !config_enable_misaligned_access
 let mtval_has_illegal_inst_bits ()   = !config_mtval_has_illegal_inst_bits
+let enable_zcb ()                    = !config_enable_zcb
 let enable_zfinx ()                  = false
 let enable_writable_fiom ()          = !config_enable_writable_fiom
 let pmp_count ()                     = !config_pmp_count
diff --git a/ocaml_emulator/riscv_ocaml_sim.ml b/ocaml_emulator/riscv_ocaml_sim.ml
index 03887b7..8dad8a4 100644
--- a/ocaml_emulator/riscv_ocaml_sim.ml
+++ b/ocaml_emulator/riscv_ocaml_sim.ml
@@ -53,6 +53,9 @@ let options = Arg.align ([("-dump-dts",
                           ("-mtval-has-illegal-inst-bits",
                            Arg.Set P.config_mtval_has_illegal_inst_bits,
                            " mtval stores instruction bits on an illegal instruction exception");
+                          ("-enable-zcb",
+                           Arg.Set P.config_enable_zcb,
+                           " enable Zcb (simple code size) extension");
                           ("-enable-writable-fiom",
                            Arg.Set P.config_enable_writable_fiom,
                            " enable FIOM (Fence of I/O implies Memory) bit in menvcfg");