From 66289aa8ecfa07b20bad424eb9860b196641ef52 Mon Sep 17 00:00:00 2001
From: Brett Weiland <brett_weiland@bpcspace.com>
Date: Fri, 19 Mar 2021 10:54:25 -0500
Subject: first commit

---
 src/kernel/libs/page.c | 107 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 src/kernel/libs/page.c

(limited to 'src/kernel/libs/page.c')

diff --git a/src/kernel/libs/page.c b/src/kernel/libs/page.c
new file mode 100644
index 0000000..88d0c2f
--- /dev/null
+++ b/src/kernel/libs/page.c
@@ -0,0 +1,107 @@
+#include <printf.h>
+#include <paging.h>
+#include <stdint.h>
+
+// for now, this will always remain the same. 
+// If this ever isn't the case, we'll add paramaters to the paging functions.
+// We will also never need to mess with many bits, 
+// as we are not implimenting security for a bare metal fractal generator.
+// Also, is this really the cleanest way to do things?
+
+//after we get paging working, we can probably remove these structs and replace them with plain old uint_16ts.
+
+void debug_print_memory() {
+  struct memory_table *memtable = (struct memory_table *)&_meminfo_loc; 
+  printf(" __________________________________________________________________________\n");
+  printf("| type\tstart\t\t\tend\t\t\tsize\t\t   |\n");
+  printf("|--------------------------------------------------------------------------|\n");
+  for(unsigned int i = 0; memtable[i].length > 0; i++) {
+    printf("| %u %u\t0x%p\t0x%p\t0x%p |\n", memtable[i].type, memtable[i].ACPI, memtable[i].base, (memtable[i].base + memtable[i].length), memtable[i].length);
+  }
+  printf("----------------------------------------------------------------------------\n");
+}
+
+
+/**
+ * You can critisise the quality of this function all you want, it's messy due to planning mistakes
+ * and I'm planning on sanatising it. 
+ * BUT, don't critisise it _just_ for using goto, that's bullshit. See the following links.
+ *    
+ *    https://www.kernel.org/doc/html/v4.17/process/coding-style.html "goto" section
+ *    https://koblents.com/Ches/Links/Month-Mar-2013/20-Using-Goto-in-Linux-Kernel-Code/
+**/
+
+bool map_page(uintptr_t virtual_addr, uintptr_t physical_addr, uint8_t size) {
+  printf("map page called\n");
+  if((virtual_addr % (1 << size)) || (physical_addr % (1 << size))) {
+    return 0; 
+  }
+  page_table *table = (page_table *)PAGEMAP_LOCATION;
+  int pte_i = (virtual_addr >> 12) & 0x1ff;
+  int pde_i = (virtual_addr >> 21) & 0x1ff;
+  int pdpe_i = (virtual_addr >> 30) & 0x1ff;
+  int pml4e_i = (virtual_addr >> 39) & 0x1ff;
+  //TODO remove this debugging info
+  printf("Virtual offsets:\npte:\t\t%i\npde:\t\t%i\npdpe:\t\t%i\npml4e\t\t%i\n", pte_i, pde_i, pdpe_i, pml4e_i);
+
+  if(table->pml4e[pml4e_i].present) {
+    if(table->pml4e[pml4e_i].base_ptr != (uintptr_t)&table->pdpe[pdpe_i] >> 12) goto error;
+    if(table->pdpe[pdpe_i].present) {
+      if(size == PAGE_SIZE_1G) {
+        if(table->pdpe[pdpe_i].base_ptr == (uintptr_t)physical_addr >> 30 & 0x1ff)
+          return true;
+        goto error;
+      }
+      if(table->pdpe[pdpe_i].base_ptr != (uintptr_t)&table->pde[pde_i] >> 12) goto error;
+
+      if(table->pde[pde_i].present) { 
+        if(size == PAGE_SIZE_2M) {
+          if(table->pde[pde_i].base_ptr == (uintptr_t)physical_addr >> 21 & 0x1ff)
+            return true;
+          goto error;
+        }
+        if(table->pde[pde_i].base_ptr != (uintptr_t)&table->pte[pte_i] >> 12) goto error;
+        if(table->pte[pte_i].present) {
+          if(table->pte[pte_i].base_ptr != ((physical_addr >> 12) & 0x1ff)) goto error;
+          return true;
+        }
+        else goto mod_page_pte;
+      }
+      else goto mod_page_pde;
+    }
+    else goto mod_page_pdpe;
+  }
+  else {
+    table->pml4e[pml4e_i].base_ptr = (uintptr_t)&table->pdpe[pdpe_i] >> 12;
+    table->pdpe[pml4e_i].read_write = 1;
+    table->pml4e[pml4e_i].present = 1;
+mod_page_pdpe:
+    table->pdpe[pdpe_i].read_write = 1;
+    if(size == PAGE_SIZE_1G) {
+      table->pdpe[pdpe_i].size = 1;
+      table->pdpe[pdpe_i].base_ptr = physical_addr >> 30;
+      table->pdpe[pdpe_i].present = 1;
+      return true;
+    }
+    table->pdpe[pdpe_i].base_ptr = (uintptr_t)&table->pde[pde_i] >> 12;
+    table->pdpe[pdpe_i].present = 1;
+mod_page_pde:
+    table->pde[pde_i].read_write = 1;
+    if(size == PAGE_SIZE_2M) {
+      table->pde[pde_i].size = 1;
+      table->pde[pde_i].base_ptr = physical_addr >> 21;
+      table->pde[pde_i].present = 1;
+      return true;
+    }
+    table->pde[pde_i].base_ptr = (uintptr_t)&table->pte[pte_i] >> 12;
+    table->pde[pde_i].present = 1;
+mod_page_pte:
+    table->pte[pte_i].base_ptr = (physical_addr >> 12);
+    table->pte[pte_i].read_write = 1;
+    table->pte[pte_i].present = 1;
+    return true;
+  }
+error:
+  printf("Page allocation error!\n");
+  return false;
+}
-- 
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