From 4299874ad4b07ef457776513a64e5b2397a6a75e Mon Sep 17 00:00:00 2001
From: Andrew Waterman <andrew@sifive.com>
Date: Thu, 22 Feb 2018 15:19:26 -0800
Subject: [PATCH] Implement clearing-misa.C-while-PC-is-misaligned proposal

See https://github.com/riscv/riscv-isa-manual/pull/139

Not adopted yet, but I'm putting the implementation here for reference.
---
 riscv/decode.h       | 6 +++---
 riscv/execute.cc     | 1 +
 riscv/insns/csrrc.h  | 1 +
 riscv/insns/csrrci.h | 1 +
 riscv/insns/csrrs.h  | 1 +
 riscv/insns/csrrsi.h | 1 +
 riscv/insns/csrrw.h  | 1 +
 riscv/insns/csrrwi.h | 1 +
 riscv/processor.h    | 5 +++++
 9 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/riscv/decode.h b/riscv/decode.h
index 7f5effc..596a2ad 100644
--- a/riscv/decode.h
+++ b/riscv/decode.h
@@ -201,18 +201,18 @@ private:
 #define zext_xlen(x) (((reg_t)(x) << (64-xlen)) >> (64-xlen))
 
 #define set_pc(x) \
-  do { if (unlikely(((x) & 2)) && !p->supports_extension('C')) \
-         throw trap_instruction_address_misaligned(x); \
+  do { p->check_pc_alignment(x); \
        npc = sext_xlen(x); \
      } while(0)
 
 #define set_pc_and_serialize(x) \
   do { reg_t __npc = (x); \
-       set_pc(__npc); /* check alignment */ \
        npc = PC_SERIALIZE_AFTER; \
        STATE.pc = __npc; \
      } while(0)
 
+#define serialize() set_pc_and_serialize(npc)
+
 /* Sentinel PC values to serialize simulator pipeline */
 #define PC_SERIALIZE_BEFORE 3
 #define PC_SERIALIZE_AFTER 5
diff --git a/riscv/execute.cc b/riscv/execute.cc
index e60ffd1..c5cafc2 100644
--- a/riscv/execute.cc
+++ b/riscv/execute.cc
@@ -114,6 +114,7 @@ void processor_t::step(size_t n)
          default: abort(); \
        } \
        pc = state.pc; \
+       check_pc_alignment(pc); \
        break; \
      } else { \
        state.pc = pc; \
diff --git a/riscv/insns/csrrc.h b/riscv/insns/csrrc.h
index eae91fe..0472d80 100644
--- a/riscv/insns/csrrc.h
+++ b/riscv/insns/csrrc.h
@@ -5,3 +5,4 @@ if (write) {
   p->set_csr(csr, old & ~RS1);
 }
 WRITE_RD(sext_xlen(old));
+serialize();
diff --git a/riscv/insns/csrrci.h b/riscv/insns/csrrci.h
index 986d601..4d83cc0 100644
--- a/riscv/insns/csrrci.h
+++ b/riscv/insns/csrrci.h
@@ -5,3 +5,4 @@ if (write) {
   p->set_csr(csr, old & ~(reg_t)insn.rs1());
 }
 WRITE_RD(sext_xlen(old));
+serialize();
diff --git a/riscv/insns/csrrs.h b/riscv/insns/csrrs.h
index ec61b42..4e8bde9 100644
--- a/riscv/insns/csrrs.h
+++ b/riscv/insns/csrrs.h
@@ -5,3 +5,4 @@ if (write) {
   p->set_csr(csr, old | RS1);
 }
 WRITE_RD(sext_xlen(old));
+serialize();
diff --git a/riscv/insns/csrrsi.h b/riscv/insns/csrrsi.h
index aa44dcc..b673725 100644
--- a/riscv/insns/csrrsi.h
+++ b/riscv/insns/csrrsi.h
@@ -5,3 +5,4 @@ if (write) {
   p->set_csr(csr, old | insn.rs1());
 }
 WRITE_RD(sext_xlen(old));
+serialize();
diff --git a/riscv/insns/csrrw.h b/riscv/insns/csrrw.h
index 9f2324f..e45420b 100644
--- a/riscv/insns/csrrw.h
+++ b/riscv/insns/csrrw.h
@@ -2,3 +2,4 @@ int csr = validate_csr(insn.csr(), true);
 reg_t old = p->get_csr(csr);
 p->set_csr(csr, RS1);
 WRITE_RD(sext_xlen(old));
+serialize();
diff --git a/riscv/insns/csrrwi.h b/riscv/insns/csrrwi.h
index cf0710f..decadf4 100644
--- a/riscv/insns/csrrwi.h
+++ b/riscv/insns/csrrwi.h
@@ -2,3 +2,4 @@ int csr = validate_csr(insn.csr(), true);
 reg_t old = p->get_csr(csr);
 p->set_csr(csr, insn.rs1());
 WRITE_RD(sext_xlen(old));
+serialize();
diff --git a/riscv/processor.h b/riscv/processor.h
index 1b94b1f..070fccf 100644
--- a/riscv/processor.h
+++ b/riscv/processor.h
@@ -5,6 +5,7 @@
 #include "decode.h"
 #include "config.h"
 #include "devices.h"
+#include "trap.h"
 #include <string>
 #include <vector>
 #include <map>
@@ -184,6 +185,10 @@ public:
     if (ext >= 'a' && ext <= 'z') ext += 'A' - 'a';
     return ext >= 'A' && ext <= 'Z' && ((isa >> (ext - 'A')) & 1);
   }
+  void check_pc_alignment(reg_t pc) {
+    if (unlikely(pc & 2) && !supports_extension('C'))
+      throw trap_instruction_address_misaligned(pc);
+  }
   reg_t legalize_privilege(reg_t);
   void set_privilege(reg_t);
   void yield_load_reservation() { state.load_reservation = (reg_t)-1; }
-- 
2.30.2