pkg/aflow/action/kernel: add build action

Author: dvyukov

pkg/aflow/action/kernel/build.go

@@ -0,0 +1,63 @@
+// Copyright 2025 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 kernel
+
+import (
+	"fmt"
+	"io/fs"
+	"os"
+	"path"
+	"path/filepath"
+	"runtime"
+	"time"
+
+	"github.com/google/syzkaller/pkg/aflow"
+	"github.com/google/syzkaller/pkg/build"
+	"github.com/google/syzkaller/pkg/hash"
+	"github.com/google/syzkaller/pkg/osutil"
+	"github.com/google/syzkaller/sys/targets"
+)
+
+// Build action builds the Linux kernel from the given sources,
+// outputs directory with build artifacts.
+var Build = aflow.NewFuncAction("kernel-builder", buildKernel)
+
+type buildArgs struct {
+	KernelSrc    string
+	KernelCommit string
+	KernelConfig string
+}
+
+type buildResult struct {
+	KernelObj string // Directory with build artifacts.
+}
+
+func buildKernel(ctx *aflow.Context, args buildArgs) (buildResult, error) {
+	desc := fmt.Sprintf("kernel commit %v, kernel config hash %v",
+		args.KernelCommit, hash.String(args.KernelConfig))
+	dir, err := ctx.Cache("build", desc, func(dir string) error {
+		if err := osutil.WriteFile(filepath.Join(dir, ".config"), []byte(args.KernelConfig)); err != nil {
+			return err
+		}
+		target := targets.List[targets.Linux][targets.AMD64]
+		image := filepath.FromSlash(build.LinuxKernelImage(targets.AMD64))
+		makeArgs := build.LinuxMakeArgs(target, targets.DefaultLLVMCompiler, targets.DefaultLLVMLinker,
+			"ccache", dir, runtime.NumCPU())
+		makeArgs = append(makeArgs, path.Base(image), "compile_commands.json")
+		if _, err := osutil.RunCmd(time.Hour, args.KernelSrc, "make", makeArgs...); err != nil {
+			return err
+		}
+		// Remove main intermediate build files, we don't need them anymore
+		// and they take lots of space. Keep generated source files.
+		keepExt := map[string]bool{"h": true, "c": true, "s": true, "S": true}
+		keepFiles := map[string]bool{image: true}
+		return filepath.WalkDir(dir, func(path string, d fs.DirEntry, err error) error {
+			if err != nil || d.IsDir() || keepFiles[path] || keepExt[filepath.Ext(d.Name())] {
+				return err
+			}
+			return os.Remove(path)
+		})
+	})
+	return buildResult{KernelObj: dir}, err
+}