StackThreads/MP: version 0.77 User's Guide

11.7: Segmentation fault

Q: When I ran a program compiled via stgcc, I got a segmentation fault. Why?

A: Ninty nine times out of hundred, it is not my fault :-) Here is some possible ways to isolate the problem.

• If the error occurs on a single processor, debug the program normally using GDB. If you suspect it is my bug, try to compile it using gcc if possible (by commenting out all StackThreads/MP primitives).
• When the error does not show up on a single processor but does on multiple processors, you are out of luck. The program is most likely to contain some race conditions.
• Some programs use a considerable amount of stack space when run on multiple processors. This happens when a program uses synchronizations between threads that are not in parent-child relationships. You can tell that your program caused a stack overflow by GDB. Run that program on GDB. If stack overflows, the program will stop at the opening brace of a procedure (This is most clearly seen when you run GDB from Emacs using M-x gdb command, because an arrow displays the location of the offending instruction).

  If this is the case, you can increase the stack size by giving -ss S option to your program, where S specifies a stack size in bytes (-ss S is automatically recognized by StackThreads/MP runtime. See Command Line Options Common for All StackThreadsMP Programs for details). S can be a number or a number followed by a k (for Kbytes) or m (for Mbytes). For example, -ss 4m sets the stack size of each worker to 4Mbytes.

  Also See Stacks and Contexts for examining stack size at various program points.