xamarin-macios/tools/mtouch/Target.cs

// Copyright 2013--2014 Xamarin Inc. All rights reserved.

using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;
using System.Threading.Tasks;
using System.Xml;

using MonoTouch.Tuner;

using Mono.Cecil;
using Mono.Tuner;
using Mono.Linker;
using Xamarin.Linker;

using Xamarin.Utils;

using XamCore.Registrar;

namespace Xamarin.Bundler
{
	public partial class Target {
		public string TargetDirectory;
		public string AppTargetDirectory;

		public MonoTouchManifestResolver ManifestResolver = new MonoTouchManifestResolver ();
		public AssemblyDefinition ProductAssembly;

		// directories used during the build process
		public string ArchDirectory;
		public string PreBuildDirectory;
		public string BuildDirectory;
		public string LinkDirectory;

		// Note that each 'Target' can have multiple abis: armv7+armv7s for instance.
		public List<Abi> Abis;

		// This is a list of native libraries to into the final executable.
		// All the native libraries are included here (this means all the libraries
		// that were AOTed from managed code, main, registrar, extra static libraries, etc).
		List<string> link_with = new List<string> ();

		// If we didn't link because the existing (cached) assemblyes are up-to-date.
		bool cached_link;

		// If any assemblies were updated (only set to false if the linker is disabled and no assemblies were modified).
		bool any_assembly_updated = true;

		BuildTasks compile_tasks = new BuildTasks ();

		// If we didn't link the final executable because the existing binary is up-to-date.
		public bool cached_executable; 

		// If the assemblies were symlinked.
		public bool Symlinked;

		public bool Is32Build { get { return Application.IsArchEnabled (Abis, Abi.Arch32Mask); } } // If we're targetting a 32 bit arch for this target.
		public bool Is64Build { get { return Application.IsArchEnabled (Abis, Abi.Arch64Mask); } } // If we're targetting a 64 bit arch for this target.

		List<string> link_with_and_ship = new List<string> ();
		public IEnumerable<string> LibrariesToShip { get { return link_with_and_ship; } }

		PInvokeWrapperGenerator pinvoke_state;
		PInvokeWrapperGenerator MarshalNativeExceptionsState {
			get {
				if (!App.RequiresPInvokeWrappers)
					return null;

				if (pinvoke_state == null) {
					pinvoke_state = new PInvokeWrapperGenerator ()
					{
						App = App,
						SourcePath = Path.Combine (ArchDirectory, "pinvokes.m"),
						HeaderPath = Path.Combine (ArchDirectory, "pinvokes.h"),
						Registrar = (StaticRegistrar) StaticRegistrar,
					};
				}

				return pinvoke_state;
			}
		}

		public string Executable {
			get {
				return Path.Combine (TargetDirectory, App.ExecutableName);
			}
		}

		public void Initialize (bool show_warnings)
		{
			// we want to load our own mscorlib[-runtime].dll, not something else we're being feeded
			// (e.g. bug #6612) since it might not match the libmono[-sgen].a library we'll link with,
			// so load the corlib we want first.

			var corlib_path = Path.Combine (Resolver.FrameworkDirectory, "mscorlib.dll");
			var corlib = ManifestResolver.Load (corlib_path);
			if (corlib == null)
				throw new MonoTouchException (2006, true, "Can not load mscorlib.dll from: '{0}'. Please reinstall Xamarin.iOS.", corlib_path);

			foreach (var reference in App.References) {
				var ad = ManifestResolver.Load (reference);
				if (ad == null)
					throw new MonoTouchException (2002, true, "Can not resolve reference: {0}", reference);
				if (ad.MainModule.Runtime > TargetRuntime.Net_4_0)
					ErrorHelper.Show (new MonoTouchException (11, false, "{0} was built against a more recent runtime ({1}) than Xamarin.iOS supports.", Path.GetFileName (reference), ad.MainModule.Runtime));

				// Figure out if we're referencing Xamarin.iOS or monotouch.dll
				if (Path.GetFileNameWithoutExtension (ad.MainModule.FileName) == Driver.GetProductAssembly (App))
					ProductAssembly = ad;
			}

			ComputeListOfAssemblies ();

			if (App.LinkMode == LinkMode.None && App.I18n != I18nAssemblies.None)
				AddI18nAssemblies ();

			// an extension is a .dll and it would match itself
			if (App.IsExtension)
				return;

			var root_wo_ext = Path.GetFileNameWithoutExtension (App.RootAssembly);
			foreach (var assembly in Assemblies) {
				if (!assembly.FullPath.EndsWith (".exe", StringComparison.OrdinalIgnoreCase)) {
					if (root_wo_ext == Path.GetFileNameWithoutExtension (assembly.FullPath))
						throw new MonoTouchException (23, true, "Application name '{0}.exe' conflicts with another user assembly.", root_wo_ext);
				}
			}
		}

		// This is to load the symbols for all assemblies, so that we can give better error messages
		// (with file name / line number information).
		public void LoadSymbols ()
		{
			foreach (var a in Assemblies)
				a.LoadSymbols ();
		}

		IEnumerable<AssemblyDefinition> GetAssemblies ()
		{
			if (App.LinkMode == LinkMode.None)
				return ManifestResolver.GetAssemblies ();

			List<AssemblyDefinition> assemblies = new List<AssemblyDefinition> ();
			if (LinkContext == null) {
				// use data from cache
				foreach (var assembly in Assemblies)
					assemblies.Add (assembly.AssemblyDefinition);
			} else {
				foreach (var assembly in LinkContext.GetAssemblies ()) {
					if (LinkContext.Annotations.GetAction (assembly) == AssemblyAction.Delete)
						continue;

					assemblies.Add (assembly);
				}
			}
			return assemblies;
		}

		public void ComputeLinkerFlags ()
		{
			foreach (var a in Assemblies)
				a.ComputeLinkerFlags ();

			if (App.Platform != ApplePlatform.WatchOS && App.Platform != ApplePlatform.TVOS)
				Frameworks.Add ("CFNetwork"); // required by xamarin_start_wwan
		}

		Dictionary<string, List<MemberReference>> entry_points;
		public IDictionary<string, List<MemberReference>> GetEntryPoints ()
		{
			if (entry_points == null)
				GetRequiredSymbols ();
			return entry_points;
		}

		public IEnumerable<string> GetRequiredSymbols ()
		{
			if (entry_points != null)  
				return entry_points.Keys;

			var cache_location = Path.Combine (App.Cache.Location, "entry-points.txt");
			if (cached_link || !any_assembly_updated) {
				entry_points = new Dictionary<string, List<MemberReference>> ();
				foreach (var ep in File.ReadAllLines (cache_location))
					entry_points.Add (ep, null);
			} else {
				List<MethodDefinition> marshal_exception_pinvokes;
				if (LinkContext == null) {
					// This happens when using the simlauncher and the msbuild tasks asked for a list
					// of symbols (--symbollist). In that case just produce an empty list, since the
					// binary shouldn't end up stripped anyway.
					entry_points = new Dictionary<string, List<MemberReference>> ();
					marshal_exception_pinvokes = new List<MethodDefinition> ();
				} else {
					entry_points = LinkContext.RequiredSymbols;
					marshal_exception_pinvokes = LinkContext.MarshalExceptionPInvokes;
				}
				
				// keep the debugging helper in debugging binaries only
				if (App.EnableDebug && !App.EnableBitCode)
					entry_points.Add ("mono_pmip", null);

				if (App.IsSimulatorBuild) {
					entry_points.Add ("xamarin_dyn_objc_msgSend", null);
					entry_points.Add ("xamarin_dyn_objc_msgSendSuper", null);
					entry_points.Add ("xamarin_dyn_objc_msgSend_stret", null);
					entry_points.Add ("xamarin_dyn_objc_msgSendSuper_stret", null);
				}

				File.WriteAllText (cache_location, string.Join ("\n", entry_points.Keys.ToArray ()));
			}
			return entry_points.Keys;
		}

		public IEnumerable<string> GetRequiredSymbols (Assembly assembly, bool includeObjectiveCClasses)
		{
			if (entry_points == null)
				GetRequiredSymbols ();

			foreach (var ep in entry_points) {
				if (ep.Value == null)
					continue;
				foreach (var mr in ep.Value) {
					if (mr.Module.Assembly == assembly.AssemblyDefinition)
						yield return ep.Key;
				}
			}

			if (includeObjectiveCClasses) {
				foreach (var kvp in LinkContext.ObjectiveCClasses) {
					if (kvp.Value.Module.Assembly == assembly.AssemblyDefinition)
						yield return $"OBJC_CLASS_$_{kvp.Key}";
				}
			}
		}

		public List<MemberReference> GetMembersForSymbol (string symbol)
		{
			List<MemberReference> rv = null;
			entry_points?.TryGetValue (symbol, out rv);
			return rv;
		}

		//
		// Gets a flattened list of all the assemblies pulled by the root assembly
		//
		public void ComputeListOfAssemblies ()
		{
			var exceptions = new List<Exception> ();
			var assemblies = new HashSet<string> ();

			try {
				var assembly = ManifestResolver.Load (App.RootAssembly);
				ComputeListOfAssemblies (assemblies, assembly, exceptions);
			} catch (MonoTouchException mte) {
				exceptions.Add (mte);
			} catch (Exception e) {
				exceptions.Add (new MonoTouchException (9, true, e, "Error while loading assemblies: {0}", e.Message));
			}

			if (App.LinkMode == LinkMode.None)
				exceptions.AddRange (ManifestResolver.list);

			if (exceptions.Count > 0)
				throw new AggregateException (exceptions);
		}

		void ComputeListOfAssemblies (HashSet<string> assemblies, AssemblyDefinition assembly, List<Exception> exceptions)
		{
			if (assembly == null)
				return;

			var fqname = assembly.MainModule.FileName;
			if (assemblies.Contains (fqname))
				return;

			assemblies.Add (fqname);

			var asm = new Assembly (this, assembly);
			asm.ComputeSatellites ();
			this.Assemblies.Add (asm);

			var main = assembly.MainModule;
			foreach (AssemblyNameReference reference in main.AssemblyReferences) {
				// Verify that none of the references references an incorrect platform assembly.
				switch (reference.Name) {
				case "monotouch":
				case "Xamarin.iOS":
				case "Xamarin.TVOS":
				case "Xamarin.WatchOS":
					if (reference.Name != Driver.GetProductAssembly (App))
						exceptions.Add (ErrorHelper.CreateError (34, "Cannot reference '{0}.dll' in a {1} project - it is implicitly referenced by '{2}'.", reference.Name, Driver.TargetFramework.Identifier, assembly.FullName));
					break;
				}

				var reference_assembly = ManifestResolver.Resolve (reference);
				ComputeListOfAssemblies (assemblies, reference_assembly, exceptions);
			}

			// Custom Attribute metadata can include references to other assemblies, e.g. [X (typeof (Y)], 
			// but it is not reflected in AssemblyReferences :-( ref: #37611
			// so we must scan every custom attribute to look for System.Type
			GetCustomAttributeReferences (assembly, assemblies, exceptions);
			GetCustomAttributeReferences (main, assemblies, exceptions);
			if (main.HasTypes) {
				foreach (var ca in main.GetCustomAttributes ())
					GetCustomAttributeReferences (ca, assemblies, exceptions);
			}
		}

		void GetCustomAttributeReferences (ICustomAttributeProvider cap, HashSet<string> assemblies, List<Exception> exceptions)
		{
			if (!cap.HasCustomAttributes)
				return;
			foreach (var ca in cap.CustomAttributes)
				GetCustomAttributeReferences (ca, assemblies, exceptions);
		}

		void GetCustomAttributeReferences (CustomAttribute ca, HashSet<string> assemblies, List<Exception> exceptions)
		{
			if (ca.HasConstructorArguments) {
				foreach (var arg in ca.ConstructorArguments)
					GetCustomAttributeArgumentReference (arg, assemblies, exceptions);
			}
			if (ca.HasFields) {
				foreach (var arg in ca.Fields)
					GetCustomAttributeArgumentReference (arg.Argument, assemblies, exceptions);
			}
			if (ca.HasProperties) {
				foreach (var arg in ca.Properties)
					GetCustomAttributeArgumentReference (arg.Argument, assemblies, exceptions);
			}
		}

		void GetCustomAttributeArgumentReference (CustomAttributeArgument arg, HashSet<string> assemblies, List<Exception> exceptions)
		{
			if (!arg.Type.Is ("System", "Type"))
				return;
			var ar = (arg.Value as TypeReference)?.Scope as AssemblyNameReference;
			if (ar == null)
				return;
			var reference_assembly = ManifestResolver.Resolve (ar);
			ComputeListOfAssemblies (assemblies, reference_assembly, exceptions);
		}

		bool IncludeI18nAssembly (Mono.Linker.I18nAssemblies assembly)
		{
			return (App.I18n & assembly) != 0;
		}

		public void AddI18nAssemblies ()
		{
			Assemblies.Add (LoadI18nAssembly ("I18N"));

			if (IncludeI18nAssembly (Mono.Linker.I18nAssemblies.CJK))
				Assemblies.Add (LoadI18nAssembly ("I18N.CJK"));

			if (IncludeI18nAssembly (Mono.Linker.I18nAssemblies.MidEast))
				Assemblies.Add (LoadI18nAssembly ("I18N.MidEast"));

			if (IncludeI18nAssembly (Mono.Linker.I18nAssemblies.Other))
				Assemblies.Add (LoadI18nAssembly ("I18N.Other"));

			if (IncludeI18nAssembly (Mono.Linker.I18nAssemblies.Rare))
				Assemblies.Add (LoadI18nAssembly ("I18N.Rare"));

			if (IncludeI18nAssembly (Mono.Linker.I18nAssemblies.West))
				Assemblies.Add (LoadI18nAssembly ("I18N.West"));
		}

		Assembly LoadI18nAssembly (string name)
		{
			var assembly = ManifestResolver.Resolve (AssemblyNameReference.Parse (name));
			return new Assembly (this, assembly);
		}

		public void LinkAssemblies (string main, ref List<string> assemblies, string output_dir, out MonoTouchLinkContext link_context)
		{
			if (Driver.Verbosity > 0)
				Console.WriteLine ("Linking {0} into {1} using mode '{2}'", main, output_dir, App.LinkMode);

			var cache = Resolver.ToResolverCache ();
			var resolver = cache != null
				? new AssemblyResolver (cache)
				: new AssemblyResolver ();

			resolver.AddSearchDirectory (Resolver.RootDirectory);
			resolver.AddSearchDirectory (Resolver.FrameworkDirectory);

			LinkerOptions = new LinkerOptions {
				MainAssembly = Resolver.Load (main),
				OutputDirectory = output_dir,
				LinkMode = App.LinkMode,
				Resolver = resolver,
				SkippedAssemblies = App.LinkSkipped,
				I18nAssemblies = App.I18n,
				LinkSymbols = true,
				LinkAway = App.LinkAway,
				ExtraDefinitions = App.Definitions,
				Device = App.IsDeviceBuild,
				// by default we keep the code to ensure we're executing on the UI thread (for UI code) for debug builds
				// but this can be overridden to either (a) remove it from debug builds or (b) keep it in release builds
				EnsureUIThread = App.ThreadCheck.HasValue ? App.ThreadCheck.Value : App.EnableDebug,
				DebugBuild = App.EnableDebug,
				Arch = Is64Build ? 8 : 4,
				IsDualBuild = App.IsDualBuild,
				DumpDependencies = App.LinkerDumpDependencies,
				RuntimeOptions = App.RuntimeOptions,
				MarshalNativeExceptionsState = MarshalNativeExceptionsState,
				Target = this,
			};

			MonoTouch.Tuner.Linker.Process (LinkerOptions, out link_context, out assemblies);

			Driver.Watch ("Link Assemblies", 1);
		}

		public void ManagedLink ()
		{
			var cache_path = Path.Combine (ArchDirectory, "linked-assemblies.txt");

			foreach (var a in Assemblies)
				a.CopyToDirectory (LinkDirectory, false, check_case: true);

			// Check if we can use a previous link result.
			if (!Driver.Force) {
				var input = new List<string> ();
				var output = new List<string> ();
				var cached_output = new List<string> ();

				if (File.Exists (cache_path)) {
					cached_output.AddRange (File.ReadAllLines (cache_path));

					var cached_loaded = new HashSet<string> ();
					// Only add the previously linked assemblies (and their satellites) as the input/output assemblies.
					// Do not add assemblies which the linker process removed.
					foreach (var a in Assemblies) {
						if (!cached_output.Contains (a.FullPath))
							continue;
						cached_loaded.Add (a.FullPath);
						input.Add (a.FullPath);
						output.Add (Path.Combine (PreBuildDirectory, a.FileName));
						if (File.Exists (a.FullPath + ".mdb")) {
							// Debug files can change without the assemblies themselves changing
							// This should also invalidate the cached linker results, since the non-linked mdbs can't be copied.
							input.Add (a.FullPath + ".mdb");
							output.Add (Path.Combine (PreBuildDirectory, a.FileName) + ".mdb");
						}
						
						if (a.Satellites != null) {
							foreach (var s in a.Satellites) {
								input.Add (s);
								output.Add (Path.Combine (PreBuildDirectory, Path.GetFileName (Path.GetDirectoryName (s)), Path.GetFileName (s)));
								// No need to copy satellite mdb files, satellites are resource-only assemblies.
							}
						}
					}

					// The linker might have added assemblies that weren't specified/reachable
					// from the command line arguments (such as I18N assemblies). Those are not
					// in the Assemblies list at this point (since we haven't run the linker yet)
					// so make sure we take those into account as well.
					var not_loaded = cached_output.Except (cached_loaded);
					foreach (var path in not_loaded) {
						input.Add (path);
						output.Add (Path.Combine (PreBuildDirectory, Path.GetFileName (path)));
					}

					// Include mtouch here too?
					// input.Add (Path.Combine (MTouch.MonoTouchDirectory, "usr", "bin", "mtouch"));

					if (Application.IsUptodate (input, output)) {
						cached_link = true;
						for (int i = Assemblies.Count - 1; i >= 0; i--) {
							var a = Assemblies [i];
							if (!cached_output.Contains (a.FullPath)) {
								Assemblies.RemoveAt (i);
								continue;
							}
							// Load the cached assembly
							a.LoadAssembly (Path.Combine (PreBuildDirectory, a.FileName));
							Driver.Log (3, "Target '{0}' is up-to-date.", a.FullPath);
						}

						foreach (var path in not_loaded) {
							var a = new Assembly (this, path);
							a.LoadAssembly (Path.Combine (PreBuildDirectory, a.FileName));
							Assemblies.Add (a);
						}

						Driver.Watch ("Cached assemblies reloaded", 1);
						Driver.Log ("Cached assemblies reloaded.");

						return;
					}
				}
			}

			// Load the assemblies into memory.
			foreach (var a in Assemblies)
				a.LoadAssembly (a.FullPath);

			var assemblies = new List<string> ();
			foreach (var a in Assemblies)
				assemblies.Add (a.FullPath);
			var linked_assemblies = new List<string> (assemblies);

			LinkAssemblies (App.RootAssembly, ref linked_assemblies, PreBuildDirectory, out LinkContext);

			// Remove assemblies that were linked away
			var removed = new HashSet<string> (assemblies);
			removed.ExceptWith (linked_assemblies);

			foreach (var assembly in removed) {
				for (int i = Assemblies.Count - 1; i >= 0; i--) {
					var ad = Assemblies [i];
					if (assembly != ad.FullPath)
						continue;

					Assemblies.RemoveAt (i);
				}
			}

			// anything added by the linker will have it's original path
			var added = new HashSet<string> ();
			foreach (var assembly in linked_assemblies)
				added.Add (Path.GetFileName (assembly));
			var original = new HashSet<string> ();
			foreach (var assembly in assemblies)
				original.Add (Path.GetFileName (assembly));
			added.ExceptWith (original);

			foreach (var assembly in added) {
				// the linker already copied the assemblies (linked or not) into the output directory
				// and we must NOT overwrite the linker work with an original (unlinked) assembly
				string path = Path.Combine (PreBuildDirectory, assembly);
				var ad = ManifestResolver.Load (path);
				var a = new Assembly (this, ad);
				a.CopyToDirectory (PreBuildDirectory);
				Assemblies.Add (a);
			}

			assemblies = linked_assemblies;

			// Make the assemblies point to the right path.
			foreach (var a in Assemblies)
				a.FullPath = Path.Combine (PreBuildDirectory, a.FileName);

			File.WriteAllText (cache_path, string.Join ("\n", linked_assemblies));
		}
			
		public void ProcessAssemblies ()
		{
			//
			// * Linking
			//   Copy assemblies to LinkDirectory
			//   Link and save to PreBuildDirectory
			//   If marshalling native exceptions:
			//     * Generate/calculate P/Invoke wrappers and save to PreBuildDirectory
			//   [AOT assemblies in BuildDirectory]
			//   Strip managed code save to TargetDirectory (or just copy the file if stripping is disabled).
			//
			// * No linking
			//   If marshalling native exceptions:
			//     Generate/calculate P/Invoke wrappers and save to PreBuildDirectory.
			//   If not marshalling native exceptions:
			//     Copy assemblies to PreBuildDirectory
			//     Copy unmodified assemblies to BuildDirectory
			//   [AOT assemblies in BuildDirectory]
			//   Strip managed code save to TargetDirectory (or just copy the file if stripping is disabled).
			//
			// Note that we end up copying assemblies around quite much,
			// this is because we we're comparing contents instead of 
			// filestamps, so we need the previous file around to be
			// able to do the actual comparison. For instance: in the
			// 'No linking' case above, we copy the assembly to PreBuild
			// before removing the resources and saving that result to Build.
			// The copy in PreBuild is required for the next build iteration,
			// to see if the original assembly has been modified or not (the
			// file in the Build directory might be different due to resource
			// removal even if the original assembly didn't change).
			//
			// This can probably be improved by storing digests/hashes instead
			// of the entire files, but this turned out a bit messy when
			// trying to make it work with the linker, so I decided to go for
			// simple file copying for now.
			//

			// 
			// Other notes:
			//
			// * We need all assemblies in the same directory when doing AOT-compilation.
			// * We cannot overwrite in-place, because it will mess up dependency tracking 
			//   and besides if we overwrite in place we might not be able to ignore
			//   insignificant changes (such as only a GUID change - the code is identical,
			//   but we still need the original assembly since the AOT-ed image also stores
			//   the GUID, and we fail at runtime if the GUIDs in the assembly and the AOT-ed
			//   image don't match - if we overwrite in-place we lose the original assembly and
			//   its GUID).
			// 

			LinkDirectory = Path.Combine (ArchDirectory, "Link");
			if (!Directory.Exists (LinkDirectory))
				Directory.CreateDirectory (LinkDirectory);

			PreBuildDirectory = Path.Combine (ArchDirectory, "PreBuild");
			if (!Directory.Exists (PreBuildDirectory))
				Directory.CreateDirectory (PreBuildDirectory);
			
			BuildDirectory = Path.Combine (ArchDirectory, "Build");
			if (!Directory.Exists (BuildDirectory))
				Directory.CreateDirectory (BuildDirectory);

			if (!Directory.Exists (TargetDirectory))
				Directory.CreateDirectory (TargetDirectory);

			ManagedLink ();

			if (App.RequiresPInvokeWrappers) {
				// Write P/Invokes
				var state = MarshalNativeExceptionsState;
				if (state.Started) {
					// The generator is 'started' by the linker, which means it may not
					// be started if the linker was not executed due to re-using cached results.
					state.End ();
				}
				
				PinvokesTask.Create (compile_tasks, Abis, this, state.SourcePath);

				if (App.FastDev) {
					// In this case assemblies must link with the resulting dylib,
					// so we can't compile the pinvoke dylib in parallel with later
					// stuff.
					compile_tasks.ExecuteInParallel ();
				}
			}

			// Now the assemblies are in PreBuildDirectory.

			foreach (var a in Assemblies) {
				var target = Path.Combine (BuildDirectory, a.FileName);
				if (!a.CopyAssembly (a.FullPath, target))
					Driver.Log (3, "Target '{0}' is up-to-date.", target);
				a.FullPath = target;
			}

			Driver.GatherFrameworks (this, Frameworks, WeakFrameworks);

			// Make sure there are no duplicates between frameworks and weak frameworks.
			// Keep the weak ones.
			Frameworks.ExceptWith (WeakFrameworks);
		}

		public void SelectStaticRegistrar ()
		{
			switch (App.Registrar) {
			case RegistrarMode.Static:
			case RegistrarMode.Dynamic:
			case RegistrarMode.Default:
				StaticRegistrar = new StaticRegistrar (this)
				{
					LinkContext = LinkContext,
				};
				break;
			}
		}

		public void Compile ()
		{
			// Compile the managed assemblies into object files or shared libraries
			if (App.IsDeviceBuild) {
				foreach (var a in Assemblies)
					a.CreateCompilationTasks (compile_tasks, BuildDirectory, Abis);
			}

			// The static registrar.
			List<string> registration_methods = null;
			if (App.Registrar == RegistrarMode.Static) {
				var registrar_m = Path.Combine (ArchDirectory, "registrar.m");
				var registrar_h = Path.Combine (ArchDirectory, "registrar.h");
				if (!Application.IsUptodate (Assemblies.Select (v => v.FullPath), new string[] { registrar_m, registrar_h })) {
					StaticRegistrar.Generate (Assemblies.Select ((a) => a.AssemblyDefinition), registrar_h, registrar_m);
					registration_methods = new List<string> ();
					registration_methods.Add ("xamarin_create_classes");
					Driver.Watch ("Registrar", 1);
				} else {
					Driver.Log (3, "Target '{0}' is up-to-date.", registrar_m);
				}

				RegistrarTask.Create (compile_tasks, Abis, this, registrar_m);
			}

			if (App.Registrar == RegistrarMode.Dynamic && App.IsSimulatorBuild && App.LinkMode == LinkMode.None) {
				if (registration_methods == null)
					registration_methods = new List<string> ();

				string method;
				string library;
				switch (App.Platform) {
				case ApplePlatform.iOS:
					method = "xamarin_create_classes_Xamarin_iOS";
					library = "Xamarin.iOS.registrar.a";
					break;
				case ApplePlatform.WatchOS:
					method = "xamarin_create_classes_Xamarin_WatchOS";
					library = "Xamarin.WatchOS.registrar.a";
					break;					
				case ApplePlatform.TVOS:
					method = "xamarin_create_classes_Xamarin_TVOS";
					library = "Xamarin.TVOS.registrar.a";
					break;
				default:
					throw ErrorHelper.CreateError (71, "Unknown platform: {0}. This usually indicates a bug in Xamarin.iOS; please file a bug report at http://bugzilla.xamarin.com with a test case.", App.Platform);
				}

				registration_methods.Add (method);
				link_with.Add (Path.Combine (Driver.GetProductSdkDirectory (App), "usr", "lib", library));
			}

			// The main method.
			foreach (var abi in Abis)
				MainTask.Create (compile_tasks, this, abi, Assemblies, App.AssemblyName, registration_methods);

			// Start compiling.
			compile_tasks.ExecuteInParallel ();

			if (App.FastDev) {
				foreach (var a in Assemblies) {
					if (a.Dylibs == null)
						continue;
					foreach (var dylib in a.Dylibs)
						LinkWith (dylib);
				}
			}

			Driver.Watch ("Compile", 1);
		}

		public void NativeLink ()
		{
			if (!string.IsNullOrEmpty (App.UserGccFlags))
				App.DeadStrip = false;
			if (App.EnableLLVMOnlyBitCode)
				App.DeadStrip = false;

			var compiler_flags = new CompilerFlags () { Target = this };

			// Get global frameworks
			compiler_flags.AddFrameworks (App.Frameworks, App.WeakFrameworks);
			compiler_flags.AddFrameworks (Frameworks, WeakFrameworks);

			// Collect all LinkWith flags and frameworks from all assemblies.
			foreach (var a in Assemblies) {
				compiler_flags.AddFrameworks (a.Frameworks, a.WeakFrameworks);
				if (!App.FastDev || App.IsSimulatorBuild)
					compiler_flags.AddLinkWith (a.LinkWith, a.ForceLoad);
				compiler_flags.AddOtherFlags (a.LinkerFlags);
			}

			var bitcode = App.EnableBitCode;
			if (bitcode)
				compiler_flags.AddOtherFlag (App.EnableMarkerOnlyBitCode ? "-fembed-bitcode-marker" : "-fembed-bitcode");
			
			if (App.EnablePie.HasValue && App.EnablePie.Value && (App.DeploymentTarget < new Version (4, 2)))
				ErrorHelper.Error (28, "Cannot enable PIE (-pie) when targeting iOS 4.1 or earlier. Please disable PIE (-pie:false) or set the deployment target to at least iOS 4.2");

			if (!App.EnablePie.HasValue)
				App.EnablePie = true;

			if (App.Platform == ApplePlatform.iOS) {
				if (App.EnablePie.Value && (App.DeploymentTarget >= new Version (4, 2))) {
					compiler_flags.AddOtherFlag ("-Wl,-pie");
				} else {
					compiler_flags.AddOtherFlag ("-Wl,-no_pie");
				}
			}

			CompileTask.GetArchFlags (compiler_flags, Abis);
			if (App.IsDeviceBuild) {
				compiler_flags.AddOtherFlag ($"-m{Driver.GetTargetMinSdkName (App)}-version-min={App.DeploymentTarget}");
				compiler_flags.AddOtherFlag ($"-isysroot {Driver.Quote (Driver.GetFrameworkDirectory (App))}");
			} else {
				CompileTask.GetSimulatorCompilerFlags (compiler_flags, null, App);
			}
			compiler_flags.LinkWithMono ();
			compiler_flags.LinkWithXamarin ();

			compiler_flags.AddLinkWith (link_with);
			compiler_flags.AddOtherFlag ($"-o {Driver.Quote (Executable)}");

			compiler_flags.AddOtherFlag ("-lz");
			compiler_flags.AddOtherFlag ("-liconv");

			bool need_libcpp = false;
			if (App.EnableBitCode)
				need_libcpp = true;
#if ENABLE_BITCODE_ON_IOS
			need_libcpp = true;
#endif
			if (need_libcpp)
				compiler_flags.AddOtherFlag ("-lc++");

			// allow the native linker to remove unused symbols (if the caller was removed by the managed linker)
			if (!bitcode) {
				// Note that we include *all* (__Internal) p/invoked symbols here
				// We also include any fields from [Field] attributes.
				compiler_flags.ReferenceSymbols (GetRequiredSymbols ());
			}

			string mainlib;
			if (App.IsWatchExtension) {
				mainlib = "libwatchextension.a";
				compiler_flags.AddOtherFlag (" -e _xamarin_watchextension_main");
			} else if (App.IsTVExtension) {
				mainlib = "libtvextension.a";
			} else if (App.IsExtension) {
				mainlib = "libextension.a";
			} else {
				mainlib = "libapp.a";
			}
			var libdir = Path.Combine (Driver.GetProductSdkDirectory (App), "usr", "lib");
			var libmain = Path.Combine (libdir, mainlib);
			compiler_flags.AddLinkWith (libmain, true);

			if (App.EnableProfiling) {
				string libprofiler;
				if (App.FastDev) {
					libprofiler = Path.Combine (libdir, "libmono-profiler-log.dylib");
					compiler_flags.AddLinkWith (libprofiler);
				} else {
					libprofiler = Path.Combine (libdir, "libmono-profiler-log.a");
					compiler_flags.AddLinkWith (libprofiler);
					if (!App.EnableBitCode)
						compiler_flags.ReferenceSymbol ("mono_profiler_startup_log");
				}
			}

			if (!string.IsNullOrEmpty (App.UserGccFlags))
				compiler_flags.AddOtherFlag (App.UserGccFlags);

			if (App.DeadStrip)
				compiler_flags.AddOtherFlag ("-dead_strip");

			if (App.IsExtension) {
				if (App.Platform == ApplePlatform.iOS && Driver.XcodeVersion.Major < 7) {
					compiler_flags.AddOtherFlag ("-lpkstart");
					compiler_flags.AddOtherFlag ($"-F {Driver.Quote (Path.Combine (Driver.GetFrameworkDirectory (App), "System/Library/PrivateFrameworks"))} -framework PlugInKit");
				}
				compiler_flags.AddOtherFlag ("-fapplication-extension");
			}

			compiler_flags.Inputs = new List<string> ();
			var flags = compiler_flags.ToString (); // This will populate Inputs.

			if (!Application.IsUptodate (compiler_flags.Inputs, new string [] { Executable } )) {
				// always show the native linker warnings since many of them turn out to be very important
				// and very hard to diagnose otherwise when hidden from the build output. Ref: bug #2430
				var linker_errors = new List<Exception> ();
				var output = new StringBuilder ();
				var code = Driver.RunCommand (App.CompilerPath, flags, null, output);

				Application.ProcessNativeLinkerOutput (this, output.ToString (), link_with, linker_errors, code != 0);

				if (code != 0) {
					// if the build failed - it could be because of missing frameworks / libraries we identified earlier
					foreach (var assembly in Assemblies) {
						if (assembly.UnresolvedModuleReferences == null)
							continue;
						
						foreach (var mr in assembly.UnresolvedModuleReferences) {
							// TODO: add more diagnose information on the warnings
							var name = Path.GetFileNameWithoutExtension (mr.Name);
							linker_errors.Add (new MonoTouchException (5215, false, "References to '{0}' might require additional -framework=XXX or -lXXX instructions to the native linker", name));
						}
					}
					// mtouch does not validate extra parameters given to GCC when linking (--gcc_flags)
					if (!String.IsNullOrEmpty (App.UserGccFlags))
						linker_errors.Add (new MonoTouchException (5201, true, "Native linking failed. Please review the build log and the user flags provided to gcc: {0}", App.UserGccFlags));
					linker_errors.Add (new MonoTouchException (5202, true, "Native linking failed. Please review the build log.", App.UserGccFlags));
				}
				ErrorHelper.Show (linker_errors);
			} else {
				cached_executable = true;
				Driver.Log (3, "Target '{0}' is up-to-date.", Executable);
			}
			// the native linker can prefer private (and existing) over public (but non-existing) framework when weak_framework are used
			// on an iOS target version where the framework does not exists, e.g. targeting iOS6 for JavaScriptCore added in iOS7 results in
			// /System/Library/PrivateFrameworks/JavaScriptCore.framework/JavaScriptCore instead of
			// /System/Library/Frameworks/JavaScriptCore.framework/JavaScriptCore
			// more details in https://bugzilla.xamarin.com/show_bug.cgi?id=31036
			if (WeakFrameworks.Count > 0)
				AdjustDylibs ();
			Driver.Watch ("Native Link", 1);
		}

		void AdjustDylibs ()
		{
			var sb = new StringBuilder ();
			foreach (var dependency in Xamarin.MachO.GetNativeDependencies (Executable)) {
				if (!dependency.StartsWith ("/System/Library/PrivateFrameworks/", StringComparison.Ordinal))
					continue;
				var fixed_dep = dependency.Replace ("/PrivateFrameworks/", "/Frameworks/");
				sb.Append (" -change ").Append (dependency).Append (' ').Append (fixed_dep);
			}
			if (sb.Length > 0) {
				var quoted_name = Driver.Quote (Executable);
				sb.Append (' ').Append (quoted_name);
				Driver.XcodeRun ("install_name_tool", sb.ToString ());
				sb.Clear ();
			}
		}

		public bool CanWeSymlinkTheApplication ()
		{
			if (!Driver.CanWeSymlinkTheApplication (App))
				return false;

			foreach (var a in Assemblies)
				if (!a.CanSymLinkForApplication ())
					return false;

			return true;
		}

		public void Symlink ()
		{
			foreach (var a in Assemblies)
				a.Symlink ();

			var targetExecutable = Executable;

			Application.TryDelete (targetExecutable);

			try {
				var launcher = new StringBuilder ();
				launcher.Append (Path.Combine (Driver.MonoTouchDirectory, "bin", "simlauncher"));
				if (Is32Build)
					launcher.Append ("32");
				else if (Is64Build)
					launcher.Append ("64");
				launcher.Append ("-sgen");
				File.Copy (launcher.ToString (), Executable);
				File.SetLastWriteTime (Executable, DateTime.Now);
			} catch (MonoTouchException) {
				throw;
			} catch (Exception ex) {
				throw new MonoTouchException (1015, true, ex, "Failed to create the executable '{0}': {1}", targetExecutable, ex.Message);
			}

			Symlinked = true;

			if (Driver.Verbosity > 0)
				Console.WriteLine ("Application ({0}) was built using fast-path for simulator.", string.Join (", ", Abis.ToArray ()));
		}

		// Thread-safe
		public void LinkWith (string native_library)
		{
			lock (link_with)
				link_with.Add (native_library);
		}

		public void LinkWithAndShip (string dylib)
		{
			link_with_and_ship.Add (dylib);
		}

		public void StripManagedCode ()
		{
			var strip = false;

			strip = App.ManagedStrip && App.IsDeviceBuild && !App.EnableDebug && !App.PackageMdb;

			if (!Directory.Exists (AppTargetDirectory))
				Directory.CreateDirectory (AppTargetDirectory);

			if (strip) {
				// note: this is much slower when Parallel.ForEach is used
				Parallel.ForEach (Assemblies, new ParallelOptions () { MaxDegreeOfParallelism = Driver.Concurrency }, (assembly) => 
					{
						var file = assembly.FullPath;
						var output = Path.Combine (AppTargetDirectory, Path.GetFileName (assembly.FullPath));
						if (Application.IsUptodate (file, output)) {
							Driver.Log (3, "Target '{0}' is up-to-date", output);
						} else {
							Driver.Log (1, "Stripping assembly {0}", file);
							Driver.FileDelete (output);
							Stripper.Process (file, output);
						}
						// The stripper will only copy the main assembly.
						// We need to copy .config files and satellite assemblies too
						if (App.PackageMdb)
							assembly.CopyMdbToDirectory (AppTargetDirectory);
						assembly.CopyConfigToDirectory (AppTargetDirectory);
						assembly.CopySatellitesToDirectory (AppTargetDirectory);
					});

				Driver.Watch ("Strip Assemblies", 1);
			} else if (!Symlinked) {
				foreach (var assembly in Assemblies)
					assembly.CopyToDirectory (AppTargetDirectory, reload: false, copy_mdb: App.PackageMdb);
			}
		}
	}
}