GDB Debugging Assistant

Overview

A GDB debugging skill designed for AI agents. Combines source code analysis with runtime state inspection using gdb-cli to provide intelligent debugging assistance for C/C++ programs.

When to Use This Skill

• Analyze core dumps or crash dumps
• Debug running processes with GDB attach
• Investigate crashes, deadlocks, or memory issues
• Get intelligent debugging assistance with source code context
• Debug multi-threaded applications

Do Not Use This Skill When

• The task is unrelated to C/C++ debugging
• The user needs general-purpose assistance without debugging
• No GDB is available (GDB 9.0+ with Python support required)

Prerequisites

# Install gdb-cli
pip install gdb-cli

# Or from GitHub
pip install git+https://github.com/Cerdore/gdb-cli.git

# Verify GDB has Python support
gdb -nx -q -batch -ex "python print('OK')"

Requirements:

• Python 3.6.8+
• GDB 9.0+ with Python support enabled
• Linux OS

How It Works

Step 1: Initialize Debug Session

For core dump analysis:

gdb-cli load --binary <binary_path> --core <core_path> [--gdb-path <gdb_path>]

For live process debugging:

gdb-cli attach --pid <pid> [--binary <binary_path>]

Output: A session_id like "session_id": "a1b2c3". Store this for subsequent commands.

Step 2: Gather Initial Information

SESSION="<session_id>"

# List all threads
gdb-cli threads -s $SESSION

# Get backtrace (with local variables)
gdb-cli bt -s $SESSION --full

# Get registers
gdb-cli registers -s $SESSION

Step 3: Correlate Source Code (CRITICAL)

For each frame in the backtrace:

1. Extract frame info: {file}:{line} in {function}
2. Read source context: Get ±20 lines around the crash point
3. Get local variables: gdb-cli locals-cmd -s $SESSION --frame <N>
4. Analyze: Correlate code logic with variable values

Example correlation:

Frame #0: process_data() at src/worker.c:87
Source code shows:
  85: Node* node = get_node(id);
  86: if (node == NULL) return;
  87: node->data = value;  <- Crash here

Variables show:
  node = 0x0 (NULL)

Analysis: The NULL check on line 86 didn't catch the issue.

Step 4: Deep Investigation

# Examine variables
gdb-cli eval-cmd -s $SESSION "variable_name"
gdb-cli eval-cmd -s $SESSION "ptr->field"
gdb-cli ptype -s $SESSION "struct_name"

# Memory inspection
gdb-cli memory -s $SESSION "0x7fffffffe000" --size 64

# Disassembly
gdb-cli disasm -s $SESSION --count 20

# Check all threads (for deadlock analysis)
gdb-cli thread-apply -s $SESSION bt --all

# View shared libraries
gdb-cli sharedlibs -s $SESSION

Step 5: Session Management

# List active sessions
gdb-cli sessions

# Check session status
gdb-cli status -s $SESSION

# Stop session (cleanup)
gdb-cli stop -s $SESSION

Common Debugging Patterns

Pattern: Null Pointer Dereference

Indicators:

• Crash on memory access instruction
• Pointer variable is 0x0

Investigation:

gdb-cli registers -s $SESSION  # Check RIP
gdb-cli eval-cmd -s $SESSION "ptr"  # Check pointer value

Pattern: Deadlock

Indicators:

• Multiple threads stuck in lock functions
• pthread_mutex_lock in backtrace

Investigation:

gdb-cli thread-apply -s $SESSION bt --all
# Look for circular wait patterns

Pattern: Memory Corruption

Indicators:

• Crash in malloc/free
• Garbage values in variables

Investigation:

gdb-cli memory -s $SESSION "&variable" --size 128
gdb-cli registers -s $SESSION

Examples

Example 1: Core Dump Analysis

# Load core dump
gdb-cli load --binary ./myapp --core /tmp/core.1234

# Get crash location
gdb-cli bt -s a1b2c3 --full

# Examine crash frame
gdb-cli locals-cmd -s a1b2c3 --frame 0

Example 2: Live Process Debugging

# Attach to stuck server
gdb-cli attach --pid 12345

# Check all threads
gdb-cli threads -s b2c3d4

# Get all backtraces
gdb-cli thread-apply -s b2c3d4 bt --all

Best Practices

• Always read source code before drawing conclusions from variable values
• Use --range for pagination on large thread counts or deep backtraces
• Use ptype to understand complex data structures before examining values
• Check all threads for multi-threaded issues
• Cross-reference types with source code definitions

Security & Safety Notes

• This skill requires GDB access to processes and core dumps

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