android_system_image that generates linker.config.pb

android_system_image module type is a specialization of the
android_filesystem module type. Currently, it adds a build rule for
creating linker.config.pb from the information about all the other files
in the filesystem and includes linker.config.pb to the filesystem as
well.

To do so, the filesystem module now provides a function pointer which
subtype modules like android_system_image can implement to pass extra
files that they want to package in the filesystem.

In addition, the linkerconfig package is revised to make it possible to
build linker.config.pb file outside of the package.

Bug: 185391776
Test: m microdroid and inspect etc/linker.config.pb in it.

Change-Id: Id89c40b519213062860d7306029b8413d8d36a2d

filesystem/system_image.go

@@ -0,0 +1,68 @@
+// Copyright (C) 2021 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package filesystem
+
+import (
+	"android/soong/android"
+	"android/soong/linkerconfig"
+)
+
+type systemImage struct {
+	filesystem
+
+	properties systemImageProperties
+}
+
+type systemImageProperties struct {
+	// Path to the input linker config json file.
+	Linker_config_src *string
+}
+
+// android_system_image is a specialization of android_filesystem for the 'system' partition.
+// Currently, the only difference is the inclusion of linker.config.pb file which specifies
+// the provided and the required libraries to and from APEXes.
+func systemImageFactory() android.Module {
+	module := &systemImage{}
+	module.AddProperties(&module.properties)
+	module.filesystem.buildExtraFiles = module.buildExtraFiles
+	initFilesystemModule(&module.filesystem)
+	return module
+}
+
+func (s *systemImage) buildExtraFiles(ctx android.ModuleContext, root android.OutputPath) android.OutputPaths {
+	lc := s.buildLinkerConfigFile(ctx, root)
+	// Add more files if needed
+	return []android.OutputPath{lc}
+}
+
+func (s *systemImage) buildLinkerConfigFile(ctx android.ModuleContext, root android.OutputPath) android.OutputPath {
+	input := android.PathForModuleSrc(ctx, android.String(s.properties.Linker_config_src))
+	output := root.Join(ctx, "system", "etc", "linker.config.pb")
+	var otherModules []android.Module
+	ctx.WalkDeps(func(child, parent android.Module) bool {
+		// Don't track direct dependencies that aren't not packaged
+		if parent == s {
+			if pi, ok := ctx.OtherModuleDependencyTag(child).(android.PackagingItem); !ok || !pi.IsPackagingItem() {
+				return false
+			}
+		}
+		otherModules = append(otherModules, child)
+		return true
+	})
+	builder := android.NewRuleBuilder(pctx, ctx)
+	linkerconfig.BuildLinkerConfig(ctx, builder, input, otherModules, output)
+	builder.Build("conv_linker_config", "Generate linker config protobuf "+output.String())
+	return output
+}