diff --git a/android/bazel.go b/android/bazel.go
index 6fbffcc..1cd84c9 100644
--- a/android/bazel.go
+++ b/android/bazel.go
@@ -272,11 +272,6 @@
 	// still be generated via bp2build.
 	mixedBuildsDisabledList = []string{
 		"libbrotli",                            // http://b/198585397, ld.lld: error: bionic/libc/arch-arm64/generic/bionic/memmove.S:95:(.text+0x10): relocation R_AARCH64_CONDBR19 out of range: -1404176 is not in [-1048576, 1048575]; references __memcpy
-		"libc++fs",                             // http://b/198403271, Missing symbols/members in the global namespace when referenced from headers in //external/libcxx/includes
-		"libc++_experimental",                  // http://b/198403271, Missing symbols/members in the global namespace when referenced from headers in //external/libcxx/includes
-		"libc++_static",                        // http://b/198403271, Missing symbols/members in the global namespace when referenced from headers in //external/libcxx/includes
-		"libc++abi",                            // http://b/195970501, cc_library_static, duplicate symbols because it propagates libc objects.
-		"libc++demangle",                       // http://b/195970501, cc_library_static, duplicate symbols because it propagates libc objects.
 		"func_to_syscall_nrs",                  // http://b/200899432, bazel-built cc_genrule does not work in mixed build when it is a dependency of another soong module.
 		"libseccomp_policy_app_zygote_sources", // http://b/200899432, bazel-built cc_genrule does not work in mixed build when it is a dependency of another soong module.
 		"libseccomp_policy_app_sources",        // http://b/200899432, bazel-built cc_genrule does not work in mixed build when it is a dependency of another soong module.
diff --git a/cc/cc.go b/cc/cc.go
index d2f8a12..57e7887 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -1711,7 +1711,9 @@
 func (c *Module) maybeGenerateBazelActions(actx android.ModuleContext) bool {
 	bazelModuleLabel := c.GetBazelLabel(actx, c)
 	bazelActionsUsed := false
-	if c.MixedBuildsEnabled(actx) && c.bazelHandler != nil {
+	// Mixed builds mode is disabled for modules outside of device OS.
+	// TODO(b/200841190): Support non-device OS in mixed builds.
+	if c.MixedBuildsEnabled(actx) && c.bazelHandler != nil && actx.Os().Class == android.Device {
 		bazelActionsUsed = c.bazelHandler.GenerateBazelBuildActions(actx, bazelModuleLabel)
 	}
 	return bazelActionsUsed
diff --git a/java/robolectric.go b/java/robolectric.go
index a0c9c7f..5d62aee 100644
--- a/java/robolectric.go
+++ b/java/robolectric.go
@@ -417,10 +417,10 @@
 		}
 		runtimeFromSourceJar := android.OutputFileForModule(ctx, runtimeFromSourceModule, "")
 
-		// TODO(murj) Update this to ctx.Config().PlatformSdkCodename() once the platform
-		// classes like android.os.Build are updated to S.
-		runtimeName := fmt.Sprintf("android-all-%s-robolectric-r0.jar",
-			"R")
+		// "TREE" name is essential here because it hooks into the "TREE" name in
+		// Robolectric's SdkConfig.java that will always correspond to the NEWEST_SDK
+		// in Robolectric configs.
+		runtimeName := "android-all-current-robolectric-r0.jar"
 		installedRuntime := ctx.InstallFile(androidAllDir, runtimeName, runtimeFromSourceJar)
 		r.runtimes = append(r.runtimes, installedRuntime)
 	}
diff --git a/rust/Android.bp b/rust/Android.bp
index 221014e..0ee673d 100644
--- a/rust/Android.bp
+++ b/rust/Android.bp
@@ -50,6 +50,7 @@
         "fuzz_test.go",
         "image_test.go",
         "library_test.go",
+        "proc_macro_test.go",
         "project_json_test.go",
         "protobuf_test.go",
         "rust_test.go",
diff --git a/rust/compiler.go b/rust/compiler.go
index 7bd9af4..1ce71f6 100644
--- a/rust/compiler.go
+++ b/rust/compiler.go
@@ -231,6 +231,7 @@
 	for _, cfg := range compiler.Properties.Cfgs {
 		flags = append(flags, "--cfg '"+cfg+"'")
 	}
+
 	return flags
 }
 
@@ -239,6 +240,24 @@
 	for _, feature := range compiler.Properties.Features {
 		flags = append(flags, "--cfg 'feature=\""+feature+"\"'")
 	}
+
+	return flags
+}
+
+func (compiler *baseCompiler) featureFlags(ctx ModuleContext, flags Flags) Flags {
+	flags.RustFlags = append(flags.RustFlags, compiler.featuresToFlags()...)
+	flags.RustdocFlags = append(flags.RustdocFlags, compiler.featuresToFlags()...)
+
+	return flags
+}
+
+func (compiler *baseCompiler) cfgFlags(ctx ModuleContext, flags Flags) Flags {
+	if ctx.RustModule().UseVndk() {
+		compiler.Properties.Cfgs = append(compiler.Properties.Cfgs, "android_vndk")
+	}
+
+	flags.RustFlags = append(flags.RustFlags, compiler.cfgsToFlags()...)
+	flags.RustdocFlags = append(flags.RustdocFlags, compiler.cfgsToFlags()...)
 	return flags
 }
 
@@ -269,10 +288,6 @@
 
 	flags.RustFlags = append(flags.RustFlags, lintFlags)
 	flags.RustFlags = append(flags.RustFlags, compiler.Properties.Flags...)
-	flags.RustFlags = append(flags.RustFlags, compiler.cfgsToFlags()...)
-	flags.RustFlags = append(flags.RustFlags, compiler.featuresToFlags()...)
-	flags.RustdocFlags = append(flags.RustdocFlags, compiler.cfgsToFlags()...)
-	flags.RustdocFlags = append(flags.RustdocFlags, compiler.featuresToFlags()...)
 	flags.RustFlags = append(flags.RustFlags, "--edition="+compiler.edition())
 	flags.RustdocFlags = append(flags.RustdocFlags, "--edition="+compiler.edition())
 	flags.LinkFlags = append(flags.LinkFlags, compiler.Properties.Ld_flags...)
@@ -296,10 +311,6 @@
 		flags.LinkFlags = append(flags.LinkFlags, "-Wl,-rpath,"+rpathPrefix+"../"+rpath)
 	}
 
-	if ctx.RustModule().UseVndk() {
-		flags.RustFlags = append(flags.RustFlags, "--cfg 'android_vndk'")
-	}
-
 	return flags
 }
 
diff --git a/rust/library.go b/rust/library.go
index 8c10e29..38dae4d 100644
--- a/rust/library.go
+++ b/rust/library.go
@@ -430,15 +430,25 @@
 	return library.getStem(ctx) + ctx.toolchain().SharedLibSuffix()
 }
 
-func (library *libraryDecorator) compilerFlags(ctx ModuleContext, flags Flags) Flags {
-	flags.RustFlags = append(flags.RustFlags, "-C metadata="+ctx.ModuleName())
+func (library *libraryDecorator) cfgFlags(ctx ModuleContext, flags Flags) Flags {
+	flags = library.baseCompiler.cfgFlags(ctx, flags)
 	if library.dylib() {
 		// We need to add a dependency on std in order to link crates as dylibs.
 		// The hack to add this dependency is guarded by the following cfg so
 		// that we don't force a dependency when it isn't needed.
 		library.baseCompiler.Properties.Cfgs = append(library.baseCompiler.Properties.Cfgs, "android_dylib")
 	}
+
+	flags.RustFlags = append(flags.RustFlags, library.baseCompiler.cfgsToFlags()...)
+	flags.RustdocFlags = append(flags.RustdocFlags, library.baseCompiler.cfgsToFlags()...)
+
+	return flags
+}
+
+func (library *libraryDecorator) compilerFlags(ctx ModuleContext, flags Flags) Flags {
 	flags = library.baseCompiler.compilerFlags(ctx, flags)
+
+	flags.RustFlags = append(flags.RustFlags, "-C metadata="+ctx.ModuleName())
 	if library.shared() || library.static() {
 		library.includeDirs = append(library.includeDirs, android.PathsForModuleSrc(ctx, library.Properties.Include_dirs)...)
 	}
diff --git a/rust/proc_macro.go b/rust/proc_macro.go
index c217959..804d79f 100644
--- a/rust/proc_macro.go
+++ b/rust/proc_macro.go
@@ -63,6 +63,12 @@
 		&procMacro.Properties)
 }
 
+func (procMacro *procMacroDecorator) compilerFlags(ctx ModuleContext, flags Flags) Flags {
+	flags = procMacro.baseCompiler.compilerFlags(ctx, flags)
+	flags.RustFlags = append(flags.RustFlags, "--extern proc_macro")
+	return flags
+}
+
 func (procMacro *procMacroDecorator) compile(ctx ModuleContext, flags Flags, deps PathDeps) android.Path {
 	fileName := procMacro.getStem(ctx) + ctx.toolchain().ProcMacroSuffix()
 	outputFile := android.PathForModuleOut(ctx, fileName)
diff --git a/rust/proc_macro_test.go b/rust/proc_macro_test.go
new file mode 100644
index 0000000..cc81938
--- /dev/null
+++ b/rust/proc_macro_test.go
@@ -0,0 +1,36 @@
+// Copyright 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 rust
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestRustProcMacro(t *testing.T) {
+	ctx := testRust(t, `
+          rust_proc_macro {
+	    name: "libprocmacro",
+	    srcs: ["foo.rs"],
+	    crate_name: "procmacro",
+	  }
+	`)
+
+	libprocmacro := ctx.ModuleForTests("libprocmacro", "linux_glibc_x86_64").Rule("rustc")
+
+	if !strings.Contains(libprocmacro.Args["rustcFlags"], "--extern proc_macro") {
+		t.Errorf("--extern proc_macro flag not being passed to rustc for proc macro %#v", libprocmacro.Args["rustcFlags"])
+	}
+}
diff --git a/rust/rust.go b/rust/rust.go
index 0cd299d..0a7d68d 100644
--- a/rust/rust.go
+++ b/rust/rust.go
@@ -436,6 +436,8 @@
 type compiler interface {
 	initialize(ctx ModuleContext)
 	compilerFlags(ctx ModuleContext, flags Flags) Flags
+	cfgFlags(ctx ModuleContext, flags Flags) Flags
+	featureFlags(ctx ModuleContext, flags Flags) Flags
 	compilerProps() []interface{}
 	compile(ctx ModuleContext, flags Flags, deps PathDeps) android.Path
 	compilerDeps(ctx DepsContext, deps Deps) Deps
@@ -847,8 +849,11 @@
 		Toolchain: toolchain,
 	}
 
+	// Calculate rustc flags
 	if mod.compiler != nil {
 		flags = mod.compiler.compilerFlags(ctx, flags)
+		flags = mod.compiler.cfgFlags(ctx, flags)
+		flags = mod.compiler.featureFlags(ctx, flags)
 	}
 	if mod.coverage != nil {
 		flags, deps = mod.coverage.flags(ctx, flags, deps)