Drops into Simulator Debugger only in a session that is already interactive.

runtime/vm/disassembler_x64.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/disassembler.h"
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_IA32.
 #if defined(TARGET_ARCH_X64)
 #include "platform/utils.h"
 #include "vm/allocation.h"
@@ skipping 1847 matching lines @@
 
   ASSERT(buffer_[buffer_pos_] == '\0');
 
   int instr_len = data - reinterpret_cast<uint8_t*>(pc);
   ASSERT(instr_len > 0);  // Ensure progress.
 
   return instr_len;
 }
 
 
-bool Disassembler::DecodeInstruction(char* hex_buffer, intptr_t hex_size,
-                                    char* human_buffer, intptr_t human_size,
-                                    int* out_instr_len, uword pc) {
+void Disassembler::DecodeInstruction(char* hex_buffer, intptr_t hex_size,
+                                     char* human_buffer, intptr_t human_size,
+                                     int* out_instr_len, uword pc) {
   ASSERT(hex_size > 0);
   ASSERT(human_size > 0);
   DisassemblerX64 decoder(human_buffer, human_size);
   int instruction_length = decoder.InstructionDecode(pc);
   uint8_t* pc_ptr = reinterpret_cast<uint8_t*>(pc);
   int hex_index = 0;
   int remaining_size = hex_size - hex_index;
   for (int i = 0; (i < instruction_length) && (remaining_size > 2); ++i) {
     OS::SNPrint(&hex_buffer[hex_index], remaining_size, "%02x", pc_ptr[i]);
     hex_index += 2;
     remaining_size -= 2;
   }
   hex_buffer[hex_index] = '\0';
   if (out_instr_len) {
     *out_instr_len = instruction_length;
   }
-  return true;
 }
 
 
-bool Disassembler::Disassemble(uword start,
+void Disassembler::Disassemble(uword start,
                                uword end,
                                DisassemblyFormatter* formatter,
                                const Code::Comments& comments) {
   ASSERT(formatter != NULL);
   char hex_buffer[kHexadecimalBufferSize];  // Instruction in hexadecimal form.
   char human_buffer[kUserReadableBufferSize];  // Human-readable instruction.
   uword pc = start;
   intptr_t comment_finger = 0;
   while (pc < end) {
     const intptr_t offset = pc - start;
@@ skipping 11 matching lines @@
                       sizeof(human_buffer),
                       &instruction_length, pc);
     formatter->ConsumeInstruction(hex_buffer,
                                   sizeof(hex_buffer),
                                   human_buffer,
                                   sizeof(human_buffer),
                                   pc);
     pc += instruction_length;
   }
 
-  return true;
+  return;
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64