fix(loader): encode initial pcdata safe value

loader/pcdata.go

@@ -71,13 +71,14 @@ func (self Pcdata) MarshalBinary() (data []byte, err error) {
     sv := int32(_PCDATA_START_VAL)
     sp := uint32(0)
     buf := make([]byte, binary.MaxVarintLen32)
+    started := false
     for _, v := range self {
         if v.PC < sp {
             panic("PC must be in ascending order!")
         }
         dp := uint64(v.PC - sp)
         dv := int64(v.Val - sv)
-        if dv == 0 || dp == 0 {
+        if dp == 0 || (dv == 0 && started) {
             continue
         }
         n := binary.PutVarint(buf, dv)
@@ -86,6 +87,7 @@ func (self Pcdata) MarshalBinary() (data []byte, err error) {
         data = append(data, buf[:n2]...)
         sp = v.PC
         sv = v.Val
+        started = true
     }
     // put 0 to indicate ends
     data = append(data, 0)

loader/pcdata_test.go

@@ -0,0 +1,42 @@
+package loader
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestPcdataMarshalBinarySingleSafeEntry(t *testing.T) {
+	data, err := (Pcdata{{PC: 32, Val: PCDATA_UnsafePointSafe}}).MarshalBinary()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	want := []byte{0, 32, 0}
+	if !bytes.Equal(data, want) {
+		t.Fatalf("unexpected encoded table: got %x want %x", data, want)
+	}
+}
+
+func TestPcdataMarshalBinarySingleUnsafeEntry(t *testing.T) {
+	data, err := (Pcdata{{PC: 32, Val: PCDATA_UnsafePointUnsafe}}).MarshalBinary()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	want := []byte{1, 32, 0}
+	if !bytes.Equal(data, want) {
+		t.Fatalf("unexpected encoded table: got %x want %x", data, want)
+	}
+}
+
+func TestBuildLoadFuncNoPreemptEncodesSafeUnsafePoint(t *testing.T) {
+	fn := buildLoadFunc(false, LoadOneItem{FuncName: "spin"}, 32, 0)
+
+	data, err := fn.PcUnsafePoint.MarshalBinary()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(data) <= 1 {
+		t.Fatalf("encoded unsafe-point table has no entries: %x", data)
+	}
+}