pkg/build: refactor cuttlefish image code to embedFiles()

Since most of the image mounting code is duplicated, we can instead
extract it to an embedFiles() function that takes a callback. The Linux-
or Android-specific code can be in the callback.

5 files changed, 81 insertions, 87 deletions

diff --git a/pkg/build/android.go b/pkg/build/android.go
index 9fb38bd5c..cc4e041da 100644
--- a/pkg/build/android.go
+++ b/pkg/build/android.go
@@ -4,7 +4,11 @@
 package build
 
 import (
+	"archive/tar"
+	"compress/gzip"
 	"fmt"
+	"io/ioutil"
+	"os"
 	"path/filepath"
 	"time"
 
@@ -27,6 +31,40 @@ func (a android) runBuild(kernelDir, buildConfig string) error {
 	return err
 }
 
+func (a android) readCompiler(archivePath string) (string, error) {
+	f, err := os.Open(archivePath)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+
+	gr, err := gzip.NewReader(f)
+	if err != nil {
+		return "", err
+	}
+	defer gr.Close()
+
+	tr := tar.NewReader(gr)
+
+	h, err := tr.Next()
+	for ; err == nil; h, err = tr.Next() {
+		if filepath.Base(h.Name) == "compile.h" {
+			bytes, err := ioutil.ReadAll(tr)
+			if err != nil {
+				return "", err
+			}
+			result := linuxCompilerRegexp.FindSubmatch(bytes)
+			if result == nil {
+				return "", fmt.Errorf("include/generated/compile.h does not contain build information")
+			}
+
+			return string(result[1]), nil
+		}
+	}
+
+	return "", fmt.Errorf("archive %s doesn't contain include/generated/compile.h", archivePath)
+}
+
 func (a android) build(params Params) (ImageDetails, error) {
 	var details ImageDetails
 
@@ -44,13 +82,37 @@ func (a android) build(params Params) (ImageDetails, error) {
 		return details, fmt.Errorf("failed to build modules: %s", err)
 	}
 
-	buildOutDir := filepath.Join(params.KernelDir, "out/dist")
+	buildOutDir := filepath.Join(params.KernelDir, "out", "dist")
 	bzImage := filepath.Join(buildOutDir, "bzImage")
 	vmlinux := filepath.Join(buildOutDir, "vmlinux")
 	initramfs := filepath.Join(buildOutDir, "initramfs.img")
 
-	if err := buildCuttlefishImage(params, bzImage, vmlinux, initramfs); err != nil {
-		return details, fmt.Errorf("failed to build image: %s", err)
+	var err error
+	details.CompilerID, err = a.readCompiler(filepath.Join(buildOutDir, "kernel-headers.tar.gz"))
+	if err != nil {
+		return details, err
+	}
+
+	if err := embedFiles(params, func(mountDir string) error {
+		homeDir := filepath.Join(mountDir, "root")
+
+		if _, err := osutil.RunCmd(time.Hour, homeDir, "./fetchcvd"); err != nil {
+			return err
+		}
+
+		if err := osutil.CopyFile(bzImage, filepath.Join(homeDir, "bzImage")); err != nil {
+			return err
+		}
+		if err := osutil.CopyFile(vmlinux, filepath.Join(homeDir, "vmlinux")); err != nil {
+			return err
+		}
+		if err := osutil.CopyFile(initramfs, filepath.Join(homeDir, "initramfs.img")); err != nil {
+			return err
+		}
+
+		return nil
+	}); err != nil {
+		return details, err
 	}
 
 	if err := osutil.CopyFile(vmlinux, filepath.Join(params.OutputDir, "kernel")); err != nil {
@@ -60,7 +122,6 @@ func (a android) build(params Params) (ImageDetails, error) {
 		return details, err
 	}
 
-	var err error
 	details.Signature, err = elfBinarySignature(vmlinux)
 	if err != nil {
 		return details, fmt.Errorf("failed to generate signature: %s", err)
diff --git a/pkg/build/android_linux.go b/pkg/build/android_linux.go
deleted file mode 100644
index a6e4e086c..000000000
--- a/pkg/build/android_linux.go
+++ /dev/null
@@ -1,67 +0,0 @@
-// Copyright 2022 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 build
-
-import (
-	"fmt"
-	"io/ioutil"
-	"os"
-	"path/filepath"
-	"time"
-
-	"golang.org/x/sys/unix"
-
-	"github.com/google/syzkaller/pkg/osutil"
-)
-
-// buildCuttlefishImage mounts a disk image, fetches and installs a Cuttlefish emulator binary,
-// and copies in the required kernel artifacts.
-func buildCuttlefishImage(params Params, bzImage, vmlinux, initramfs string) error {
-	tempDir, err := ioutil.TempDir("", "syz-build")
-	if err != nil {
-		return err
-	}
-	defer os.RemoveAll(tempDir)
-	imageFile := filepath.Join(tempDir, "image")
-	if err := osutil.CopyFile(params.UserspaceDir, imageFile); err != nil {
-		return err
-	}
-	loop, loopFile, err := linuxSetupLoop(imageFile)
-	if err != nil {
-		return err
-	}
-	defer func() {
-		unix.IoctlGetInt(loop, unix.LOOP_CLR_FD)
-		unix.Close(loop)
-	}()
-	mountDir := filepath.Join(tempDir, "mnt")
-	if err := osutil.MkdirAll(mountDir); err != nil {
-		return err
-	}
-	if err := tryMount(loopFile+"p1", mountDir); err != nil {
-		return fmt.Errorf("mount(%vp1, %v) failed: %v", loopFile, mountDir, err)
-	}
-	defer unix.Unmount(mountDir, 0)
-
-	imageHomeDir := filepath.Join(mountDir, "root")
-	if _, err := osutil.RunCmd(time.Hour, imageHomeDir, "./fetchcvd"); err != nil {
-		return fmt.Errorf("run fetch_cvd: %s", err)
-	}
-
-	if err := osutil.CopyFile(bzImage, filepath.Join(imageHomeDir, "bzImage")); err != nil {
-		return err
-	}
-	if err := osutil.CopyFile(vmlinux, filepath.Join(imageHomeDir, "vmlinux")); err != nil {
-		return err
-	}
-	if err := osutil.CopyFile(initramfs, filepath.Join(imageHomeDir, "initramfs.img")); err != nil {
-		return err
-	}
-
-	if err := unix.Unmount(mountDir, 0); err != nil {
-		return err
-	}
-
-	return osutil.CopyFile(imageFile, filepath.Join(params.OutputDir, "image"))
-}
diff --git a/pkg/build/android_nolinux.go b/pkg/build/android_nolinux.go
deleted file mode 100644
index 100d7669c..000000000
--- a/pkg/build/android_nolinux.go
+++ /dev/null
@@ -1,15 +0,0 @@
-// Copyright 2022 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.
-
-//go:build !linux
-// +build !linux
-
-package build
-
-import (
-	"errors"
-)
-
-func buildCuttlefishImage(params Params, bzImage, vmlinux, initramfs string) error {
-	return errors.New("building android cuttlefish image is only supported on linux")
-}
diff --git a/pkg/build/linux_linux.go b/pkg/build/linux_linux.go
index 4a8270353..55f21a7ee 100644
--- a/pkg/build/linux_linux.go
+++ b/pkg/build/linux_linux.go
@@ -23,6 +23,17 @@ import (
 // - cmdline file is not supported (should be moved to kernel config)
 // - the kernel is stored in the image in /vmlinuz file.
 func embedLinuxKernel(params Params, kernelPath string) error {
+	return embedFiles(params, func(mountDir string) error {
+		if err := copyKernel(mountDir, kernelPath); err != nil {
+			return err
+		}
+		return nil
+	})
+}
+
+// embedFiles mounts the disk image specified by params.UserspaceDir and then calls the given
+// callback function which should copy files into the image as needed.
+func embedFiles(params Params, callback func(mountDir string) error) error {
 	if params.CmdlineFile != "" {
 		return fmt.Errorf("cmdline file is not supported for linux images")
 	}
@@ -51,7 +62,7 @@ func embedLinuxKernel(params Params, kernelPath string) error {
 		return fmt.Errorf("mount(%vp1, %v) failed: %v", loopFile, mountDir, err)
 	}
 	defer unix.Unmount(mountDir, 0)
-	if err := copyKernel(mountDir, kernelPath); err != nil {
+	if err := callback(mountDir); err != nil {
 		return err
 	}
 	if params.SysctlFile != "" {
diff --git a/pkg/build/linux_nolinux.go b/pkg/build/linux_nolinux.go
index 0210627f5..03ea0da27 100644
--- a/pkg/build/linux_nolinux.go
+++ b/pkg/build/linux_nolinux.go
@@ -13,3 +13,7 @@ import (
 func embedLinuxKernel(params Params, kernelPath string) error {
 	return errors.New("building linux image is only supported on linux")
 }
+
+func embedFiles(params Params, callback func(mountDir string) error) error {
+	return errors.New("building linux image is only supported on linux")
+}