58  * The stack tracer looks for a maximum stack at each call from a function. It
59  * registers a callback from ftrace, and in that callback it examines the stack
60  * size. It determines the stack size from the variable passed in, which is the
62  * The stack size is calculated by the address of the local variable to the top
63  * of the current stack. If that size is smaller than the currently saved max
64  * stack size, nothing more is done.
66  * If the size of the stack is greater than the maximum recorded size, then the
70  * saving the function's local variables, the stack will look something like
73  *   [ top of stack ]
80  *   31: [ do trace stack here ]
83  * current stack. Which would be (from the bottom of the stack to the top):
90  * a search of the stack is made to find these values. When a match is made, it
91  * is added to the stack_dump_trace[] array. The offset into the stack is saved
101  * each function's portion of the stack.
119  * this will cause the stack to look a little different:
121  * [ top of stack ]
127  * 30: [ do trace stack here ]
130  * placement in the stack will be different. Using the same algorithm as above
141  *   kernel_func_bar stack frame size is 29 - 19 not 30 - 29!
145  * stack trace entries is decremented by one.
153  * will still include the stack size of it.
155 static void check_stack(unsigned long ip, unsigned long *stack)  in check_stack()  argument
162 	this_size = ((unsigned long)stack) & (THREAD_SIZE-1);  in check_stack()
171 	if (!object_is_on_stack(stack))  in check_stack()
195 	/* Skip over the overhead of the stack tracer itself */  in check_stack()
209 	 * Now find where in the stack these are.  in check_stack()
212 	start = stack;  in check_stack()
218 	 * for some reason be missed on the stack, so we may  in check_stack()
232 			 * this is not a stack-out-of-bounds error.  in check_stack()
243 				 * of the stack tracer stack in the  in check_stack()
244 				 * max stack. If we haven't figured  in check_stack()
249 					tracer_frame = (p - stack) *  in check_stack()
295 	unsigned long stack;  in stack_trace_call()  local
304 	/* If rcu is not watching, then save stack trace can fail */  in stack_trace_call()
310 	check_stack(ip, &stack);  in stack_trace_call()
427 		 "#  Stack tracer disabled\n"  in print_disabled()
429 		 "# To enable the stack tracer, either add 'stacktrace' to the\n"  in print_disabled()