pkg/kernels: add cross-compilation feature

For example, on amd64, if the 'gcc-aarch64-linux-gnu' package is installed, LVH can cross compile an arm64 kernel on amd64. On arm64, if the 'gcc-x86-64-linux-gnu' package is install, LVH can cross compile an amd64 kernel on arm64. Signed-off-by: Mahe Tardy <[email protected]>
cilium · Mar 12, 2024 · 7e43e94 · 7e43e94
1 parent 3b98951
commit 7e43e94
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Showing 5 changed files with 71 additions and 18 deletions.
diff --git a/cmd/lvh/kernels/build.go b/cmd/lvh/kernels/build.go
@@ -12,14 +12,20 @@ import (
 )
 
 func buildCommand() *cobra.Command {
-	return &cobra.Command{
+	var arch string
+
+	cmd := &cobra.Command{
 		Use:   "build <kernel>",
 		Short: "build kernel",
 		Args:  cobra.ExactArgs(1),
 		RunE: func(cmd *cobra.Command, args []string) error {
 			log := logrus.New()
 			kname := args[0]
-			return kernels.BuildKernel(context.Background(), log, dirName, kname, false /* TODO: add fetch flag */)
+			return kernels.BuildKernel(context.Background(), log, dirName, kname, false /* TODO: add fetch flag */, arch)
 		},
 	}
+
+	cmd.Flags().StringVar(&arch, "arch", "", "target architecture to build the kernel, e.g. 'amd64' or 'arm64' (default to native architecture)")
+
+	return cmd
 }
diff --git a/cmd/lvh/kernels/configure.go b/cmd/lvh/kernels/configure.go
@@ -12,7 +12,9 @@ import (
 )
 
 func configureCommand() *cobra.Command {
-	return &cobra.Command{
+	var arch string
+
+	cmd := &cobra.Command{
 		Use:   "configure <kernel>",
 		Short: "configure kernel",
 		Args:  cobra.ExactArgs(1),
@@ -24,12 +26,16 @@ func configureCommand() *cobra.Command {
 			}
 
 			kname := args[0]
-			if err := kd.ConfigureKernel(context.Background(), log, kname); err != nil {
+			if err := kd.ConfigureKernel(context.Background(), log, kname, arch); err != nil {
 				log.Fatal(err)
 			}
 
 		},
 	}
+
+	cmd.Flags().StringVar(&arch, "arch", "", "target architecture to configure the kernel, e.g. 'amd64' or 'arm64' (default to native architecture)")
+
+	return cmd
 }
 
 func rawConfigureCommand() *cobra.Command {

diff --git a/pkg/arch/arch.go b/pkg/arch/arch.go
@@ -9,15 +9,36 @@ var ErrUnsupportedArch = fmt.Errorf("unsupported architecture: %s", runtime.GOAR
 
 // Target returns the Linux Makefile target to build the kernel, for historical
 // reasons, those are different between architectures.
-func Target() (string, error) {
-	switch runtime.GOARCH {
+func Target(arch string) (string, error) {
+	if arch == "" {
+		arch = runtime.GOARCH
+	}
+	switch arch {
 	case "amd64":
 		return "bzImage", nil
 	case "arm64":
 		return "Image.gz", nil
 	default:
-		return "", ErrUnsupportedArch
+		return "", fmt.Errorf("unsupported architecture for Makefile target: %s", arch)
+	}
+}
+
+func CrossCompiling(targetArch string) bool {
+	return targetArch != "" && targetArch != runtime.GOARCH
+}
+
+func CrossCompileMakeArgs(targetArch string) ([]string, error) {
+	if !CrossCompiling(targetArch) {
+		return nil, nil
+	}
+
+	switch targetArch {
+	case "arm64":
+		return []string{"ARCH=arm64", "CROSS_COMPILE=aarch64-linux-gnu-"}, nil
+	case "amd64":
+		return []string{"ARCH=x86_64", "CROSS_COMPILE=x86_64-linux-gnu-"}, nil
 	}
+	return nil, fmt.Errorf("unsupported architecture for cross-compilation: %s", targetArch)
 }
 
 func QemuBinary() (string, error) {

diff --git a/pkg/kernels/dir.go b/pkg/kernels/dir.go
@@ -46,12 +46,12 @@ func (kd *KernelsDir) RemoveKernelConfig(name string) *KernelConf {
 	return nil
 }
 
-func (kd *KernelsDir) ConfigureKernel(ctx context.Context, log *logrus.Logger, kernName string) error {
+func (kd *KernelsDir) ConfigureKernel(ctx context.Context, log *logrus.Logger, kernName string, targetArch string) error {
 	kc := kd.KernelConfig(kernName)
 	if kc == nil {
 		return fmt.Errorf("kernel '%s' not found", kernName)
 	}
-	return kd.configureKernel(ctx, log, kc)
+	return kd.configureKernel(ctx, log, kc, targetArch)
 }
 
 func (kd *KernelsDir) RawConfigure(ctx context.Context, log *logrus.Logger, kernDir, kernName string) error {
@@ -206,13 +206,21 @@ func (kd *KernelsDir) rawConfigureKernel(
 	return nil
 }
 
-func (kd *KernelsDir) configureKernel(ctx context.Context, log *logrus.Logger, kc *KernelConf) error {
+func (kd *KernelsDir) configureKernel(ctx context.Context, log *logrus.Logger, kc *KernelConf, targetArch string) error {
 	srcDir := filepath.Join(kd.Dir, kc.Name)
-	return kd.rawConfigureKernel(ctx, log, kc, srcDir, "defconfig", "prepare")
+	crossCompilationArgs, err := arch.CrossCompileMakeArgs(targetArch)
+	if err != nil {
+		return fmt.Errorf("failed to retrieve cross compilation args: %w", err)
+	}
+
+	configureMakeArgs := []string{"defconfig", "prepare"}
+	configureMakeArgs = append(configureMakeArgs, crossCompilationArgs...)
+
+	return kd.rawConfigureKernel(ctx, log, kc, srcDir, configureMakeArgs...)
 
 }
 
-func (kd *KernelsDir) buildKernel(ctx context.Context, log *logrus.Logger, kc *KernelConf) error {
+func (kd *KernelsDir) buildKernel(ctx context.Context, log *logrus.Logger, kc *KernelConf, targetArch string) error {
 	if err := CheckEnvironment(); err != nil {
 		return err
 	}
@@ -224,23 +232,35 @@ func (kd *KernelsDir) buildKernel(ctx context.Context, log *logrus.Logger, kc *K
 		return err
 	} else if !exists {
 		log.Info("Configuring kernel")
-		err = kd.configureKernel(ctx, log, kc)
+		err = kd.configureKernel(ctx, log, kc, targetArch)
 		if err != nil {
 			return fmt.Errorf("failed to configure kernel: %w", err)
 		}
 	}
 
 	ncpus := fmt.Sprintf("%d", runtime.NumCPU())
 
-	target, err := arch.Target()
+	target, err := arch.Target(targetArch)
 	if err != nil {
 		return fmt.Errorf("failed to get make target: %w", err)
 	}
-	if err := runAndLogMake(ctx, log, kc, "-C", srcDir, "-j", ncpus, target, "modules"); err != nil {
+
+	buildMakeArgs := []string{"-C", srcDir, "-j", ncpus, target, "modules"}
+
+	crossCompilationArgs, err := arch.CrossCompileMakeArgs(targetArch)
+	if err != nil {
+		return fmt.Errorf("failed to retrieve cross compilation args: %w", err)
+	}
+	buildMakeArgs = append(buildMakeArgs, crossCompilationArgs...)
+
+	if err := runAndLogMake(ctx, log, kc, buildMakeArgs...); err != nil {
 		return fmt.Errorf("buiding bzImage && modules failed: %w", err)
 	}
 
-	if err := runAndLogMake(ctx, log, kc, "-C", srcDir, "tar-pkg"); err != nil {
+	archiveMakeArgs := []string{"-C", srcDir, "tar-pkg"}
+	archiveMakeArgs = append(archiveMakeArgs, crossCompilationArgs...)
+
+	if err := runAndLogMake(ctx, log, kc, archiveMakeArgs...); err != nil {
 		return fmt.Errorf("build dir failed: %w", err)
 	}
 

diff --git a/pkg/kernels/kernels.go b/pkg/kernels/kernels.go
@@ -163,7 +163,7 @@ func FetchKernel(ctx context.Context, log *logrus.Logger, dir, kname string) err
 	return kurl.fetch(ctx, log, kd.Dir, kc.Name)
 }
 
-func BuildKernel(ctx context.Context, log *logrus.Logger, dir, kname string, fetch bool) error {
+func BuildKernel(ctx context.Context, log *logrus.Logger, dir, kname string, fetch bool, arch string) error {
 	kd, kc, kurl, err := getKernelInfo(dir, kname)
 	if err != nil {
 		return err
@@ -176,5 +176,5 @@ func BuildKernel(ctx context.Context, log *logrus.Logger, dir, kname string, fet
 
 	}
 
-	return kd.buildKernel(ctx, log, kc)
+	return kd.buildKernel(ctx, log, kc, arch)
 }