LLDB MCP Server

Instructions

Implementation Reference

• lldb_mcp_server.py:865-911 (handler)

  The main handler function for the 'lldb_backtrace' tool. It constructs LLDB commands to generate a backtrace, executes them using _run_lldb_script, optionally parses the output to JSON, and formats the response.
  async def lldb_backtrace(params: BacktraceInput) -> str: """Get a stack backtrace showing the call chain. The backtrace shows: - Frame numbers (0 is current frame) - Function names and addresses - Source file and line numbers (if available) - Module/library names Args: params: BacktraceInput with executable and stopping point Returns: str: Stack backtrace with frame information """ commands = [] if params.core_file: commands.append(f"target create {params.executable} --core {params.core_file}") else: commands.append(f"target create {params.executable}") if params.breakpoint: commands.append(f"breakpoint set --name {params.breakpoint}") commands.append("run" + (" " + " ".join(params.args) if params.args else "")) bt_cmd = "thread backtrace" if params.all_threads: bt_cmd = "thread backtrace all" bt_cmd += f" -c {params.limit}" commands.append(bt_cmd) if not params.core_file: commands.append("quit") result = _run_lldb_script(commands) if params.response_format == ResponseFormat.JSON: frames = _parse_backtrace(result["output"]) return json.dumps( {"success": result["success"], "frames": frames, "raw_output": result["output"]}, indent=2, ) lines = ["## Stack Backtrace", "", "```", result["output"].strip(), "```"] return "\n".join(lines)
• lldb_mcp_server.py:296-316 (schema)

  Pydantic model defining the input schema/validation for the lldb_backtrace tool parameters.
  class BacktraceInput(BaseModel): """Input for getting a backtrace.""" model_config = ConfigDict(str_strip_whitespace=True) executable: str = Field(..., description="Path to the executable", min_length=1) breakpoint: str | None = Field( default=None, description="Breakpoint location to stop at (or use with core file)" ) core_file: str | None = Field( default=None, description="Path to core dump file for post-mortem analysis" ) all_threads: bool = Field(default=False, description="Show backtraces for all threads") limit: int = Field(default=50, description="Maximum number of frames to show", ge=1, le=1000) args: list[str] | None = Field( default=None, description="Command-line arguments to pass to the program" ) response_format: ResponseFormat = Field( default=ResponseFormat.MARKDOWN, description="Output format" )
• lldb_mcp_server.py:855-864 (registration)

  MCP tool registration decorator that registers the lldb_backtrace handler with the FastMCP server, including metadata annotations.
  @mcp.tool( name="lldb_backtrace", annotations={ "title": "Get Backtrace", "readOnlyHint": True, "destructiveHint": False, "idempotentHint": True, "openWorldHint": False, }, )
• lldb_mcp_server.py:462-485 (helper)

  Helper function used by lldb_backtrace to parse raw LLDB backtrace output into a structured list of frame dictionaries for JSON output.
  def _parse_backtrace(output: str) -> list[dict[str, Any]]: """Parse LLDB backtrace output into structured data.""" frames = [] frame_pattern = re.compile( r"frame #(\d+): (0x[0-9a-fA-F]+) (.+?)(?:`(.+?))?(?:\s+\+\s+(\d+))?(?:\s+at\s+(.+):(\d+))?" ) for line in output.split("\n"): match = frame_pattern.search(line) if match: frames.append( { "frame_number": int(match.group(1)), "address": match.group(2), "module": match.group(3).strip() if match.group(3) else None, "function": match.group(4).strip() if match.group(4) else None, "offset": int(match.group(5)) if match.group(5) else None, "file": match.group(6) if match.group(6) else None, "line": int(match.group(7)) if match.group(7) else None, } ) return frames