arch-riscv: Fix disassembling for fence and fence.i

The original Gem5 does not give correct disassembly for instruction fence
and fence.i. This patch fixes the problem by adding two bitfields PRED and
SUCC and a new format FenceOp and a template FenceExecute, in which
operands are generated based on PRED and SUCC in the disassembling
function.

Change-Id: I78dbf125fef86ce40785c498a318ffb1569da46c
Signed-off-by: Ian Jiang <ianjiang.ict@gmail.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/22569
Reviewed-by: Alec Roelke <alec.roelke@gmail.com>
Maintainer: Alec Roelke <alec.roelke@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

3 files changed, 64 insertions, 1 deletions

diff --git a/src/arch/riscv/isa/bitfields.isa b/src/arch/riscv/isa/bitfields.isa
index 20f1fc0de..fcda90cf7 100644
--- a/src/arch/riscv/isa/bitfields.isa
+++ b/src/arch/riscv/isa/bitfields.isa
@@ -54,6 +54,10 @@ def bitfield SHAMT6 <25:20>;
 // I-Type
 def bitfield IMM12  <31:20>;
 
+// Sync
+def bitfield SUCC  <23:20>;
+def bitfield PRED  <27:24>;
+
 // S-Type
 def bitfield IMM5   <11:7>;
 def bitfield IMM7   <31:25>;
diff --git a/src/arch/riscv/isa/decoder.isa b/src/arch/riscv/isa/decoder.isa
index fd9c574e1..c53420347 100644
--- a/src/arch/riscv/isa/decoder.isa
+++ b/src/arch/riscv/isa/decoder.isa
@@ -400,7 +400,7 @@ decode QUADRANT default Unknown::unknown() {
         }
 
         0x03: decode FUNCT3 {
-            format IOp {
+            format FenceOp {
                 0x0: fence({{
                 }}, uint64_t, IsMemBarrier, No_OpClass);
                 0x1: fence_i({{
diff --git a/src/arch/riscv/isa/formats/standard.isa b/src/arch/riscv/isa/formats/standard.isa
index e67fdfcbd..78d8144f8 100644
--- a/src/arch/riscv/isa/formats/standard.isa
+++ b/src/arch/riscv/isa/formats/standard.isa
@@ -90,6 +90,54 @@ def template ImmExecute {{
     }
 }};
 
+def template FenceExecute {{
+    Fault
+    %(class_name)s::execute(
+        ExecContext *xc, Trace::InstRecord *traceData) const
+    {
+        Fault fault = NoFault;
+
+        %(op_decl)s;
+        %(op_rd)s;
+        if (fault == NoFault) {
+            %(code)s;
+            if (fault == NoFault) {
+                %(op_wb)s;
+            }
+        }
+        return fault;
+    }
+
+    std::string
+    %(class_name)s::generateDisassembly(Addr pc,
+            const SymbolTable *symtab) const
+    {
+        std::stringstream ss;
+        ss << mnemonic;
+        if (!FUNCT3) {
+            ss << ' ';
+            if (PRED & 0x8)
+                ss << 'i';
+            if (PRED & 0x4)
+                ss << 'o';
+            if (PRED & 0x2)
+                ss << 'r';
+            if (PRED & 0x1)
+                ss << 'w';
+            ss << ", ";
+            if (SUCC & 0x8)
+                ss << 'i';
+            if (SUCC & 0x4)
+                ss << 'o';
+            if (SUCC & 0x2)
+                ss << 'r';
+            if (SUCC & 0x1)
+                ss << 'w';
+        }
+        return ss.str();
+    }
+}};
+
 def template BranchDeclare {{
     //
     // Static instruction class for "%(mnemonic)s".
@@ -307,6 +355,17 @@ def format IOp(code, imm_type='int64_t', *opt_flags) {{
     exec_output = ImmExecute.subst(iop)
 }};
 
+def format FenceOp(code, imm_type='int64_t', *opt_flags) {{
+    regs = ['_destRegIdx[0]','_srcRegIdx[0]']
+    iop = InstObjParams(name, Name, 'ImmOp<%s>' % imm_type,
+        {'code': code, 'imm_code': 'imm = sext<12>(IMM12);',
+         'regs': ','.join(regs)}, opt_flags)
+    header_output = ImmDeclare.subst(iop)
+    decoder_output = ImmConstructor.subst(iop)
+    decode_block = BasicDecode.subst(iop)
+    exec_output = FenceExecute.subst(iop)
+}};
+
 def format BOp(code, *opt_flags) {{
     imm_code = """
                 imm = BIMM12BITS4TO1 << 1  |