From b4b30fbac6510efd65a9215074cc3356826c5b40 Mon Sep 17 00:00:00 2001
From: g1n <g1n@ttm.sh>
Date: Wed, 2 Feb 2022 20:10:52 +0200
Subject: [PATCH] Add paging

---
 src/Makefile         |  2 ++
 src/early_kernel.c   |  2 ++
 src/include/paging.h |  9 ++++++++
 src/paging.c         | 50 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 63 insertions(+)
 create mode 100644 src/include/paging.h
 create mode 100644 src/paging.c

diff --git a/src/Makefile b/src/Makefile
index 0a6b83e..28f589f 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -22,6 +22,7 @@ build/early_kernel.o \
 build/kernel.o \
 build/vga.o \
 build/idt.o \
+build/paging.o \
 $(CRTEND_OBJ) $(CRTN_OBJ)
 
 KERNELFILE = build/orion.bin
@@ -41,6 +42,7 @@ all:
 	
 	i686-elf-gcc -c vga.c -o build/vga.o $(CFLAGS)
 	i686-elf-gcc -c idt.c -o build/idt.o $(CFLAGS) 
+	i686-elf-gcc -c paging.c -o build/paging.o $(CFLAGS) 
 	i686-elf-gcc -c kernel.c -o build/kernel.o $(CFLAGS)
 	i686-elf-gcc -c early_kernel.c -o build/early_kernel.o $(CFLAGS)
 
diff --git a/src/early_kernel.c b/src/early_kernel.c
index 5335954..f0ec313 100644
--- a/src/early_kernel.c
+++ b/src/early_kernel.c
@@ -1,9 +1,11 @@
 #include <idt.h>
 #include <vga.h>
+#include <paging.h>
 #include <stdio.h>
 #include <stdlib.h>
 
 void early_kernel_main() {
   terminal_initialize();
   idt_init();
+  paging_init();
 }
diff --git a/src/include/paging.h b/src/include/paging.h
new file mode 100644
index 0000000..c12ac83
--- /dev/null
+++ b/src/include/paging.h
@@ -0,0 +1,9 @@
+#ifndef PAGING_H
+#define PAGING_H
+
+#include <idt.h>
+
+void paging_init();
+void page_fault(registers_t regs);
+
+#endif
diff --git a/src/paging.c b/src/paging.c
new file mode 100644
index 0000000..014add4
--- /dev/null
+++ b/src/paging.c
@@ -0,0 +1,50 @@
+#include <paging.h>
+#include <stdio.h>
+#include <string.h>
+
+uint32_t page_directory[1024] __attribute__((aligned(4096)));
+uint32_t first_page_table[1024] __attribute__((aligned(4096)));
+
+void page_fault(registers_t regs) {
+  uint32_t faulting_address;
+  __asm__ volatile("mov %%cr2, %0" : "=r" (faulting_address));
+   
+  // The error code gives us details of what happened.
+  int present   = !(regs.err_code & 0x1); // Page not present
+  int rw = regs.err_code & 0x2;           // Write operation?
+  int us = regs.err_code & 0x4;           // Processor was in user-mode?
+  int reserved = regs.err_code & 0x8;     // Overwritten CPU-reserved bits of page entry?
+  //int id = regs.err_code & 0x10;          // Caused by an instruction fetch?
+  
+  kprintf("Page fault: ( ");
+  if (present) {kprintf("present ");}
+  if (rw) {kprintf("read-only ");}
+  if (us) {kprintf("user-mode ");}
+  if (reserved) {kprintf("reserved ");}
+  kprintf(") at 0x%x\n", faulting_address);
+  kprintf("PAGE FAULT\n");
+}
+
+void enable_paging(uint32_t *dir) {
+  __asm__ volatile("mov %0, %%cr3":: "r"(dir));
+  uint32_t cr0;
+  __asm__ volatile("mov %%cr0, %0": "=r"(cr0));
+  cr0 |= 0x80000001; // Enable paging!
+  __asm__ volatile("mov %0, %%cr0":: "r"(cr0));
+}
+
+void paging_init() {
+  int i;
+  for(i = 0; i < 1024; i++) {
+    page_directory[i] = 0x00000002;
+  }
+
+  for(i = 0; i < 1024; i++) {
+    first_page_table[i] = (i * 0x1000) | 3; // attributes: supervisor level, read/write, present.
+  }
+  
+  page_directory[0] = ((unsigned int)first_page_table) | 3;
+  
+  register_interrupt_handler(14, &page_fault);
+  enable_paging(page_directory);
+}