The ustack() function

void ustack(int nframes, int strsize)
void ustack(int nframes)
void ustack(void)

The ustack() action records a user stack trace to the directed buffer. The depth of the user stack is equal to the value specified in nframes. If there is no value for nframes, the ustack action records a number of stack frames that is specified by the ustackframes option. The ustack() action determines the address of the calling frames when the probe fires. The ustack() action does not translate the stack frames into symbols until the DTrace consumer processes the ustack() action at the user level. If a value for strsize is specified and not zero, the ustack() action allocates the specified amount of string space and uses it to perform address-to-symbol translation directly from the kernel.