From 5481848e27fdd4fc859def9841a0283665531a46 Mon Sep 17 00:00:00 2001
From: Benji Dial <benji6283@gmail.com>
Date: Sun, 13 Sep 2020 17:12:29 -0400
Subject: fixed some paging bugs, added fault handlers and new programs

---
 src/kernel/paging.c | 53 +++++++++++++++++++++++------------------------------
 1 file changed, 23 insertions(+), 30 deletions(-)

(limited to 'src/kernel/paging.c')

diff --git a/src/kernel/paging.c b/src/kernel/paging.c
index a0f7c3d..fbc33de 100644
--- a/src/kernel/paging.c
+++ b/src/kernel/paging.c
@@ -20,28 +20,16 @@ enum {
   PE_PRESENT  = 0x001
 };
 
-//TODO:
-//  try_elf_run needs to call these new functions.
-
-void *new_pd() {
-  uint32_t *pd = allocate_kernel_pages(1);
-  for (uint16_t i = 0; i < 1024; ++i)
-    pd[i] = 0;
-  return pd;
-}
-
-void free_pd(void *pd) {
-  uint32_t *pd_32 = pd;
-  for (uint16_t i = 0; i < 1024; ++i)
-    if (pd_32[i] & PE_PRESENT)
-      free_pages((void *)(pd_32[i] & PE_ADDR_MASK), 1);
-  free_pages(pd, 1);
-}
+#define KERNEL_END (0x08000000)
 
-void pd_map(void *pd, uint32_t physical_addr, uint32_t virtual_addr, bool writable) {
+static void pd_map(void *pd, uint32_t physical_addr, uint32_t virtual_addr, bool writable) {
   uint32_t *ptp = (uint32_t *)pd + (virtual_addr >> 22);
-  if (!(*ptp & PE_PRESENT))
-    *ptp = (uint32_t)allocate_kernel_pages(1) | PE_USER | PE_WRITABLE | PE_PRESENT;
+  if (!(*ptp & PE_PRESENT)) {
+    uint32_t *new_pt = allocate_kernel_pages(1);
+    for (uint16_t i = 0; i < 1024; ++i)
+      new_pt[i] = 0;
+    *ptp = (uint32_t)new_pt | PE_USER | PE_WRITABLE | PE_PRESENT;
+  }
   ((uint32_t *)(*ptp & PE_ADDR_MASK))[(virtual_addr >> 12) % 1024] = physical_addr | PE_USER | PE_PRESENT | (PE_WRITABLE * writable);
 }
 
@@ -51,26 +39,28 @@ static bool pd_is_mapped(void *pd, uint32_t vma) {
   return (pde & PE_PRESENT) && (((uint32_t *)(pde & PE_ADDR_MASK))[(vma >> 12) % 1024] & PE_PRESENT);
 }
 
-#define KERNEL_END (0x08000000)
-
 void free_task_pd(void *pd) {
   uint32_t *pd_32 = pd;
-  for (uint16_t i = 0; i < 1024; ++i)
+  for (uint16_t i = KERNEL_END / 4096 / 1024; i < 1024; ++i)
     if (pd_32[i] & PE_PRESENT) {
       uint32_t *pt_32 = (uint32_t *)(pd_32[i] & PE_ADDR_MASK);
-      if (i >= KERNEL_END >> 22)
-        for (uint16_t j = 0; j < 1024; ++j)
-          if (pt_32[j] & PE_PRESENT)
-            free_pages((void *)(pt_32[j] & PE_ADDR_MASK), 1);
+      for (uint16_t j = 0; j < 1024; ++j)
+        if (pt_32[j] & PE_PRESENT)
+          free_pages((void *)(pt_32[j] & PE_ADDR_MASK), 1);
       free_pages(pt_32, 1);
     }
   free_pages(pd, 1);
 }
 
+__attribute__ ((aligned (4096)))
+static uint32_t kmap[KERNEL_END / 4096];
+
 void *new_task_pd() {
-  uint32_t *pd = new_pd();
-  for (uint32_t addr = 0; addr < KERNEL_END; addr += 4096)
-    pd_map(pd, addr, addr, false);
+  uint32_t *pd = allocate_kernel_pages(1);
+  for (uint8_t i = 0; i < KERNEL_END / 4096 / 1024; ++i)
+    pd[i] = (uint32_t)(kmap + i * 1024) | PE_USER | PE_PRESENT;
+  for (uint16_t i = KERNEL_END / 4096 / 1024; i < 1024; ++i)
+    pd[i] = 0;
   return pd;
 }
 
@@ -129,6 +119,9 @@ void init_paging() {
   for (uint16_t i = 0; i < 1024; ++i)
     KPAGE_DIR[i] = (uint32_t)(KPAGE_TABLE_0 + i * 1024) | PE_WRITABLE | PE_PRESENT;
 
+  for (uint16_t i = 0; i < KERNEL_END / 4096; ++i)
+    kmap[i] = (i * 4096) | PE_USER | PE_PRESENT;
+
   asm volatile (
     "mov $0x00005000, %%eax\n"
     "mov %%eax, %%cr3\n"
-- 
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