Working PIT irqs, fix GDT bugs

kernel/platform/i386_pc/boot/bootmain.c

@@ -36,6 +36,8 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <sys/multiboot.h>
 #include <sys/serialdbg.h>
 #include <sys/mm.h>
+#include <sys/pic.h>
+#include <sys/pit.h>
 #include <mm/pmm.h>
 #include <mm/bba.h>
 #include <mm/liballoc.h>
@@ -56,13 +58,22 @@ static void dump_multiboot_header(void) {
 static void mregmap_init1(void) {
   struct multiboot *mb = multiboot_get();
 
+  mregmap_init();
+
   struct multiboot_mmap_entry *mmap;
+  usize_t i = 0;
   for (mmap = (struct multiboot_mmap_entry *)(mb->mmap_addr + VIRT_BASE);
       (uptr_t)mmap < (mb->mmap_addr + VIRT_BASE + mb->mmap_length);
       mmap = (struct multiboot_mmap_entry *)((uptr_t)mmap + mmap->size + sizeof(mmap->size))) {
     dbgf("mmap entry: size=%08x, addr=%08x, len=%08x, type=%u\n",
         mmap->size, mmap->addr1, mmap->len1, mmap->type);
 
+    /* always skip the first memory map region, because we can't use it */
+    if (i == 0) {
+      i++;
+      continue;
+    }
+
     static int type_map[] = {
       [1] = MREG_AVAIL_RAM,
       [2] = MREG_I386_PC_RESERVED,
@@ -78,6 +89,7 @@ static void mregmap_init1(void) {
     };
 
     mregmap_add_region(&mreg);
+    i++;
   }
 }
 
@@ -89,7 +101,7 @@ static void pmm_init1(void) {
   usize_t usable_ram_bytes = avail_ram->size;
   dbgf("usable ram = %08x\n", usable_ram_bytes);
 
-  uptr_t ram_start = ALIGN_UP((uptr_t)&__kernel_end - VIRT_BASE, 0x1000);
+  uptr_t ram_start = ALIGN_UP((uptr_t)&__kernel_end + 0x1000 - VIRT_BASE, 0x1000);
   uptr_t ram_end = ALIGN_DOWN(0x100000 + usable_ram_bytes, 0x1000);
 
   usize_t block_size = CFG_I386_PC_PMM_BLOCK_SIZE;
@@ -122,6 +134,9 @@ void bootmain(void *mbootptr) {
   pmm_init1();
   bba_init();
   mm_init();
+  pit_init();
+  pic_unmask();
+  __asm__ volatile("sti");
 
   char *string = malloc(12);
   memset(string, 0, 12);