arm: automatically determine stack sizes

This is a big change that will determine the stack size for many
goroutines automatically. Functions that aren't recursive and don't call
function pointers can in many cases have an automatically determined
worst case stack size. This is useful, as the stack size is usually much
lower than the previous hardcoded default of 1024 bytes: somewhere
around 200-500 bytes is common.

A side effect of this change is that the default stack sizes (including
the stack size for other architectures such as AVR) can now be changed
in the config JSON file, making it tunable per application.

stacksize/stacksize.go

@@ -14,19 +14,38 @@ import (
 // set to true to print information useful for debugging
 const debugPrint = false
 
-type sizeType uint8
+// SizeType indicates whether a stack or frame size could be determined and if
+// not, why.
+type SizeType uint8
 
 // Results after trying to determine the stack size of a function in the call
 // graph. The goal is to find a maximum (bounded) stack size, but sometimes this
 // is not possible for some reasons such as recursion or indirect calls.
 const (
-	Undefined sizeType = iota // not yet calculated
+	Undefined SizeType = iota // not yet calculated
 	Unknown                   // child has unknown stack size
 	Bounded                   // stack size is fixed at compile time (no recursion etc)
 	Recursive
 	IndirectCall
 )
 
+func (s SizeType) String() string {
+	switch s {
+	case Undefined:
+		return "undefined"
+	case Unknown:
+		return "unknown"
+	case Bounded:
+		return "bounded"
+	case Recursive:
+		return "recursive"
+	case IndirectCall:
+		return "indirect call"
+	default:
+		return "<?>"
+	}
+}
+
 // CallNode is a node in the call graph (that is, a function). Because this is
 // determined after linking, there may be multiple names for a single function
 // (due to aliases). It is also possible multiple functions have the same name
@@ -37,9 +56,9 @@ type CallNode struct {
 	Size             uint64      // symbol size, in bytes
 	Children         []*CallNode // functions this function calls
 	FrameSize        uint64      // frame size, if FrameSizeType is Bounded
-	FrameSizeType    sizeType    // can be Undefined or Bounded
+	FrameSizeType    SizeType    // can be Undefined or Bounded
 	stackSize        uint64
-	stackSizeType    sizeType
+	stackSizeType    SizeType
 	missingFrameInfo *CallNode // the child function that is the cause for not being able to determine the stack size
 }
 
@@ -236,7 +255,7 @@ func findSymbol(symbolList []*CallNode, address uint64) *CallNode {
 // returns the maximum stack size, whether this size can be known at compile
 // time and the call node responsible for failing to determine the maximum stack
 // usage. The stack size is only valid if sizeType is Bounded.
-func (node *CallNode) StackSize() (uint64, sizeType, *CallNode) {
+func (node *CallNode) StackSize() (uint64, SizeType, *CallNode) {
 	if node.stackSizeType == Undefined {
 		node.determineStackSize(make(map[*CallNode]struct{}))
 	}