diff --git a/android/androidmk.go b/android/androidmk.go
index a670656..6ab4a24 100644
--- a/android/androidmk.go
+++ b/android/androidmk.go
@@ -12,6 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// This file offers AndroidMkEntriesProvider, which individual modules implement to output
+// Android.mk entries that contain information about the modules built through Soong. Kati reads
+// and combines them with the legacy Make-based module definitions to produce the complete view of
+// the source tree, which makes this a critical point of Make-Soong interoperability.
+//
+// Naturally, Soong-only builds do not rely on this mechanism.
+
 package android
 
 import (
@@ -36,8 +43,8 @@
 	ctx.RegisterSingletonType("androidmk", AndroidMkSingleton)
 }
 
-// Deprecated: consider using AndroidMkEntriesProvider instead, especially if you're not going to
-// use the Custom function.
+// Deprecated: Use AndroidMkEntriesProvider instead, especially if you're not going to use the
+// Custom function. It's easier to use and test.
 type AndroidMkDataProvider interface {
 	AndroidMk() AndroidMkData
 	BaseModuleName() string
@@ -63,37 +70,82 @@
 
 type AndroidMkExtraFunc func(w io.Writer, outputFile Path)
 
-// Allows modules to customize their Android*.mk output.
+// Interface for modules to declare their Android.mk outputs. Note that every module needs to
+// implement this in order to be included in the final Android-<product_name>.mk output, even if
+// they only need to output the common set of entries without any customizations.
 type AndroidMkEntriesProvider interface {
+	// Returns AndroidMkEntries objects that contain all basic info plus extra customization data
+	// if needed. This is the core func to implement.
+	// Note that one can return multiple objects. For example, java_library may return an additional
+	// AndroidMkEntries object for its hostdex sub-module.
 	AndroidMkEntries() []AndroidMkEntries
+	// Modules don't need to implement this as it's already implemented by ModuleBase.
+	// AndroidMkEntries uses BaseModuleName() instead of ModuleName() because certain modules
+	// e.g. Prebuilts, override the Name() func and return modified names.
+	// If a different name is preferred, use SubName or OverrideName in AndroidMkEntries.
 	BaseModuleName() string
 }
 
+// The core data struct that modules use to provide their Android.mk data.
 type AndroidMkEntries struct {
-	Class           string
-	SubName         string
-	OverrideName    string
-	DistFiles       TaggedDistFiles
-	OutputFile      OptionalPath
-	Disabled        bool
-	Include         string
-	Required        []string
-	Host_required   []string
+	// Android.mk class string, e.g EXECUTABLES, JAVA_LIBRARIES, ETC
+	Class string
+	// Optional suffix to append to the module name. Useful when a module wants to return multiple
+	// AndroidMkEntries objects. For example, when a java_library returns an additional entry for
+	// its hostdex sub-module, this SubName field is set to "-hostdex" so that it can have a
+	// different name than the parent's.
+	SubName string
+	// If set, this value overrides the base module name. SubName is still appended.
+	OverrideName string
+	// Dist files to output
+	DistFiles TaggedDistFiles
+	// The output file for Kati to process and/or install. If absent, the module is skipped.
+	OutputFile OptionalPath
+	// If true, the module is skipped and does not appear on the final Android-<product name>.mk
+	// file. Useful when a module needs to be skipped conditionally.
+	Disabled bool
+	// The postprocessing mk file to include, e.g. $(BUILD_SYSTEM)/soong_cc_prebuilt.mk
+	// If not set, $(BUILD_SYSTEM)/prebuilt.mk is used.
+	Include string
+	// Required modules that need to be built and included in the final build output when building
+	// this module.
+	Required []string
+	// Required host modules that need to be built and included in the final build output when
+	// building this module.
+	Host_required []string
+	// Required device modules that need to be built and included in the final build output when
+	// building this module.
 	Target_required []string
 
 	header bytes.Buffer
 	footer bytes.Buffer
 
+	// Funcs to append additional Android.mk entries or modify the common ones. Multiple funcs are
+	// accepted so that common logic can be factored out as a shared func.
 	ExtraEntries []AndroidMkExtraEntriesFunc
+	// Funcs to add extra lines to the module's Android.mk output. Unlike AndroidMkExtraEntriesFunc,
+	// which simply sets Make variable values, this can be used for anything since it can write any
+	// Make statements directly to the final Android-*.mk file.
+	// Primarily used to call macros or declare/update Make targets.
 	ExtraFooters []AndroidMkExtraFootersFunc
 
-	EntryMap   map[string][]string
+	// A map that holds the up-to-date Make variable values. Can be accessed from tests.
+	EntryMap map[string][]string
+	// A list of EntryMap keys in insertion order. This serves a few purposes:
+	// 1. Prevents churns. Golang map doesn't provide consistent iteration order, so without this,
+	// the outputted Android-*.mk file may change even though there have been no content changes.
+	// 2. Allows modules to refer to other variables, like LOCAL_BAR_VAR := $(LOCAL_FOO_VAR),
+	// without worrying about the variables being mixed up in the actual mk file.
+	// 3. Makes troubleshooting and spotting errors easier.
 	entryOrder []string
 }
 
 type AndroidMkExtraEntriesFunc func(entries *AndroidMkEntries)
 type AndroidMkExtraFootersFunc func(w io.Writer, name, prefix, moduleDir string, entries *AndroidMkEntries)
 
+// Utility funcs to manipulate Android.mk variable entries.
+
+// SetString sets a Make variable with the given name to the given value.
 func (a *AndroidMkEntries) SetString(name, value string) {
 	if _, ok := a.EntryMap[name]; !ok {
 		a.entryOrder = append(a.entryOrder, name)
@@ -101,6 +153,7 @@
 	a.EntryMap[name] = []string{value}
 }
 
+// SetPath sets a Make variable with the given name to the given path string.
 func (a *AndroidMkEntries) SetPath(name string, path Path) {
 	if _, ok := a.EntryMap[name]; !ok {
 		a.entryOrder = append(a.entryOrder, name)
@@ -108,12 +161,15 @@
 	a.EntryMap[name] = []string{path.String()}
 }
 
+// SetOptionalPath sets a Make variable with the given name to the given path string if it is valid.
+// It is a no-op if the given path is invalid.
 func (a *AndroidMkEntries) SetOptionalPath(name string, path OptionalPath) {
 	if path.Valid() {
 		a.SetPath(name, path.Path())
 	}
 }
 
+// AddPath appends the given path string to a Make variable with the given name.
 func (a *AndroidMkEntries) AddPath(name string, path Path) {
 	if _, ok := a.EntryMap[name]; !ok {
 		a.entryOrder = append(a.entryOrder, name)
@@ -121,12 +177,15 @@
 	a.EntryMap[name] = append(a.EntryMap[name], path.String())
 }
 
+// AddOptionalPath appends the given path string to a Make variable with the given name if it is
+// valid. It is a no-op if the given path is invalid.
 func (a *AndroidMkEntries) AddOptionalPath(name string, path OptionalPath) {
 	if path.Valid() {
 		a.AddPath(name, path.Path())
 	}
 }
 
+// SetPaths sets a Make variable with the given name to a slice of the given path strings.
 func (a *AndroidMkEntries) SetPaths(name string, paths Paths) {
 	if _, ok := a.EntryMap[name]; !ok {
 		a.entryOrder = append(a.entryOrder, name)
@@ -134,12 +193,15 @@
 	a.EntryMap[name] = paths.Strings()
 }
 
+// SetOptionalPaths sets a Make variable with the given name to a slice of the given path strings
+// only if there are a non-zero amount of paths.
 func (a *AndroidMkEntries) SetOptionalPaths(name string, paths Paths) {
 	if len(paths) > 0 {
 		a.SetPaths(name, paths)
 	}
 }
 
+// AddPaths appends the given path strings to a Make variable with the given name.
 func (a *AndroidMkEntries) AddPaths(name string, paths Paths) {
 	if _, ok := a.EntryMap[name]; !ok {
 		a.entryOrder = append(a.entryOrder, name)
@@ -147,6 +209,8 @@
 	a.EntryMap[name] = append(a.EntryMap[name], paths.Strings()...)
 }
 
+// SetBoolIfTrue sets a Make variable with the given name to true if the given flag is true.
+// It is a no-op if the given flag is false.
 func (a *AndroidMkEntries) SetBoolIfTrue(name string, flag bool) {
 	if flag {
 		if _, ok := a.EntryMap[name]; !ok {
@@ -156,6 +220,7 @@
 	}
 }
 
+// SetBool sets a Make variable with the given name to if the given bool flag value.
 func (a *AndroidMkEntries) SetBool(name string, flag bool) {
 	if _, ok := a.EntryMap[name]; !ok {
 		a.entryOrder = append(a.entryOrder, name)
@@ -167,6 +232,7 @@
 	}
 }
 
+// AddStrings appends the given strings to a Make variable with the given name.
 func (a *AndroidMkEntries) AddStrings(name string, value ...string) {
 	if len(value) == 0 {
 		return
@@ -368,6 +434,8 @@
 	return generateDistContributionsForMake(distContributions)
 }
 
+// fillInEntries goes through the common variable processing and calls the extra data funcs to
+// generate and fill in AndroidMkEntries's in-struct data, ready to be flushed to a file.
 func (a *AndroidMkEntries) fillInEntries(config Config, bpPath string, mod blueprint.Module) {
 	a.EntryMap = make(map[string][]string)
 	amod := mod.(Module).base()
@@ -488,6 +556,8 @@
 	}
 }
 
+// write  flushes the AndroidMkEntries's in-struct data populated by AndroidMkEntries into the
+// given Writer object.
 func (a *AndroidMkEntries) write(w io.Writer) {
 	if a.Disabled {
 		return
@@ -508,6 +578,8 @@
 	return strings.Split(string(a.footer.Bytes()), "\n")
 }
 
+// AndroidMkSingleton is a singleton to collect Android.mk data from all modules and dump them into
+// the final Android-<product_name>.mk file output.
 func AndroidMkSingleton() Singleton {
 	return &androidMkSingleton{}
 }
@@ -515,6 +587,7 @@
 type androidMkSingleton struct{}
 
 func (c *androidMkSingleton) GenerateBuildActions(ctx SingletonContext) {
+	// Skip if Soong wasn't invoked from Make.
 	if !ctx.Config().KatiEnabled() {
 		return
 	}
@@ -525,6 +598,8 @@
 		androidMkModulesList = append(androidMkModulesList, module)
 	})
 
+	// Sort the module list by the module names to eliminate random churns, which may erroneously
+	// invoke additional build processes.
 	sort.SliceStable(androidMkModulesList, func(i, j int) bool {
 		return ctx.ModuleName(androidMkModulesList[i]) < ctx.ModuleName(androidMkModulesList[j])
 	})
@@ -617,6 +692,8 @@
 	}
 }
 
+// A simple, special Android.mk entry output func to make it possible to build blueprint tools using
+// m by making them phony targets.
 func translateGoBinaryModule(ctx SingletonContext, w io.Writer, mod blueprint.Module,
 	goBinary bootstrap.GoBinaryTool) error {
 
@@ -649,6 +726,8 @@
 	data.Target_required = data.Entries.Target_required
 }
 
+// A support func for the deprecated AndroidMkDataProvider interface. Use AndroidMkEntryProvider
+// instead.
 func translateAndroidModule(ctx SingletonContext, w io.Writer, mod blueprint.Module,
 	provider AndroidMkDataProvider) error {
 
@@ -695,6 +774,8 @@
 	return nil
 }
 
+// A support func for the deprecated AndroidMkDataProvider interface. Use AndroidMkEntryProvider
+// instead.
 func WriteAndroidMkData(w io.Writer, data AndroidMkData) {
 	if data.Disabled {
 		return
@@ -742,11 +823,14 @@
 		module.Os() == LinuxBionic
 }
 
+// A utility func to format LOCAL_TEST_DATA outputs. See the comments on DataPath to understand how
+// to use this func.
 func AndroidMkDataPaths(data []DataPath) []string {
 	var testFiles []string
 	for _, d := range data {
 		rel := d.SrcPath.Rel()
 		path := d.SrcPath.String()
+		// LOCAL_TEST_DATA requires the rel portion of the path to be removed from the path.
 		if !strings.HasSuffix(path, rel) {
 			panic(fmt.Errorf("path %q does not end with %q", path, rel))
 		}
diff --git a/android/arch.go b/android/arch.go
index df407d4..34f9b29 100644
--- a/android/arch.go
+++ b/android/arch.go
@@ -1337,17 +1337,6 @@
 		addTarget(BuildOs, *variables.HostSecondaryArch, nil, nil, nil, NativeBridgeDisabled, nil, nil)
 	}
 
-	// An optional host target that uses the Bionic glibc runtime.
-	if Bool(config.Host_bionic) {
-		addTarget(LinuxBionic, "x86_64", nil, nil, nil, NativeBridgeDisabled, nil, nil)
-	}
-
-	// An optional cross-compiled host target that uses the Bionic glibc runtime on an arm64
-	// architecture.
-	if Bool(config.Host_bionic_arm64) {
-		addTarget(LinuxBionic, "arm64", nil, nil, nil, NativeBridgeDisabled, nil, nil)
-	}
-
 	// Optional cross-compiled host targets, generally Windows.
 	if String(variables.CrossHost) != "" {
 		crossHostOs := osByName(*variables.CrossHost)
@@ -1437,53 +1426,6 @@
 	abi         []string
 }
 
-// getMegaDeviceConfig returns a list of archConfigs for every architecture simultaneously.
-func getMegaDeviceConfig() []archConfig {
-	return []archConfig{
-		{"arm", "armv7-a", "generic", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "generic", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a7", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a8", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a9", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a15", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a53", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a53.a57", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a72", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a73", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a75", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "cortex-a76", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "krait", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "kryo", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "kryo385", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "exynos-m1", []string{"armeabi-v7a"}},
-		{"arm", "armv7-a-neon", "exynos-m2", []string{"armeabi-v7a"}},
-		{"arm64", "armv8-a", "cortex-a53", []string{"arm64-v8a"}},
-		{"arm64", "armv8-a", "cortex-a72", []string{"arm64-v8a"}},
-		{"arm64", "armv8-a", "cortex-a73", []string{"arm64-v8a"}},
-		{"arm64", "armv8-a", "kryo", []string{"arm64-v8a"}},
-		{"arm64", "armv8-a", "exynos-m1", []string{"arm64-v8a"}},
-		{"arm64", "armv8-a", "exynos-m2", []string{"arm64-v8a"}},
-		{"arm64", "armv8-2a", "kryo385", []string{"arm64-v8a"}},
-		{"arm64", "armv8-2a-dotprod", "cortex-a55", []string{"arm64-v8a"}},
-		{"arm64", "armv8-2a-dotprod", "cortex-a75", []string{"arm64-v8a"}},
-		{"arm64", "armv8-2a-dotprod", "cortex-a76", []string{"arm64-v8a"}},
-		{"x86", "", "", []string{"x86"}},
-		{"x86", "atom", "", []string{"x86"}},
-		{"x86", "haswell", "", []string{"x86"}},
-		{"x86", "ivybridge", "", []string{"x86"}},
-		{"x86", "sandybridge", "", []string{"x86"}},
-		{"x86", "silvermont", "", []string{"x86"}},
-		{"x86", "stoneyridge", "", []string{"x86"}},
-		{"x86", "x86_64", "", []string{"x86"}},
-		{"x86_64", "", "", []string{"x86_64"}},
-		{"x86_64", "haswell", "", []string{"x86_64"}},
-		{"x86_64", "ivybridge", "", []string{"x86_64"}},
-		{"x86_64", "sandybridge", "", []string{"x86_64"}},
-		{"x86_64", "silvermont", "", []string{"x86_64"}},
-		{"x86_64", "stoneyridge", "", []string{"x86_64"}},
-	}
-}
-
 // getNdkAbisConfig returns a list of archConfigs for the ABIs supported by the NDK.
 func getNdkAbisConfig() []archConfig {
 	return []archConfig{
diff --git a/android/config.go b/android/config.go
index 57ab70b..9882d55 100644
--- a/android/config.go
+++ b/android/config.go
@@ -54,28 +54,9 @@
 	isPreview: true,
 }
 
-// configFileName is the name the file containing FileConfigurableOptions from
-// soong_ui for the soong_build primary builder.
-const configFileName = "soong.config"
-
-// productVariablesFileName contain the product configuration variables from soong_ui for the
-// soong_build primary builder and Kati.
+// The product variables file name, containing product config from Kati.
 const productVariablesFileName = "soong.variables"
 
-// A FileConfigurableOptions contains options which can be configured by the
-// config file. These will be included in the config struct.
-type FileConfigurableOptions struct {
-	Mega_device       *bool `json:",omitempty"`
-	Host_bionic       *bool `json:",omitempty"`
-	Host_bionic_arm64 *bool `json:",omitempty"`
-}
-
-// SetDefaultConfig resets the receiving FileConfigurableOptions to default
-// values.
-func (f *FileConfigurableOptions) SetDefaultConfig() {
-	*f = FileConfigurableOptions{}
-}
-
 // A Config object represents the entire build configuration for Android.
 type Config struct {
 	*config
@@ -97,12 +78,8 @@
 type VendorConfig soongconfig.SoongConfig
 
 // Definition of general build configuration for soong_build. Some of these
-// configuration values are generated from soong_ui for soong_build,
-// communicated over JSON files like soong.config or soong.variables.
+// product configuration values are read from Kati-generated soong.variables.
 type config struct {
-	// Options configurable with soong.confg
-	FileConfigurableOptions
-
 	// Options configurable with soong.variables
 	productVariables productVariables
 
@@ -113,7 +90,6 @@
 	// purposes.
 	BazelContext BazelContext
 
-	ConfigFileName           string
 	ProductVariablesFileName string
 
 	Targets                  map[OsType][]Target
@@ -170,11 +146,6 @@
 }
 
 func loadConfig(config *config) error {
-	err := loadFromConfigFile(&config.FileConfigurableOptions, absolutePath(config.ConfigFileName))
-	if err != nil {
-		return err
-	}
-
 	return loadFromConfigFile(&config.productVariables, absolutePath(config.ProductVariablesFileName))
 }
 
@@ -384,7 +355,6 @@
 func NewConfig(srcDir, buildDir string, moduleListFile string) (Config, error) {
 	// Make a config with default options.
 	config := &config{
-		ConfigFileName:           filepath.Join(buildDir, configFileName),
 		ProductVariablesFileName: filepath.Join(buildDir, productVariablesFileName),
 
 		env: originalEnv,
@@ -439,9 +409,7 @@
 	targets[CommonOS] = []Target{commonTargetMap[CommonOS.Name]}
 
 	var archConfig []archConfig
-	if Bool(config.Mega_device) {
-		archConfig = getMegaDeviceConfig()
-	} else if config.NdkAbis() {
+	if config.NdkAbis() {
 		archConfig = getNdkAbisConfig()
 	} else if config.AmlAbis() {
 		archConfig = getAmlAbisConfig()
@@ -864,11 +832,6 @@
 	return c.Targets[Android][0].Arch.ArchType
 }
 
-func (c *config) SkipMegaDeviceInstall(path string) bool {
-	return Bool(c.Mega_device) &&
-		strings.HasPrefix(path, filepath.Join(c.buildDir, "target", "product"))
-}
-
 func (c *config) SanitizeHost() []string {
 	return append([]string(nil), c.productVariables.SanitizeHost...)
 }
diff --git a/android/config_test.go b/android/config_test.go
index 68f68a0..7bfc800 100644
--- a/android/config_test.go
+++ b/android/config_test.go
@@ -78,11 +78,6 @@
 	if err != nil {
 		t.Errorf(err.Error())
 	}
-
-	validateConfigAnnotations(&FileConfigurableOptions{})
-	if err != nil {
-		t.Errorf(err.Error())
-	}
 }
 
 func TestMissingVendorConfig(t *testing.T) {
diff --git a/android/module.go b/android/module.go
index d680baa..b6729c0 100644
--- a/android/module.go
+++ b/android/module.go
@@ -2399,10 +2399,6 @@
 		if m.Config().KatiEnabled() && !m.InstallBypassMake() {
 			return true
 		}
-
-		if m.Config().SkipMegaDeviceInstall(fullInstallPath.String()) {
-			return true
-		}
 	}
 
 	return false
diff --git a/cc/binary.go b/cc/binary.go
index fbd293e..fa3966f 100644
--- a/cc/binary.go
+++ b/cc/binary.go
@@ -373,7 +373,7 @@
 	if String(binary.Properties.Prefix_symbols) != "" {
 		afterPrefixSymbols := outputFile
 		outputFile = android.PathForModuleOut(ctx, "unprefixed", fileName)
-		TransformBinaryPrefixSymbols(ctx, String(binary.Properties.Prefix_symbols), outputFile,
+		transformBinaryPrefixSymbols(ctx, String(binary.Properties.Prefix_symbols), outputFile,
 			builderFlags, afterPrefixSymbols)
 	}
 
@@ -428,13 +428,13 @@
 	linkerDeps = append(linkerDeps, flags.LdFlagsDeps...)
 
 	// Register link action.
-	TransformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs, deps.StaticLibs,
+	transformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs, deps.StaticLibs,
 		deps.LateStaticLibs, deps.WholeStaticLibs, linkerDeps, deps.CrtBegin, deps.CrtEnd, true,
 		builderFlags, outputFile, nil)
 
 	objs.coverageFiles = append(objs.coverageFiles, deps.StaticLibObjs.coverageFiles...)
 	objs.coverageFiles = append(objs.coverageFiles, deps.WholeStaticLibObjs.coverageFiles...)
-	binary.coverageOutputFile = TransformCoverageFilesToZip(ctx, objs, binary.getStem(ctx))
+	binary.coverageOutputFile = transformCoverageFilesToZip(ctx, objs, binary.getStem(ctx))
 
 	// Need to determine symlinks early since some targets (ie APEX) need this
 	// information but will not call 'install'
diff --git a/cc/builder.go b/cc/builder.go
index 81c09b1..439e372 100644
--- a/cc/builder.go
+++ b/cc/builder.go
@@ -19,7 +19,6 @@
 // functions.
 
 import (
-	"fmt"
 	"path/filepath"
 	"runtime"
 	"strings"
@@ -40,6 +39,7 @@
 var (
 	pctx = android.NewPackageContext("android/soong/cc")
 
+	// Rule to invoke gcc with given command, flags, and dependencies. Outputs a .d depfile.
 	cc = pctx.AndroidRemoteStaticRule("cc", android.RemoteRuleSupports{Goma: true, RBE: true},
 		blueprint.RuleParams{
 			Depfile:     "${out}.d",
@@ -49,6 +49,7 @@
 		},
 		"ccCmd", "cFlags")
 
+	// Rule to invoke gcc with given command and flags, but no dependencies.
 	ccNoDeps = pctx.AndroidStaticRule("ccNoDeps",
 		blueprint.RuleParams{
 			Command:     "$relPwd $ccCmd -c $cFlags -o $out $in",
@@ -56,6 +57,8 @@
 		},
 		"ccCmd", "cFlags")
 
+	// Rules to invoke ld to link binaries. Uses a .rsp file to list dependencies, as there may
+	// be many.
 	ld, ldRE = remoteexec.StaticRules(pctx, "ld",
 		blueprint.RuleParams{
 			Command: "$reTemplate$ldCmd ${crtBegin} @${out}.rsp " +
@@ -76,6 +79,7 @@
 			Platform:        map[string]string{remoteexec.PoolKey: "${config.RECXXLinksPool}"},
 		}, []string{"ldCmd", "crtBegin", "libFlags", "crtEnd", "ldFlags", "extraLibFlags"}, []string{"implicitInputs", "implicitOutputs"})
 
+	// Rules for .o files to combine to other .o files, using ld partial linking.
 	partialLd, partialLdRE = remoteexec.StaticRules(pctx, "partialLd",
 		blueprint.RuleParams{
 			// Without -no-pie, clang 7.0 adds -pie to link Android files,
@@ -91,6 +95,7 @@
 			Platform:        map[string]string{remoteexec.PoolKey: "${config.RECXXLinksPool}"},
 		}, []string{"ldCmd", "ldFlags"}, []string{"implicitInputs", "inCommaList", "implicitOutputs"})
 
+	// Rule to invoke `ar` with given cmd and flags, but no static library depenencies.
 	ar = pctx.AndroidStaticRule("ar",
 		blueprint.RuleParams{
 			Command:        "rm -f ${out} && $arCmd $arFlags $out @${out}.rsp",
@@ -100,6 +105,8 @@
 		},
 		"arCmd", "arFlags")
 
+	// Rule to invoke `ar` with given cmd, flags, and library dependencies. Generates a .a
+	// (archive) file from .o files.
 	arWithLibs = pctx.AndroidStaticRule("arWithLibs",
 		blueprint.RuleParams{
 			Command:        "rm -f ${out} && $arCmd $arObjFlags $out @${out}.rsp && $arCmd $arLibFlags $out $arLibs",
@@ -109,12 +116,7 @@
 		},
 		"arCmd", "arObjFlags", "arObjs", "arLibFlags", "arLibs")
 
-	darwinStrip = pctx.AndroidStaticRule("darwinStrip",
-		blueprint.RuleParams{
-			Command:     "${config.MacStripPath} -u -r -o $out $in",
-			CommandDeps: []string{"${config.MacStripPath}"},
-		})
-
+	// Rule to run objcopy --prefix-symbols (to prefix all symbols in a file with a given string).
 	prefixSymbols = pctx.AndroidStaticRule("prefixSymbols",
 		blueprint.RuleParams{
 			Command:     "$objcopyCmd --prefix-symbols=${prefix} ${in} ${out}",
@@ -125,6 +127,24 @@
 	_ = pctx.SourcePathVariable("stripPath", "build/soong/scripts/strip.sh")
 	_ = pctx.SourcePathVariable("xzCmd", "prebuilts/build-tools/${config.HostPrebuiltTag}/bin/xz")
 
+	// Rule to invoke `strip` (to discard symbols and data from object files).
+	strip = pctx.AndroidStaticRule("strip",
+		blueprint.RuleParams{
+			Depfile:     "${out}.d",
+			Deps:        blueprint.DepsGCC,
+			Command:     "CROSS_COMPILE=$crossCompile XZ=$xzCmd CLANG_BIN=${config.ClangBin} $stripPath ${args} -i ${in} -o ${out} -d ${out}.d",
+			CommandDeps: []string{"$stripPath", "$xzCmd"},
+			Pool:        darwinStripPool,
+		},
+		"args", "crossCompile")
+
+	// Rule to invoke `strip` (to discard symbols and data from object files) on darwin architecture.
+	darwinStrip = pctx.AndroidStaticRule("darwinStrip",
+		blueprint.RuleParams{
+			Command:     "${config.MacStripPath} -u -r -o $out $in",
+			CommandDeps: []string{"${config.MacStripPath}"},
+		})
+
 	// b/132822437: objcopy uses a file descriptor per .o file when called on .a files, which runs the system out of
 	// file descriptors on darwin.  Limit concurrent calls to 5 on darwin.
 	darwinStripPool = func() blueprint.Pool {
@@ -137,18 +157,9 @@
 		}
 	}()
 
-	strip = pctx.AndroidStaticRule("strip",
-		blueprint.RuleParams{
-			Depfile:     "${out}.d",
-			Deps:        blueprint.DepsGCC,
-			Command:     "CROSS_COMPILE=$crossCompile XZ=$xzCmd CLANG_BIN=${config.ClangBin} $stripPath ${args} -i ${in} -o ${out} -d ${out}.d",
-			CommandDeps: []string{"$stripPath", "$xzCmd"},
-			Pool:        darwinStripPool,
-		},
-		"args", "crossCompile")
-
 	_ = pctx.SourcePathVariable("archiveRepackPath", "build/soong/scripts/archive_repack.sh")
 
+	// Rule to repack an archive (.a) file with a subset of object files.
 	archiveRepack = pctx.AndroidStaticRule("archiveRepack",
 		blueprint.RuleParams{
 			Depfile:     "${out}.d",
@@ -158,6 +169,7 @@
 		},
 		"objects")
 
+	// Rule to create an empty file at a given path.
 	emptyFile = pctx.AndroidStaticRule("emptyFile",
 		blueprint.RuleParams{
 			Command: "rm -f $out && touch $out",
@@ -165,6 +177,7 @@
 
 	_ = pctx.SourcePathVariable("tocPath", "build/soong/scripts/toc.sh")
 
+	// A rule for extracting a table of contents from a shared library (.so).
 	toc = pctx.AndroidStaticRule("toc",
 		blueprint.RuleParams{
 			Depfile:     "${out}.d",
@@ -175,6 +188,7 @@
 		},
 		"crossCompile", "format")
 
+	// Rule for invoking clang-tidy (a clang-based linter).
 	clangTidy, clangTidyRE = remoteexec.StaticRules(pctx, "clangTidy",
 		blueprint.RuleParams{
 			Command:     "rm -f $out && $reTemplate${config.ClangBin}/clang-tidy $tidyFlags $in -- $cFlags && touch $out",
@@ -193,6 +207,7 @@
 
 	_ = pctx.SourcePathVariable("yasmCmd", "prebuilts/misc/${config.HostPrebuiltTag}/yasm/yasm")
 
+	// Rule for invoking yasm to compile .asm assembly files.
 	yasm = pctx.AndroidStaticRule("yasm",
 		blueprint.RuleParams{
 			Command:     "$yasmCmd $asFlags -o $out $in && $yasmCmd $asFlags -M $in >$out.d",
@@ -202,6 +217,7 @@
 		},
 		"asFlags")
 
+	// Rule to invoke windres, for interaction with Windows resources.
 	windres = pctx.AndroidStaticRule("windres",
 		blueprint.RuleParams{
 			Command:     "$windresCmd $flags -I$$(dirname $in) -i $in -o $out --preprocessor \"${config.ClangBin}/clang -E -xc-header -DRC_INVOKED\"",
@@ -220,13 +236,15 @@
 			Labels:       map[string]string{"type": "abi-dump", "tool": "header-abi-dumper"},
 			ExecStrategy: "${config.REAbiDumperExecStrategy}",
 			Platform: map[string]string{
-				remoteexec.PoolKey:      "${config.RECXXPool}",
+				remoteexec.PoolKey: "${config.RECXXPool}",
 			},
 		}, []string{"cFlags", "exportDirs"}, nil)
 
 	_ = pctx.SourcePathVariable("sAbiLinker", "prebuilts/clang-tools/${config.HostPrebuiltTag}/bin/header-abi-linker")
 	_ = pctx.SourcePathVariable("sAbiLinkerLibs", "prebuilts/clang-tools/${config.HostPrebuiltTag}/lib64")
 
+	// Rule to combine .dump sAbi dump files from multiple source files into a single .ldump
+	// sAbi dump file.
 	sAbiLink, sAbiLinkRE = remoteexec.StaticRules(pctx, "sAbiLink",
 		blueprint.RuleParams{
 			Command:        "$reTemplate$sAbiLinker -o ${out} $symbolFilter -arch $arch  $exportedHeaderFlags @${out}.rsp ",
@@ -245,6 +263,7 @@
 
 	_ = pctx.SourcePathVariable("sAbiDiffer", "prebuilts/clang-tools/${config.HostPrebuiltTag}/bin/header-abi-diff")
 
+	// Rule to compare linked sAbi dump files (.ldump).
 	sAbiDiff = pctx.RuleFunc("sAbiDiff",
 		func(ctx android.PackageRuleContext) blueprint.RuleParams {
 			commandStr := "($sAbiDiffer ${extraFlags} -lib ${libName} -arch ${arch} -o ${out} -new ${in} -old ${referenceDump})"
@@ -258,11 +277,13 @@
 		},
 		"extraFlags", "referenceDump", "libName", "arch", "createReferenceDumpFlags")
 
+	// Rule to unzip a reference abi dump.
 	unzipRefSAbiDump = pctx.AndroidStaticRule("unzipRefSAbiDump",
 		blueprint.RuleParams{
 			Command: "gunzip -c $in > $out",
 		})
 
+	// Rule to zip files.
 	zip = pctx.AndroidStaticRule("zip",
 		blueprint.RuleParams{
 			Command:        "${SoongZipCmd} -o ${out} -C $$OUT_DIR -r ${out}.rsp",
@@ -278,6 +299,8 @@
 		func(ctx android.PackageVarContext) string { return ctx.Config().XrefCorpusName() })
 	_ = pctx.VariableFunc("kytheCuEncoding",
 		func(ctx android.PackageVarContext) string { return ctx.Config().XrefCuEncoding() })
+
+	// Rule to use kythe extractors to generate .kzip files, used to build code cross references.
 	kytheExtract = pctx.StaticRule("kythe",
 		blueprint.RuleParams{
 			Command: `rm -f $out && ` +
@@ -310,7 +333,11 @@
 	pctx.Import("android/soong/remoteexec")
 }
 
+// builderFlags contains various types of command line flags (and settings) for use in building
+// build statements related to C++.
 type builderFlags struct {
+	// Global flags (which build system or toolchain is responsible for). These are separate from
+	// local flags because they should appear first (so that they may be overridden by local flags).
 	globalCommonFlags     string
 	globalAsFlags         string
 	globalYasmFlags       string
@@ -321,6 +348,7 @@
 	globalCppFlags        string
 	globalLdFlags         string
 
+	// Local flags (which individual modules are responsible for). These may override global flags.
 	localCommonFlags     string
 	localAsFlags         string
 	localYasmFlags       string
@@ -331,32 +359,37 @@
 	localCppFlags        string
 	localLdFlags         string
 
-	libFlags      string
-	extraLibFlags string
-	tidyFlags     string
-	sAbiFlags     string
-	aidlFlags     string
-	rsFlags       string
+	libFlags      string // Flags to add to the linker directly after specifying libraries to link.
+	extraLibFlags string // Flags to add to the linker last.
+	tidyFlags     string // Flags that apply to clang-tidy
+	sAbiFlags     string // Flags that apply to header-abi-dumps
+	aidlFlags     string // Flags that apply to aidl source files
+	rsFlags       string // Flags that apply to renderscript source files
 	toolchain     config.Toolchain
-	tidy          bool
-	gcovCoverage  bool
-	sAbiDump      bool
-	emitXrefs     bool
 
-	assemblerWithCpp bool
+	// True if these extra features are enabled.
+	tidy         bool
+	gcovCoverage bool
+	sAbiDump     bool
+	emitXrefs    bool
+
+	assemblerWithCpp bool // True if .s files should be processed with the c preprocessor.
 
 	systemIncludeFlags string
 
+	// True if static libraries should be grouped (using `-Wl,--start-group` and `-Wl,--end-group`).
 	groupStaticLibs bool
 
 	proto            android.ProtoFlags
-	protoC           bool
-	protoOptionsFile bool
+	protoC           bool // If true, compile protos as `.c` files. Otherwise, output as `.cc`.
+	protoOptionsFile bool // If true, output a proto options file.
 
 	yacc *YaccProperties
 	lex  *LexProperties
 }
 
+// StripFlags represents flags related to stripping. This is separate from builderFlags, as these
+// flags are useful outside of this package (such as for Rust).
 type StripFlags struct {
 	Toolchain                     config.Toolchain
 	StripKeepSymbols              bool
@@ -367,6 +400,7 @@
 	StripUseGnuStrip              bool
 }
 
+// Objects is a collection of file paths corresponding to outputs for C++ related build statements.
 type Objects struct {
 	objFiles      android.Paths
 	tidyFiles     android.Paths
@@ -396,9 +430,10 @@
 }
 
 // Generate rules for compiling multiple .c, .cpp, or .S files to individual .o files
-func TransformSourceToObj(ctx android.ModuleContext, subdir string, srcFiles android.Paths,
+func transformSourceToObj(ctx android.ModuleContext, subdir string, srcFiles android.Paths,
 	flags builderFlags, pathDeps android.Paths, cFlagsDeps android.Paths) Objects {
 
+	// Source files are one-to-one with tidy, coverage, or kythe files, if enabled.
 	objFiles := make(android.Paths, len(srcFiles))
 	var tidyFiles android.Paths
 	if flags.tidy {
@@ -468,6 +503,7 @@
 
 		objFiles[i] = objFile
 
+		// Register compilation build statements. The actual rule used depends on the source file type.
 		switch srcFile.Ext() {
 		case ".asm":
 			ctx.Build(pctx, android.BuildParams{
@@ -562,6 +598,7 @@
 			},
 		})
 
+		// Register post-process build statements (such as for tidy or kythe).
 		if emitXref {
 			kytheFile := android.ObjPathWithExt(ctx, subdir, srcFile, "kzip")
 			ctx.Build(pctx, android.BuildParams{
@@ -639,7 +676,7 @@
 }
 
 // Generate a rule for compiling multiple .o files to a static library (.a)
-func TransformObjToStaticLib(ctx android.ModuleContext,
+func transformObjToStaticLib(ctx android.ModuleContext,
 	objFiles android.Paths, wholeStaticLibs android.Paths,
 	flags builderFlags, outputFile android.ModuleOutPath, deps android.Paths) {
 
@@ -682,7 +719,7 @@
 
 // Generate a rule for compiling multiple .o files, plus static libraries, whole static libraries,
 // and shared libraries, to a shared library (.so) or dynamic executable
-func TransformObjToDynamicBinary(ctx android.ModuleContext,
+func transformObjToDynamicBinary(ctx android.ModuleContext,
 	objFiles, sharedLibs, staticLibs, lateStaticLibs, wholeStaticLibs, deps android.Paths,
 	crtBegin, crtEnd android.OptionalPath, groupLate bool, flags builderFlags, outputFile android.WritablePath, implicitOutputs android.WritablePaths) {
 
@@ -763,7 +800,7 @@
 
 // Generate a rule to combine .dump sAbi dump files from multiple source files
 // into a single .ldump sAbi dump file
-func TransformDumpToLinkedDump(ctx android.ModuleContext, sAbiDumps android.Paths, soFile android.Path,
+func transformDumpToLinkedDump(ctx android.ModuleContext, sAbiDumps android.Paths, soFile android.Path,
 	baseName, exportedHeaderFlags string, symbolFile android.OptionalPath,
 	excludedSymbolVersions, excludedSymbolTags []string) android.OptionalPath {
 
@@ -810,7 +847,8 @@
 	return android.OptionalPathForPath(outputFile)
 }
 
-func UnzipRefDump(ctx android.ModuleContext, zippedRefDump android.Path, baseName string) android.Path {
+// unzipRefDump registers a build statement to unzip a reference abi dump.
+func unzipRefDump(ctx android.ModuleContext, zippedRefDump android.Path, baseName string) android.Path {
 	outputFile := android.PathForModuleOut(ctx, baseName+"_ref.lsdump")
 	ctx.Build(pctx, android.BuildParams{
 		Rule:        unzipRefSAbiDump,
@@ -821,7 +859,8 @@
 	return outputFile
 }
 
-func SourceAbiDiff(ctx android.ModuleContext, inputDump android.Path, referenceDump android.Path,
+// sourceAbiDiff registers a build statement to compare linked sAbi dump files (.ldump).
+func sourceAbiDiff(ctx android.ModuleContext, inputDump android.Path, referenceDump android.Path,
 	baseName, exportedHeaderFlags string, checkAllApis, isLlndk, isNdk, isVndkExt bool) android.OptionalPath {
 
 	outputFile := android.PathForModuleOut(ctx, baseName+".abidiff")
@@ -872,7 +911,7 @@
 }
 
 // Generate a rule for extracting a table of contents from a shared library (.so)
-func TransformSharedObjectToToc(ctx android.ModuleContext, inputFile android.Path,
+func transformSharedObjectToToc(ctx android.ModuleContext, inputFile android.Path,
 	outputFile android.WritablePath, flags builderFlags) {
 
 	var format string
@@ -901,7 +940,7 @@
 }
 
 // Generate a rule for compiling multiple .o files to a .o using ld partial linking
-func TransformObjsToObj(ctx android.ModuleContext, objFiles android.Paths,
+func transformObjsToObj(ctx android.ModuleContext, objFiles android.Paths,
 	flags builderFlags, outputFile android.WritablePath, deps android.Paths) {
 
 	ldCmd := "${config.ClangBin}/clang++"
@@ -926,8 +965,8 @@
 	})
 }
 
-// Generate a rule for runing objcopy --prefix-symbols on a binary
-func TransformBinaryPrefixSymbols(ctx android.ModuleContext, prefix string, inputFile android.Path,
+// Generate a rule for running objcopy --prefix-symbols on a binary
+func transformBinaryPrefixSymbols(ctx android.ModuleContext, prefix string, inputFile android.Path,
 	flags builderFlags, outputFile android.WritablePath) {
 
 	objcopyCmd := gccCmd(flags.toolchain, "objcopy")
@@ -944,7 +983,8 @@
 	})
 }
 
-func TransformStrip(ctx android.ModuleContext, inputFile android.Path,
+// Registers a build statement to invoke `strip` (to discard symbols and data from object files).
+func transformStrip(ctx android.ModuleContext, inputFile android.Path,
 	outputFile android.WritablePath, flags StripFlags) {
 
 	crossCompile := gccCmd(flags.Toolchain, "")
@@ -980,7 +1020,8 @@
 	})
 }
 
-func TransformDarwinStrip(ctx android.ModuleContext, inputFile android.Path,
+// Registers build statement to invoke `strip` on darwin architecture.
+func transformDarwinStrip(ctx android.ModuleContext, inputFile android.Path,
 	outputFile android.WritablePath) {
 
 	ctx.Build(pctx, android.BuildParams{
@@ -991,7 +1032,8 @@
 	})
 }
 
-func TransformCoverageFilesToZip(ctx android.ModuleContext,
+// Registers build statement to zip one or more coverage files.
+func transformCoverageFilesToZip(ctx android.ModuleContext,
 	inputs Objects, baseName string) android.OptionalPath {
 
 	if len(inputs.coverageFiles) > 0 {
@@ -1010,7 +1052,8 @@
 	return android.OptionalPath{}
 }
 
-func TransformArchiveRepack(ctx android.ModuleContext, inputFile android.Path,
+// Rule to repack an archive (.a) file with a subset of object files.
+func transformArchiveRepack(ctx android.ModuleContext, inputFile android.Path,
 	outputFile android.WritablePath, objects []string) {
 
 	ctx.Build(pctx, android.BuildParams{
@@ -1027,33 +1070,3 @@
 func gccCmd(toolchain config.Toolchain, cmd string) string {
 	return filepath.Join(toolchain.GccRoot(), "bin", toolchain.GccTriple()+"-"+cmd)
 }
-
-func splitListForSize(list android.Paths, limit int) (lists []android.Paths, err error) {
-	var i int
-
-	start := 0
-	bytes := 0
-	for i = range list {
-		l := len(list[i].String())
-		if l > limit {
-			return nil, fmt.Errorf("list element greater than size limit (%d)", limit)
-		}
-		if bytes+l > limit {
-			lists = append(lists, list[start:i])
-			start = i
-			bytes = 0
-		}
-		bytes += l + 1 // count a space between each list element
-	}
-
-	lists = append(lists, list[start:])
-
-	totalLen := 0
-	for _, l := range lists {
-		totalLen += len(l)
-	}
-	if totalLen != len(list) {
-		panic(fmt.Errorf("Failed breaking up list, %d != %d", len(list), totalLen))
-	}
-	return lists, nil
-}
diff --git a/cc/cc_test.go b/cc/cc_test.go
index 7c98585..af9b943 100644
--- a/cc/cc_test.go
+++ b/cc/cc_test.go
@@ -2913,114 +2913,6 @@
 	}
 }
 
-var (
-	str11 = "01234567891"
-	str10 = str11[:10]
-	str9  = str11[:9]
-	str5  = str11[:5]
-	str4  = str11[:4]
-)
-
-var splitListForSizeTestCases = []struct {
-	in   []string
-	out  [][]string
-	size int
-}{
-	{
-		in:   []string{str10},
-		out:  [][]string{{str10}},
-		size: 10,
-	},
-	{
-		in:   []string{str9},
-		out:  [][]string{{str9}},
-		size: 10,
-	},
-	{
-		in:   []string{str5},
-		out:  [][]string{{str5}},
-		size: 10,
-	},
-	{
-		in:   []string{str11},
-		out:  nil,
-		size: 10,
-	},
-	{
-		in:   []string{str10, str10},
-		out:  [][]string{{str10}, {str10}},
-		size: 10,
-	},
-	{
-		in:   []string{str9, str10},
-		out:  [][]string{{str9}, {str10}},
-		size: 10,
-	},
-	{
-		in:   []string{str10, str9},
-		out:  [][]string{{str10}, {str9}},
-		size: 10,
-	},
-	{
-		in:   []string{str5, str4},
-		out:  [][]string{{str5, str4}},
-		size: 10,
-	},
-	{
-		in:   []string{str5, str4, str5},
-		out:  [][]string{{str5, str4}, {str5}},
-		size: 10,
-	},
-	{
-		in:   []string{str5, str4, str5, str4},
-		out:  [][]string{{str5, str4}, {str5, str4}},
-		size: 10,
-	},
-	{
-		in:   []string{str5, str4, str5, str5},
-		out:  [][]string{{str5, str4}, {str5}, {str5}},
-		size: 10,
-	},
-	{
-		in:   []string{str5, str5, str5, str4},
-		out:  [][]string{{str5}, {str5}, {str5, str4}},
-		size: 10,
-	},
-	{
-		in:   []string{str9, str11},
-		out:  nil,
-		size: 10,
-	},
-	{
-		in:   []string{str11, str9},
-		out:  nil,
-		size: 10,
-	},
-}
-
-func TestSplitListForSize(t *testing.T) {
-	for _, testCase := range splitListForSizeTestCases {
-		out, _ := splitListForSize(android.PathsForTesting(testCase.in...), testCase.size)
-
-		var outStrings [][]string
-
-		if len(out) > 0 {
-			outStrings = make([][]string, len(out))
-			for i, o := range out {
-				outStrings[i] = o.Strings()
-			}
-		}
-
-		if !reflect.DeepEqual(outStrings, testCase.out) {
-			t.Errorf("incorrect output:")
-			t.Errorf("     input: %#v", testCase.in)
-			t.Errorf("      size: %d", testCase.size)
-			t.Errorf("  expected: %#v", testCase.out)
-			t.Errorf("       got: %#v", outStrings)
-		}
-	}
-}
-
 var staticLinkDepOrderTestCases = []struct {
 	// This is a string representation of a map[moduleName][]moduleDependency .
 	// It models the dependencies declared in an Android.bp file.
diff --git a/cc/compiler.go b/cc/compiler.go
index 04ed80d..f71dcca 100644
--- a/cc/compiler.go
+++ b/cc/compiler.go
@@ -649,7 +649,7 @@
 func compileObjs(ctx android.ModuleContext, flags builderFlags,
 	subdir string, srcFiles, pathDeps android.Paths, cFlagsDeps android.Paths) Objects {
 
-	return TransformSourceToObj(ctx, subdir, srcFiles, flags, pathDeps, cFlagsDeps)
+	return transformSourceToObj(ctx, subdir, srcFiles, flags, pathDeps, cFlagsDeps)
 }
 
 var thirdPartyDirPrefixExceptions = []*regexp.Regexp{
diff --git a/cc/library.go b/cc/library.go
index 7ae75f2..ddc7ff7 100644
--- a/cc/library.go
+++ b/cc/library.go
@@ -897,9 +897,9 @@
 		}
 	}
 
-	TransformObjToStaticLib(ctx, library.objects.objFiles, deps.WholeStaticLibsFromPrebuilts, builderFlags, outputFile, objs.tidyFiles)
+	transformObjToStaticLib(ctx, library.objects.objFiles, deps.WholeStaticLibsFromPrebuilts, builderFlags, outputFile, objs.tidyFiles)
 
-	library.coverageOutputFile = TransformCoverageFilesToZip(ctx, library.objects, ctx.ModuleName())
+	library.coverageOutputFile = transformCoverageFilesToZip(ctx, library.objects, ctx.ModuleName())
 
 	ctx.CheckbuildFile(outputFile)
 
@@ -974,7 +974,7 @@
 	// depending on a table of contents file instead of the library itself.
 	tocFile := outputFile.ReplaceExtension(ctx, flags.Toolchain.ShlibSuffix()[1:]+".toc")
 	library.tocFile = android.OptionalPathForPath(tocFile)
-	TransformSharedObjectToToc(ctx, outputFile, tocFile, builderFlags)
+	transformSharedObjectToToc(ctx, outputFile, tocFile, builderFlags)
 
 	stripFlags := flagsToStripFlags(flags)
 	if library.stripper.NeedsStrip(ctx) {
@@ -1019,7 +1019,7 @@
 
 	if Bool(library.Properties.Sort_bss_symbols_by_size) {
 		unsortedOutputFile := android.PathForModuleOut(ctx, "unsorted", fileName)
-		TransformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs,
+		transformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs,
 			deps.StaticLibs, deps.LateStaticLibs, deps.WholeStaticLibs,
 			linkerDeps, deps.CrtBegin, deps.CrtEnd, false, builderFlags, unsortedOutputFile, implicitOutputs)
 
@@ -1029,7 +1029,7 @@
 		linkerDeps = append(linkerDeps, symbolOrderingFile)
 	}
 
-	TransformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs,
+	transformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs,
 		deps.StaticLibs, deps.LateStaticLibs, deps.WholeStaticLibs,
 		linkerDeps, deps.CrtBegin, deps.CrtEnd, false, builderFlags, outputFile, implicitOutputs)
 
@@ -1039,7 +1039,7 @@
 	objs.sAbiDumpFiles = append(objs.sAbiDumpFiles, deps.StaticLibObjs.sAbiDumpFiles...)
 	objs.sAbiDumpFiles = append(objs.sAbiDumpFiles, deps.WholeStaticLibObjs.sAbiDumpFiles...)
 
-	library.coverageOutputFile = TransformCoverageFilesToZip(ctx, objs, library.getLibName(ctx))
+	library.coverageOutputFile = transformCoverageFilesToZip(ctx, objs, library.getLibName(ctx))
 	library.linkSAbiDumpFiles(ctx, objs, fileName, unstrippedOutputFile)
 
 	var staticAnalogue *StaticLibraryInfo
@@ -1115,7 +1115,7 @@
 		return refAbiDumpTextFile.Path()
 	}
 	if refAbiDumpGzipFile.Valid() {
-		return UnzipRefDump(ctx, refAbiDumpGzipFile.Path(), fileName)
+		return unzipRefDump(ctx, refAbiDumpGzipFile.Path(), fileName)
 	}
 	return nil
 }
@@ -1141,7 +1141,7 @@
 			SourceAbiFlags = append(SourceAbiFlags, "-I"+reexportedInclude)
 		}
 		exportedHeaderFlags := strings.Join(SourceAbiFlags, " ")
-		library.sAbiOutputFile = TransformDumpToLinkedDump(ctx, objs.sAbiDumpFiles, soFile, fileName, exportedHeaderFlags,
+		library.sAbiOutputFile = transformDumpToLinkedDump(ctx, objs.sAbiDumpFiles, soFile, fileName, exportedHeaderFlags,
 			android.OptionalPathForModuleSrc(ctx, library.symbolFileForAbiCheck(ctx)),
 			library.Properties.Header_abi_checker.Exclude_symbol_versions,
 			library.Properties.Header_abi_checker.Exclude_symbol_tags)
@@ -1150,7 +1150,7 @@
 
 		refAbiDumpFile := getRefAbiDumpFile(ctx, vndkVersion, fileName)
 		if refAbiDumpFile != nil {
-			library.sAbiDiff = SourceAbiDiff(ctx, library.sAbiOutputFile.Path(),
+			library.sAbiDiff = sourceAbiDiff(ctx, library.sAbiOutputFile.Path(),
 				refAbiDumpFile, fileName, exportedHeaderFlags,
 				Bool(library.Properties.Header_abi_checker.Check_all_apis),
 				ctx.isLlndk(ctx.Config()), ctx.isNdk(ctx.Config()), ctx.isVndkExt())
diff --git a/cc/object.go b/cc/object.go
index ab2672b..3ce7676 100644
--- a/cc/object.go
+++ b/cc/object.go
@@ -124,7 +124,7 @@
 
 		if String(object.Properties.Prefix_symbols) != "" {
 			output := android.PathForModuleOut(ctx, ctx.ModuleName()+objectExtension)
-			TransformBinaryPrefixSymbols(ctx, String(object.Properties.Prefix_symbols), outputFile,
+			transformBinaryPrefixSymbols(ctx, String(object.Properties.Prefix_symbols), outputFile,
 				builderFlags, output)
 			outputFile = output
 		}
@@ -134,12 +134,12 @@
 
 		if String(object.Properties.Prefix_symbols) != "" {
 			input := android.PathForModuleOut(ctx, "unprefixed", ctx.ModuleName()+objectExtension)
-			TransformBinaryPrefixSymbols(ctx, String(object.Properties.Prefix_symbols), input,
+			transformBinaryPrefixSymbols(ctx, String(object.Properties.Prefix_symbols), input,
 				builderFlags, output)
 			output = input
 		}
 
-		TransformObjsToObj(ctx, objs.objFiles, builderFlags, output, flags.LdFlagsDeps)
+		transformObjsToObj(ctx, objs.objFiles, builderFlags, output, flags.LdFlagsDeps)
 	}
 
 	ctx.CheckbuildFile(outputFile)
diff --git a/cc/prebuilt.go b/cc/prebuilt.go
index 8873883..37df4ba 100644
--- a/cc/prebuilt.go
+++ b/cc/prebuilt.go
@@ -146,7 +146,7 @@
 			// depending on a table of contents file instead of the library itself.
 			tocFile := android.PathForModuleOut(ctx, libName+".toc")
 			p.tocFile = android.OptionalPathForPath(tocFile)
-			TransformSharedObjectToToc(ctx, outputFile, tocFile, builderFlags)
+			transformSharedObjectToToc(ctx, outputFile, tocFile, builderFlags)
 
 			if ctx.Windows() && p.properties.Windows_import_lib != nil {
 				// Consumers of this library actually links to the import library in build
diff --git a/cc/strip.go b/cc/strip.go
index e9aec91..1f10a74 100644
--- a/cc/strip.go
+++ b/cc/strip.go
@@ -54,7 +54,7 @@
 func (stripper *Stripper) strip(actx android.ModuleContext, in android.Path, out android.ModuleOutPath,
 	flags StripFlags, isStaticLib bool) {
 	if actx.Darwin() {
-		TransformDarwinStrip(actx, in, out)
+		transformDarwinStrip(actx, in, out)
 	} else {
 		if Bool(stripper.StripProperties.Strip.Keep_symbols) {
 			flags.StripKeepSymbols = true
@@ -68,7 +68,7 @@
 		if actx.Config().Debuggable() && !flags.StripKeepMiniDebugInfo && !isStaticLib {
 			flags.StripAddGnuDebuglink = true
 		}
-		TransformStrip(actx, in, out, flags)
+		transformStrip(actx, in, out, flags)
 	}
 }
 
diff --git a/cc/toolchain_library.go b/cc/toolchain_library.go
index 0c934ad..bda73ea 100644
--- a/cc/toolchain_library.go
+++ b/cc/toolchain_library.go
@@ -90,7 +90,7 @@
 	if library.Properties.Repack_objects_to_keep != nil {
 		fileName := ctx.ModuleName() + staticLibraryExtension
 		repackedPath := android.PathForModuleOut(ctx, fileName)
-		TransformArchiveRepack(ctx, outputFile, repackedPath, library.Properties.Repack_objects_to_keep)
+		transformArchiveRepack(ctx, outputFile, repackedPath, library.Properties.Repack_objects_to_keep)
 		outputFile = repackedPath
 	}
 
diff --git a/cc/vendor_snapshot.go b/cc/vendor_snapshot.go
index 6563f6e..94f859e 100644
--- a/cc/vendor_snapshot.go
+++ b/cc/vendor_snapshot.go
@@ -339,7 +339,7 @@
 		// depending on a table of contents file instead of the library itself.
 		tocFile := android.PathForModuleOut(ctx, libName+".toc")
 		p.tocFile = android.OptionalPathForPath(tocFile)
-		TransformSharedObjectToToc(ctx, in, tocFile, builderFlags)
+		transformSharedObjectToToc(ctx, in, tocFile, builderFlags)
 
 		ctx.SetProvider(SharedLibraryInfoProvider, SharedLibraryInfo{
 			SharedLibrary:           in,
diff --git a/cc/vndk.go b/cc/vndk.go
index 4a005f3..fcaf3af 100644
--- a/cc/vndk.go
+++ b/cc/vndk.go
@@ -727,7 +727,7 @@
 		var txtBuilder strings.Builder
 		for idx, k := range android.SortedStringKeys(m) {
 			if idx > 0 {
-				txtBuilder.WriteString("\\n")
+				txtBuilder.WriteString("\n")
 			}
 			txtBuilder.WriteString(k)
 			txtBuilder.WriteString(" ")
diff --git a/cc/vndk_prebuilt.go b/cc/vndk_prebuilt.go
index c0320eb..e6e2ad8 100644
--- a/cc/vndk_prebuilt.go
+++ b/cc/vndk_prebuilt.go
@@ -154,7 +154,7 @@
 		// depending on a table of contents file instead of the library itself.
 		tocFile := android.PathForModuleOut(ctx, libName+".toc")
 		p.tocFile = android.OptionalPathForPath(tocFile)
-		TransformSharedObjectToToc(ctx, in, tocFile, builderFlags)
+		transformSharedObjectToToc(ctx, in, tocFile, builderFlags)
 
 		p.androidMkSuffix = p.NameSuffix()
 
diff --git a/cmd/soong_build/main.go b/cmd/soong_build/main.go
index b88803a..d758de2 100644
--- a/cmd/soong_build/main.go
+++ b/cmd/soong_build/main.go
@@ -79,7 +79,7 @@
 	srcDir := filepath.Dir(flag.Arg(0))
 	var ctx *android.Context
 	configuration := newConfig(srcDir)
-	extraNinjaDeps := []string{configuration.ConfigFileName, configuration.ProductVariablesFileName}
+	extraNinjaDeps := []string{configuration.ProductVariablesFileName}
 
 	// Read the SOONG_DELVE again through configuration so that there is a dependency on the environment variable
 	// and soong_build will rerun when it is set for the first time.
diff --git a/java/aapt2.go b/java/aapt2.go
index 04e4de5..5346ddf 100644
--- a/java/aapt2.go
+++ b/java/aapt2.go
@@ -25,12 +25,9 @@
 	"android/soong/android"
 )
 
-const AAPT2_SHARD_SIZE = 100
-
 // Convert input resource file path to output file path.
 // values-[config]/<file>.xml -> values-[config]_<file>.arsc.flat;
-// For other resource file, just replace the last "/" with "_" and
-// add .flat extension.
+// For other resource file, just replace the last "/" with "_" and add .flat extension.
 func pathToAapt2Path(ctx android.ModuleContext, res android.Path) android.WritablePath {
 
 	name := res.Base()
@@ -43,6 +40,7 @@
 	return android.PathForModuleOut(ctx, "aapt2", subDir, name)
 }
 
+// pathsToAapt2Paths Calls pathToAapt2Path on each entry of the given Paths, i.e. []Path.
 func pathsToAapt2Paths(ctx android.ModuleContext, resPaths android.Paths) android.WritablePaths {
 	outPaths := make(android.WritablePaths, len(resPaths))
 
@@ -53,6 +51,9 @@
 	return outPaths
 }
 
+// Shard resource files for efficiency. See aapt2Compile for details.
+const AAPT2_SHARD_SIZE = 100
+
 var aapt2CompileRule = pctx.AndroidStaticRule("aapt2Compile",
 	blueprint.RuleParams{
 		Command:     `${config.Aapt2Cmd} compile -o $outDir $cFlags $in`,
@@ -60,14 +61,26 @@
 	},
 	"outDir", "cFlags")
 
+// aapt2Compile compiles resources and puts the results in the requested directory.
 func aapt2Compile(ctx android.ModuleContext, dir android.Path, paths android.Paths,
 	flags []string) android.WritablePaths {
 
+	// Shard the input paths so that they can be processed in parallel. If we shard them into too
+	// small chunks, the additional cost of spinning up aapt2 outweighs the performance gain. The
+	// current shard size, 100, seems to be a good balance between the added cost and the gain.
+	// The aapt2 compile actions are trivially short, but each action in ninja takes on the order of
+	// ~10 ms to run. frameworks/base/core/res/res has >10k resource files, so compiling each one
+	// with an individual action could take 100 CPU seconds. Sharding them reduces the overhead of
+	// starting actions by a factor of 100, at the expense of recompiling more files when one
+	// changes.  Since the individual compiles are trivial it's a good tradeoff.
 	shards := android.ShardPaths(paths, AAPT2_SHARD_SIZE)
 
 	ret := make(android.WritablePaths, 0, len(paths))
 
 	for i, shard := range shards {
+		// This should be kept in sync with pathToAapt2Path. The aapt2 compile command takes an
+		// output directory path, but not output file paths. So, outPaths is just where we expect
+		// the output files will be located.
 		outPaths := pathsToAapt2Paths(ctx, shard)
 		ret = append(ret, outPaths...)
 
@@ -82,6 +95,12 @@
 			Inputs:      shard,
 			Outputs:     outPaths,
 			Args: map[string]string{
+				// The aapt2 compile command takes an output directory path, but not output file paths.
+				// outPaths specified above is only used for dependency management purposes. In order for
+				// the outPaths values to match the actual outputs from aapt2, the dir parameter value
+				// must be a common prefix path of the paths values, and the top-level path segment used
+				// below, "aapt2", must always be kept in sync with the one in pathToAapt2Path.
+				// TODO(b/174505750): Make this easier and robust to use.
 				"outDir": android.PathForModuleOut(ctx, "aapt2", dir.String()).String(),
 				"cFlags": strings.Join(flags, " "),
 			},
@@ -104,6 +123,8 @@
 		},
 	}, "cFlags", "resZipDir", "zipSyncFlags")
 
+// Unzips the given compressed file and compiles the resource source files in it. The zipPrefix
+// parameter points to the subdirectory in the zip file where the resource files are located.
 func aapt2CompileZip(ctx android.ModuleContext, flata android.WritablePath, zip android.Path, zipPrefix string,
 	flags []string) {
 
@@ -163,6 +184,7 @@
 	var inFlags []string
 
 	if len(compiledRes) > 0 {
+		// Create a file that contains the list of all compiled resource file paths.
 		resFileList := android.PathForModuleOut(ctx, "aapt2", "res.list")
 		// Write out file lists to files
 		ctx.Build(pctx, android.BuildParams{
@@ -174,10 +196,12 @@
 
 		deps = append(deps, compiledRes...)
 		deps = append(deps, resFileList)
+		// aapt2 filepath arguments that start with "@" mean file-list files.
 		inFlags = append(inFlags, "@"+resFileList.String())
 	}
 
 	if len(compiledOverlay) > 0 {
+		// Compiled overlay files are processed the same way as compiled resources.
 		overlayFileList := android.PathForModuleOut(ctx, "aapt2", "overlay.list")
 		ctx.Build(pctx, android.BuildParams{
 			Rule:        fileListToFileRule,
@@ -188,9 +212,11 @@
 
 		deps = append(deps, compiledOverlay...)
 		deps = append(deps, overlayFileList)
+		// Compiled overlay files are passed over to aapt2 using -R option.
 		inFlags = append(inFlags, "-R", "@"+overlayFileList.String())
 	}
 
+	// Set auxiliary outputs as implicit outputs to establish correct dependency chains.
 	implicitOutputs := append(splitPackages, proguardOptions, genJar, rTxt, extraPackages)
 	linkOutput := packageRes
 
@@ -212,6 +238,10 @@
 		Implicits:       deps,
 		Output:          linkOutput,
 		ImplicitOutputs: implicitOutputs,
+		// Note the absence of splitPackages. The caller is supposed to compose and provide --split flag
+		// values via the flags parameter when it wants to split outputs.
+		// TODO(b/174509108): Perhaps we can process it in this func while keeping the code reasonably
+		// tidy.
 		Args: map[string]string{
 			"flags":           strings.Join(flags, " "),
 			"inFlags":         strings.Join(inFlags, " "),
@@ -230,6 +260,8 @@
 		CommandDeps: []string{"${config.Aapt2Cmd}"},
 	})
 
+// Converts xml files and resource tables (resources.arsc) in the given jar/apk file to a proto
+// format. The proto definition is available at frameworks/base/tools/aapt2/Resources.proto.
 func aapt2Convert(ctx android.ModuleContext, out android.WritablePath, in android.Path) {
 	ctx.Build(pctx, android.BuildParams{
 		Rule:        aapt2ConvertRule,