pkg/manager: split off diff fuzzer functionality

Move the code to a separate pkg/manager/diff package. Split the
code into several files.

1 files changed, 109 insertions, 0 deletions

diff --git a/pkg/manager/diff/patch_test.go b/pkg/manager/diff/patch_test.go
new file mode 100644
index 000000000..43b2f32a2
--- /dev/null
+++ b/pkg/manager/diff/patch_test.go
@@ -0,0 +1,109 @@
+// Copyright 2026 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package diff
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/google/syzkaller/pkg/mgrconfig"
+	"github.com/google/syzkaller/pkg/osutil"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestPatchFocusAreas(t *testing.T) {
+	cfg := &mgrconfig.Config{
+		KernelSrc: t.TempDir(),
+	}
+	require.NoError(t, osutil.FillDirectory(cfg.KernelSrc, map[string]string{
+		"header.h": `Test`,
+		"a.c": `#include <header.h>
+int main(void) { }`,
+		"b.c": `int main(void) { }`,
+		"c.c": `int main(void) { }`,
+	}))
+
+	baseHashes, patchedHashes := dummySymbolHashes(), dummySymbolHashes()
+	baseHashes["function"] = "hash1"
+	patchedHashes["function"] = "hash2"
+
+	PatchFocusAreas(cfg, [][]byte{
+		[]byte(`diff --git a/b.c b/b.c
+index 103167d..fbf7a68 100644
+--- a/b.c
++++ b/b.c
+@@ -1 +1 @@
+-int main(void) { }
+\ No newline at end of file
++int main(void) { return 1; }
+\ No newline at end of file`),
+		// Also, emulate an update to header.h.
+		[]byte(`diff --git a/header.h b/header.h
+index 103167d..fbf7a68 100644
+--- a/header.h
++++ b/header.h
+@@ -1 +1 @@
+-Test
+\ No newline at end of file
++Test2
+\ No newline at end of file`),
+	}, baseHashes, patchedHashes)
+
+	assert.Equal(t, []mgrconfig.FocusArea{
+		{
+			Name: symbolsArea,
+			Filter: mgrconfig.CovFilterCfg{
+				Functions: []string{"^function$"},
+			},
+			Weight: 6.0,
+		},
+		{
+			Name: filesArea,
+			Filter: mgrconfig.CovFilterCfg{
+				Files: []string{"b.c", "header.h"},
+			},
+			Weight: 3.0,
+		},
+		{
+			Name: includesArea,
+			Filter: mgrconfig.CovFilterCfg{
+				Files: []string{"a.c"},
+			},
+			Weight: 2.0,
+		},
+		{
+			Weight: 1.0,
+		},
+	}, cfg.Experimental.FocusAreas)
+}
+
+func dummySymbolHashes() map[string]string {
+	ret := map[string]string{}
+	for i := 0; i < 100; i++ {
+		ret[fmt.Sprint(i)] = fmt.Sprint(i)
+	}
+	return ret
+}
+
+func TestModifiedSymbols(t *testing.T) {
+	t.Run("too many changed", func(t *testing.T) {
+		ret := modifiedSymbols(map[string]string{
+			"functionA": "hash1",
+			"functionB": "hash2",
+		}, map[string]string{
+			"functionA": "hash1",
+			"functionB": "hash is not hash2",
+		})
+		assert.Empty(t, ret)
+	})
+	t.Run("less than threshold", func(t *testing.T) {
+		base, patched := dummySymbolHashes(), dummySymbolHashes()
+		base["function"] = "hash1"
+		patched["function"] = "hash2"
+		base["function2"] = "hash1"
+		patched["function2"] = "hash2"
+		assert.Equal(t, []string{"function", "function2"}, modifiedSymbols(base, patched))
+	})
+}