From a68fda52c366653ed73c240a6b9c3f4e750ccdfd Mon Sep 17 00:00:00 2001
From: Grigory Bazilevich <g.bazilevich@ispras.ru>
Date: Wed, 11 Mar 2026 09:42:40 +0300
Subject: pkg/fuzzer,pkg/corpus: detection and preservation of programs with
 probability coverage

---
 pkg/fuzzer/cover.go  |  8 ++++++++
 pkg/fuzzer/fuzzer.go | 12 +++++++-----
 pkg/fuzzer/job.go    | 32 +++++++++++++++++++++++++-------
 3 files changed, 40 insertions(+), 12 deletions(-)

(limited to 'pkg/fuzzer')

diff --git a/pkg/fuzzer/cover.go b/pkg/fuzzer/cover.go
index e2dca3d88..191ff1491 100644
--- a/pkg/fuzzer/cover.go
+++ b/pkg/fuzzer/cover.go
@@ -36,6 +36,14 @@ func (cover *Cover) addRawMaxSignal(signal []uint64, prio uint8) signal.Signal {
 	return diff
 }
 
+func (cover *Cover) addMaxSignal(signal signal.Signal) signal.Signal {
+	cover.mu.Lock()
+	defer cover.mu.Unlock()
+	diff := cover.maxSignal.MergeDiff(signal)
+	cover.newSignal.Merge(diff)
+	return diff
+}
+
 func (cover *Cover) CopyMaxSignal() signal.Signal {
 	cover.mu.RLock()
 	defer cover.mu.RUnlock()
diff --git a/pkg/fuzzer/fuzzer.go b/pkg/fuzzer/fuzzer.go
index bd55ca9c6..3241cb63a 100644
--- a/pkg/fuzzer/fuzzer.go
+++ b/pkg/fuzzer/fuzzer.go
@@ -24,8 +24,9 @@ import (
 
 type Fuzzer struct {
 	Stats
-	Config *Config
-	Cover  *Cover
+	Config    *Config
+	Cover     *Cover
+	ProbCover *Cover
 
 	ctx          context.Context
 	mu           sync.Mutex
@@ -50,9 +51,10 @@ func NewFuzzer(ctx context.Context, cfg *Config, rnd *rand.Rand,
 		}
 	}
 	f := &Fuzzer{
-		Stats:  newStats(target),
-		Config: cfg,
-		Cover:  newCover(),
+		Stats:     newStats(target),
+		Config:    cfg,
+		Cover:     newCover(),
+		ProbCover: new(Cover),
 
 		ctx:         ctx,
 		rnd:         rnd,
diff --git a/pkg/fuzzer/job.go b/pkg/fuzzer/job.go
index bbac544f6..1f450ff7e 100644
--- a/pkg/fuzzer/job.go
+++ b/pkg/fuzzer/job.go
@@ -93,7 +93,9 @@ type triageCall struct {
 
 	// Filled after deflake:
 	signals         [deflakeNeedRuns]signal.Signal
+	probSignal      signal.Signal
 	stableSignal    signal.Signal
+	newProbSignal   signal.Signal
 	newStableSignal signal.Signal
 	cover           cover.Cover
 	rawCover        []uint64
@@ -162,12 +164,16 @@ func (job *triageJob) run(fuzzer *Fuzzer) {
 }
 
 func (job *triageJob) handleCall(call int, info *triageCall) {
-	if info.newStableSignal.Empty() {
+	skip := true
+	skip = skip && info.newStableSignal.Empty()
+	skip = skip && (info.newProbSignal.Empty() || info.newProbSignal.Len() < 4 && info.newProbSignal.Metric() < (1<<2))
+
+	if skip {
 		return
 	}
 
 	p := job.p
-	if job.flags&ProgMinimized == 0 {
+	if job.flags&ProgMinimized == 0 && !info.newStableSignal.Empty() {
 		p, call = job.minimize(call, info)
 		if p == nil {
 			return
@@ -209,11 +215,13 @@ func (job *triageJob) handleCall(call int, info *triageCall) {
 	}
 	job.fuzzer.Logf(2, "added new input for %v to the corpus: %s", callName, p)
 	input := corpus.NewInput{
-		Prog:     p,
-		Call:     call,
-		Signal:   info.stableSignal,
-		Cover:    info.cover.Serialize(),
-		RawCover: info.rawCover,
+		Prog:         p,
+		Call:         call,
+		ProbOnly:     info.newStableSignal.Empty(),
+		Signal:       info.probSignal,
+		StableSignal: info.stableSignal,
+		Cover:        info.cover.Serialize(),
+		RawCover:     info.rawCover,
 	}
 	job.fuzzer.Config.Corpus.Save(input)
 }
@@ -290,6 +298,16 @@ func (job *triageJob) deflake(exec func(*queue.Request, ProgFlags) *queue.Result
 		deflakeCall(-1, result.Info.Extra)
 	}
 	job.info.Logf("deflake complete")
+	for call, info := range job.calls {
+		for i := range needRuns - 1 {
+			info.probSignal.Merge(info.signals[i].CopyWithPrio(uint8(i) << 2))
+		}
+		info.newProbSignal = job.fuzzer.ProbCover.addMaxSignal(info.probSignal)
+		job.info.Logf("call #%d [%s]: |probability signal|=%d, |new probability signal|=%d%s",
+			call, job.p.CallName(call), info.probSignal.Len(), info.newProbSignal.Len(),
+			signalPreview(info.newProbSignal))
+	}
+
 	for call, info := range job.calls {
 		info.stableSignal = info.signals[needRuns-1]
 		info.newStableSignal = info.newSignal.Intersection(info.stableSignal)
-- 
cgit mrf-deployment