[arm64] Build NDK with PAuth and BTI

This change adds a new arch named "armv8-a-branchprot". The new target
is no different from the usual "armv8-a" variant except it has the
compiler flag "-mbranch-protection=standard" set.

With this flag compiler emits Armv8.3-A Pointer Authentication and
Armv8.5-A Branch Target Identification instructions. All of these
instructions are in the hint space; therefore devices which do not
support any of these extensions would execute them as NOPs.

In terms of directory structure there is no change in the output of
build/soong/scripts/build-ndk-prebuilts.sh script.

Test: build NDK prebuilts

Change-Id: Ie52ccba5653fbf567f0b7ca312d8a8e71602ad06

android/arch.go

@@ -1434,7 +1434,7 @@ type archConfig struct {
 func getNdkAbisConfig() []archConfig {
 	return []archConfig{
 		{"arm", "armv7-a", "", []string{"armeabi-v7a"}},
-		{"arm64", "armv8-a", "", []string{"arm64-v8a"}},
+		{"arm64", "armv8-a-branchprot", "", []string{"arm64-v8a"}},
 		{"x86", "", "", []string{"x86"}},
 		{"x86_64", "", "", []string{"x86_64"}},
 	}

android/arch_list.go

@@ -41,6 +41,7 @@ var archVariants = map[ArchType][]string{
 	},
 	Arm64: {
 		"armv8_a",
+		"armv8_a_branchprot",
 		"armv8_2a",
 		"armv8-2a-dotprod",
 		"cortex-a53",

cc/config/arm64_device.go

@@ -31,6 +31,10 @@ var (
 		"armv8-a": []string{
 			"-march=armv8-a",
 		},
+		"armv8-a-branchprot": []string{
+			"-march=armv8-a",
+			"-mbranch-protection=standard",
+		},
 		"armv8-2a": []string{
 			"-march=armv8.2-a",
 		},
@@ -102,6 +106,7 @@ func init() {
 	pctx.StaticVariable("Arm64ClangCppflags", strings.Join(ClangFilterUnknownCflags(arm64Cppflags), " "))
 
 	pctx.StaticVariable("Arm64ClangArmv8ACflags", strings.Join(arm64ArchVariantCflags["armv8-a"], " "))
+	pctx.StaticVariable("Arm64ClangArmv8ABranchProtCflags", strings.Join(arm64ArchVariantCflags["armv8-a-branchprot"], " "))
 	pctx.StaticVariable("Arm64ClangArmv82ACflags", strings.Join(arm64ArchVariantCflags["armv8-2a"], " "))
 	pctx.StaticVariable("Arm64ClangArmv82ADotprodCflags", strings.Join(arm64ArchVariantCflags["armv8-2a-dotprod"], " "))
 
@@ -124,6 +129,7 @@ func init() {
 var (
 	arm64ClangArchVariantCflagsVar = map[string]string{
 		"armv8-a":  "${config.Arm64ClangArmv8ACflags}",
+		"armv8-a-branchprot": "${config.Arm64ClangArmv8ABranchProtCflags}",
 		"armv8-2a": "${config.Arm64ClangArmv82ACflags}",
 		"armv8-2a-dotprod": "${config.Arm64ClangArmv82ADotprodCflags}",
 	}
@@ -202,6 +208,7 @@ func (toolchainArm64) LibclangRuntimeLibraryArch() string {
 func arm64ToolchainFactory(arch android.Arch) Toolchain {
 	switch arch.ArchVariant {
 	case "armv8-a":
+	case "armv8-a-branchprot":
 	case "armv8-2a":
 	case "armv8-2a-dotprod":
 		// Nothing extra for armv8-a/armv8-2a

rust/config/arm64_device.go

@@ -26,9 +26,10 @@ var (
 	Arm64LinkFlags            = []string{}
 
 	Arm64ArchVariantRustFlags = map[string][]string{
-		"armv8-a":          []string{},
-		"armv8-2a":         []string{},
-		"armv8-2a-dotprod": []string{},
+		"armv8-a":            []string{},
+		"armv8-a-branchprot": []string{},
+		"armv8-2a":           []string{},
+		"armv8-2a-dotprod":   []string{},
 	}
 )