| As someone who teaches this stuff at university, I see students getting confused every single year by how textbooks draw memory. The problem is mostly visual, not conceptual. Most diagrams in books and slides use an old hardware-centric convention: they draw higher addresses at the top of the page and lower addresses at the bottom. People sometimes justify this with an analogy like “floors in a building go up,” so address 0x7fffffffe000 is drawn “higher” than 0x400000. But this is backwards from how humans read almost everything today. When you look at code in VS Code or any other IDE, line 1 is at the top, then line 2 is below it, then 3, 4, etc. Numbers go up as you go down. Your brain learns: “down = bigger index.” Memory in a real Linux process actually matches the VS Code model much more closely than the textbook diagrams suggest. You can see it yourself with: cat /proc/$$/maps (pick any PID instead of $$). ...
[0x00000000] lower addresses ...
[0x00620000] HEAP start[0x00643000] HEAP extended ↓ (more allocations => higher addresses) ...
[0x7ffd8c3f7000] STACK top (<- stack pointer) ↑ the stack pointer starts here and moves upward
(toward lower addresses) when you push
[0x7ffd8c418000] STACK start ...
[0xffffffffff600000] higher addresses ...
The output is printed from low addresses to high addresses. At the top of the output you'll usually see the binary, shared libs, heap, etc. Those all live at lower virtual addresses. Farther down in the output you'll eventually see the stack, which lives at a higher virtual address. In other words: as you scroll down, the addresses get bigger. Exactly like scrolling down in an editor gives you bigger line numbers.The phrases “the heap grows up” and “the stack grows down” aren't wrong. They're just describing what happens to the numeric addresses: the heap expands toward higher addresses, and the stack moves into lower addresses. The real problem is how we draw it. We label “up” on the page as “higher address,” which is the opposite of how people read code or even how /proc/<pid>/maps is printed. So students have to mentally flip the diagram before they can even think about what the stack and heap are doing. If we just drew memory like an editor (low addresses at the top, high addresses further down) it would click instantly. Scroll down, addresses go up, and the stack sits at the bottom. At that point it’s no longer “the stack grows down”: it’s just the stack pointer being decremented, moving to lower addresses (which, in the diagram, means moving upward). |
The core of the issue is that the direction stack growth differs from "usual" memory access patterns which usually allocate from lower to higher addresses (consider array access, or how strings are laid out in memory. And little-endian systems are the majority)
But if we're going with visualization options I prefer to visualize it horizontally, with lower addresses on left. This has a natural correspondence with how you access an array or lay out strings in memory.