[arm64] Support CSDB instruction

Add support for CSDB, equivalent to HINT #20, in the system instruction space.

Additionally, relax the "unallocated" identification of hint instructions that
we don't support, such that they'll now disassemble as "unimplemented (System)"
rather than "unallocated".

Change-Id: Ia36d13fe17a98edb872f234e7cdda33d033618e8
Reviewed-on: https://chromium-review.googlesource.com/926806Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Martyn Capewell <martyn.capewell@arm.com>
Cr-Commit-Position: refs/heads/master@{#51420}

src/arm64/assembler-arm64.cc

@@ -2989,6 +2989,8 @@ void Assembler::isb() {
   Emit(ISB | ImmBarrierDomain(FullSystem) | ImmBarrierType(BarrierAll));
 }
 
+void Assembler::csdb() { hint(CSDB); }
+
 void Assembler::fmov(const VRegister& vd, double imm) {
   if (vd.IsScalar()) {
     DCHECK(vd.Is1D());

src/arm64/assembler-arm64.h

@@ -1752,6 +1752,9 @@ class Assembler : public AssemblerBase {
   // Instruction synchronization barrier
   void isb();
 
+  // Conditional speculation barrier.
+  void csdb();
+
   // Alias for system instructions.
   void nop() { hint(NOP); }
 

src/arm64/constants-arm64.h

@@ -407,12 +407,13 @@ enum Extend {
 };
 
 enum SystemHint {
-  NOP   = 0,
+  NOP = 0,
   YIELD = 1,
-  WFE   = 2,
-  WFI   = 3,
-  SEV   = 4,
-  SEVL  = 5
+  WFE = 2,
+  WFI = 3,
+  SEV = 4,
+  SEVL = 5,
+  CSDB = 20
 };
 
 enum BarrierDomain {

src/arm64/decoder-arm64-inl.h

@@ -168,11 +168,6 @@ void Decoder<V>::DecodeBranchSystemException(Instruction* instr) {
                 (instr->Mask(0x0039E000) == 0x00002000) ||
                 (instr->Mask(0x003AE000) == 0x00002000) ||
                 (instr->Mask(0x003CE000) == 0x00042000) ||
-                (instr->Mask(0x003FFFC0) == 0x000320C0) ||
-                (instr->Mask(0x003FF100) == 0x00032100) ||
-                (instr->Mask(0x003FF200) == 0x00032200) ||
-                (instr->Mask(0x003FF400) == 0x00032400) ||
-                (instr->Mask(0x003FF800) == 0x00032800) ||
                 (instr->Mask(0x0038F000) == 0x00005000) ||
                 (instr->Mask(0x0038E000) == 0x00006000)) {
               V::VisitUnallocated(instr);

src/arm64/disasm-arm64.cc

@@ -1246,6 +1246,11 @@ void DisassemblingDecoder::VisitSystem(Instruction* instr) {
         form = nullptr;
         break;
       }
+      case CSDB: {
+        mnemonic = "csdb";
+        form = nullptr;
+        break;
+      }
     }
   } else if (instr->Mask(MemBarrierFMask) == MemBarrierFixed) {
     switch (instr->Mask(MemBarrierMask)) {

src/arm64/macro-assembler-arm64-inl.h

@@ -416,6 +416,11 @@ void MacroAssembler::CmovX(const Register& rd,
   }
 }
 
+void TurboAssembler::Csdb() {
+  DCHECK(allow_macro_instructions());
+  csdb();
+}
+
 void TurboAssembler::Cset(const Register& rd, Condition cond) {
   DCHECK(allow_macro_instructions());
   DCHECK(!rd.IsZero());

src/arm64/macro-assembler-arm64.h

@@ -559,6 +559,7 @@ class TurboAssembler : public Assembler {
   inline void Dmb(BarrierDomain domain, BarrierType type);
   inline void Dsb(BarrierDomain domain, BarrierType type);
   inline void Isb();
+  inline void Csdb();
 
   bool AllowThisStubCall(CodeStub* stub);
   void CallStubDelayed(CodeStub* stub);

src/arm64/simulator-arm64.cc

@@ -2955,7 +2955,9 @@ void Simulator::VisitSystem(Instruction* instr) {
   } else if (instr->Mask(SystemHintFMask) == SystemHintFixed) {
     DCHECK(instr->Mask(SystemHintMask) == HINT);
     switch (instr->ImmHint()) {
-      case NOP: break;
+      case NOP:
+      case CSDB:
+        break;
       default: UNIMPLEMENTED();
     }
   } else if (instr->Mask(MemBarrierFMask) == MemBarrierFixed) {

test/cctest/test-assembler-arm64.cc

@@ -11849,8 +11849,7 @@ TEST(system_msr) {
   TEARDOWN();
 }
 
-
-TEST(system_nop) {
+TEST(system) {
   INIT_V8();
   SETUP();
   RegisterDump before;
@@ -11858,6 +11857,7 @@ TEST(system_nop) {
   START();
   before.Dump(&masm);
   __ Nop();
+  __ Csdb();
   END();
 
   RUN();

test/cctest/test-disasm-arm64.cc

@@ -2038,6 +2038,9 @@ TEST_(barriers) {
   // ISB
   COMPARE(Isb(), "isb");
 
+  // CSDB
+  COMPARE(Csdb(), "csdb");
+
   CLEANUP();
 }