[arm] Support CSDB instruction

Add support for CSDB in the 32-bit assembler, disassembler and simulator.

Change-Id: I0e5432e4d219dd4699d5f9b7f911791acc87114c
Reviewed-on: https://chromium-review.googlesource.com/928522Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Martyn Capewell <martyn.capewell@arm.com>
Cr-Commit-Position: refs/heads/master@{#51425}

src/arm/assembler-arm.cc

@@ -2371,6 +2371,11 @@ void Assembler::isb(BarrierOption option) {
   }
 }
 
+void Assembler::csdb() {
+  // Details available in Arm Cache Speculation Side-channels white paper,
+  // version 1.1, page 4.
+  emit(0xE320F014);
+}
 
 // Coprocessor instructions.
 void Assembler::cdp(Coprocessor coproc,

src/arm/assembler-arm.h

@@ -960,6 +960,9 @@ class Assembler : public AssemblerBase {
   void dsb(BarrierOption option);
   void isb(BarrierOption option);
 
+  // Conditional speculation barrier.
+  void csdb();
+
   // Coprocessor instructions
 
   void cdp(Coprocessor coproc, int opcode_1,

src/arm/constants-arm.h

@@ -641,8 +641,8 @@ class Instruction {
                                            && (Bit(20) == 0)
                                            && ((Bit(7) == 0)); }
 
-  // Test for a nop instruction, which falls under type 1.
-  inline bool IsNopType1() const { return Bits(24, 0) == 0x0120F000; }
+  // Test for nop-like instructions which fall under type 1.
+  inline bool IsNopLikeType1() const { return Bits(24, 8) == 0x120F0; }
 
   // Test for a stop instruction.
   inline bool IsStop() const {

src/arm/disasm-arm.cc

@@ -937,8 +937,14 @@ void Decoder::DecodeType01(Instruction* instr) {
     } else {
       Unknown(instr);  // not used by V8
     }
-  } else if ((type == 1) && instr->IsNopType1()) {
-    Format(instr, "nop'cond");
+  } else if ((type == 1) && instr->IsNopLikeType1()) {
+    if (instr->BitField(7, 0) == 0) {
+      Format(instr, "nop'cond");
+    } else if (instr->BitField(7, 0) == 20) {
+      Format(instr, "csdb");
+    } else {
+      Unknown(instr);  // Not used in V8.
+    }
   } else {
     switch (instr->OpcodeField()) {
       case AND: {

src/arm/simulator-arm.cc

@@ -2308,8 +2308,15 @@ void Simulator::DecodeType01(Instruction* instr) {
       PrintF("%08x\n", instr->InstructionBits());
       UNIMPLEMENTED();
     }
-  } else if ((type == 1) && instr->IsNopType1()) {
-    // NOP.
+  } else if ((type == 1) && instr->IsNopLikeType1()) {
+    if (instr->BitField(7, 0) == 0) {
+      // NOP.
+    } else if (instr->BitField(7, 0) == 20) {
+      // CSDB.
+    } else {
+      PrintF("%08x\n", instr->InstructionBits());
+      UNIMPLEMENTED();
+    }
   } else {
     int rd = instr->RdValue();
     int rn = instr->RnValue();

test/cctest/test-disasm-arm.cc

@@ -1568,6 +1568,9 @@ TEST(Barrier) {
   COMPARE(mcr(p15, 0, r0, cr7, cr10, 4, ne), "1e070f9a       mcrne (CP15DSB)");
   COMPARE(mcr(p15, 0, r0, cr7, cr5, 4, mi), "4e070f95       mcrmi (CP15ISB)");
 
+  // Conditional speculation barrier.
+  COMPARE(csdb(), "e320f014       csdb");
+
   VERIFY_RUN();
 }