Implemented Higher Half Kernel!

- Minor makefile chnages
- stage3.c "prekernel", sets up memory stuff and jumps to kernel
- kernel is now at 0xC0000000 - 3GB+ "higher half"
- Added some global variables in memory/addresses.h

src/stage3.c

@@ -0,0 +1,62 @@
+#include <memory/physical.h>
+#include <memory/virtual.h>
+#include <memory/addresses.h>
+#include <disk/disk.h>
+#include <disk/filesys.h>
+#include <screen/text.h>
+
+__attribute__ ((section("entry")))
+void main() {
+    diskRead(15, 1, filetable); // Load filetable into memory; TODO: Make a filetableUpdate() function that just keeps the stored and memory verisons in sync
+    
+    // Physical memory manager setup
+    uint32_t smapEntryCount = *(uint32_t*)SMAP_ENTRY_COUNT;
+    smapEntry_t* smapEntries = (smapEntry_t*)SMAP_ENTRIES; // After a unit32_t
+    uint32_t totalMemory = smapEntries[smapEntryCount - 1].baseAddress + smapEntries[smapEntryCount - 1].length - 1;
+
+    setupPhysicalMemoryManager(MEMMAP_AREA, totalMemory);
+
+    for (uint32_t i = 0; i < smapEntryCount; i++) {
+        if (smapEntries[i].type == 1) {
+            initMemoryRegion(smapEntries[i].baseAddress, smapEntries[i].length);
+        }
+    }
+
+    deinitMemoryRegion(0x1000, 0x9000); // Reserve kernel memory (under 0xa000)
+    deinitMemoryRegion(MEMMAP_AREA, maxBlocks / BLOCKS_PER_BYTE);
+
+    // Load kernel into memory
+    if (readFile("kernel.bin", (void*)KERNEL_LOC) != 0) { // Check if kernel.bin was loaded
+        // TODO: Add error messages
+        while (1);
+    }
+
+    // Virtual memory manager setup
+    if (setupVirtualMemoryManager() != 0) {
+        while (1);
+    }
+
+    // Identity map VBE framebuffer
+    uint32_t fbSize = (gfxMode->yRes * gfxMode->linearBytesPerScanline) / PAGE_SIZE;
+    if (fbSize % PAGE_SIZE > 0) { fbSize++; }
+    fbSize *= 2; // Double for hardware
+    for (uint32_t i = 0, fbStart = gfxMode->physicalBasePtr; i < fbSize; i++, fbStart += PAGE_SIZE) {
+        mapPage((void*)fbStart, (void*)fbStart);
+    }
+    deinitMemoryRegion(gfxMode->physicalBasePtr, fbSize * BLOCK_SIZE);
+
+    *(uint32_t*)PHYS_MEM_MAX_BLOCKS = maxBlocks;
+    *(uint32_t*)PHYS_MEM_USED_BLOCKS = usedBlocks;
+
+    for (uint32_t virt = KERNEL_LOC; virt < 0x400000; virt += PAGE_SIZE) {
+        unmapPage((void*)virt);
+    }
+
+    __asm__ volatile ("movl %cr3, %ecx; movl %ecx, %cr3");
+
+    *(uint32_t*)CURRENT_PAGE_DIR_ADDR = (uint32_t)currentPd;
+
+    // Call/jump to kernel
+    ((void(*)(void))0xC0000000)();
+}
+