#include <inc/mmu.h>
#include <inc/pmap.h>

.data


// Define the global symbols 'envs', 'pages', 'vpt', and 'vpd'
// so that they can be used in C as if they were ordinary global arrays.
	.globl envs
	.set envs, UENVS
	.globl pages
	.set pages, UPAGES
	.globl vpt
	.set vpt, UVPT
	.globl vpd
	.set vpd, (UVPT+(UVPT>>12)*4)


// Entrypoint - this is where the kernel (or our parent environment)
// starts us running when we are initially loaded into a new environment.
.text
.globl _start
_start:
	// See if we were started with arguments on the stack
	cmpl $USTACKTOP, %esp
	jne args_exist

	// If not, push dummy argc/argv arguments.
	// This happens when we are loaded by the kernel,
	// because the kernel does not know about passing arguments.
	pushl $0
	pushl $0

args_exist:
	call libmain
1:      jmp 1b


.data
.globl _pgfault_handler
_pgfault_handler:
	.long 0


// Page fault handler entrypoint -
// this is where we ask the kernel
// (by calling sys_set_pgfault_handler)
// to redirect us to whenever we cause a page fault in user space.
//
// When a page fault actually occurs, 
// the kernel switches our ESP to point to the user exception stack
// if we're not already on the user exception stack,
// and then it pushes the following minimal trap frame
// onto our user exception stack:
//
//	[ 5 spare words ]
//	trap-time eip
//	trap-time eflags
//	trap-time esp
//	trap-time errcode
//	trap-time va		<-- %esp
//
// We then have to save additional callee-saved registers
// and call up to the appropriate page fault handler in C code,
// pointed to by the global variable '_pgfault_handler' declared above.

.text
.globl _asm_pgfault_handler
_asm_pgfault_handler:
	// save the caller-save registers
	//	(your code here)

	// call the C page fault handler
	movl _pgfault_handler, %eax
	call *%eax

	// push trap-time eip, eflags onto trap-time stack
	//	(your code here)

	// restore the caller-save registers
	//	(your code here)

	// switch to the trap-time stack 
	//	(your code here)

	// restore eflags and eip from the stack
	//	(your code here)