HELLO: Create page tables to identity map available RAM prior to jumping to kernel

src/common/hos/page_table.d

@@ -0,0 +1,33 @@
+struct PageTableEntry
+{
+    ulong entry;
+
+    this(ulong address, ulong no_execute, ulong global,
+            ulong huge, ulong disable_cache, ulong write_through, ulong user,
+            ulong writable, ulong present)
+    {
+        entry = (present |
+                (writable << 1) |
+                (user << 2) |
+                (write_through << 3) |
+                (disable_cache << 4) |
+                (huge << 7) |
+                (global << 8) |
+                (no_execute << 63)) | address;
+    }
+
+    bool present()
+    {
+        return (entry & 0x1u) != 0u;
+    }
+
+    PageTableEntry * next()
+    {
+        return cast(PageTableEntry *)(entry & 0x7FFF_FFFF_FFFF_F000u);
+    }
+
+    static ulong page_table_index(ulong address, size_t level)
+    {
+        return ((address >> (39u - 9u * level)) & 0x1FFu);
+    }
+}

src/hello/hello.d

@@ -2,6 +2,8 @@ import uefi;
 import output;
 import scratch;
 import hulk.bootinfo;
+import hos.page_table;
+import hos.cpu;
 
 __gshared EFI_SYSTEM_TABLE * st;
 __gshared BootInfo bootinfo;
@@ -111,7 +113,7 @@ private bool get_memory_map()
             (descriptor.Type == EfiBootServicesCode) ||
             (descriptor.Type == EfiBootServicesData))
         {
-            bootinfo.memory_map[di].base = cast(void *)descriptor.PhysicalStart;
+            bootinfo.memory_map[di].base = descriptor.PhysicalStart;
             bootinfo.memory_map[di].size = descriptor.NumberOfPages * 4096u;
             di++;
         }
@@ -120,6 +122,57 @@ private bool get_memory_map()
     return true;
 }
 
+private PageTableEntry * new_page_table()
+{
+    return cast(PageTableEntry *)scratch_alloc(1u);
+}
+
+private void map(ulong source_page, ulong dest_page, PageTableEntry * pt_base)
+{
+    PageTableEntry * pt = pt_base;
+    PageTableEntry * next_pt;
+    for (size_t level = 0; level < 4u; level++)
+    {
+        size_t pt_index = PageTableEntry.page_table_index(source_page, level);
+        if (pt[pt_index].present())
+        {
+            pt = pt[pt_index].next();
+        }
+        else
+        {
+            ulong addr;
+            if (level < 3u)
+            {
+                next_pt = new_page_table();
+                addr = cast(ulong)next_pt;
+            }
+            else
+            {
+                addr = dest_page;
+            }
+            pt[pt_index] = PageTableEntry(addr,
+                    0u, 0u, 0u, 0u, 0u, 0u, 1u, 1u);
+            pt = next_pt;
+        }
+    }
+}
+
+private void build_page_tables()
+{
+    PageTableEntry * pt_base = new_page_table();
+    for (size_t i = 0u; i < bootinfo.memory_map_count; i++)
+    {
+        size_t n_pages = bootinfo.memory_map[i].size / 4096u;
+        for (size_t p = 0u; p < n_pages; p++)
+        {
+            ulong page_addr = bootinfo.memory_map[i].base + 4096u * p;
+            /* Identity map all pages. */
+            map(page_addr, page_addr, pt_base);
+        }
+    }
+    write_cr3(cast(ulong)pt_base);
+}
+
 extern (C) EFI_STATUS efi_main(EFI_HANDLE image_handle, EFI_SYSTEM_TABLE * st)
 {
     .st = st;
@@ -153,5 +206,7 @@ extern (C) EFI_STATUS efi_main(EFI_HANDLE image_handle, EFI_SYSTEM_TABLE * st)
         return EFI_SUCCESS;
     }
 
+    build_page_tables();
+
     return EFI_SUCCESS;
 }

src/hulk/hulk/bootinfo.d

@@ -2,7 +2,7 @@ struct BootInfo
 {
     struct MemoryRegion
     {
-        void * base;
+        ulong base;
         size_t size;
     }
     struct Framebuffer