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, 140 insertions, 0 deletions

diff --git a/pkg/manager/diff/patch.go b/pkg/manager/diff/patch.go
new file mode 100644
index 000000000..f493a8d77
--- /dev/null
+++ b/pkg/manager/diff/patch.go
@@ -0,0 +1,140 @@
+// 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"
+	"regexp"
+	"sort"
+	"strings"
+
+	"github.com/google/syzkaller/pkg/log"
+	"github.com/google/syzkaller/pkg/mgrconfig"
+	"github.com/google/syzkaller/pkg/osutil"
+	"github.com/google/syzkaller/pkg/vcs"
+)
+
+const (
+	symbolsArea  = "symbols"
+	filesArea    = "files"
+	includesArea = "included"
+)
+
+func PatchFocusAreas(cfg *mgrconfig.Config, gitPatches [][]byte, baseHashes, patchedHashes map[string]string) {
+	funcs := modifiedSymbols(baseHashes, patchedHashes)
+	if len(funcs) > 0 {
+		log.Logf(0, "adding modified_functions to focus areas: %q", funcs)
+		var regexps []string
+		for _, name := range funcs {
+			regexps = append(regexps, fmt.Sprintf("^%s$", regexp.QuoteMeta(name)))
+		}
+		cfg.Experimental.FocusAreas = append(cfg.Experimental.FocusAreas,
+			mgrconfig.FocusArea{
+				Name: symbolsArea,
+				Filter: mgrconfig.CovFilterCfg{
+					Functions: regexps,
+				},
+				Weight: 6.0,
+			})
+	}
+
+	direct, transitive := affectedFiles(cfg, gitPatches)
+	if len(direct) > 0 {
+		sort.Strings(direct)
+		log.Logf(0, "adding directly modified files to focus areas: %q", direct)
+		cfg.Experimental.FocusAreas = append(cfg.Experimental.FocusAreas,
+			mgrconfig.FocusArea{
+				Name: filesArea,
+				Filter: mgrconfig.CovFilterCfg{
+					Files: direct,
+				},
+				Weight: 3.0,
+			})
+	}
+
+	if len(transitive) > 0 {
+		sort.Strings(transitive)
+		log.Logf(0, "adding transitively affected to focus areas: %q", transitive)
+		cfg.Experimental.FocusAreas = append(cfg.Experimental.FocusAreas,
+			mgrconfig.FocusArea{
+				Name: includesArea,
+				Filter: mgrconfig.CovFilterCfg{
+					Files: transitive,
+				},
+				Weight: 2.0,
+			})
+	}
+
+	// Still fuzz the rest of the kernel.
+	if len(cfg.Experimental.FocusAreas) > 0 {
+		cfg.Experimental.FocusAreas = append(cfg.Experimental.FocusAreas,
+			mgrconfig.FocusArea{
+				Weight: 1.0,
+			})
+	}
+}
+
+func affectedFiles(cfg *mgrconfig.Config, gitPatches [][]byte) (direct, transitive []string) {
+	const maxAffectedByHeader = 50
+
+	directMap := make(map[string]struct{})
+	transitiveMap := make(map[string]struct{})
+	var allFiles []string
+	for _, patch := range gitPatches {
+		for _, diff := range vcs.ParseGitDiff(patch) {
+			allFiles = append(allFiles, diff.Name)
+		}
+	}
+	for _, file := range allFiles {
+		directMap[file] = struct{}{}
+		if !strings.HasSuffix(file, ".h") || cfg.KernelSrc == "" {
+			continue
+		}
+		// For .h files, we want to determine all the .c files that include them.
+		// Ideally, we should combine this with the recompilation process - then we know
+		// exactly which files were affected by the patch.
+		matching, err := osutil.GrepFiles(cfg.KernelSrc, `.c`,
+			[]byte(`<`+strings.TrimPrefix(file, "include/")+`>`))
+		if err != nil {
+			log.Logf(0, "failed to grep for includes: %s", err)
+			continue
+		}
+		if len(matching) >= maxAffectedByHeader {
+			// It's too widespread. It won't help us focus on anything.
+			log.Logf(0, "the header %q is included in too many files (%d)", file, len(matching))
+			continue
+		}
+		for _, name := range matching {
+			transitiveMap[name] = struct{}{}
+		}
+	}
+	for name := range directMap {
+		direct = append(direct, name)
+	}
+	for name := range transitiveMap {
+		if _, ok := directMap[name]; ok {
+			continue
+		}
+		transitive = append(transitive, name)
+	}
+	return
+}
+
+// If there are too many different symbols, they are no longer specific enough.
+// Don't use them to focus the fuzzer.
+const modifiedSymbolThreshold = 0.05
+
+func modifiedSymbols(baseHashes, patchedHashes map[string]string) []string {
+	var ret []string
+	for name, hash := range patchedHashes {
+		if baseHash, ok := baseHashes[name]; !ok || baseHash != hash {
+			ret = append(ret, name)
+			if float64(len(ret)) > float64(len(patchedHashes))*modifiedSymbolThreshold {
+				return nil
+			}
+		}
+	}
+	sort.Strings(ret)
+	return ret
+}