# MCP-Debugger Rust Language Testing - Issues Analysis Report
**Test Date:** November 17, 2025
**Test Environment:** Windows 11, x86_64-pc-windows-gnu/msvc
**Test Objective:** Identify and categorize issues with Rust debugging using mcp-debugger
## Executive Summary
Testing revealed that mcp-debugger can successfully debug Rust programs on Windows when properly configured. However, there are significant toolchain compatibility and configuration issues that need to be addressed for a reliable setup.
## Test Results Summary
### ✅ What Works
1. **Basic Debugging with GNU Toolchain**
- Successfully debugged `hello_world` example
- Breakpoints work correctly (hit at expected lines)
- Step-over functionality works
- Stack traces show correct Rust function names and file locations
- Local variable inspection works (parameters visible in functions)
- GDB 16.3 successfully interfaces with CodeLLDB
2. **Debug Infrastructure**
- CodeLLDB is properly vendored at `packages/adapter-rust/vendor/codelldb/win32-x64/`
- Session creation and management works
- Breakpoint setting with absolute paths works
- Debug state transitions (paused/running) work correctly
### ❌ What Doesn't Work
1. **GNU Toolchain Compilation Issues**
- Cannot build new projects with GNU toolchain
- Missing MinGW runtime libraries (crt2.o, libkernel32, etc.)
- dlltool.exe CreateProcess errors
- x86_64-w64-mingw32-gcc linker failures
2. **MSVC Toolchain Debugging Limitations**
- CodeLLDB cannot read MSVC PDB debug symbols
- Variable values show as `<unavailable>`
- String contents appear corrupted
- Complex types (Vec, HashMap, async state) missing data
- Limited to control flow debugging only
3. **Path Resolution Issues**
- Relative paths for breakpoint files don't work
- Must use absolute paths for file references
## Issue Categories
### Category 1: Toolchain Issues
| Issue | Severity | Impact | Root Cause |
|-------|----------|--------|------------|
| GNU linker missing libraries | Critical | Cannot build with GNU | MinGW toolchain incomplete |
| MSVC PDB incompatibility | High | No variable inspection | CodeLLDB limitation |
| dlltool CreateProcess error | Critical | Build failures | Path/permission issues |
**Example Error:**
```
ld: cannot find crt2.o: No such file or directory
ld: cannot find -lkernel32: No such file or directory
dlltool.exe: CreateProcess
```
### Category 2: MCP-Debugger Issues
| Issue | Severity | Impact | Root Cause |
|-------|----------|--------|------------|
| Relative path resolution | Medium | Must use absolute paths | Path handling logic |
| No toolchain auto-detection | Low | Manual configuration needed | Missing detection logic |
### Category 3: Environment Configuration
| Issue | Severity | Impact | Root Cause |
|-------|----------|--------|------------|
| MinGW not properly configured | Critical | GNU builds fail | Incomplete MSYS2 setup |
| PATH configuration complex | Medium | Manual setup required | Multiple toolchain paths |
## Detailed Test Log
### Test 1: Hello World (Success with pre-built binary)
```json
{
"session": "b1ddb7cc-8841-4f12-9bb8-eb9b90feec8f",
"executable": "hello_world.exe (pre-built)",
"toolchain": "GNU",
"result": "SUCCESS",
"features_tested": [
"Breakpoint at line 10 - HIT",
"Step-over - WORKS",
"Local variables - VISIBLE (name=\"Rust\")",
"Function parameters - VISIBLE (a=5, b=10)",
"Stack trace - CORRECT"
]
}
```
### Test 2: Async Example (Failed - Toolchain Issues)
```json
{
"session": "9bfaa185-9874-4f0e-b82f-c6f700fefe61",
"executable": "async_example.exe",
"toolchain_attempts": [
{
"toolchain": "GNU",
"result": "BUILD_FAILED",
"error": "Linker missing libraries"
},
{
"toolchain": "MSVC",
"result": "BUILD_SUCCESS_DEBUG_LIMITED",
"error": "PDB symbols unreadable by CodeLLDB"
}
]
}
```
## Root Cause Analysis
### 1. GNU Toolchain Issues
The GNU toolchain on Windows requires a complete MinGW-w64 environment. The current setup has:
- ✅ Rust GNU toolchain installed
- ✅ dlltool.exe available in rustup
- ❌ MinGW runtime libraries missing
- ❌ MSYS2 gcc toolchain incomplete
### 2. MSVC Toolchain Limitations
CodeLLDB (the Rust debug adapter) is built on LLDB, which has limited support for Microsoft's PDB format:
- LLDB primarily supports DWARF debug format (used by GNU)
- PDB support is incomplete in LLDB
- This is a known upstream limitation
### 3. Configuration Complexity
The Windows Rust debugging setup requires coordinating multiple components:
- Rust toolchain (GNU vs MSVC)
- Debug adapter (CodeLLDB)
- System debugger (GDB for GNU, CDB for MSVC)
- Runtime libraries (MinGW for GNU, Visual C++ for MSVC)
## Recommended Solution
### For Reliable Rust Debugging on Windows
#### Option 1: Complete GNU Setup (Recommended)
```powershell
# 1. Install MSYS2 (if not present)
winget install MSYS2.MSYS2
# 2. Install MinGW toolchain
pacman -S mingw-w64-ucrt-x86_64-toolchain
# 3. Add to PATH
$env:PATH = "C:\msys64\ucrt64\bin;$env:PATH"
# 4. Set dlltool
$env:DLLTOOL = "$env:USERPROFILE\.rustup\toolchains\stable-x86_64-pc-windows-gnu\lib\rustlib\x86_64-pc-windows-gnu\bin\self-contained\dlltool.exe"
# 5. Use GNU toolchain
rustup default stable-x86_64-pc-windows-gnu
cargo build
```
#### Option 2: Use Pre-built Binaries
- Build on a properly configured system
- Distribute debug binaries
- Debug without rebuilding
#### Option 3: WSL2 Environment
- Use Linux debugging tools
- Avoid Windows-specific issues
- Full GNU toolchain support
## Configuration Validation Checklist
```bash
# Check GNU toolchain
rustup show | grep gnu
# Check GDB
gdb --version
# Check MinGW GCC
x86_64-w64-mingw32-gcc --version
# Check dlltool
echo $env:DLLTOOL
# Check CodeLLDB
ls packages/adapter-rust/vendor/codelldb/
# Test build
cargo +stable-gnu build --target x86_64-pc-windows-gnu
# Test debug
mcp-debugger create rust session
```
## Known Workarounds
1. **For Path Issues:**
- Always use absolute paths for files
- Use forward slashes or escaped backslashes
2. **For GNU Build Issues:**
- Pre-build binaries on configured system
- Use Docker/WSL for consistent environment
3. **For MSVC Debug Issues:**
- Use Visual Studio or VS Code C++ extension
- Accept limited debugging (breakpoints only)
## Future Improvements
1. **MCP-Debugger Enhancements:**
- Add toolchain detection and validation
- Improve path resolution
- Add setup validation command
- Better error messages for missing dependencies
2. **Documentation:**
- Windows-specific setup guide
- Troubleshooting decision tree
- Video tutorials for setup
3. **Automation:**
- PowerShell setup script improvements
- Automated dependency installation
- CI/CD for Windows testing
## Conclusion
The mcp-debugger works well for Rust debugging when properly configured, but Windows users face significant setup challenges. The primary issues stem from toolchain incompatibilities and missing dependencies rather than mcp-debugger bugs. A properly configured GNU toolchain provides the best debugging experience, while MSVC toolchain users face inherent limitations due to CodeLLDB's incomplete PDB support.
## Appendix: Error Messages
### GNU Linker Errors
```
ld: cannot find crt2.o: No such file or directory
ld: cannot find crtbegin.o: No such file or directory
ld: cannot find -lkernel32: No such file or directory
ld: cannot find -lntdll: No such file or directory
ld: cannot find -luserenv: No such file or directory
ld: cannot find -lws2_32: No such file or directory
ld: cannot find -ldbghelp: No such file or directory
ld: cannot find -lgcc_eh: No such file or directory
ld: cannot find -l:libpthread.a: No such file or directory
ld: cannot find -lmsvcrt: No such file or directory
ld: cannot find -lmingwex: No such file or directory
ld: cannot find -lmingw32: No such file or directory
ld: cannot find -lgcc: No such file or directory
ld: cannot find -luser32: No such file or directory
ld: cannot find crtend.o: No such file or directory
```
### MSVC Debugging Warning
```
MSVC toolchain detected - limited debugging support.
This Rust binary was compiled with the MSVC toolchain. CodeLLDB cannot fully
read MSVC PDB debug symbols, which causes:
- Variable values to appear as <unavailable>
- Corrupted string contents
- Missing data for complex types (Vec, HashMap, async state)
