Question

I’m reading APUE these days, and just found an issue.

One common way to use pthread_attr_setstack is to

1. malloc a chuck of memory
2. set the addr and length by the method

Then, here comes my question, what if I want to use the guard-size to protect my data? Say I need A bytes of memory, and B bytes for guard-size.

Shall I malloc A+B bytes, or malloc A bytes?

Answer 1

Actually pthread library itself provides an API to set the guard size

int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);

But note that if you are setting the stack location or size, either using functions like pthread_attr_setstack(3) or pthread_attr_setstackaddr(3), which you are, then the guard size attribute is ignored (i.e., no guard area is created by the system): it is the your responsibility to handle stack overflow (perhaps by using mprotect(2) to manually define a guard area at the end of the stack that you have allocated.

So, coming to your specific question, yes, you need to malloc A+B bytes to include the guard area yourself if you wish to use pthread_attr_setstack. Else, if you are OK with the default stack size, then you use the pthread_attr_setstack function.

Read about pthreads here. Also read specifically about thread stack management here under the section Stack Management