Introduction to Memory Leaks

Fundamentals on Computing for Robotics, Graphics and Computer Vision

Darío Suárez - Adolfo Muñoz

Introduction to Memory Leaks and how to fix them

Goals

  • Understand why memory leaks occur
  • Learn how tofind and fix memory leaks
  • use memory leak detection tools

Introduction

  • A memory leak is a heap-allocated unreachable memory location
  • Consequences: resource depletion and memory leaks
  • In large programs, hard to detect
  • For large enough executions and notable leaks, after a long time the operating system can kill an application that would return out of memory error
  • NoteIn this topic, we will not cover buffer overflow issues

Valgrind

  • Open source tool for memory leaks detection
  • Broadly, an instrumentation framework for building dynamic analysis tools
  • Other usages: profiling or concurrency issues …
  • Supported in platforms such as: AMD64, AARCH64, …
  • More information available at https://valgrind.org>

Using Valgrind

  1. Compile with -g and 0 or 1 optimization level, -O[01]
  2. Higher optimization levels may generate inexisting uninitialised-value errors
  3. Run your application within valgrind environment: 
    valgrind --leak-check=yes app <list of args>

Valgrind's output

  • The output can be large, so you could preserve it on a file; e.g, 
    valgrind --leak-check=yes app <list of args> 2>1 | tee output.txt | less
  • Memory leaks looks as: 
    ==19182== 40 bytes in 1 blocks are definitely lost in loss record 1 of 1
==19182==    at 0x1B8FF5CD: malloc (vg_replace_malloc.c:130)
==19182==    by 0x8048385: f (a.c:5)
==19182==    by 0x80483AB: main (a.c:11)

Suggested workflow

  • With the least of memory leaks from valgrind try to remove them all
  • When working with external libraries, being leakage free may be impossible

Quiz

  • Can Valgrind detect this error?

Address Sanitizers

  • Address Sanitizers (ASan) detects memory issues at runtime
  • Contrary to valgrind, ASan requires linking with its library
  • To use, you have to add the following compilation flags: 
    -fsanitize=address -static-libasan

Summary

  • Remeber to use smart pointers
  • Test your code with memory-issues tools
  • Explore tools such linters as well