Copies Simulator Debugger from ARM to MIPS.

runtime/vm/simulator_mips.cc

Index: runtime/vm/simulator_mips.cc
===================================================================
--- runtime/vm/simulator_mips.cc	(revision 19939)
+++ runtime/vm/simulator_mips.cc	(working copy)
@@ -18,6 +18,468 @@
 
 DEFINE_FLAG(int, stop_sim_at, 0, "Address to stop simulator at.");
 
+
+// This macro provides a platform independent use of sscanf. The reason for
+// SScanF not being implemented in a platform independent way through
+// OS in the same way as SNPrint is that the Windows C Run-Time
+// Library does not provide vsscanf.
+#define SScanF sscanf  // NOLINT
+
+
+// The SimulatorDebugger class is used by the simulator while debugging
+// simulated MIPS code.
+class SimulatorDebugger {
+ public:
+  explicit SimulatorDebugger(Simulator* sim);
+  ~SimulatorDebugger();
+
+  void Stop(Instr* instr, const char* message);
+  void Debug();
+  char* ReadLine(const char* prompt);
+
+ private:
+  Simulator* sim_;
+
+  bool GetValue(char* desc, uint32_t* value);
+  bool GetFValue(char* desc, double* value);
+
+  // Set or delete a breakpoint. Returns true if successful.
+  bool SetBreakpoint(Instr* breakpc);
+  bool DeleteBreakpoint(Instr* breakpc);
+
+  // Undo and redo all breakpoints. This is needed to bracket disassembly and
+  // execution to skip past breakpoints when run from the debugger.
+  void UndoBreakpoints();
+  void RedoBreakpoints();
+};
+
+
+SimulatorDebugger::SimulatorDebugger(Simulator* sim) {
+  sim_ = sim;
+}
+
+
+SimulatorDebugger::~SimulatorDebugger() {
+}
+
+
+void SimulatorDebugger::Stop(Instr* instr, const char* message) {
+  OS::Print("Simulator hit %s\n", message);
+  Debug();
+}
+
+
+static Register LookupCpuRegisterByName(const char* name) {
+  static const char* kNames[] = {
+      "r0",  "r1",  "r2",  "r3",
+      "r4",  "r5",  "r6",  "r7",
+      "r8",  "r9",  "r10", "r11",
+      "r12", "r13", "r14", "r15",
+      "r16", "r17", "r18", "r19",
+      "r20", "r21", "r22", "r23",
+      "r24", "r25", "r26", "r27",
+      "r28", "r29", "r30", "r31",
+
+      "zr",  "at",  "v0",  "v1",
+      "a0",  "a1",  "a2",  "a3",
+      "t0",  "t1",  "t2",  "t3",
+      "t4",  "t5",  "t6",  "t7",
+      "s0",  "s1",  "s2",  "s3",
+      "s4",  "s5",  "s6",  "s7",
+      "t8",  "t9",  "k0",  "k1",
+      "gp",  "sp",  "fp",  "ra"
+  };
+  static const Register kRegisters[] = {
+      R0,  R1,  R2,  R3,
+      R4,  R5,  R6,  R7,
+      R8,  R9,  R10, R11,
+      R12, R13, R14, R15,
+      R16, R17, R18, R19,
+      R20, R21, R22, R23,
+      R24, R25, R26, R27,
+      R28, R29, R30, R31,
+
+      ZR,  AT,  V0,  V1,
+      A0,  A1,  A2,  A3,
+      T0,  T1,  T2,  T3,
+      T4,  T5,  T6,  T7,
+      S0,  S1,  S2,  S3,
+      S4,  S5,  S6,  S7,
+      T8,  T9,  K0,  K1,
+      GP,  SP,  FP,  RA
+  };
+  ASSERT(ARRAY_SIZE(kNames) == ARRAY_SIZE(kRegisters));
+  for (unsigned i = 0; i < ARRAY_SIZE(kNames); i++) {
+    if (strcmp(kNames[i], name) == 0) {
+      return kRegisters[i];
+    }
+  }
+  return kNoRegister;
+}
+
+
+static FRegister LookupFRegisterByName(const char* name) {
+  int reg_nr = -1;
+  bool ok = SScanF(name, "f%d", &reg_nr);
+  if (ok && (0 <= reg_nr) && (reg_nr < kNumberOfFRegisters)) {
+    return static_cast<FRegister>(reg_nr);
+  }
+  return kNoFRegister;
+}
+
+
+bool SimulatorDebugger::GetValue(char* desc, uint32_t* value) {
+  Register reg = LookupCpuRegisterByName(desc);
+  if (reg != kNoRegister) {
+    *value = sim_->get_register(reg);
+    return true;
+  }
+  if ((desc[0] == '*')) {
+    uint32_t addr;
+    if (GetValue(desc + 1, &addr)) {
+      if (Simulator::IsIllegalAddress(addr)) {
+        return false;
+      }
+      *value = *(reinterpret_cast<uint32_t*>(addr));
+      return true;
+    }
+  }
+  if (strcmp("pc", desc) == 0) {
+    *value = sim_->get_pc();
+    return true;
+  }
+  bool retval = SScanF(desc, "0x%x", value) == 1;
+  if (!retval) {
+    retval = SScanF(desc, "%x", value) == 1;
+  }
+  return retval;
+}
+
+
+bool SimulatorDebugger::GetFValue(char* desc, double* value) {
+  FRegister freg = LookupFRegisterByName(desc);
+  if (freg != kNoFRegister) {
+    *value = sim_->get_fregister(freg);
+    return true;
+  }
+  if ((desc[0] == '*')) {
+    uint32_t addr;
+    if (GetValue(desc + 1, &addr)) {
+      if (Simulator::IsIllegalAddress(addr)) {
+        return false;
+      }
+      *value = *(reinterpret_cast<float*>(addr));
+      return true;
+    }
+  }
+  return false;
+}
+
+
+bool SimulatorDebugger::SetBreakpoint(Instr* breakpc) {
+  // Check if a breakpoint can be set. If not return without any side-effects.
+  if (sim_->break_pc_ != NULL) {
+    return false;
+  }
+
+  // Set the breakpoint.
+  sim_->break_pc_ = breakpc;
+  sim_->break_instr_ = breakpc->InstructionBits();
+  // Not setting the breakpoint instruction in the code itself. It will be set
+  // when the debugger shell continues.
+  return true;
+}
+
+
+bool SimulatorDebugger::DeleteBreakpoint(Instr* breakpc) {
+  if (sim_->break_pc_ != NULL) {
+    sim_->break_pc_->SetInstructionBits(sim_->break_instr_);
+  }
+
+  sim_->break_pc_ = NULL;
+  sim_->break_instr_ = 0;
+  return true;
+}
+
+
+void SimulatorDebugger::UndoBreakpoints() {
+  if (sim_->break_pc_ != NULL) {
+    sim_->break_pc_->SetInstructionBits(sim_->break_instr_);
+  }
+}
+
+
+void SimulatorDebugger::RedoBreakpoints() {
+  if (sim_->break_pc_ != NULL) {
+    sim_->break_pc_->SetInstructionBits(Instr::kBreakPointInstruction);
+  }
+}
+
+
+void SimulatorDebugger::Debug() {
+  intptr_t last_pc = -1;
+  bool done = false;
+  bool decoded = true;
+
+#define COMMAND_SIZE 63
+#define ARG_SIZE 255
+
+#define STR(a) #a
+#define XSTR(a) STR(a)
+
+  char cmd[COMMAND_SIZE + 1];
+  char arg1[ARG_SIZE + 1];
+  char arg2[ARG_SIZE + 1];
+
+  // make sure to have a proper terminating character if reaching the limit
+  cmd[COMMAND_SIZE] = 0;
+  arg1[ARG_SIZE] = 0;
+  arg2[ARG_SIZE] = 0;
+
+  // Undo all set breakpoints while running in the debugger shell. This will
+  // make them invisible to all commands.
+  UndoBreakpoints();
+
+  while (!done) {
+    if (last_pc != sim_->get_pc()) {
+      last_pc = sim_->get_pc();
+      decoded = Disassembler::Disassemble(last_pc, last_pc + Instr::kInstrSize);
+    }
+    char* line = ReadLine("sim> ");
+    if (line == NULL) {
+      break;
+    } else {
+      // Use sscanf to parse the individual parts of the command line. At the
+      // moment no command expects more than two parameters.
+      int args = SScanF(line,
+                        "%" XSTR(COMMAND_SIZE) "s "
+                        "%" XSTR(ARG_SIZE) "s "
+                        "%" XSTR(ARG_SIZE) "s",
+                        cmd, arg1, arg2);
+      if ((strcmp(cmd, "h") == 0) || (strcmp(cmd, "help") == 0)) {
+        OS::Print("c/cont -- continue execution\n"
+                  "disasm -- disassemble instrs at current pc location\n"
+                  "  other variants are:\n"
+                  "    disasm <address>\n"
+                  "    disasm <address> <number_of_instructions>\n"
+                  "  by default 10 instrs are disassembled\n"
+                  "del -- delete breakpoints\n"
+                  "gdb -- transfer control to gdb\n"
+                  "h/help -- print this help string\n"
+                  "break <address> -- set break point at specified address\n"
+                  "p/print <reg or value or *addr> -- print integer value\n"
+                  "pf/printfloat <freg or *addr> -- print float value\n"
+                  "po/printobject <*reg or *addr> -- print object\n"
+                  "si/stepi -- single step an instruction\n"
+                  "unstop -- if current pc is a stop instr make it a nop\n"
+                  "q/quit -- Quit the debugger and exit the program\n");
+      } else if ((strcmp(cmd, "quit") == 0) || (strcmp(cmd, "q") == 0)) {
+        OS::Print("Quitting\n");
+        OS::Exit(0);
+      } else if ((strcmp(cmd, "si") == 0) || (strcmp(cmd, "stepi") == 0)) {
+        if (decoded) {
+          sim_->InstructionDecode(reinterpret_cast<Instr*>(sim_->get_pc()));
+        } else {
+          OS::Print("Instruction could not be decoded. Stepping disabled.\n");
+        }
+      } else if ((strcmp(cmd, "c") == 0) || (strcmp(cmd, "cont") == 0)) {
+        if (decoded) {
+          // Execute the one instruction we broke at with breakpoints disabled.
+          sim_->InstructionDecode(reinterpret_cast<Instr*>(sim_->get_pc()));
+          // Leave the debugger shell.
+          done = true;
+        } else {
+          OS::Print("Instruction could not be decoded. Cannot continue.\n");
+        }
+      } else if ((strcmp(cmd, "p") == 0) || (strcmp(cmd, "print") == 0)) {
+        if (args == 2) {
+          uint32_t value;
+          if (GetValue(arg1, &value)) {
+            OS::Print("%s: %u 0x%x\n", arg1, value, value);
+          } else {
+            OS::Print("%s unrecognized\n", arg1);
+          }
+        } else {
+          OS::Print("print <reg or value or *addr>\n");
+        }
+      } else if ((strcmp(cmd, "pf") == 0) ||
+                 (strcmp(cmd, "printfloat") == 0)) {
+        if (args == 2) {
+          double dvalue;
+          if (GetFValue(arg1, &dvalue)) {
+            uint64_t long_value = bit_cast<uint64_t, double>(dvalue);
+            OS::Print("%s: %llu 0x%llx %.8g\n",
+                arg1, long_value, long_value, dvalue);
+          } else {
+            OS::Print("%s unrecognized\n", arg1);
+          }
+        } else {
+          OS::Print("printfloat <dreg or *addr>\n");
+        }
+      } else if ((strcmp(cmd, "po") == 0) ||
+                 (strcmp(cmd, "printobject") == 0)) {
+        if (args == 2) {
+          uint32_t value;
+          // Make the dereferencing '*' optional.
+          if (((arg1[0] == '*') && GetValue(arg1 + 1, &value)) ||
+              GetValue(arg1, &value)) {
+            if (Isolate::Current()->heap()->Contains(value)) {
+              OS::Print("%s: \n", arg1);
+#if defined(DEBUG)
+              const Object& obj = Object::Handle(
+                  reinterpret_cast<RawObject*>(value));
+              obj.Print();
+#endif  // defined(DEBUG)
+            } else {
+              OS::Print("0x%x is not an object reference\n", value);
+            }
+          } else {
+            OS::Print("%s unrecognized\n", arg1);
+          }
+        } else {
+          OS::Print("printobject <*reg or *addr>\n");
+        }
+      } else if (strcmp(cmd, "disasm") == 0) {
+        uint32_t start = 0;
+        uint32_t end = 0;
+        if (args == 1) {
+          start = sim_->get_pc();
+          end = start + (10 * Instr::kInstrSize);
+        } else if (args == 2) {
+          if (GetValue(arg1, &start)) {
+            // no length parameter passed, assume 10 instructions
+            if (Simulator::IsIllegalAddress(start)) {
+              // If start isn't a valid address, warn and use PC instead
+              OS::Print("First argument yields invalid address: 0x%x\n", start);
+              OS::Print("Using PC instead");
+              start = sim_->get_pc();
+            }
+            end = start + (10 * Instr::kInstrSize);
+          }
+        } else {
+          uint32_t length;
+          if (GetValue(arg1, &start) && GetValue(arg2, &length)) {
+            if (Simulator::IsIllegalAddress(start)) {
+              // If start isn't a valid address, warn and use PC instead
+              OS::Print("First argument yields invalid address: 0x%x\n", start);
+              OS::Print("Using PC instead\n");
+              start = sim_->get_pc();
+            }
+            end = start + (length * Instr::kInstrSize);
+          }
+        }
+
+        Disassembler::Disassemble(start, end);
+      } else if (strcmp(cmd, "gdb") == 0) {
+        OS::Print("relinquishing control to gdb\n");
+        OS::DebugBreak();
+        OS::Print("regaining control from gdb\n");
+      } else if (strcmp(cmd, "break") == 0) {
+        if (args == 2) {
+          uint32_t addr;
+          if (GetValue(arg1, &addr)) {
+            if (!SetBreakpoint(reinterpret_cast<Instr*>(addr))) {
+              OS::Print("setting breakpoint failed\n");
+            }
+          } else {
+            OS::Print("%s unrecognized\n", arg1);
+          }
+        } else {
+          OS::Print("break <addr>\n");
+        }
+      } else if (strcmp(cmd, "del") == 0) {
+        if (!DeleteBreakpoint(NULL)) {
+          OS::Print("deleting breakpoint failed\n");
+        }
+      } else if (strcmp(cmd, "unstop") == 0) {
+        intptr_t stop_pc = sim_->get_pc() - Instr::kInstrSize;
+        Instr* stop_instr = reinterpret_cast<Instr*>(stop_pc);
+        if (stop_instr->IsBreakPoint()) {
+          stop_instr->SetInstructionBits(Instr::kNopInstruction);
+        } else {
+          OS::Print("Not at debugger stop.\n");
+        }
+      } else {
+        OS::Print("Unknown command: %s\n", cmd);
+      }
+    }
+    delete[] line;
+  }
+
+  // Add all the breakpoints back to stop execution and enter the debugger
+  // shell when hit.
+  RedoBreakpoints();
+
+#undef COMMAND_SIZE
+#undef ARG_SIZE
+
+#undef STR
+#undef XSTR
+}
+
+
+char* SimulatorDebugger::ReadLine(const char* prompt) {
+  char* result = NULL;
+  char line_buf[256];
+  int offset = 0;
+  bool keep_going = true;
+  fprintf(stdout, "%s", prompt);
+  fflush(stdout);
+  while (keep_going) {
+    if (fgets(line_buf, sizeof(line_buf), stdin) == NULL) {
+      // fgets got an error. Just give up.
+      if (result != NULL) {
+        delete[] result;
+      }
+      return NULL;
+    }
+    int len = strlen(line_buf);
+    if (len > 1 &&
+        line_buf[len - 2] == '\\' &&
+        line_buf[len - 1] == '\n') {
+      // When we read a line that ends with a "\" we remove the escape and
+      // append the remainder.
+      line_buf[len - 2] = '\n';
+      line_buf[len - 1] = 0;
+      len -= 1;
+    } else if ((len > 0) && (line_buf[len - 1] == '\n')) {
+      // Since we read a new line we are done reading the line. This
+      // will exit the loop after copying this buffer into the result.
+      keep_going = false;
+    }
+    if (result == NULL) {
+      // Allocate the initial result and make room for the terminating '\0'
+      result = new char[len + 1];
+      if (result == NULL) {
+        // OOM, so cannot readline anymore.
+        return NULL;
+      }
+    } else {
+      // Allocate a new result with enough room for the new addition.
+      int new_len = offset + len + 1;
+      char* new_result = new char[new_len];
+      if (new_result == NULL) {
+        // OOM, free the buffer allocated so far and return NULL.
+        delete[] result;
+        return NULL;
+      } else {
+        // Copy the existing input into the new array and set the new
+        // array as the result.
+        memmove(new_result, result, offset);
+        delete[] result;
+        result = new_result;
+      }
+    }
+    // Copy the newly read line into the result.
+    memmove(result + offset, line_buf, len);
+    offset += len;
+  }
+  ASSERT(result != NULL);
+  result[offset] = '\0';
+  return result;
+}
+
+
 void Simulator::InitOnce() {
 }
 
@@ -34,6 +496,8 @@
                      kSimulatorStackUnderflowSize)];
   icount_ = 0;
   delay_slot_ = false;
+  break_pc_ = NULL;
+  break_instr_ = 0;
 
   // Setup architecture state.
   // All registers are initialized to zero to start with.
@@ -85,6 +549,46 @@
 }
 
 
+void Simulator::set_fregister(FRegister reg, double value) {
+  ASSERT((reg >= 0) && (reg < kNumberOfFRegisters));
+  fregisters_[reg] = value;
+}
+
+
+double Simulator::get_fregister(FRegister reg) const {
+  ASSERT((reg >= 0) && (reg < kNumberOfFRegisters));
+  return fregisters_[reg];
+}
+
+
+void Simulator::HandleIllegalAccess(uword addr, Instr* instr) {
+  uword fault_pc = get_pc();
+  // The debugger will not be able to single step past this instruction, but
+  // it will be possible to disassemble the code and inspect registers.
+  char buffer[128];
+  snprintf(buffer, sizeof(buffer),
+           "illegal memory access at 0x%"Px", pc=0x%"Px"\n",
+           addr, fault_pc);
+  SimulatorDebugger dbg(this);
+  dbg.Stop(instr, buffer);
+  // The debugger will return control in non-interactive mode.
+  FATAL("Cannot continue execution after illegal memory access.");
+}
+
+
+void Simulator::UnalignedAccess(const char* msg, uword addr, Instr* instr) {
+  // The debugger will not be able to single step past this instruction, but
+  // it will be possible to disassemble the code and inspect registers.
+  char buffer[64];
+  snprintf(buffer, sizeof(buffer),
+           "unaligned %s at 0x%"Px", pc=%p\n", msg, addr, instr);
+  SimulatorDebugger dbg(this);
+  dbg.Stop(instr, buffer);
+  // The debugger will return control in non-interactive mode.
+  FATAL("Cannot continue execution after unaligned access.");
+}
+
+
 // Returns the top of the stack area to enable checking for stack pointer
 // validity.
 uword Simulator::StackTop() const {
@@ -118,8 +622,7 @@
     int16_t* ptr = reinterpret_cast<int16_t*>(addr);
     return *ptr;
   }
-  // TODO(zra) unaligned access. Trap into debugger.
-  UNIMPLEMENTED();
+  UnalignedAccess("signed halfword read", addr, instr);
   return 0;
 }
 
@@ -129,8 +632,7 @@
     uint16_t* ptr = reinterpret_cast<uint16_t*>(addr);
     return *ptr;
   }
-  // TODO(zra) unaligned access. Trap into debugger.
-  UNIMPLEMENTED();
+  UnalignedAccess("unsigned halfword read", addr, instr);
   return 0;
 }
 
@@ -140,8 +642,7 @@
     intptr_t* ptr = reinterpret_cast<intptr_t*>(addr);
     return *ptr;
   }
-  // TODO(zra) unaligned access. Trap into debugger.
-  UNIMPLEMENTED();
+  UnalignedAccess("read", addr, instr);
   return 0;
 }
 
@@ -158,8 +659,7 @@
     *ptr = value;
     return;
   }
-  // TODO(zra) unaligned access. Trap into debugger.
-  UNIMPLEMENTED();
+  UnalignedAccess("halfword write", addr, instr);
 }
 
 
@@ -169,8 +669,7 @@
     *ptr = value;
     return;
   }
-  // TODO(zra) unaligned access. Trap into debugger.
-  UNIMPLEMENTED();
+  UnalignedAccess("write", addr, instr);
 }
 
 
@@ -211,6 +710,11 @@
       set_register(instr->RdField(), rs_val & rt_val);
       break;
     }
+    case BREAK: {
+      SimulatorDebugger dbg(this);
+      dbg.Stop(instr, "breakpoint");
+      break;
+    }
     case DIV: {
       ASSERT(instr->RdField() == 0);
       ASSERT(instr->SaField() == 0);
@@ -295,7 +799,7 @@
     }
     default: {
       OS::PrintErr("DecodeSpecial: 0x%x\n", instr->InstructionBits());
-      UNREACHABLE();
+      UNIMPLEMENTED();

[Ivan Posva, 2013/03/13 21:50:34]

What are you planning to implement here?

[zra, 2013/03/14 15:48:14]

There are several Special instructions remaining to be implemented.

       break;
     }
   }
@@ -337,25 +841,13 @@
     }
     default: {
       OS::PrintErr("DecodeSpecial2: 0x%x\n", instr->InstructionBits());
-      UNREACHABLE();
+      UNIMPLEMENTED();
       break;
     }
   }
 }
 
 
-void Simulator::DecodeSpecial3(Instr* instr) {
-  ASSERT(instr->OpcodeField() == SPECIAL3);
-  switch (instr->FunctionField()) {
-    default: {
-      OS::PrintErr("DecodeSpecial3: 0x%x\n", instr->InstructionBits());
-      UNREACHABLE();
-      break;
-    }
-  }
-}
-
-
 void Simulator::InstructionDecode(Instr* instr) {
   switch (instr->OpcodeField()) {
     case SPECIAL: {
@@ -366,10 +858,6 @@
       DecodeSpecial2(instr);
       break;
     }
-    case SPECIAL3: {
-      DecodeSpecial3(instr);
-      break;
-    }
     case ADDIU: {
       // Format(instr, "addiu 'rt, 'rs, 'imms");
       int32_t rs_val = get_register(instr->RsField());
@@ -391,8 +879,7 @@
       int32_t imm_val = instr->SImmField();
       uword addr = base_val + imm_val;
       if (Simulator::IsIllegalAddress(addr)) {
-        // TODO(zra) trap into debugger.
-        UNIMPLEMENTED();
+        HandleIllegalAccess(addr, instr);
       } else {
         int32_t res = ReadB(addr);
         set_register(instr->RtField(), res);
@@ -405,8 +892,7 @@
       int32_t imm_val = instr->SImmField();
       uword addr = base_val + imm_val;
       if (Simulator::IsIllegalAddress(addr)) {
-        // TODO(zra) trap into debugger.
-        UNIMPLEMENTED();
+        HandleIllegalAccess(addr, instr);
       } else {
         int32_t res = ReadBU(addr);
         set_register(instr->RtField(), res);
@@ -419,8 +905,7 @@
       int32_t imm_val = instr->SImmField();
       uword addr = base_val + imm_val;
       if (Simulator::IsIllegalAddress(addr)) {
-        // TODO(zra) trap into debugger.
-        UNIMPLEMENTED();
+        HandleIllegalAccess(addr, instr);
       } else {
         int32_t res = ReadH(addr, instr);
         set_register(instr->RtField(), res);
@@ -433,8 +918,7 @@
       int32_t imm_val = instr->SImmField();
       uword addr = base_val + imm_val;
       if (Simulator::IsIllegalAddress(addr)) {
-        // TODO(zra) trap into debugger.
-        UNIMPLEMENTED();
+        HandleIllegalAccess(addr, instr);
       } else {
         int32_t res = ReadHU(addr, instr);
         set_register(instr->RtField(), res);
@@ -452,8 +936,7 @@
       int32_t imm_val = instr->SImmField();
       uword addr = base_val + imm_val;
       if (Simulator::IsIllegalAddress(addr)) {
-        // TODO(zra) trap into debugger.
-        UNIMPLEMENTED();
+        HandleIllegalAccess(addr, instr);
       } else {
         int32_t res = ReadW(addr, instr);
         set_register(instr->RtField(), res);
@@ -473,8 +956,7 @@
       int32_t imm_val = instr->SImmField();
       uword addr = base_val + imm_val;
       if (Simulator::IsIllegalAddress(addr)) {
-        // TODO(zra) trap into debugger.
-        UNIMPLEMENTED();
+        HandleIllegalAccess(addr, instr);
       } else {
         WriteB(addr, rt_val & 0xff);
       }
@@ -487,8 +969,7 @@
       int32_t imm_val = instr->SImmField();
       uword addr = base_val + imm_val;
       if (Simulator::IsIllegalAddress(addr)) {
-        // TODO(zra) trap into debugger.
-        UNIMPLEMENTED();
+        HandleIllegalAccess(addr, instr);
       } else {
         WriteH(addr, rt_val & 0xffff, instr);
       }
@@ -501,16 +982,16 @@
       int32_t imm_val = instr->SImmField();
       uword addr = base_val + imm_val;
       if (Simulator::IsIllegalAddress(addr)) {
-        // TODO(zra) trap into debugger.
-        UNIMPLEMENTED();
+        HandleIllegalAccess(addr, instr);
       } else {
         WriteW(addr, rt_val, instr);
       }
       break;
     }
     default: {
-      OS::PrintErr("Undecoded instruction: 0x%x\n", instr->InstructionBits());
-      UNREACHABLE();
+      OS::PrintErr("Undecoded instruction: 0x%x at %p\n",
+                    instr->InstructionBits(), instr);
+      UNIMPLEMENTED();
       break;
     }
   }