prog: add insertionPoint param in generateCall func

3 files changed, 6 insertions, 5 deletions

diff --git a/prog/generation.go b/prog/generation.go
index dcb8dc2ac..85d1bbb02 100644
--- a/prog/generation.go
+++ b/prog/generation.go
@@ -16,7 +16,7 @@ func (target *Target) Generate(rs rand.Source, ncalls int, ct *ChoiceTable) *Pro
 	r := newRand(target, rs)
 	s := newState(target, ct, nil)
 	for len(p.Calls) < ncalls {
-		calls := r.generateCall(s, p)
+		calls := r.generateCall(s, p, len(p.Calls))
 		for _, c := range calls {
 			s.analyze(c)
 			p.Calls = append(p.Calls, c)
diff --git a/prog/mutation.go b/prog/mutation.go
index b0702ebba..f19813148 100644
--- a/prog/mutation.go
+++ b/prog/mutation.go
@@ -134,7 +134,7 @@ func (ctx *mutator) insertCall() bool {
 		c = p.Calls[idx]
 	}
 	s := analyze(ctx.ct, ctx.corpus, p, c)
-	calls := r.generateCall(s, p)
+	calls := r.generateCall(s, p, idx)
 	// TODO: the program might have more than ncalls
 	p.insertBefore(c, calls)
 	return true
diff --git a/prog/rand.go b/prog/rand.go
index 3306ced66..f8c640161 100644
--- a/prog/rand.go
+++ b/prog/rand.go
@@ -490,14 +490,15 @@ func (r *randGen) nOutOf(n, outOf int) bool {
 	return v < n
 }
 
-func (r *randGen) generateCall(s *state, p *Prog) []*Call {
+func (r *randGen) generateCall(s *state, p *Prog, insertionPoint int) []*Call {
 	idx := 0
-	if s.ct == nil {
+	if s.ct == nil || insertionPoint <= 0 {
 		idx = r.Intn(len(r.target.Syscalls))
 	} else {
 		call := -1
 		if len(p.Calls) != 0 {
-			call = p.Calls[r.Intn(len(p.Calls))].Meta.ID
+			// Choosing the base call is based on the insertion point of the new calls sequence.
+			call = p.Calls[r.Intn(insertionPoint)].Meta.ID
 		}
 		idx = s.ct.Choose(r.Rand, call)
 	}