[CoreCLR] use string blob for environment variables

Eliminates N*2 relocations

Author: grendello

src/Xamarin.Android.Build.Tasks/Utilities/ApplicationConfigNativeAssemblyGeneratorCLR.cs

@@ -134,6 +134,42 @@ sealed class RuntimePropertyIndexEntry
 		public uint index;
 	}
 
+	sealed class AppEnvironmentVariableContextDataProvider : NativeAssemblerStructContextDataProvider
+	{
+		public override string GetComment (object data, string fieldName)
+		{
+			var envVar = EnsureType<AppEnvironmentVariable> (data);
+
+			if (String.Compare ("name_index", fieldName, StringComparison.Ordinal) == 0) {
+				return $" '{envVar.Name}'";
+			}
+
+			if (String.Compare ("value_index", fieldName, StringComparison.Ordinal) == 0) {
+				return $" '{envVar.Value}'";
+			}
+
+			return String.Empty;
+		}
+	}
+
+	// Order of fields and their type must correspond *exactly* to that in
+	// src/native/clr/include/xamarin-app.hh AppEnvironmentVariable structure
+	[NativeAssemblerStructContextDataProvider (typeof (AppEnvironmentVariableContextDataProvider))]
+	sealed class AppEnvironmentVariable
+	{
+		[NativeAssembler (Ignore = true)]
+		public string Name;
+
+		[NativeAssembler (Ignore = true)]
+		public string Value;
+
+		[NativeAssembler (UsesDataProvider = true)]
+		public uint name_index;
+
+		[NativeAssembler (UsesDataProvider = true)]
+		public uint value_index;
+	}
+
 	sealed class XamarinAndroidBundledAssemblyContextDataProvider : NativeAssemblerStructContextDataProvider
 	{
 		public override ulong GetBufferSize (object data, string fieldName)
@@ -195,6 +231,7 @@ sealed class XamarinAndroidBundledAssembly
 	StructureInfo? runtimePropertyIndexEntryStructureInfo;
 	StructureInfo? hostConfigurationPropertyStructureInfo;
 	StructureInfo? hostConfigurationPropertiesStructureInfo;
+	StructureInfo? appEnvironmentVariableStructureInfo;
 
 	public bool UsesAssemblyPreload { get; set; }
 	public string AndroidPackageName { get; set; }
@@ -244,10 +281,32 @@ protected override void Construct (LlvmIrModule module)
 
 		module.AddGlobalVariable ("format_tag", FORMAT_TAG, comment: $" 0x{FORMAT_TAG:x}");
 
-		var envVars = new LlvmIrGlobalVariable (environmentVariables, "app_environment_variables") {
+		var envVarsBlob = new LlvmIrStringBlob ();
+		var appEnvVars = new List<StructureInstance<AppEnvironmentVariable>> ();
+
+		if (environmentVariables != null) {
+			// TODO: skip variables with no name
+			foreach (var kvp in environmentVariables) {
+				(int nameOffset, int _) = envVarsBlob.Add (kvp.Key);
+				(int valueOffset, int _) = envVarsBlob.Add (kvp.Value);
+
+				var appEnvVar = new AppEnvironmentVariable {
+					Name = kvp.Key,
+					Value = kvp.Value,
+
+					name_index = (uint)nameOffset,
+					value_index = (uint)valueOffset,
+				};
+				appEnvVars.Add (new StructureInstance<AppEnvironmentVariable> (appEnvironmentVariableStructureInfo, appEnvVar));
+			}
+		}
+
+		var envVars = new LlvmIrGlobalVariable (appEnvVars, "app_environment_variables") {
 			Comment = " Application environment variables array, name:value",
+			Options = LlvmIrVariableOptions.GlobalConstant,
 		};
-		module.Add (envVars, stringGroupName: "env", stringGroupComment: " Application environment variables name:value pairs");
+		module.Add (envVars);
+		module.AddGlobalVariable ("app_environment_variable_contents", envVarsBlob, LlvmIrVariableOptions.GlobalConstant);
 
 		var sysProps = new LlvmIrGlobalVariable (systemProperties, "app_system_properties") {
 			Comment = " System properties defined by the application",
@@ -263,7 +322,7 @@ protected override void Construct (LlvmIrModule module)
 			ignore_split_configs = IgnoreSplitConfigs,
 			number_of_runtime_properties = (uint)(runtimeProperties == null ? 0 : runtimeProperties.Count),
 			package_naming_policy = (uint)PackageNamingPolicy,
-			environment_variable_count = (uint)(environmentVariables == null ? 0 : environmentVariables.Count * 2),
+			environment_variable_count = (uint)(environmentVariables == null ? 0 : environmentVariables.Count),
 			system_property_count = (uint)(systemProperties == null ? 0 : systemProperties.Count * 2),
 			number_of_assemblies_in_apk = (uint)NumberOfAssembliesInApk,
 			number_of_shared_libraries = (uint)NativeLibraries.Count,
@@ -541,5 +600,6 @@ void MapStructures (LlvmIrModule module)
 		dsoApkEntryStructureInfo = module.MapStructure<DSOApkEntry> ();
 		runtimePropertyStructureInfo = module.MapStructure<RuntimeProperty> ();
 		runtimePropertyIndexEntryStructureInfo = module.MapStructure<RuntimePropertyIndexEntry> ();
+		appEnvironmentVariableStructureInfo = module.MapStructure<AppEnvironmentVariable> ();
 	}
 }

src/native/clr/include/xamarin-app.hh

@@ -322,6 +322,12 @@ struct JniRemappingTypeReplacementEntry
 	const char      *replacement;
 };
 
+struct AppEnvironmentVariable
+{
+	const uint32_t name_index;
+	const uint32_t value_index;
+};
+
 extern "C" {
 	[[gnu::visibility("default")]] extern const JniRemappingIndexTypeEntry jni_remapping_method_replacement_index[];
 	[[gnu::visibility("default")]] extern const JniRemappingTypeReplacementEntry jni_remapping_type_replacements[];
@@ -353,7 +359,8 @@ extern "C" {
 	[[gnu::visibility("default")]] extern uint32_t uncompressed_assemblies_data_size;
 	[[gnu::visibility("default")]] extern uint8_t uncompressed_assemblies_data_buffer[];
 	[[gnu::visibility("default")]] extern const ApplicationConfig application_config;
-	[[gnu::visibility("default")]] extern const char* const app_environment_variables[];
+	[[gnu::visibility("default")]] extern const AppEnvironmentVariable app_environment_variables[];
+	[[gnu::visibility("default")]] extern const char app_environment_variable_contents[];
 	[[gnu::visibility("default")]] extern const char* const app_system_properties[];
 
 	[[gnu::visibility("default")]] extern const char* const mono_aot_mode_name;

src/native/clr/runtime-base/android-system.cc

@@ -230,16 +230,10 @@ AndroidSystem::setup_environment () noexcept
 
 	const char *var_name;
 	const char *var_value;
-	for (size_t i = 0uz; i < application_config.environment_variable_count; i += 2) {
-		var_name = app_environment_variables [i];
-		if (var_name == nullptr || *var_name == '\0') {
-			continue;
-		}
-
-		var_value = app_environment_variables [i + 1uz];
-		if (var_value == nullptr) {
-			var_value = "";
-		}
+	for (size_t i = 0uz; i < application_config.environment_variable_count; i++) {
+		AppEnvironmentVariable const& env_var = app_environment_variables [i];
+		var_name = &app_environment_variable_contents[env_var.name_index];
+		var_value = &app_environment_variable_contents[env_var.value_index];
 
 		if constexpr (Constants::is_debug_build) {
 			log_info (LOG_DEFAULT, "Setting environment variable '{}' to '{}'", var_name, var_value);

src/native/clr/xamarin-app-stub/application_dso_stub.cc

@@ -72,7 +72,8 @@ const ApplicationConfig application_config = {
 };
 
 // TODO: migrate to std::string_view for these two
-const char* const app_environment_variables[] = {};
+const AppEnvironmentVariable app_environment_variables[] = {};
+const char app_environment_variable_contents[] = {};
 const char* const app_system_properties[] = {};
 
 static constexpr size_t AssemblyNameWidth = 128uz;