prog: mutate len arguments

Fixes #183

4 files changed, 71 insertions, 14 deletions

diff --git a/prog/mutation.go b/prog/mutation.go
index 1aeef4fa4..0b2a5b026 100644
--- a/prog/mutation.go
+++ b/prog/mutation.go
@@ -62,14 +62,15 @@ func (p *Prog) Mutate(rs rand.Source, ncalls int, ct *ChoiceTable, corpus []*Pro
 				continue
 			}
 			s := analyze(ct, p, c)
+			updateSizes := true
 			for stop := false; !stop; stop = r.oneOf(3) {
-				args, bases := p.Target.mutationArgs(c)
+				args, bases, parents := p.Target.mutationArgs(c)
 				if len(args) == 0 {
 					retry = true
 					continue
 				}
 				idx := r.Intn(len(args))
-				arg, base := args[idx], bases[idx]
+				arg, base, parent := args[idx], bases[idx], parents[idx]
 				var baseSize uint64
 				if base != nil {
 					b, ok := base.(*PointerArg)
@@ -94,6 +95,12 @@ func (p *Prog) Mutate(rs rand.Source, ncalls int, ct *ChoiceTable, corpus []*Pro
 							a.Val ^= 1 << uint64(r.Intn(64))
 						}
 					}
+				case *LenType:
+					if !r.mutateSize(arg.(*ConstArg), *parent) {
+						retry = true
+						continue
+					}
+					updateSizes = false
 				case *ResourceType, *VmaType, *ProcType:
 					arg1, calls1 := r.generateArg(s, arg.Type())
 					p.replaceArg(c, arg, arg1, calls1)
@@ -200,8 +207,6 @@ func (p *Prog) Mutate(rs rand.Source, ncalls int, ct *ChoiceTable, corpus []*Pro
 					opt, calls := r.generateArg(s, optType)
 					arg1 := MakeUnionArg(t, opt, optType)
 					p.replaceArg(c, arg, arg1, calls)
-				case *LenType:
-					panic("bad arg returned by mutationArgs: LenType")
 				case *CsumType:
 					panic("bad arg returned by mutationArgs: CsumType")
 				case *ConstType:
@@ -227,7 +232,9 @@ func (p *Prog) Mutate(rs rand.Source, ncalls int, ct *ChoiceTable, corpus []*Pro
 				}
 
 				// Update all len fields.
-				p.Target.assignSizesCall(c)
+				if updateSizes {
+					p.Target.assignSizesCall(c)
+				}
 			}
 		default:
 			// Remove a random call.
@@ -501,8 +508,8 @@ func (p *Prog) TrimAfter(idx int) {
 	p.Calls = p.Calls[:idx+1]
 }
 
-func (target *Target) mutationArgs(c *Call) (args, bases []Arg) {
-	foreachArg(c, func(arg, base Arg, _ *[]Arg) {
+func (target *Target) mutationArgs(c *Call) (args, bases []Arg, parents []*[]Arg) {
+	foreachArg(c, func(arg, base Arg, parent *[]Arg) {
 		switch typ := arg.Type().(type) {
 		case *StructType:
 			if target.SpecialStructs[typ.Name()] == nil {
@@ -515,9 +522,6 @@ func (target *Target) mutationArgs(c *Call) (args, bases []Arg) {
 			if typ.Kind == ArrayRangeLen && typ.RangeBegin == typ.RangeEnd {
 				return
 			}
-		case *LenType:
-			// Size is updated when the size-of arg change.
-			return
 		case *CsumType:
 			// Checksum is updated when the checksummed data changes.
 			return
@@ -541,6 +545,7 @@ func (target *Target) mutationArgs(c *Call) (args, bases []Arg) {
 		}
 		args = append(args, arg)
 		bases = append(bases, base)
+		parents = append(parents, parent)
 	})
 	return
 }
diff --git a/prog/rand.go b/prog/rand.go
index 173248599..2b5148181 100644
--- a/prog/rand.go
+++ b/prog/rand.go
@@ -96,7 +96,7 @@ func (r *randGen) randRangeInt(begin uint64, end uint64) uint64 {
 	if r.oneOf(100) {
 		return r.randInt()
 	}
-	return begin + uint64(r.Int63n(int64(end-begin+1)))
+	return begin + (r.Uint64() % (end - begin + 1))
 }
 
 // biasedRand returns a random int in range [0..n),
diff --git a/prog/size.go b/prog/size.go
index 718e0c426..5dd1310b4 100644
--- a/prog/size.go
+++ b/prog/size.go
@@ -106,3 +106,58 @@ func (target *Target) assignSizesArray(args []Arg) {
 func (target *Target) assignSizesCall(c *Call) {
 	target.assignSizesArray(c.Args)
 }
+
+func (r *randGen) mutateSize(arg *ConstArg, parent []Arg) bool {
+	typ := arg.Type().(*LenType)
+	elemSize := typ.ByteSize
+	if elemSize == 0 {
+		elemSize = 1
+		for _, field := range parent {
+			if typ.Buf != field.Type().FieldName() {
+				continue
+			}
+			if inner := InnerArg(field); inner != nil {
+				switch targetType := inner.Type().(type) {
+				case *VmaType:
+					return false
+				case *ArrayType:
+					elemSize = targetType.Type.Size()
+				}
+			}
+			break
+		}
+	}
+	if r.oneOf(100) {
+		arg.Val = r.rand64()
+		return true
+	}
+	if r.bin() {
+		// Small adjustment to trigger missed size checks.
+		if arg.Val != 0 && r.bin() {
+			arg.Val = r.randRangeInt(0, arg.Val-1)
+		} else {
+			arg.Val = r.randRangeInt(arg.Val+1, arg.Val+1000)
+		}
+		return true
+	}
+	// Try to provoke int overflows.
+	max := ^uint64(0)
+	if r.oneOf(3) {
+		max = 1<<32 - 1
+		if r.oneOf(2) {
+			max = 1<<16 - 1
+			if r.oneOf(2) {
+				max = 1<<8 - 1
+			}
+		}
+	}
+	n := max / elemSize
+	delta := uint64(1000 - r.biasedRand(1000, 10))
+	if elemSize == 1 || r.oneOf(10) {
+		n -= delta
+	} else {
+		n += delta
+	}
+	arg.Val = n
+	return true
+}
diff --git a/prog/size_test.go b/prog/size_test.go
index 02c6470d4..d6a950fd6 100644
--- a/prog/size_test.go
+++ b/prog/size_test.go
@@ -25,9 +25,6 @@ func TestAssignSizeRandom(t *testing.T) {
 		for _, call := range p.Calls {
 			target.assignSizesCall(call)
 		}
-		if data1 := p.Serialize(); !bytes.Equal(data0, data1) {
-			t.Fatalf("different lens assigned, initial:\n%s\nnew:\n%s", data0, data1)
-		}
 	}
 }