diff --git a/java/Android.bp b/java/Android.bp
index 8334b85..f8ba1b6 100644
--- a/java/Android.bp
+++ b/java/Android.bp
@@ -42,6 +42,7 @@
         "gen.go",
         "genrule.go",
         "hiddenapi.go",
+        "hiddenapi_modular.go",
         "hiddenapi_singleton.go",
         "jacoco.go",
         "java.go",
diff --git a/java/hiddenapi_modular.go b/java/hiddenapi_modular.go
new file mode 100644
index 0000000..eef0320
--- /dev/null
+++ b/java/hiddenapi_modular.go
@@ -0,0 +1,61 @@
+// 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 java
+
+import (
+	"android/soong/android"
+)
+
+// Contains support for processing hiddenAPI in a modular fashion.
+
+// hiddenAPIAugmentationInfo contains paths to the files that can be used to augment the information
+// obtained from annotations within the source code in order to create the complete set of flags
+// that should be applied to the dex implementation jars on the bootclasspath.
+//
+// Each property contains a list of paths. With the exception of the Unsupported_packages the paths
+// of each property reference a plain text file that contains a java signature per line. The flags
+// for each of those signatures will be updated in a property specific way.
+//
+// The Unsupported_packages property contains a list of paths, each of which is a plain text file
+// with one Java package per line. All members of all classes within that package (but not nested
+// packages) will be updated in a property specific way.
+type hiddenAPIAugmentationInfo struct {
+	// Marks each signature in the referenced files as being unsupported.
+	Unsupported android.Paths
+
+	// Marks each signature in the referenced files as being unsupported because it has been removed.
+	// Any conflicts with other flags are ignored.
+	Removed android.Paths
+
+	// Marks each signature in the referenced files as being supported only for targetSdkVersion <= R
+	// and low priority.
+	Max_target_r_low_priority android.Paths
+
+	// Marks each signature in the referenced files as being supported only for targetSdkVersion <= Q.
+	Max_target_q android.Paths
+
+	// Marks each signature in the referenced files as being supported only for targetSdkVersion <= P.
+	Max_target_p android.Paths
+
+	// Marks each signature in the referenced files as being supported only for targetSdkVersion <= O
+	// and low priority. Any conflicts with other flags are ignored.
+	Max_target_o_low_priority android.Paths
+
+	// Marks each signature in the referenced files as being blocked.
+	Blocked android.Paths
+
+	// Marks each signature in every package in the referenced files as being unsupported.
+	Unsupported_packages android.Paths
+}
diff --git a/java/hiddenapi_singleton.go b/java/hiddenapi_singleton.go
index 7e9477b..341381a 100644
--- a/java/hiddenapi_singleton.go
+++ b/java/hiddenapi_singleton.go
@@ -346,39 +346,82 @@
 		ctx.Errorf("Failed to find combined-removed-dex.")
 	}
 
-	rule := android.NewRuleBuilder(pctx, ctx)
-
 	outputPath := hiddenAPISingletonPaths(ctx).flags
-	tempPath := android.PathForOutput(ctx, outputPath.Rel()+".tmp")
 
 	stubFlags := hiddenAPISingletonPaths(ctx).stubFlags
 
-	rule.Command().
+	pathsForSource := func(paths ...string) android.Paths { return android.PathsForSource(ctx, paths) }
+
+	ruleToGenerateHiddenApiFlags(ctx, outputPath, stubFlags, flagsCSV, hiddenAPIAugmentationInfo{
+		Unsupported:               pathsForSource("frameworks/base/boot/hiddenapi/hiddenapi-unsupported.txt"),
+		Removed:                   android.Paths{combinedRemovedApis},
+		Max_target_r_low_priority: pathsForSource("frameworks/base/boot/hiddenapi/hiddenapi-max-target-r-loprio.txt"),
+		Max_target_q:              pathsForSource("frameworks/base/boot/hiddenapi/hiddenapi-max-target-q.txt"),
+		Max_target_p:              pathsForSource("frameworks/base/boot/hiddenapi/hiddenapi-max-target-p.txt"),
+		Max_target_o_low_priority: pathsForSource("frameworks/base/boot/hiddenapi/hiddenapi-max-target-o.txt"),
+		Blocked:                   pathsForSource("frameworks/base/boot/hiddenapi/hiddenapi-force-blocked.txt"),
+		Unsupported_packages:      pathsForSource("frameworks/base/boot/hiddenapi/hiddenapi-unsupported-packages.txt"),
+	})
+
+	return outputPath
+}
+
+// ruleToGenerateHiddenApiFlags creates a rule to create the monolithic hidden API flags from the
+// flags from all the modules, the stub flags, augmented with some additional configuration files.
+//
+// baseFlagsPath is the path to the flags file containing all the information from the stubs plus
+// an entry for every single member in the dex implementation jars of the individual modules. Every
+// signature in any of the other files MUST be included in this file.
+//
+// moduleSpecificFlagsPaths are the paths to the flags files generated by each module using
+// information from the baseFlagsPath as well as from annotations within the source.
+//
+// augmentationInfo is a struct containing paths to files that augment the information provided by
+// the moduleSpecificFlagsPaths.
+func ruleToGenerateHiddenApiFlags(ctx android.BuilderContext, outputPath android.WritablePath, baseFlagsPath android.Path, moduleSpecificFlagsPaths android.Paths, augmentationInfo hiddenAPIAugmentationInfo) {
+	tempPath := android.PathForOutput(ctx, outputPath.Rel()+".tmp")
+	rule := android.NewRuleBuilder(pctx, ctx)
+	command := rule.Command().
 		BuiltTool("generate_hiddenapi_lists").
-		FlagWithInput("--csv ", stubFlags).
-		Inputs(flagsCSV).
-		FlagWithInput("--unsupported ",
-			android.PathForSource(ctx, "frameworks/base/boot/hiddenapi/hiddenapi-unsupported.txt")).
-		FlagWithInput("--unsupported ", combinedRemovedApis).Flag("--ignore-conflicts ").FlagWithArg("--tag ", "removed").
-		FlagWithInput("--max-target-r ",
-			android.PathForSource(ctx, "frameworks/base/boot/hiddenapi/hiddenapi-max-target-r-loprio.txt")).FlagWithArg("--tag ", "lo-prio").
-		FlagWithInput("--max-target-q ",
-			android.PathForSource(ctx, "frameworks/base/boot/hiddenapi/hiddenapi-max-target-q.txt")).
-		FlagWithInput("--max-target-p ",
-			android.PathForSource(ctx, "frameworks/base/boot/hiddenapi/hiddenapi-max-target-p.txt")).
-		FlagWithInput("--max-target-o ", android.PathForSource(
-			ctx, "frameworks/base/boot/hiddenapi/hiddenapi-max-target-o.txt")).Flag("--ignore-conflicts ").FlagWithArg("--tag ", "lo-prio").
-		FlagWithInput("--blocked ",
-			android.PathForSource(ctx, "frameworks/base/boot/hiddenapi/hiddenapi-force-blocked.txt")).
-		FlagWithInput("--unsupported ", android.PathForSource(
-			ctx, "frameworks/base/boot/hiddenapi/hiddenapi-unsupported-packages.txt")).Flag("--packages ").
+		FlagWithInput("--csv ", baseFlagsPath).
+		Inputs(moduleSpecificFlagsPaths).
 		FlagWithOutput("--output ", tempPath)
 
+	for _, path := range augmentationInfo.Unsupported {
+		command.FlagWithInput("--unsupported ", path)
+	}
+
+	for _, path := range augmentationInfo.Removed {
+		command.FlagWithInput("--unsupported ", path).Flag("--ignore-conflicts ").FlagWithArg("--tag ", "removed")
+	}
+
+	for _, path := range augmentationInfo.Max_target_r_low_priority {
+		command.FlagWithInput("--max-target-r ", path).FlagWithArg("--tag ", "lo-prio")
+	}
+
+	for _, path := range augmentationInfo.Max_target_q {
+		command.FlagWithInput("--max-target-q ", path)
+	}
+
+	for _, path := range augmentationInfo.Max_target_p {
+		command.FlagWithInput("--max-target-p ", path)
+	}
+
+	for _, path := range augmentationInfo.Max_target_o_low_priority {
+		command.FlagWithInput("--max-target-o ", path).Flag("--ignore-conflicts ").FlagWithArg("--tag ", "lo-prio")
+	}
+
+	for _, path := range augmentationInfo.Blocked {
+		command.FlagWithInput("--blocked ", path)
+	}
+
+	for _, path := range augmentationInfo.Unsupported_packages {
+		command.FlagWithInput("--unsupported ", path).Flag("--packages ")
+	}
+
 	commitChangeForRestat(rule, tempPath, outputPath)
 
 	rule.Build("hiddenAPIFlagsFile", "hiddenapi flags")
-
-	return outputPath
 }
 
 // emptyFlagsRule creates a rule to build an empty hiddenapi-flags.csv, which is needed by master-art-host builds that