diff --git a/java/hiddenapi_modular.go b/java/hiddenapi_modular.go
index 86ab825..8a06a99 100644
--- a/java/hiddenapi_modular.go
+++ b/java/hiddenapi_modular.go
@@ -297,7 +297,7 @@
 //
 // The rule is initialized but not built so that the caller can modify it and select an appropriate
 // name.
-func buildRuleToGenerateHiddenAPIStubFlagsFile(ctx android.BuilderContext, name, desc string, outputPath android.WritablePath, bootDexJars android.Paths, input HiddenAPIFlagInput, moduleStubFlagsPaths android.Paths) {
+func buildRuleToGenerateHiddenAPIStubFlagsFile(ctx android.BuilderContext, name, desc string, outputPath android.WritablePath, bootDexJars android.Paths, input HiddenAPIFlagInput, stubFlagSubsets SignatureCsvSubsets) {
 	// Singleton rule which applies hiddenapi on all boot class path dex files.
 	rule := android.NewRuleBuilder(pctx, ctx)
 
@@ -317,7 +317,7 @@
 
 	// If no module stub flags paths are provided then this must be being called for a
 	// bootclasspath_fragment and not the whole platform_bootclasspath.
-	if moduleStubFlagsPaths == nil {
+	if stubFlagSubsets == nil {
 		// This is being run on a fragment of the bootclasspath.
 		command.Flag("--fragment")
 	}
@@ -342,8 +342,8 @@
 
 	// If there are stub flag files that have been generated by fragments on which this depends then
 	// use them to validate the stub flag file generated by the rules created by this method.
-	if len(moduleStubFlagsPaths) > 0 {
-		validFile := buildRuleValidateOverlappingCsvFiles(ctx, name, desc, outputPath, moduleStubFlagsPaths)
+	if len(stubFlagSubsets) > 0 {
+		validFile := buildRuleValidateOverlappingCsvFiles(ctx, name, desc, outputPath, stubFlagSubsets)
 
 		// Add the file that indicates that the file generated by this is valid.
 		//
@@ -546,6 +546,20 @@
 	}
 }
 
+// StubFlagSubset returns a SignatureCsvSubset that contains a path to a stub-flags.csv file and a
+// path to a signature-patterns.csv file that defines a subset of the monolithic stub flags file,
+// i.e. out/soong/hiddenapi/hiddenapi-stub-flags.txt, against which it will be compared.
+func (i *HiddenAPIInfo) StubFlagSubset() SignatureCsvSubset {
+	return SignatureCsvSubset{i.StubFlagsPath, i.SignaturePatternsPath}
+}
+
+// FlagSubset returns a SignatureCsvSubset that contains a path to an all-flags.csv file and a
+// path to a signature-patterns.csv file that defines a subset of the monolithic flags file, i.e.
+// out/soong/hiddenapi/hiddenapi-flags.csv, against which it will be compared.
+func (i *HiddenAPIInfo) FlagSubset() SignatureCsvSubset {
+	return SignatureCsvSubset{i.AllFlagsPath, i.SignaturePatternsPath}
+}
+
 var HiddenAPIInfoProvider = blueprint.NewProvider(HiddenAPIInfo{})
 
 // ModuleStubDexJars contains the stub dex jars provided by a single module.
@@ -782,6 +796,10 @@
 
 	// The path to the generated all-flags.csv file.
 	AllFlagsPath android.Path
+
+	// The path to the generated signature-patterns.txt file which defines the subset of the
+	// monolithic hidden API files provided in this.
+	SignaturePatternsPath android.Path
 }
 
 // bootDexJarByModule is a map from base module name (without prebuilt_ prefix) to the boot dex
@@ -848,7 +866,7 @@
 // the annotationFlags.
 func buildRuleToGenerateHiddenApiFlags(ctx android.BuilderContext, name, desc string,
 	outputPath android.WritablePath, baseFlagsPath android.Path, annotationFlagPaths android.Paths,
-	flagFilesByCategory FlagFilesByCategory, allFlagsPaths android.Paths, generatedRemovedDexSignatures android.OptionalPath) {
+	flagFilesByCategory FlagFilesByCategory, flagSubsets SignatureCsvSubsets, generatedRemovedDexSignatures android.OptionalPath) {
 
 	// Create the rule that will generate the flag files.
 	tempPath := tempPathForRestat(ctx, outputPath)
@@ -877,8 +895,8 @@
 
 	// If there are flag files that have been generated by fragments on which this depends then use
 	// them to validate the flag file generated by the rules created by this method.
-	if len(allFlagsPaths) > 0 {
-		validFile := buildRuleValidateOverlappingCsvFiles(ctx, name, desc, outputPath, allFlagsPaths)
+	if len(flagSubsets) > 0 {
+		validFile := buildRuleValidateOverlappingCsvFiles(ctx, name, desc, outputPath, flagSubsets)
 
 		// Add the file that indicates that the file generated by this is valid.
 		//
@@ -890,20 +908,66 @@
 	rule.Build(name, desc)
 }
 
+// SignatureCsvSubset describes a subset of a monolithic flags file, i.e. either
+// out/soong/hiddenapi/hiddenapi-stub-flags.txt or out/soong/hiddenapi/hiddenapi-flags.csv
+type SignatureCsvSubset struct {
+	// The path to the CSV file containing hidden API flags.
+	//
+	// It has the dex member signature as the first column, with flags, one per column, in the
+	// subsequent columns.
+	CsvFile android.Path
+
+	// The path to the CSV file containing the signature patterns.
+	//
+	// It is a single column CSV file with the column containing a signature pattern.
+	SignaturePatternsFile android.Path
+}
+
+type SignatureCsvSubsets []SignatureCsvSubset
+
+func (s SignatureCsvSubsets) RelativeToTop() []string {
+	result := []string{}
+	for _, subset := range s {
+		result = append(result, fmt.Sprintf("%s:%s", subset.CsvFile.RelativeToTop(), subset.SignaturePatternsFile.RelativeToTop()))
+	}
+	return result
+}
+
+// buildRuleSignaturePatternsFile creates a rule to generate a file containing the set of signature
+// patterns that will select a subset of the monolithic flags.
+func buildRuleSignaturePatternsFile(ctx android.ModuleContext, flagsPath android.Path) android.Path {
+	patternsFile := android.PathForModuleOut(ctx, "modular-hiddenapi", "signature-patterns.csv")
+	// Create a rule to validate the output from the following rule.
+	rule := android.NewRuleBuilder(pctx, ctx)
+	rule.Command().
+		BuiltTool("signature_patterns").
+		FlagWithInput("--flags ", flagsPath).
+		FlagWithOutput("--output ", patternsFile)
+	rule.Build("hiddenAPISignaturePatterns", "hidden API signature patterns")
+
+	return patternsFile
+}
+
 // buildRuleValidateOverlappingCsvFiles checks that the modular CSV files, i.e. the files generated
 // by the individual bootclasspath_fragment modules are subsets of the monolithic CSV file.
-func buildRuleValidateOverlappingCsvFiles(ctx android.BuilderContext, name string, desc string, monolithicFilePath android.WritablePath, modularFilePaths android.Paths) android.WritablePath {
+func buildRuleValidateOverlappingCsvFiles(ctx android.BuilderContext, name string, desc string, monolithicFilePath android.WritablePath, csvSubsets SignatureCsvSubsets) android.WritablePath {
 	// The file which is used to record that the flags file is valid.
 	validFile := pathForValidation(ctx, monolithicFilePath)
 
 	// Create a rule to validate the output from the following rule.
 	rule := android.NewRuleBuilder(pctx, ctx)
-	rule.Command().
+	command := rule.Command().
 		BuiltTool("verify_overlaps").
-		Input(monolithicFilePath).
-		Inputs(modularFilePaths).
-		// If validation passes then update the file that records that.
-		Text("&& touch").Output(validFile)
+		Input(monolithicFilePath)
+
+	for _, subset := range csvSubsets {
+		command.
+			Textf("%s:%s", subset.CsvFile, subset.SignaturePatternsFile).
+			Implicit(subset.CsvFile).Implicit(subset.SignaturePatternsFile)
+	}
+
+	// If validation passes then update the file that records that.
+	command.Text("&& touch").Output(validFile)
 	rule.Build(name+"Validation", desc+" validation")
 
 	return validFile