Add initial register states to meta section; remove entry directive

It makes sense to allow users to set the initial register values. This
allows someone to e.g. enable interrupts once the VM has started, or set
the initial stack pointer value.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

tests/test_interrupts.asm

@@ -0,0 +1,52 @@
+.section code $0x0 {
+    main:
+        ; Test divide by zero interrupts
+
+        ; div
+        mov %status, $1
+        mov %r0, $1
+        div %r0, $0
+        cmpeq (count), $1
+        jz end
+
+        ; idiv
+        mov %status, $2
+        idiv %r0, $0
+        cmpeq (count), $2
+        jz end
+
+        mov %status, $0
+    end:
+        halt
+
+    .align u64
+    divide_by_zero:
+        add (count), $1
+        iret
+
+    .export main
+    .export divide_by_zero
+}
+
+.section ivt $0x1000 {
+    ivt:
+    .interrupt $1, divide_by_zero
+    .export ivt
+}
+
+.section shared $0x2000 {
+    count: .u64 $0
+    .export count
+}
+
+.section stack $0x4000 .. $0x5000 {
+    stack_base:
+    .export stack_base
+}
+
+.meta {
+    ip: main
+    flags: $0b100
+    sp: stack_base
+    ivt: ivt
+}