// User-level page fault handler support.
// We use an assembly language wrapper around a C function.
// The assembly wrapper is in pfentry.S.

#include <inc/lib.h>



// Assembly language pgfault entrypoint defined in lib/pgfaultentry.S.
extern void _pgfault_upcall(void);

// Pointer to currently installed C-language pgfault handler.
void (*_pgfault_handler)(struct UTrapframe *utf);

//
// Set the page fault handler function.
// If there isn't one yet, _pgfault_handler will be 0.
// The first time we register a handler, we need to 
// allocate an exception stack (one page of memory with its top
// at UXSTACKTOP), and tell the kernel to call the assembly-language
// _pgfault_upcall routine when a page fault occurs.
//
void
set_pgfault_handler(void (*handler)(struct UTrapframe *utf))
{
	int r;

	if (_pgfault_handler == 0) {
		// First time through!
		// LAB 4: Your code here.
		struct Page * pp;
		if (sys_page_alloc(sys_getenvid(), (void *)(UXSTACKTOP - PGSIZE), PTE_U | PTE_W | PTE_P) < 0) {
			panic("sys_page_alloc returned < 0 when allocating page for exception stack");
		}
		
		sys_env_set_pgfault_upcall(sys_getenvid(), _pgfault_upcall);
		
		
		
	}
 
	
	// Save handler pointer for assembly to call.
	_pgfault_handler = handler;
	
}