Added a kernel

kernel.c

@@ -0,0 +1,48 @@
+#include "util.h"
+#include "stdint.h"
+
+struct mem_region {
+    uint32_t valid;
+    uint32_t base;
+    uint32_t length;
+};
+
+struct mem_regions {
+    uint32_t count;
+    struct mem_region regions[1];
+};
+
+static const char* fact = "Today is tomorrow's yesterday.";
+
+uint32_t
+fib(uint32_t n)
+{
+    if (n == 0) return 0;
+    if (n == 1) return 1;
+    return n + fib(n-1);
+}
+
+void _start(uint32_t meaning_of_life)
+{
+    __asm__ volatile ("andq $0xFFFFFFFFFFFFFFFF, %rsp");
+
+    cls();
+    kprintf("The kernel has discovered the following facts:\n");
+    kprintf("  2+2 = %d\n", 2+2);
+    kprintf("  fib(10) = %d\n", fib(10));
+    kprintf("  meaning_of_life = %d\n", meaning_of_life);
+    kprintf("  %s\n", fact);
+    kprintf("\n");
+    kprintf("Please stand by for more interesting facts as they are discovered...\n");
+
+    struct mem_regions *regions = (void*)meaning_of_life;
+    for (uint32_t i = 0; i < regions->count; ++i) {
+        struct mem_region *region = &(regions->regions[i]);
+        kprintf("Region %d: base: 0x%x length 0x%x\n", i, region->base, region->length);
+    }
+
+    for (;;) {
+        __asm__ volatile ("cli");
+        __asm__ volatile ("hlt");
+    }
+}

loader/loader.c

@@ -228,9 +228,9 @@ load_kernel(const multiboot_info_t *info)
 
     unsigned char *mod_addr = (unsigned char*)m;
 
-    if (*(mod_addr) != 0x7f &&
-        *(mod_addr+1) != 'E' &&
-        *(mod_addr+2) != 'L' &&
+    if (*(mod_addr)   != 0x7f &&
+        *(mod_addr+1) != 'E'  &&
+        *(mod_addr+2) != 'L'  &&
         *(mod_addr+3) != 'F')
     {
         kprintf("Kernel does not appear to be an ELF binary.\n");

util.c

@@ -32,14 +32,15 @@ unsigned char* const video = (unsigned char*)0xB8000;
 uint32_t xpos = 0;
 uint32_t ypos = 0;
 
-
 void
 cls(void)
 {
     int i;
 
-    for (i = 0; i < COLUMNS * LINES * 2; i++)
-        *(video + i) = 0;
+    for (i = 0; i < COLUMNS * LINES * 2; i++) {
+        if (*(video + i) != 0)
+            *(video + i) = 0;
+    }
 
     xpos = 0;
     ypos = 0;