OSTEP Ch. 14: malloc, free and 7 Ways to Break Memory

I read OSTEP Chapter 14, the Memory API interlude: stack vs heap, malloc() and free(), why sizeof can fool you, the seven classic memory bugs (segfaults, buffer overflows, leaks, dangling pointers, double frees...), and what malloc is really built on: brk, sbrk and mmap. Operating Systems: Three Easy Pieces (free online): https://pages.cs.wisc.edu/~remzi/OSTEP/ This chapter (PDF): https://pages.cs.wisc.edu/~remzi/OSTE... Chapters 0:00 Chapter 14 recap 1:00 Intro 2:33 14.1 Types of memory 5:07 14.2 The malloc() call 8:33 sizeof: pointer vs array 9:46 14.3 The free() call 10:18 14.4 Common errors 15:24 What Rust actually fixes 16:55 Two levels of memory management 18:46 Tools: valgrind and AddressSanitizer 18:57 14.5 Underlying OS support 20:16 14.6 Other calls: calloc and realloc 20:50 14.7 Summary Quick notes sizeof is compile-time. On a pointer it gives the pointer size (8 on 64-bit), on an array the whole array. Strings need malloc(strlen(s) + 1) for the terminating zero byte. free() takes only the pointer: the allocator remembers the size. Seven ways to get it wrong: forget to allocate, allocate too little, read uninitialized memory, forget to free, free too early, free twice, free something malloc never gave you. malloc and free are library calls. Underneath, the C library asks the kernel for memory with brk/sbrk and mmap. On a Mac: valgrind runs in a Linux VM (Docker Desktop, OrbStack, Lima); natively use clang -fsanitize=address or leaks. #operatingsystems #ostep #cprogramming #memorymanagement #computerscience