feat(compiler, wasm): do not hard code memory addresses to uninitialized sections

Rather, allocate unitialized segments as needed.

vm/compiler/wasm_macros.go

@@ -5,39 +5,70 @@ import (
 	"encoding/binary"
 )
 
+// WasmMacros are the macros called from .wat templates
+//
+// NOTE! Due to the single pass nature of the compilation and the way memory is
+// organized, you should initialize all initialized data in the .wat files using
+// DataB, DataW and DataD macros _before_ any calls to Block. Block allocates
+// uninitialized data blocks from the memory.
 type WasmMacros struct {
-	data   *bytes.Buffer
-	Labels map[string]int
+	data       *bytes.Buffer
+	blockStart int
+	blockAlign int
+	Labels     map[string]int
 }
 
 func NewWasmMacros() *WasmMacros {
 	return &WasmMacros{
-		data:   new(bytes.Buffer),
-		Labels: map[string]int{},
+		data:       new(bytes.Buffer),
+		blockAlign: 128,
+		Labels:     map[string]int{},
 	}
 }
 
-func (wm *WasmMacros) SetLabel(label string) string {
+func (wm *WasmMacros) SetDataLabel(label string) string {
 	wm.Labels[label] = wm.data.Len()
 	return ""
 }
 
+func (wm *WasmMacros) SetBlockLabel(label string) string {
+	wm.Labels[label] = wm.blockStart
+	return ""
+}
+
+func (wm *WasmMacros) Align() string {
+	wm.blockStart += wm.blockAlign - 1 - ((wm.blockStart + wm.blockAlign - 1) % wm.blockAlign)
+	return ""
+}
+
+func (wm *WasmMacros) MemoryPages() int {
+	return (wm.blockStart + 65535) / 65536
+}
+
 func (wm *WasmMacros) GetLabel(label string) int {
 	return wm.Labels[label]
 }
 
 func (wm *WasmMacros) DataB(value byte) string {
 	binary.Write(wm.data, binary.LittleEndian, value)
+	wm.blockStart++
 	return ""
 }
 
 func (wm *WasmMacros) DataW(value uint16) string {
 	binary.Write(wm.data, binary.LittleEndian, value)
+	wm.blockStart += 2
 	return ""
 }
 
 func (wm *WasmMacros) DataD(value uint32) string {
 	binary.Write(wm.data, binary.LittleEndian, value)
+	wm.blockStart += 4
+	return ""
+}
+
+func (wm *WasmMacros) Block(value int) string {
+	wm.blockStart += value
 	return ""
 }