runtime: implement a simple mark/sweep garbage collector

src/runtime/arch_tinygoarm.go

@@ -4,6 +4,8 @@ package runtime
 
 import (
 	"unsafe"
+
+	"device/arm"
 )
 
 const GOARCH = "arm"
@@ -17,12 +19,28 @@ var heapStartSymbol unsafe.Pointer
 //go:extern _heap_end
 var heapEndSymbol unsafe.Pointer
 
+//go:extern _globals_start
+var globalsStartSymbol unsafe.Pointer
+
+//go:extern _globals_end
+var globalsEndSymbol unsafe.Pointer
+
+//go:extern _stack_top
+var stackTopSymbol unsafe.Pointer
+
 var (
-	heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
-	heapEnd   = uintptr(unsafe.Pointer(&heapEndSymbol))
+	heapStart    = uintptr(unsafe.Pointer(&heapStartSymbol))
+	heapEnd      = uintptr(unsafe.Pointer(&heapEndSymbol))
+	globalsStart = uintptr(unsafe.Pointer(&globalsStartSymbol))
+	globalsEnd   = uintptr(unsafe.Pointer(&globalsEndSymbol))
+	stackTop     = uintptr(unsafe.Pointer(&stackTopSymbol))
 )
 
 // Align on word boundary.
 func align(ptr uintptr) uintptr {
 	return (ptr + 3) &^ 3
 }
+
+func getCurrentStackPointer() uintptr {
+	return arm.ReadRegister("sp")
+}