8 files changed, 102 insertions, 0 deletions
diff --git a/riscv/insns/amocas_d.h b/riscv/insns/amocas_d.h
new file mode 100644
index 0000000..e002e6a
--- /dev/null
+++ b/riscv/insns/amocas_d.h
@@ -0,0 +1,37 @@
+require_extension(EXT_ZACAS);
+
+if (xlen == 32) {
+  // RV32: the spec defines two 32-bit comparisons. Since we're
+  // loading 64-bit for memory we have to adjust for endianness.
+  uint64_t comp, swap, res;
+
+  require_align(insn.rd(), 2);
+  require_align(insn.rs2(), 2);
+  if (insn.rd() == 0) {
+    comp = 0;
+  } else if (MMU.is_target_big_endian()) {
+    comp = (uint32_t)READ_REG(insn.rd() + 1) | (RD << 32);
+  } else {
+    comp = (uint32_t)RD | (READ_REG(insn.rd() + 1) << 32);
+  }
+  if (insn.rs2() == 0) {
+    swap = 0;
+  } else if (MMU.is_target_big_endian()) {
+    swap = (uint32_t)READ_REG(insn.rs2() + 1) | (RS2 << 32);
+  } else {
+    swap = (uint32_t)RS2 | (READ_REG(insn.rs2() + 1) << 32);
+  }
+  res = MMU.amo_compare_and_swap<uint64_t>(RS1, comp, swap);
+  if (insn.rd() != 0) {
+    if (MMU.is_target_big_endian()) {
+      WRITE_REG(insn.rd() + 1, sext32((uint32_t)res));
+      WRITE_REG(insn.rd(), sext32(res >> 32));
+    } else {
+      WRITE_REG(insn.rd(), sext32((uint32_t)res));
+      WRITE_REG(insn.rd() + 1, sext32(res >> 32));
+    }
+  }
+ } else {
+  // RV64
+  WRITE_RD(MMU.amo_compare_and_swap<uint64_t>(RS1, RD, RS2));
+}
diff --git a/riscv/insns/amocas_q.h b/riscv/insns/amocas_q.h
new file mode 100644
index 0000000..0b7593b
--- /dev/null
+++ b/riscv/insns/amocas_q.h
@@ -0,0 +1,34 @@
+require_extension(EXT_ZACAS);
+require_rv64;
+require_align(insn.rd(), 2);
+require_align(insn.rs2(), 2);
+
+// The spec defines two 64-bit comparisons. Since we're loading
+// 128-bit for memory we have to adjust for endianness.
+
+uint128_t comp, swap, res;
+
+if (insn.rd() == 0) {
+  comp = 0;
+} else if (MMU.is_target_big_endian()) {
+  comp = READ_REG(insn.rd() + 1) | ((uint128_t)RD << 64);
+} else  {
+  comp = RD | ((uint128_t)READ_REG(insn.rd() + 1) << 64);
+}
+if (insn.rs2() == 0) {
+  swap = 0;
+} else if (MMU.is_target_big_endian()) {
+  swap = READ_REG(insn.rs2() + 1) | ((uint128_t)RS2 << 64);
+} else {
+  swap = RS2 | ((uint128_t)READ_REG(insn.rs2() + 1) << 64);
+}
+res = MMU.amo_compare_and_swap<uint128_t>(RS1, comp, swap);
+if (insn.rd() != 0) {
+  if (MMU.is_target_big_endian()) {
+    WRITE_REG(insn.rd(), res >> 64);
+    WRITE_REG(insn.rd() + 1, res);
+  } else {
+    WRITE_REG(insn.rd(), res);
+    WRITE_REG(insn.rd() + 1, res >> 64);
+  }
+}
diff --git a/riscv/insns/amocas_w.h b/riscv/insns/amocas_w.h
new file mode 100644
index 0000000..a78c21c
--- /dev/null
+++ b/riscv/insns/amocas_w.h
@@ -0,0 +1,2 @@
+require_extension(EXT_ZACAS);
+WRITE_RD(sext32(MMU.amo_compare_and_swap<uint32_t>(RS1, RD, RS2)));
diff --git a/riscv/isa_parser.cc b/riscv/isa_parser.cc
index 8bb8c49..1c4300c 100644
--- a/riscv/isa_parser.cc
+++ b/riscv/isa_parser.cc
@@ -120,6 +120,8 @@ isa_parser_t::isa_parser_t(const char* str, const char *priv)
       // HINTs encoded in base-ISA instructions are always present.
     } else if (ext_str == "zihintntl") {
       // HINTs encoded in base-ISA instructions are always present.
+    } else if (ext_str == "zacas") {
+      extension_table[EXT_ZACAS] = true;
     } else if (ext_str == "zmmul") {
       extension_table[EXT_ZMMUL] = true;
     } else if (ext_str == "zba") {
@@ -301,6 +303,10 @@ isa_parser_t::isa_parser_t(const char* str, const char *priv)
     bad_isa_string(str, "'Zcf/Zcd/Zcb/Zcmp/Zcmt' extensions require 'Zca' extension");
   }
 
+  if (extension_table[EXT_ZACAS] && !extension_table['A']) {
+    bad_isa_string(str, "'Zacas' extension requires 'A' extension");
+  }
+
   std::string lowercase = strtolower(priv);
   bool user = false, supervisor = false;
 
diff --git a/riscv/isa_parser.h b/riscv/isa_parser.h
index 4e68561..3cbee7d 100644
--- a/riscv/isa_parser.h
+++ b/riscv/isa_parser.h
@@ -61,6 +61,7 @@ typedef enum {
   EXT_ZVFBFMIN,
   EXT_ZVFBFWMA,
   EXT_SSTC,
+  EXT_ZACAS,
   EXT_INTERNAL_ZFH_MOVE,
   NUM_ISA_EXTENSIONS
 } isa_extension_t;
diff --git a/riscv/mmu.h b/riscv/mmu.h
index efc6e9d..46c54ce 100644
--- a/riscv/mmu.h
+++ b/riscv/mmu.h
@@ -187,6 +187,17 @@ public:
     })
   }
 
+  template<typename T>
+  T amo_compare_and_swap(reg_t addr, T comp, T swap) {
+    convert_load_traps_to_store_traps({
+      store_slow_path(addr, sizeof(T), nullptr, {false, false, false}, false, true);
+      auto lhs = load<T>(addr);
+      if (lhs == comp)
+        store<T>(addr, swap);
+      return lhs;
+    })
+  }
+
   void store_float128(reg_t addr, float128_t val)
   {
     if (unlikely(addr & (sizeof(float128_t)-1)) && !is_misaligned_enabled()) {
diff --git a/riscv/processor.cc b/riscv/processor.cc
index a75b0ff..1d5675a 100644
--- a/riscv/processor.cc
+++ b/riscv/processor.cc
@@ -47,6 +47,11 @@ processor_t::processor_t(const isa_parser_t *isa, const cfg_t *cfg,
     fprintf(stderr, "V extension is not supported on platforms without __int128 type\n");
     abort();
   }
+
+  if (isa->extension_enabled(EXT_ZACAS) && isa->get_max_xlen() == 64) {
+    fprintf(stderr, "Zacas extension is not supported on 64-bit platforms without __int128 type\n");
+    abort();
+  }
 #endif
 
   parse_varch_string(cfg->varch());
diff --git a/riscv/riscv.mk.in b/riscv/riscv.mk.in
index db63290..6472982 100644
--- a/riscv/riscv.mk.in
+++ b/riscv/riscv.mk.in
@@ -1335,6 +1335,11 @@ riscv_insn_ext_bf16 = \
 	$(riscv_insn_ext_zvfbfmin) \
 	$(riscv_insn_ext_zvfbfwma) \
 
+riscv_insn_ext_zacas = \
+	amocas_w \
+	amocas_d \
+	$(if $(HAVE_INT128),amocas_q)
+
 riscv_insn_list = \
 	$(riscv_insn_ext_a) \
 	$(riscv_insn_ext_c) \
@@ -1360,6 +1365,7 @@ riscv_insn_list = \
 	$(riscv_insn_ext_cmo) \
 	$(riscv_insn_ext_zicond) \
 	$(riscv_insn_ext_bf16) \
+	$(riscv_insn_ext_zacas) \
 
 riscv_gen_srcs = $(addsuffix .cc,$(riscv_insn_list))