Do Gophers Dream of Stack Overflow?

2026/5/22 Slides for the presentation at GopherCon Singapore.

Transcript

1. Takuto Nagami @logica0419 Do Gophers Dream of Stack Overflow?
2. Ever heard of stack overflow?
3. Ever heard of stack overflow? No this one today!
4. Stack memory (and heap memory)
5. RAM from the application perspective . . . • Key-value store ◦ Key: Memory address ◦ Value: 1 byte for each addr • Most of high-level language (including Go) divides this store into two areas: Stack and Heap 0x0000 0x0001 0x0002 0x0003
6. . . . Stack memory area
7. . . . main() stack frame Stack memory area
8. . . . main() stack frame 5 Stack memory area {v addr}
9. . . . main() stack frame 5 a() stack frame Stack memory area {v addr}
10. . . . main() stack frame 5 a() stack frame 5 Stack memory area {arg addr} {v addr}
11. . . . main() stack frame 5 a() stack frame 5 7 Stack memory area {arg addr} {a addr} {v addr}
12. . . Stack memory area main() stack frame 5 a() stack frame {arg addr} {a addr} {v addr} 5 7 b() stack frame
13. . . Stack memory area main() stack frame 5 a() stack frame {arg addr} {arg addr} {a addr} {v addr} 5 7 b() stack frame 7
14. . . Stack memory area main() stack frame 5 a() stack frame {arg addr} {b addr} {arg addr} {a addr} {v addr} 5 7 b() stack frame 7 1
15. . . . Stack memory area main() stack frame 5 a() stack frame {arg addr} {a addr} {v addr} 5 7
16. . . . Stack memory area main() stack frame 5 {v addr}
17. . . . Stack memory area Program exits
18. Stack is not a silver bullet... • Can’t handle unknown data size (maps/slices) ◦ Stack allocation is compiler’s duty • Sometimes can’t share variables between functions → These go to heap memory area
19. Stack overflow (primary meaning)
20. Stack overflow • Language decides border between heap and stack ◦ e.g., in C on Linux, stack size is 8MB . . . . . Heap var main() stack frame
21. Stack overflow • Going over the stack limit with nested function
22. Stack overflow • Going over the stack limit with nested function → Stack overflow!!
23. Flexible stack 【Go specific】
24. Go has flexible stack • Stack for each goroutine • Each stack grows and shrinks on demand ◦ Initialized with 4kB
25. Rough idea main goroutine main() stack frame a() stack frame a2() stack frame a3() stack frame a4() stack frame m2() stack frame b() stack frame a goroutine b goroutine
26. Can Go still cause a stack overflow despite having a flexible stack?
27. Flexible stack → No stack overflow?
28. No stack overflow? Stack overflow still exists in Go!
29. Because: Each goroutine has a stack size limit It’s defined in the “runtime” package
30. Maximum stack size • Set to 1MiB on startup ◦ runtime/stack.go
31. Maximum stack size • Final size is defined when main goroutine starts ◦ runtime/proc.go ◦ 250MB for 32bit, 1GB for 64bit
32. Let’s see an actual stack overflow! • Go says “fatal error: stack overflow” ◦ 6 million+ functions were nested
33. Modifying the max size • Override with runtime/debug.SetMaxStack()
34. Modifying the max size • The same experiment with 8 MB of stack size ◦ Nested functions: 6 million -> 52,000
35. Wrapup Go’s stack does overflow
36. Thank you! Let’s have a nice conference!