Add support for reading ELF package notes with section header (#2939)

* add support for reading ELF package notes with section header

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

* add systemd elf package fields to json schema

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

---------

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

syft/pkg/cataloger/binary/elf_package.go

@@ -2,6 +2,7 @@ package binary
 
 import (
 	"github.com/anchore/packageurl-go"
+	"github.com/anchore/syft/syft/cpe"
 	"github.com/anchore/syft/syft/file"
 	"github.com/anchore/syft/syft/pkg"
 )
@@ -23,13 +24,59 @@ func newELFPackage(metadata elfBinaryPackageNotes, locations file.LocationSet) p
 }
 
 func packageURL(metadata elfBinaryPackageNotes) string {
-	// TODO: what if the System value is not set?
+	var qualifiers []packageurl.Qualifier
+
+	os := metadata.OS
+	osVersion := metadata.OSVersion
+
+	atts, err := cpe.NewAttributes(metadata.OSCPE)
+	if err == nil {
+		// only "upgrade" the OS information if there is something more specific to use in it's place
+		if os == "" && osVersion == "" || os == "" && atts.Version != "" || atts.Product != "" && osVersion == "" {
+			os = atts.Product
+			osVersion = atts.Version
+		}
+	}
+
+	if os != "" {
+		osQualifier := os
+		if osVersion != "" {
+			osQualifier += "-" + osVersion
+		}
+		qualifiers = append(qualifiers, packageurl.Qualifier{
+			Key:   "distro",
+			Value: osQualifier,
+		})
+	}
+
+	ty := purlDistroType(metadata.Type)
+
+	namespace := os
+
+	if ty == packageurl.TypeGeneric || os == "" {
+		namespace = metadata.System
+	}
+
 	return packageurl.NewPackageURL(
-		packageurl.TypeGeneric,
-		metadata.System,
+		ty,
+		namespace,
 		metadata.Name,
 		metadata.Version,
-		nil,
+		qualifiers,
 		"",
 	).ToString()
 }
+
+func purlDistroType(ty string) string {
+	switch ty {
+	case "rpm":
+		return packageurl.TypeRPM
+	case "deb":
+		return packageurl.TypeDebian
+	case "apk":
+		return packageurl.TypeAlpine
+	case "alpm":
+		return "alpm"
+	}
+	return packageurl.TypeGeneric
+}