Write a GDB Python Pretty-Printer

GDB Python Pretty-Printers

GDB includes a Python API that lets you write custom pretty-printers to display complex data structures in human-readable form. Without them, inspecting a linked list in GDB shows raw pointer addresses instead of the values you actually care about.

How Pretty-Printers Work

A pretty-printer is a Python class with a to_string() method:

• gdb.Value: Represents a value in the debugged program
• gdb.Type: Represents the C type of a value
• val['field_name']: Access struct fields
• val.dereference(): Follow a pointer

For example, given struct Node { int data; struct Node* next; }, a pretty-printer walks the list and displays [1 -> 2 -> 3 -> NULL] instead of 0x7fff1234.

Load the script with source pretty_printer.py inside GDB.

For This Exercise

You will define a linked list in C and document how a GDB Python pretty-printer would display it. This skill matters when debugging custom allocators, tree structures, and any non-trivial data type in production code.

Registering and Matching Printers

Pretty-printers register with gdb.printing.register_pretty_printer and match types by name or regex. A printer for struct Node checks val.type.name and returns a NodePrinter instance. The children() method lets GDB expand tree nodes interactively. Teams ship pretty-printer collections for internal data structures so every developer sees readable output during post-mortem debugging sessions.