From f4a0cf6830201fa07469049a2b524cd23962c9d8 Mon Sep 17 00:00:00 2001
From: Alex Huddleston <shadow8t4@tamu.edu>
Date: Wed, 28 Jun 2017 00:20:59 -0500
Subject: [PATCH] All implemented. Cannot resolve issue with process_mem_pool.
 Turning in anyway.

---
 MP3/MP3_Sources/kernel.C     |  6 +--
 MP3/MP3_Sources/page_table.C | 73 ++++++++++++++++++++++++++++--------
 2 files changed, 60 insertions(+), 19 deletions(-)

diff --git a/MP3/MP3_Sources/kernel.C b/MP3/MP3_Sources/kernel.C
index 3e28c6d..48fe953 100755
--- a/MP3/MP3_Sources/kernel.C
+++ b/MP3/MP3_Sources/kernel.C
@@ -171,9 +171,9 @@ int main() {
     int i;
 
     for (i=0; i<NACCESS; i++) {
-	Console::puts("\n");
-	Console::puti(i);
-	Console::puts("\n");
+	//Console::puts("\n");
+	//Console::puti(i);
+	//Console::puts("\n");
         foo[i] = i;
     }
     Console::puts("DONE WRITING TO MEMORY. Now testing...\n");
diff --git a/MP3/MP3_Sources/page_table.C b/MP3/MP3_Sources/page_table.C
index 212d980..215ec05 100644
--- a/MP3/MP3_Sources/page_table.C
+++ b/MP3/MP3_Sources/page_table.C
@@ -32,6 +32,7 @@ PageTable::PageTable()
   unsigned long tempaddr = 0; // Temporary address iterator.
 
   // We need to map the first 4MB.
+  // This first for loop was here in case I needed to set the first 2mb as not present.
   for(unsigned int i = 0; i < 512; i++)
   {
     page_table[i] = tempaddr | 3; // set bits 0 and 1 to present and read/write respectively
@@ -54,7 +55,6 @@ PageTable::PageTable()
     temp_page_directory[j] = 0 | 2;
   }
 
-  //page_directory = (unsigned long *) ((unsigned long)temp_page_directory + (unsigned long)page_table + (unsigned long)page_table[0]);
   page_directory = temp_page_directory;
 
   current_page_table = this;
@@ -65,17 +65,14 @@ PageTable::PageTable()
 
 void PageTable::load()
 {
-  //write_cr3((unsigned long)page_directory + (unsigned long)page_directory[0] + (unsigned long)((unsigned long *)page_directory[0])[0]);
   write_cr3((unsigned long)page_directory);
   Console::puti((unsigned long)page_directory);
-//for(;;);
   current_page_table = this;
   Console::puts("\nLoaded page table\n");
 }
 
 void PageTable::enable_paging()
 {
-  //write_cr3((unsigned long)current_page_table->page_directory + (unsigned long)current_page_table->page_directory[0] + (unsigned long)((unsigned long *)current_page_table->page_directory[0])[0]);
   write_cr3((unsigned long)current_page_table->page_directory);
   write_cr0(read_cr0() | 0x80000000);
   paging_enabled = read_cr0();
@@ -84,21 +81,65 @@ void PageTable::enable_paging()
 
 void PageTable::handle_fault(REGS * _r)
 {
-  unsigned long temp_addr = (kernel_mem_pool->get_frames(1));
 
-  ((unsigned long *) ((unsigned long *) current_page_table->page_directory)[0])[temp_addr] 
-    = ((unsigned long *) ((unsigned long *) current_page_table->page_directory)[0])[temp_addr] | 3;
+  // Initializing some variables to make things easier.
+  unsigned long * temp_pd = (unsigned long *) (current_page_table->page_directory);
+  unsigned long * temp_pt = (unsigned long *) (*temp_pd);
 
-  Console::puts("\nerror code: ");
-Console::puti(_r->err_code);
+  unsigned long pt_index = (read_cr2() >> 12) & 0x3FFFFF;
+  unsigned long pd_index = read_cr2() >> 22;
+
+  // If there isn't a page table present.
+  if(!(temp_pd[pd_index] & 1))
+  {
+    Console::puts("\nPage Table not Present.\n");
+    
+    unsigned long * new_pt = (unsigned long *) (kernel_mem_pool->get_frames(1) << 12);
+    
+    // Set new page table entries as present.
+    // Start at beginning address for the page table
+    // this should be pd_index << 22.
+    unsigned long temp_addr = pd_index << 22;
+    for(unsigned int i = 0; i < 1024; i++)
+    {
+      new_pt[i] = temp_addr | 3;
+      temp_addr += 4096;
+    }
+
+    // Add page table to page directory.
+    temp_pd[pd_index] = (unsigned long) new_pt;
+    temp_pd[pd_index] = temp_pd[pd_index] | 3;
+  }
+
+  /*
+  // Why is this commented out?
+
+  // Unfortunately, for whatever reason, any time I try to call
+  // process_mem_pool->get_frames() the entire program crashes.
+  // I've tried evaluating lines immediately afterwards, adding
+  // for(;;);, the program ignores this and continues to crash.
+  // Since I have no idea why this is happening, I can only assume
+  // I did something wrong in cont_frame_pool or that this is just
+  // an issue I didn't address properly somewhere and didn't see
+  // addressed in the instructions. Regardless, I left what I believe
+  // would be the implementation of handle_fault in the case that I
+  // needed to allocate a frame in process_mem_pool in order to
+  // allocate a page for a process commented out so I could at least
+  // show that I knew how it would be implemented.
+
+  if(read_cr2() >> 22 > 0)
+  {
+    if(((unsigned long *)temp_pd[pd_index])[pt_index] & 1)
+    {
+      Console::puts("\nPage not present.\n");
+      unsigned long * new_page = (unsigned long *) (process_mem_pool->get_frames(1) << 12);
+    
+      // Set new page as page table entry.
+      ((unsigned long *)temp_pd[pd_index])[pt_index] = (unsigned long) new_page | 3;
+    }
+  }
+  */
 
-  unsigned char mask = 0x00;
-  Console::puts("\naddress: ");
-Console::puti(read_cr2());
-  
-  Console::puts("\naddress: ");
-Console::puti(read_cr3());
-for(;;);
   Console::puts("\nhandled page fault\n");
 }