proc: lexical block support

Fixes #106

pkg/dwarf/reader/variables.go

@@ -0,0 +1,103 @@
+package reader
+
+import (
+	"errors"
+
+	"debug/dwarf"
+)
+
+// VariableReader provides a way of reading the local variables and formal
+// parameters of a function that are visible at the specified PC address.
+type VariableReader struct {
+	dwarf       *dwarf.Data
+	reader      *dwarf.Reader
+	entry       *dwarf.Entry
+	depth       int
+	onlyVisible bool
+	pc          uint64
+	err         error
+}
+
+// Variables returns a VariableReader for the function or lexical block at off.
+// If onlyVisible is true only variables visible at pc will be returned by
+// the VariableReader.
+func Variables(dwarf *dwarf.Data, off dwarf.Offset, pc uint64, onlyVisible bool) *VariableReader {
+	reader := dwarf.Reader()
+	reader.Seek(off)
+	return &VariableReader{dwarf: dwarf, reader: reader, entry: nil, depth: 0, onlyVisible: onlyVisible, pc: pc, err: nil}
+}
+
+// Next reads the next variable entry, returns false if there aren't any.
+func (vrdr *VariableReader) Next() bool {
+	if vrdr.err != nil {
+		return false
+	}
+
+	for {
+		vrdr.entry, vrdr.err = vrdr.reader.Next()
+		if vrdr.entry == nil || vrdr.err != nil {
+			return false
+		}
+
+		switch vrdr.entry.Tag {
+		case 0:
+			vrdr.depth--
+			if vrdr.depth == 0 {
+				return false
+			}
+
+		case dwarf.TagLexDwarfBlock, dwarf.TagSubprogram:
+			recur := true
+			if vrdr.onlyVisible {
+				recur, vrdr.err = vrdr.entryRangesContains()
+				if vrdr.err != nil {
+					return false
+				}
+			}
+
+			if recur {
+				vrdr.depth++
+			} else {
+				if vrdr.depth == 0 {
+					return false
+				}
+				vrdr.reader.SkipChildren()
+			}
+
+		default:
+			if vrdr.depth == 0 {
+				vrdr.err = errors.New("offset was not lexical block or subprogram")
+				return false
+			}
+			return true
+		}
+	}
+}
+
+func (vrdr *VariableReader) entryRangesContains() (bool, error) {
+	rngs, err := vrdr.dwarf.Ranges(vrdr.entry)
+	if err != nil {
+		return false, err
+	}
+	for _, rng := range rngs {
+		if vrdr.pc >= rng[0] && vrdr.pc < rng[1] {
+			return true, nil
+		}
+	}
+	return false, nil
+}
+
+// Entry returns the current variable entry.
+func (vrdr *VariableReader) Entry() *dwarf.Entry {
+	return vrdr.entry
+}
+
+// Depth returns the depth of the current scope
+func (vrdr *VariableReader) Depth() int {
+	return vrdr.depth
+}
+
+// Err returns the error if there was one.
+func (vrdr *VariableReader) Err() error {
+	return vrdr.err
+}