new(pkg,cmd): refactored builder script logic.

Builder script has been split in 3 different scripts:
* download libs
* download headers
* build

This way, we can reuse `download libs` script among all of them.
Moreover, it is useful to have a download headers script that is invokeable by itself,
because it has the logic to download and extract headers for a given distro.

Finally, fixed a couple of things with local builder:
* redirect stderr to stdout so that we catch errors too while building
* pre initialize envMap to an empty map, instead of nil
* manage KERNELDIR env var, if set, while building with dkms

The last point allows for consumer to pass `KERNELDIR` inside `envMap` local builder processor
argument to customize the build.

Signed-off-by: Federico Di Pierro <nierro92@gmail.com>

cmd/local.go

@@ -72,7 +72,7 @@ func NewLocalCmd(rootCommand *RootCmd, rootOpts *RootOptions, rootFlags *pflag.F
 	})
 	flagSet.BoolVar(&opts.useDKMS, "dkms", false, "Enforce usage of DKMS to build the kernel module.")
 	flagSet.StringVar(&opts.srcDir, "src-dir", "", "Enforce usage of local source dir to build drivers.")
-	flagSet.StringToStringVar(&opts.envMap, "env", nil, "Env variables to be enforced during the driver build.")
+	flagSet.StringToStringVar(&opts.envMap, "env", make(map[string]string), "Env variables to be enforced during the driver build.")
 	localCmd.PersistentFlags().AddFlagSet(flagSet)
 	return localCmd
 }

pkg/driverbuilder/builder/aliyunlinux.go

@@ -21,6 +21,9 @@ import (
 	"github.com/falcosecurity/driverkit/pkg/kernelrelease"
 )
 
+//go:embed templates/alinux_kernel.sh
+var alinuxKernelTemplate string
+
 //go:embed templates/alinux.sh
 var alinuxTemplate string
 
@@ -32,7 +35,6 @@ func init() {
 }
 
 type alinuxTemplateData struct {
-	commonTemplateData
 	KernelDownloadURL string
 }
 
@@ -43,6 +45,10 @@ func (c *alinux) Name() string {
 	return TargetTypeAlinux.String()
 }
 
+func (c *alinux) TemplateKernelUrlsScript() string {
+	return alinuxKernelTemplate
+}
+
 func (c *alinux) TemplateScript() string {
 	return alinuxTemplate
 }
@@ -51,10 +57,9 @@ func (c *alinux) URLs(kr kernelrelease.KernelRelease) ([]string, error) {
 	return fetchAlinuxKernelURLS(kr), nil
 }
 
-func (c *alinux) TemplateData(cfg Config, kr kernelrelease.KernelRelease, urls []string) interface{} {
+func (c *alinux) KernelTemplateData(_ kernelrelease.KernelRelease, urls []string) interface{} {
 	return alinuxTemplateData{
-		commonTemplateData: cfg.toTemplateData(c, kr),
-		KernelDownloadURL:  urls[0],
+		KernelDownloadURL: urls[0],
 	}
 }
 

pkg/driverbuilder/builder/almalinux.go

@@ -21,6 +21,9 @@ import (
 	"github.com/falcosecurity/driverkit/pkg/kernelrelease"
 )
 
+//go:embed templates/almalinux_kernel.sh
+var almaKernelTemplate string
+
 //go:embed templates/almalinux.sh
 var almaTemplate string
 
@@ -32,7 +35,6 @@ func init() {
 }
 
 type almaTemplateData struct {
-	commonTemplateData
 	KernelDownloadURL string
 }
 
@@ -44,6 +46,10 @@ func (c *alma) Name() string {
 	return TargetTypeAlma.String()
 }
 
+func (c *alma) TemplateKernelUrlsScript() string {
+	return almaKernelTemplate
+}
+
 func (c *alma) TemplateScript() string {
 	return almaTemplate
 }
@@ -52,10 +58,9 @@ func (c *alma) URLs(kr kernelrelease.KernelRelease) ([]string, error) {
 	return fetchAlmaKernelURLS(kr), nil
 }
 
-func (c *alma) TemplateData(cfg Config, kr kernelrelease.KernelRelease, urls []string) interface{} {
+func (c *alma) KernelTemplateData(_ kernelrelease.KernelRelease, urls []string) interface{} {
 	return almaTemplateData{
-		commonTemplateData: cfg.toTemplateData(c, kr),
-		KernelDownloadURL:  urls[0],
+		KernelDownloadURL: urls[0],
 	}
 }
 

pkg/driverbuilder/builder/amazonlinux.go

@@ -35,6 +35,9 @@ import (
 	"github.com/falcosecurity/driverkit/pkg/kernelrelease"
 )
 
+//go:embed templates/amazonlinux_kernel.sh
+var amazonlinuxKernelTemplate string
+
 //go:embed templates/amazonlinux.sh
 var amazonlinuxTemplate string
 
@@ -80,14 +83,15 @@ func init() {
 }
 
 type amazonlinuxTemplateData struct {
-	commonTemplateData
 	KernelDownloadURLs []string
 }
 
 func (a *amazonlinux) Name() string {
 	return TargetTypeAmazonLinux.String()
 }
 
+func (a *amazonlinux) TemplateKernelUrlsScript() string { return amazonlinuxKernelTemplate }
+
 func (a *amazonlinux) TemplateScript() string {
 	return amazonlinuxTemplate
 }
@@ -96,9 +100,8 @@ func (a *amazonlinux) URLs(kr kernelrelease.KernelRelease) ([]string, error) {
 	return fetchAmazonLinuxPackagesURLs(a, kr)
 }
 
-func (a *amazonlinux) TemplateData(c Config, kr kernelrelease.KernelRelease, urls []string) interface{} {
+func (a *amazonlinux) KernelTemplateData(_ kernelrelease.KernelRelease, urls []string) interface{} {
 	return amazonlinuxTemplateData{
-		commonTemplateData: c.toTemplateData(a, kr),
 		KernelDownloadURLs: urls,
 	}
 }

pkg/driverbuilder/builder/archlinux.go

@@ -22,6 +22,9 @@ import (
 	"github.com/falcosecurity/driverkit/pkg/kernelrelease"
 )
 
+//go:embed templates/archlinux_kernel.sh
+var archlinuxKernelTemplate string
+
 //go:embed templates/archlinux.sh
 var archlinuxTemplate string
 
@@ -37,14 +40,15 @@ type archlinux struct {
 }
 
 type archlinuxTemplateData struct {
-	commonTemplateData
 	KernelDownloadURL string
 }
 
 func (c *archlinux) Name() string {
 	return TargetTypeArchlinux.String()
 }
 
+func (c *archlinux) TemplateKernelUrlsScript() string { return archlinuxKernelTemplate }
+
 func (c *archlinux) TemplateScript() string {
 	return archlinuxTemplate
 }
@@ -140,9 +144,8 @@ func (c *archlinux) URLs(kr kernelrelease.KernelRelease) ([]string, error) {
 	return urls, nil
 }
 
-func (c *archlinux) TemplateData(cfg Config, kr kernelrelease.KernelRelease, urls []string) interface{} {
+func (c *archlinux) KernelTemplateData(_ kernelrelease.KernelRelease, urls []string) interface{} {
 	return archlinuxTemplateData{
-		commonTemplateData: cfg.toTemplateData(c, kr),
-		KernelDownloadURL:  urls[0],
+		KernelDownloadURL: urls[0],
 	}
 }

pkg/driverbuilder/builder/bottlerocket.go

@@ -35,9 +35,8 @@ func (b *bottlerocket) Name() string {
 	return TargetTypeBottlerocket.String()
 }
 
-func (b *bottlerocket) TemplateData(c Config, kr kernelrelease.KernelRelease, urls []string) interface{} {
+func (b *bottlerocket) KernelTemplateData(kr kernelrelease.KernelRelease, urls []string) interface{} {
 	return vanillaTemplateData{
-		commonTemplateData: c.toTemplateData(b, kr),
 		KernelDownloadURL:  urls[0],
 		KernelLocalVersion: kr.FullExtraversion,
 	}

pkg/driverbuilder/builder/builders.go

@@ -16,6 +16,7 @@ package builder
 
 import (
 	"bytes"
+	_ "embed"
 	"errors"
 	"fmt"
 	"log/slog"
@@ -51,6 +52,9 @@ const (
   sed -i s/'DRIVER_COMMIT ""'/'DRIVER_COMMIT "%s"'/g driver/src/driver_config.h`
 )
 
+//go:embed templates/libs_download.sh
+var libsDownloadTemplate string
+
 var HeadersNotFoundErr = errors.New("kernel headers not found")
 
 // Config contains all the configurations needed to build the kernel module or the eBPF probe.
@@ -70,33 +74,67 @@ func (c Config) ToProbeFullPath() string {
 }
 
 type commonTemplateData struct {
-	DriverBuildDir    string
-	ModuleDownloadURL string
-	ModuleDriverName  string
-	ModuleFullPath    string
-	BuildModule       bool
-	BuildProbe        bool
-	GCCVersion        string
-	CmakeCmd          string
+	DriverBuildDir   string
+	ModuleDriverName string
+	ModuleFullPath   string
+	BuildModule      bool
+	BuildProbe       bool
+	GCCVersion       string
+	CmakeCmd         string
 }
 
 // Builder represents a builder capable of generating a script for a driverkit target.
 type Builder interface {
 	Name() string
+	TemplateKernelUrlsScript() string
 	TemplateScript() string
 	URLs(kr kernelrelease.KernelRelease) ([]string, error)
-	TemplateData(c Config, kr kernelrelease.KernelRelease, urls []string) interface{} // error return type is managed
+	KernelTemplateData(kr kernelrelease.KernelRelease, urls []string) interface{} // error return type is managed
 }
 
-// MinimumURLsBuilder is an optional interface
+// MinimumURLsBuilder is an optional interface implemented by builders
 // to specify minimum number of requested headers urls
 type MinimumURLsBuilder interface {
 	MinimumURLs() int
 }
 
-func Script(b Builder, c Config, kr kernelrelease.KernelRelease) (string, error) {
-	t := template.New(b.Name())
-	parsed, err := t.Parse(b.TemplateScript())
+// TemplateDataSpecifier is an optional interface implemented by builders
+// to specify a custom template data instead of the default one.
+type TemplateDataSpecifier interface {
+	TemplateData(c Config, kr kernelrelease.KernelRelease) interface{}
+}
+
+type libsDownloadTemplateData struct {
+	DriverBuildDir    string
+	ModuleDownloadURL string
+}
+
+// LibsDownloadScript returns the script that downloads and configures libs repo at requested commit/tag
+func LibsDownloadScript(c Config) (string, error) {
+	t := template.New("download-libs")
+	parsed, err := t.Parse(libsDownloadTemplate)
+	if err != nil {
+		return "", err
+	}
+
+	td := libsDownloadTemplateData{
+		DriverBuildDir:    DriverDirectory,
+		ModuleDownloadURL: fmt.Sprintf("%s/%s.tar.gz", c.DownloadBaseURL, c.DriverVersion),
+	}
+
+	buf := bytes.NewBuffer(nil)
+	err = parsed.Execute(buf, td)
+	if err != nil {
+		return "", err
+	}
+
+	return buf.String(), nil
+}
+
+// KernelDownloadScript returns the script that will download and extract kernel headers
+func KernelDownloadScript(b Builder, c Config, kr kernelrelease.KernelRelease) (string, error) {
+	t := template.New("download-kernel")
+	parsed, err := t.Parse(b.TemplateKernelUrlsScript())
 	if err != nil {
 		return "", err
 	}
@@ -129,7 +167,7 @@ func Script(b Builder, c Config, kr kernelrelease.KernelRelease) (string, error)
 		return "", fmt.Errorf("not enough headers packages found; expected %d, found %d", minimumURLs, len(urls))
 	}
 
-	td := b.TemplateData(c, kr, urls)
+	td := b.KernelTemplateData(kr, urls)
 	if tdErr, ok := td.(error); ok {
 		return "", tdErr
 	}
@@ -139,6 +177,31 @@ func Script(b Builder, c Config, kr kernelrelease.KernelRelease) (string, error)
 	if err != nil {
 		return "", err
 	}
+
+	return buf.String(), nil
+}
+
+// Script retrieves the actually drivers building script
+func Script(b Builder, c Config, kr kernelrelease.KernelRelease) (string, error) {
+	t := template.New(b.Name())
+	parsed, err := t.Parse(b.TemplateScript())
+	if err != nil {
+		return "", err
+	}
+
+	var td interface{}
+	if bb, ok := b.(TemplateDataSpecifier); ok {
+		td = bb.TemplateData(c, kr)
+	} else {
+		td = c.toTemplateData(b, kr)
+	}
+
+	buf := bytes.NewBuffer(nil)
+	err = parsed.Execute(buf, td)
+	if err != nil {
+		return "", err
+	}
+
 	return buf.String(), nil
 }
 
@@ -305,13 +368,12 @@ func Targets() []string {
 func (c Config) toTemplateData(b Builder, kr kernelrelease.KernelRelease) commonTemplateData {
 	c.setGCCVersion(b, kr)
 	return commonTemplateData{
-		DriverBuildDir:    DriverDirectory,
-		ModuleDownloadURL: fmt.Sprintf("%s/%s.tar.gz", c.DownloadBaseURL, c.DriverVersion),
-		ModuleDriverName:  c.DriverName,
-		ModuleFullPath:    c.ToDriverFullPath(),
-		BuildModule:       len(c.ModuleFilePath) > 0,
-		BuildProbe:        len(c.ProbeFilePath) > 0,
-		GCCVersion:        c.GCCVersion,
+		DriverBuildDir:   DriverDirectory,
+		ModuleDriverName: c.DriverName,
+		ModuleFullPath:   c.ToDriverFullPath(),
+		BuildModule:      len(c.ModuleFilePath) > 0,
+		BuildProbe:       len(c.ProbeFilePath) > 0,
+		GCCVersion:       c.GCCVersion,
 		CmakeCmd: fmt.Sprintf(cmakeCmdFmt,
 			c.DriverName,
 			c.DriverName,

pkg/driverbuilder/builder/centos.go

@@ -22,6 +22,9 @@ import (
 	"github.com/falcosecurity/driverkit/pkg/kernelrelease"
 )
 
+//go:embed templates/centos_kernel.sh
+var centosKernelTemplate string
+
 //go:embed templates/centos.sh
 var centosTemplate string
 
@@ -37,14 +40,15 @@ type centos struct {
 }
 
 type centosTemplateData struct {
-	commonTemplateData
 	KernelDownloadURL string
 }
 
 func (c *centos) Name() string {
 	return TargetTypeCentos.String()
 }
 
+func (c *centos) TemplateKernelUrlsScript() string { return centosKernelTemplate }
+
 func (c *centos) TemplateScript() string {
 	return centosTemplate
 }
@@ -176,10 +180,9 @@ func (c *centos) URLs(kr kernelrelease.KernelRelease) ([]string, error) {
 	return urls, nil
 }
 
-func (c *centos) TemplateData(cfg Config, kr kernelrelease.KernelRelease, urls []string) interface{} {
+func (c *centos) KernelTemplateData(_ kernelrelease.KernelRelease, urls []string) interface{} {
 	return centosTemplateData{
-		commonTemplateData: cfg.toTemplateData(c, kr),
-		KernelDownloadURL:  urls[0],
+		KernelDownloadURL: urls[0],
 	}
 }