Segmentation Fault (Segfault)¶

Trying to access a memory location without permission

e.g., when going out of bound of an array

Workflow¶

flowchart TD
  B{Segfault?} -->|Yes| C1[Compiler Flag Strategy];
  C1 --> C2{Problem Solved?};
  C2 -->|Yes| E[No Problem];
  C2 -->|No| C3[More Advanced Strategies];
  C3 --> C2;
  B ---->|No| E;

Compiler Flag Strategy¶

Fortran provides useful compiler flags for debugging:

Function	GNU	Intel	NVHPC (PGI)
source annotation (give line numbers)	`-g`	`-g`	`-g`
provide stack trace when Segfault	`-fbacktrace`	`-traceback`
extensive checks (array bounds..., slow)	`-fcheck=all`	`-check all`	`-C`

More Advanced Strategies¶

Use a Debugger¶

See gdb Tutorial

Use a Simple Reproducer¶

Favorable simplifications:

serial
quick to reproduce (within seconds)
deterministic (no random reproducibility)
(optional) easy to compile

Bisection of the Codebase¶

prepare more info