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signal-slot

MCP GDB Server

by signal-slot

gdb_command

Execute GDB debugging commands via API to manage sessions, set breakpoints, and inspect variables within the MCP GDB Server environment.

Instructions

Execute a GDB command

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
commandYesGDB command to execute
sessionIdYesGDB session ID

Implementation Reference

  • The handleGdbCommand method implements the core logic for the 'gdb_command' tool. It validates the session ID, retrieves the GDB session, executes the provided command using the executeGdbCommand helper, and formats the output response.
    private async handleGdbCommand(args: any) {
      const { sessionId, command } = args;
      
      if (!activeSessions.has(sessionId)) {
        return {
          content: [
            {
              type: 'text',
              text: `No active GDB session with ID: ${sessionId}`
            }
          ],
          isError: true
        };
      }
      
      const session = activeSessions.get(sessionId)!;
      
      try {
        const output = await this.executeGdbCommand(session, command);
        
        return {
          content: [
            {
              type: 'text',
              text: `Command: ${command}\n\nOutput:\n${output}`
            }
          ]
        };
      } catch (error) {
        const errorMessage = error instanceof Error ? error.message : String(error);
        return {
          content: [
            {
              type: 'text',
              text: `Failed to execute command: ${errorMessage}`
            }
          ],
          isError: true
        };
      }
    }
  • Input schema for the 'gdb_command' tool defining the required parameters: sessionId (string) and command (string).
    inputSchema: {
      type: 'object',
      properties: {
        sessionId: {
          type: 'string',
          description: 'GDB session ID'
        },
        command: {
          type: 'string',
          description: 'GDB command to execute'
        }
      },
      required: ['sessionId', 'command']
    }
  • src/index.ts:103-120 (registration)
    Registration of the 'gdb_command' tool in the ListToolsRequestSchema handler, providing name, description, and input schema.
    {
      name: 'gdb_command',
      description: 'Execute a GDB command',
      inputSchema: {
        type: 'object',
        properties: {
          sessionId: {
            type: 'string',
            description: 'GDB session ID'
          },
          command: {
            type: 'string',
            description: 'GDB command to execute'
          }
        },
        required: ['sessionId', 'command']
      }
    },
  • src/index.ts:363-364 (registration)
    Routing registration in the CallToolRequestSchema switch statement that dispatches 'gdb_command' calls to the handleGdbCommand method.
    case 'gdb_command':
      return await this.handleGdbCommand(request.params.arguments);
  • Core helper function executeGdbCommand that communicates with the GDB process via stdin/stdout, captures output until response markers like '(gdb)', '^done', or '^error', with timeout and error handling.
    private executeGdbCommand(session: GdbSession, command: string): Promise<string> {
      return new Promise<string>((resolve, reject) => {
        if (!session.ready) {
          reject(new Error('GDB session is not ready'));
          return;
        }
        
        // Write command to GDB's stdin
        if (session.process.stdin) {
          session.process.stdin.write(command + '\n');
        } else {
          reject(new Error('GDB stdin is not available'));
          return;
        }
        
        let output = '';
        let responseComplete = false;
        
        // Create a one-time event handler for GDB output
        const onLine = (line: string) => {
          output += line + '\n';
          
          // Check if this line indicates the end of the GDB response
          if (line.includes('(gdb)') || line.includes('^done') || line.includes('^error')) {
            responseComplete = true;
            
            // If we've received the complete response, resolve the promise
            if (responseComplete) {
              // Remove the listener to avoid memory leaks
              session.rl.removeListener('line', onLine);
              resolve(output);
            }
          }
        };
        
        // Add the line handler to the readline interface
        session.rl.on('line', onLine);
        
        // Set a timeout to prevent hanging
        const timeout = setTimeout(() => {
          session.rl.removeListener('line', onLine);
          reject(new Error('GDB command timed out'));
        }, 10000); // 10 second timeout
        
        // Handle GDB errors
        const errorHandler = (data: Buffer) => {
          const errorText = data.toString();
          output += `[stderr] ${errorText}\n`;
        };
        
        // Add error handler
        if (session.process.stderr) {
          session.process.stderr.once('data', errorHandler);
        }
        
        // Clean up event handlers when the timeout expires
        timeout.unref();
      });
    }
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries full burden but only states the action without behavioral details. It doesn't disclose if this is read-only, destructive, requires specific permissions, or has side effects like altering debug state, which is critical for a GDB tool.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, efficient sentence with zero waste. It's front-loaded and appropriately sized for the tool's scope, earning full marks for conciseness.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given no annotations, no output schema, and a mutation-like tool (execute implies potential changes), the description is incomplete. It lacks details on behavior, return values, or error handling, making it inadequate for safe agent use.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents both parameters (command and sessionId). The description adds no additional meaning beyond what the schema provides, such as examples or constraints, meeting the baseline for high coverage.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose3/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description 'Execute a GDB command' states the action (execute) and resource (GDB command), but it's vague about what this entails compared to siblings like gdb_print or gdb_set_breakpoint. It doesn't specify if this is for arbitrary commands or a subset, making it less distinct.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance is provided on when to use this tool versus alternatives like gdb_print or gdb_set_breakpoint. The description lacks context about prerequisites (e.g., needing an active session) or exclusions, leaving usage unclear.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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