From f4b5f67ee07dabc25b5baab0a94f3420606fd0ea Mon Sep 17 00:00:00 2001
From: Martin Holst Swende <martin@swende.se>
Date: Sat, 3 Jun 2017 19:01:22 +0200
Subject: [PATCH] core/vm: improved jumpdest analysis

---
 core/vm/analysis.go      | 44 ++++++++++++++++++++++++++++++++--------
 core/vm/analysis_test.go | 37 +++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 9 deletions(-)
 create mode 100644 core/vm/analysis_test.go

diff --git a/core/vm/analysis.go b/core/vm/analysis.go
index d5f048d1d..b27dee8dc 100644
--- a/core/vm/analysis.go
+++ b/core/vm/analysis.go
@@ -41,21 +41,47 @@ func (d destinations) has(codehash common.Hash, code []byte, dest *big.Int) bool
 		m = jumpdests(code)
 		d[codehash] = m
 	}
-	return (m[udest/8] & (1 << (udest % 8))) != 0
+	return OpCode(code[udest]) == JUMPDEST && (m[udest/8]&(0x80>>(udest%8))) == 0
+	//	return (m[udest/8] & (1 << (udest % 8))) != 0
+}
+
+type bitvec struct {
+	m []byte
+}
+
+func (bits *bitvec) addone(pos uint64) {
+	bits.m[pos/8] |= 0x80 >> (pos % 8)
+}
+func (bits *bitvec) addOneByte(pos uint64) {
+	bits.m[pos/8] |= 0xFF >> (pos % 8)
+	bits.m[pos/8+1] |= ^(0xFF >> (pos % 8))
 }
 
 // jumpdests creates a map that contains an entry for each
 // PC location that is a JUMPDEST instruction.
 func jumpdests(code []byte) []byte {
-	m := make([]byte, len(code)/8+1)
-	for pc := uint64(0); pc < uint64(len(code)); pc++ {
+	//The map is 4 bytes longer than necessary, in case the code
+	// ends with a PUSH32, the algorithm will push zeroes onto the
+	// bitvector outside the bounds of the actual code.
+	m := make([]byte, len(code)/8+1+4)
+	bits := &bitvec{m}
+	for pc := uint64(0); pc < uint64(len(code)); {
 		op := OpCode(code[pc])
-		if op == JUMPDEST {
-			m[pc/8] |= 1 << (pc % 8)
-		} else if op >= PUSH1 && op <= PUSH32 {
-			a := uint64(op) - uint64(PUSH1) + 1
-			pc += a
+
+		if op >= PUSH1 && op <= PUSH32 {
+			numbits := op - PUSH1 + 1
+			pc++
+			for ; numbits >= 8; numbits -= 8 {
+				bits.addOneByte(pc) // 8
+				pc += 8
+			}
+			for ; numbits > 0; numbits-- {
+				bits.addone(pc)
+				pc++
+			}
+		} else {
+			pc++
 		}
 	}
-	return m
+	return bits.m
 }
diff --git a/core/vm/analysis_test.go b/core/vm/analysis_test.go
new file mode 100644
index 000000000..17c578e95
--- /dev/null
+++ b/core/vm/analysis_test.go
@@ -0,0 +1,37 @@
+package vm
+
+import "testing"
+
+func TestJumpDestAnalysis(t *testing.T) {
+	tests := []struct {
+		code  []byte
+		exp   byte
+		which int
+	}{
+		{[]byte{byte(PUSH1), 0x01, 0x01, 0x01}, 0x40, 0},
+		{[]byte{byte(PUSH1), byte(PUSH1), byte(PUSH1), byte(PUSH1)}, 0x50, 0},
+		{[]byte{byte(PUSH8), byte(PUSH8), byte(PUSH8), byte(PUSH8), byte(PUSH8), byte(PUSH8), byte(PUSH8), byte(PUSH8), 0x01, 0x01, 0x01}, 0x7F, 0},
+		{[]byte{byte(PUSH8), 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01}, 0x80, 1},
+		{[]byte{0x01, 0x01, 0x01, 0x01, 0x01, byte(PUSH2), byte(PUSH2), byte(PUSH2), 0x01, 0x01, 0x01}, 0x03, 0},
+		{[]byte{0x01, 0x01, 0x01, 0x01, 0x01, byte(PUSH2), 0x01, 0x01, 0x01, 0x01, 0x01}, 0x00, 1},
+		{[]byte{byte(PUSH3), 0x01, 0x01, 0x01, byte(PUSH1), 0x01, 0x01, 0x01, 0x01, 0x01, 0x01}, 0x74, 0},
+		{[]byte{byte(PUSH3), 0x01, 0x01, 0x01, byte(PUSH1), 0x01, 0x01, 0x01, 0x01, 0x01, 0x01}, 0x00, 1},
+		{[]byte{0x01, byte(PUSH8), 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01}, 0x3F, 0},
+		{[]byte{0x01, byte(PUSH8), 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01}, 0xC0, 1},
+		{[]byte{byte(PUSH16), 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01}, 0x7F, 0},
+		{[]byte{byte(PUSH16), 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01}, 0xFF, 1},
+		{[]byte{byte(PUSH16), 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01}, 0x80, 2},
+		{[]byte{byte(PUSH8), 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, byte(PUSH1), 0x01}, 0x7f, 0},
+		{[]byte{byte(PUSH8), 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, byte(PUSH1), 0x01}, 0xA0, 1},
+		{[]byte{byte(PUSH32)}, 0x7F, 0},
+		{[]byte{byte(PUSH32)}, 0xFF, 1},
+		{[]byte{byte(PUSH32)}, 0xFF, 2},
+	}
+	for _, test := range tests {
+		ret := jumpdests(test.code)
+		if ret[test.which] != test.exp {
+			t.Fatalf("expected %x, got %02x", test.exp, ret[test.which])
+		}
+	}
+
+}