Pdb support - local variables

[Josverl]

local variable access

This document describes the enhanced debugging functionality added to MicroPython through two key commits that implement comprehensive local variable introspection for the sys.settrace() functionality.

Overview

The enhancements enable debuggers and profiling tools to access local variable names and values in function frames, which is essential for interactive debugging, breakpoint inspection, and runtime analysis. The implementation includes both basic local variable access and advanced variable name preservation with correct slot mapping.

Key Features Added

1. Basic Frame Local Variables Access (frame.f_locals)

The initial implementation provides access to local variables in stack frames through the frame.f_locals property. This foundational feature enables debuggers to inspect variable values at runtime.

Key Components:

• frame_f_locals() function - Core implementation in py/profile.c
• Memory-safe access - Includes GC lock checking and state validation
• Generic fallback names - Uses local_01, local_02, etc. when variable names unavailable
• Robust error handling - Graceful handling of invalid state or memory allocation failures

Implementation Features:

• Pre-allocates dictionary size based on frame state count for efficiency
• Validates code state and state array before access
• Skips NULL values in the state array
• Safe qstr creation with error checking

2. Advanced Variable Name Storage (MICROPY_PY_SYS_SETTRACE_SAVE_NAMES)

An enhanced compile-time feature that preserves actual local variable names in compiled bytecode for professional debugging capabilities.