Add HULK header; map virtual memory for HULK bss section

src/hulk/header.d

@@ -0,0 +1,23 @@
+/**
+ * HULK image header.
+ */
+module hulk.header;
+
+/**
+ * Header describing the HULK image.
+ */
+struct Header
+{
+    /**
+     * Total size of memory to be mapped.
+     *
+     * The OS loader must ensure that virtual memory is mapped for this entire
+     * size.
+     * This value is really an integer, but is stored as a pointer because it
+     * is provided by the linker and LDC does not like us to cast it.
+     */
+    void * total_size;
+
+    /** Entry point. */
+    void * entry;
+}

src/hulk/hulk.d

@@ -3,16 +3,24 @@
  */
 module hulk.hulk;
 
+import hulk.header;
 import hulk.bootinfo;
 import hos.memory;
 import ldc.attributes;
 
+extern extern(C) __gshared ubyte _hulk_total_size;
+
+@(ldc.attributes.section(".hulk_header"))
+private __gshared Header hulk_header = {
+    &_hulk_total_size,
+    &hulk_start,
+};
+
 /**
  * HULK entry point.
  *
  * @param bootinfo Pointer to HULK boot information structure.
  */
-@(ldc.attributes.section(".hulk_start"))
 extern(C) void hulk_start(ulong rdi, ulong rsi, ulong rdx, BootInfo * bootinfo)
 {
     for (size_t y = 100u; y < 120u; y++)

src/hulk/hulk.ld

@@ -1,21 +1,19 @@
-ENTRY(hulk_start)
-
 SECTIONS
 {
     . = 0x0000400000000000;
     _hulk_mem_start = .;
 
-    .text BLOCK(4K) : ALIGN(4K)
-    {
-        *(.hulk_start)
-        *(.text)
-    }
-
     .rodata BLOCK(4K) : ALIGN(4K)
     {
+        *(.hulk_header)
         *(.rodata)
     }
 
+    .text BLOCK(4K) : ALIGN(4K)
+    {
+        *(.text)
+    }
+
     .data BLOCK(4K) : ALIGN(4K)
     {
         *(.data)
@@ -30,4 +28,5 @@ SECTIONS
     . = ALIGN(4K);
 
     _hulk_mem_end = .;
+    _hulk_total_size = _hulk_mem_end - _hulk_mem_start;
 }