Add Darwin x86_64+arm64 universal binary support

This is configured from Make by setting up Darwin+Arm64 as a HOST_CROSS
target (which is largely true, as binaries can't be executed on X86_64
machines). On the Soong side, it's a bit blurier, as we don't current
have any other users that are the same OS but not natively executable
(Linux/musl is executable, Windows/x86 is a different OS).

Instead of requiring cc_binary/etc to become multi-architecture-aware
and using something like common_first/MultiTarget, this defaults all
non-multi-architecture-aware modules to be built with both
architectures. It then adds a dependency with the
DarwinUniversalVariantTag so that supporting modules can get the outputs
of the other variant.

Cc uses that dependency tag to run lipo on shared libraries and binaries
so that the output of the x86_64 variant is actually a fat binary
including both architectures.

Bug: 203607969
Test: build sdk-repo targets on a Mac
Change-Id: Icbddb0a177c0ba19d3e0d11f8cf568e0d1ea3245

cc/binary.go

@@ -345,6 +345,12 @@ func (binary *binaryDecorator) link(ctx ModuleContext,
 		flags.Local.LdFlags = append(flags.Local.LdFlags, "-Wl,--no-dynamic-linker")
 	}
 
+	if ctx.Darwin() && deps.DarwinSecondArchOutput.Valid() {
+		fatOutputFile := outputFile
+		outputFile = android.PathForModuleOut(ctx, "pre-fat", fileName)
+		transformDarwinUniversalBinary(ctx, fatOutputFile, outputFile, deps.DarwinSecondArchOutput.Path())
+	}
+
 	builderFlags := flagsToBuilderFlags(flags)
 	stripFlags := flagsToStripFlags(flags)
 	if binary.stripper.NeedsStrip(ctx) {

cc/builder.go

@@ -165,6 +165,12 @@ var (
 		}
 	}()
 
+	darwinLipo = pctx.AndroidStaticRule("darwinLipo",
+		blueprint.RuleParams{
+			Command:     "${config.MacLipoPath} -create -output $out $in",
+			CommandDeps: []string{"${config.MacLipoPath}"},
+		})
+
 	_ = pctx.SourcePathVariable("archiveRepackPath", "build/soong/scripts/archive_repack.sh")
 
 	// Rule to repack an archive (.a) file with a subset of object files.
@@ -1060,6 +1066,15 @@ func transformDarwinStrip(ctx android.ModuleContext, inputFile android.Path,
 	})
 }
 
+func transformDarwinUniversalBinary(ctx android.ModuleContext, outputFile android.WritablePath, inputFiles ...android.Path) {
+	ctx.Build(pctx, android.BuildParams{
+		Rule:        darwinLipo,
+		Description: "lipo " + outputFile.Base(),
+		Output:      outputFile,
+		Inputs:      inputFiles,
+	})
+}
+
 // Registers build statement to zip one or more coverage files.
 func transformCoverageFilesToZip(ctx android.ModuleContext,
 	inputs Objects, baseName string) android.OptionalPath {

cc/cc.go

@@ -167,6 +167,10 @@ type PathDeps struct {
 
 	// Path to the dynamic linker binary
 	DynamicLinker android.OptionalPath
+
+	// For Darwin builds, the path to the second architecture's output that should
+	// be combined with this architectures's output into a FAT MachO file.
+	DarwinSecondArchOutput android.OptionalPath
 }
 
 // LocalOrGlobalFlags contains flags that need to have values set globally by the build system or locally by the module
@@ -2578,6 +2582,11 @@ func (c *Module) depsToPaths(ctx android.ModuleContext) PathDeps {
 		depName := ctx.OtherModuleName(dep)
 		depTag := ctx.OtherModuleDependencyTag(dep)
 
+		if depTag == android.DarwinUniversalVariantTag {
+			depPaths.DarwinSecondArchOutput = dep.(*Module).OutputFile()
+			return
+		}
+
 		ccDep, ok := dep.(LinkableInterface)
 		if !ok {
 

cc/config/darwin_host.go

@@ -87,6 +87,10 @@ func init() {
 		return getMacTools(ctx).arPath
 	})
 
+	pctx.VariableFunc("MacLipoPath", func(ctx android.PackageVarContext) string {
+		return getMacTools(ctx).lipoPath
+	})
+
 	pctx.VariableFunc("MacStripPath", func(ctx android.PackageVarContext) string {
 		return getMacTools(ctx).stripPath
 	})
@@ -118,6 +122,7 @@ type macPlatformTools struct {
 
 	sdkRoot   string
 	arPath    string
+	lipoPath  string
 	stripPath string
 	toolPath  string
 }
@@ -157,6 +162,7 @@ func getMacTools(ctx android.PathContext) *macPlatformTools {
 		macTools.sdkRoot = xcrun("--show-sdk-path")
 
 		macTools.arPath = xcrun("--find", "ar")
+		macTools.lipoPath = xcrun("--find", "lipo")
 		macTools.stripPath = xcrun("--find", "strip")
 		macTools.toolPath = filepath.Dir(xcrun("--find", "ld"))
 	})

cc/library.go

@@ -1429,6 +1429,12 @@ func (library *libraryDecorator) linkShared(ctx ModuleContext,
 
 	builderFlags := flagsToBuilderFlags(flags)
 
+	if ctx.Darwin() && deps.DarwinSecondArchOutput.Valid() {
+		fatOutputFile := outputFile
+		outputFile = android.PathForModuleOut(ctx, "pre-fat", fileName)
+		transformDarwinUniversalBinary(ctx, fatOutputFile, outputFile, deps.DarwinSecondArchOutput.Path())
+	}
+
 	// Optimize out relinking against shared libraries whose interface hasn't changed by
 	// depending on a table of contents file instead of the library itself.
 	tocFile := outputFile.ReplaceExtension(ctx, flags.Toolchain.ShlibSuffix()[1:]+".toc")