Prefer binary search over tree lookup for FDEs

FDEs previously were loaded into a red/black tree and searched. This is
significantly more expensive than a binary search over a slice. Not sure
what I was thinking using a red/black tree - this binary search
implementation is significantly more efficient.

dwarf/frame/entries.go

@@ -1,10 +1,6 @@
 package frame
 
-import (
-	"fmt"
-
-	"github.com/derekparker/rbtree"
-)
+import "fmt"
 
 // Represents a Common Information Entry in
 // the Dwarf .debug_frame section.
@@ -23,7 +19,6 @@ func (fde *FrameDescriptionEntry) Cover(addr uint64) bool {
 	if (addr - fde.begin) < fde.end {
 		return true
 	}
-
 	return false
 }
 
@@ -53,39 +48,42 @@ func (fde *FrameDescriptionEntry) ReturnAddressOffset(pc uint64) int64 {
 	return frame.cfa.offset + frame.regs[fde.CIE.ReturnAddressRegister].offset
 }
 
-type FrameDescriptionEntries struct {
-	*rbtree.RedBlackTree
+type FrameDescriptionEntries []*FrameDescriptionEntry
+
+func NewFrameIndex() FrameDescriptionEntries {
+	return make(FrameDescriptionEntries, 0, 1000)
 }
 
-func NewFrameIndex() *FrameDescriptionEntries {
-	return &FrameDescriptionEntries{rbtree.New()}
-}
-
-func (fdes *FrameDescriptionEntries) FDEForPC(pc uint64) (*FrameDescriptionEntry, error) {
-	node, ok := fdes.Find(Addr(pc))
-	if !ok {
-		return nil, fmt.Errorf("Could not find FDE for %#v", pc)
+func (fdes FrameDescriptionEntries) FDEForPC(pc uint64) (*FrameDescriptionEntry, error) {
+	frame := find(fdes, pc)
+	if frame == nil {
+		return nil, fmt.Errorf("could not find FDE for %#v", pc)
 	}
-
-	return node.(*FrameDescriptionEntry), nil
+	return frame, nil
 }
 
-func (frame *FrameDescriptionEntry) Less(item rbtree.Item) bool {
-	return frame.Begin() < item.(*FrameDescriptionEntry).Begin()
+func find(fdes FrameDescriptionEntries, pc uint64) *FrameDescriptionEntry {
+	if len(fdes) == 0 {
+		return nil
+	}
+	idx := len(fdes) / 2
+	frame := fdes[idx]
+	if frame.Cover(pc) {
+		return frame
+	}
+	if frame.Less(pc) {
+		return find(fdes[:idx], pc)
+	}
+	if frame.More(pc) {
+		return find(fdes[idx:], pc)
+	}
+	return nil
 }
 
-func (frame *FrameDescriptionEntry) More(item rbtree.Item) bool {
-	f := item.(*FrameDescriptionEntry)
-	return frame.End() > f.End()
+func (frame *FrameDescriptionEntry) Less(pc uint64) bool {
+	return frame.Begin() > pc
 }
 
-type Addr uint64
-
-func (a Addr) Less(item rbtree.Item) bool {
-	return uint64(a) < item.(*FrameDescriptionEntry).Begin()
-}
-
-func (a Addr) More(item rbtree.Item) bool {
-	f := item.(*FrameDescriptionEntry)
-	return uint64(a) > f.End()
+func (frame *FrameDescriptionEntry) More(pc uint64) bool {
+	return frame.End() < pc
 }

dwarf/frame/entries_test.go

@@ -7,23 +7,23 @@ import (
 )
 
 func TestFDEForPC(t *testing.T) {
-	fde1 := &FrameDescriptionEntry{begin: 100, end: 200}
+	fde1 := &FrameDescriptionEntry{begin: 0, end: 49}
 	fde2 := &FrameDescriptionEntry{begin: 50, end: 99}
-	fde3 := &FrameDescriptionEntry{begin: 0, end: 49}
+	fde3 := &FrameDescriptionEntry{begin: 100, end: 200}
 	fde4 := &FrameDescriptionEntry{begin: 201, end: 245}
 
-	tree := NewFrameIndex()
-	tree.Put(fde1)
-	tree.Put(fde2)
-	tree.Put(fde3)
-	tree.Put(fde4)
+	frames := NewFrameIndex()
+	frames = append(frames, fde1)
+	frames = append(frames, fde2)
+	frames = append(frames, fde3)
+	frames = append(frames, fde4)
 
-	node, ok := tree.Find(Addr(35))
-	if !ok {
+	node, err := frames.FDEForPC(35)
+	if err != nil {
 		t.Fatal("Could not find FDE")
 	}
 
-	if node != fde3 {
+	if node != fde1 {
 		t.Fatal("Got incorrect fde")
 	}
 }

dwarf/frame/parser.go

@@ -14,7 +14,7 @@ type parsefunc func(*parseContext) parsefunc
 
 type parseContext struct {
 	Buf     *bytes.Buffer
-	Entries *FrameDescriptionEntries
+	Entries FrameDescriptionEntries
 	Common  *CommonInformationEntry
 	Frame   *FrameDescriptionEntry
 	Length  uint32
@@ -23,7 +23,7 @@ type parseContext struct {
 // Parse takes in data (a byte slice) and returns a slice of
 // CommonInformationEntry structures. Each CommonInformationEntry
 // has a slice of FrameDescriptionEntry structures.
-func Parse(data []byte) *FrameDescriptionEntries {
+func Parse(data []byte) FrameDescriptionEntries {
 	var (
 		buf  = bytes.NewBuffer(data)
 		pctx = &parseContext{Buf: buf, Entries: NewFrameIndex()}
@@ -62,7 +62,7 @@ func parseFDE(ctx *parseContext) parsefunc {
 
 	// Insert into the tree after setting address range begin
 	// otherwise compares won't work.
-	ctx.Entries.Put(ctx.Frame)
+	ctx.Entries = append(ctx.Entries, ctx.Frame)
 
 	// The rest of this entry consists of the instructions
 	// so we can just grab all of the data from the buffer