compiler,runtime: implement a portable conservative GC

src/runtime/gc_stack_raw.go

@@ -0,0 +1,13 @@
+// +build gc.conservative
+// +build cortexm
+
+package runtime
+
+// markStack marks all root pointers found on the stack.
+//
+// This implementation is conservative and relies on the stack top (provided by
+// the linker) and getting the current stack pointer from a register. Also, it
+// assumes a descending stack. Thus, it is not very portable.
+func markStack() {
+	markRoots(getCurrentStackPointer(), stackTop)
+}