From e8c6577617bffa4402c07c7aa20e3c24f03c1c20 Mon Sep 17 00:00:00 2001
From: Benji Dial <benji6283@gmail.com>
Date: Sun, 6 Sep 2020 00:48:07 -0400
Subject: program loading, others

big kernel additions: paging, elf loading, separate kernel and user page allocation
it now properly loads and runs sd0:bin/init.elf
still need to determine which disk was booted from, and start the init on that disk
---
 src/kernel/paging.c | 130 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 130 insertions(+)
 create mode 100644 src/kernel/paging.c

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

diff --git a/src/kernel/paging.c b/src/kernel/paging.c
new file mode 100644
index 0000000..b92e037
--- /dev/null
+++ b/src/kernel/paging.c
@@ -0,0 +1,130 @@
+#include <stdbool.h>
+#include <stdint.h>
+#include "pmap.h"
+#include "paging.h"
+#include "boot.h"
+#include "panic.h"
+#include "task.h"
+
+enum {
+  PE_ADDR_MASK = 0xfffff000,
+
+  PT_GLOBAL   = 0x100,
+  PD_LARGE    = 0x080,
+  PT_DIRTY    = 0x040,
+  PE_ACCESSED = 0x020,
+  PE_NO_CACHE = 0x010,
+  PE_WRTHCH   = 0x008,
+  PE_USER     = 0x004,
+  PE_WRITABLE = 0x002,
+  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);
+}
+
+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;
+  ((uint32_t *)(*ptp & PE_ADDR_MASK))[(virtual_addr >> 12) % 1024] = physical_addr | PE_USER | PE_PRESENT | (PE_WRITABLE * writable);
+}
+
+bool pd_is_mapped(void *pd, uint32_t vma) {
+  uint32_t pde = ((uint32_t *)pd)[vma >> 22];
+  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)
+    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);
+      free_pages(pt_32, 1);
+    }
+  free_pages(pd, 1);
+}
+
+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);
+  return pd;
+}
+
+void *pd_user_allocate(void *pd, uint32_t vma, uint32_t pages, bool writable) {
+  void *pma = allocate_user_pages(pages);
+  if (!pma)
+    panic("Could not allocate user pages.");
+  for (uint32_t i = 0; i < pages; ++i)
+    pd_map(pd, (uint32_t)pma + (i << 12), vma + (i << 12), writable);
+  return pma;
+}
+
+void *pd_user_allocate_anywhere_writable(void *pd, uint32_t pages) {
+  uint32_t run = 0;
+  for (void *vma = (void *)KERNEL_END; vma; vma += 4096) {
+    if (pd_is_mapped(pd, vma))
+      run = 0;
+    else if (++run == pages) {
+      vma -= (pages - 1) * 4096;
+      for (uint32_t i = 0; i < pages; ++i)
+        pd_map(pd, (uint32_t)allocate_user_pages(1), (uint32_t)vma + 4096 * i, true);
+      return vma;
+    }
+  }
+}
+
+#define KPAGE_DIR     ((uint32_t *)0x00005000)
+#define KPAGE_TABLE_0 ((uint32_t *)0x00400000)
+
+void init_paging() {
+  //TODO: use PAE if possible
+
+  for (uint32_t i = 0; i < 1048576; ++i)
+    KPAGE_TABLE_0[i] = (i * 4096) | PE_WRITABLE | PE_PRESENT;
+  for (uint16_t i = 0; i < 1024; ++i)
+    KPAGE_DIR[i] = (uint32_t)(KPAGE_TABLE_0 + i * 1024) | PE_WRITABLE | PE_PRESENT;
+
+  asm volatile (
+    "mov $0x00005000, %%eax\n"
+    "mov %%eax, %%cr3\n"
+    "mov %%cr0, %%eax\n"
+    "or $0x80000000, %%eax\n"
+    "mov %%eax, %%cr0"
+  : : : "eax");
+}
+
+void switch_to_kernel_cr3() {
+  asm volatile (
+    "mov $0x00005000, %%eax\n"
+    "mov %%eax, %%cr3"
+  : : : "eax");
+}
+
+void switch_to_task_cr3() {
+  asm volatile (
+    "mov %0, %%cr3"
+  : : "a" (active_task->page_directory));
+}
\ No newline at end of file
-- 
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