Enable lld for windows

Bug: http://b/110800681

The following flags that the binutils linkers support are not available
in lld for Windows:
  -soname
  --no-undefined
  -rpath

Windows also uses "import libraries", which are stub libraries used only
for linking.  The binutils linkers accepted a DLL and treated them as an
import library.  But lld issues the following error:

  lld-link: error: ...DLL: bad file type. Did you specify a DLL instead
  of an import library?

To resolve this, pass '-out-implib=libFoo.a' to lld when linking
libFoo.dll.  Add libFoo.a as an implicit output to the 'ld' build rule.

Rewrite the shared libraries for a library/binary to use the import
library instead of the DLL.  As a side-effect, this also (correctly)
uses the AdbWinApi.a that's alongside
development/host/windows/prebuilt/usb/AdbWinApi.dll

Test: Run Windows tests (go/android-llvm-windows-testing) and check
absence of regressions.

Change-Id: I15a178589aa6882caa6e7e38650cc6ef48109764

cc/binary.go

@@ -384,7 +384,7 @@ func (binary *binaryDecorator) link(ctx ModuleContext,
 
 	TransformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs, deps.StaticLibs,
 		deps.LateStaticLibs, deps.WholeStaticLibs, linkerDeps, deps.CrtBegin, deps.CrtEnd, true,
-		builderFlags, outputFile)
+		builderFlags, outputFile, nil)
 
 	objs.coverageFiles = append(objs.coverageFiles, deps.StaticLibObjs.coverageFiles...)
 	objs.coverageFiles = append(objs.coverageFiles, deps.WholeStaticLibObjs.coverageFiles...)

cc/builder.go

@@ -26,6 +26,7 @@ import (
 	"strings"
 
 	"github.com/google/blueprint"
+	"github.com/google/blueprint/pathtools"
 
 	"android/soong/android"
 	"android/soong/cc/config"
@@ -597,7 +598,7 @@ func transformDarwinObjToStaticLib(ctx android.ModuleContext, objFiles android.P
 // and shared libraries, to a shared library (.so) or dynamic executable
 func TransformObjToDynamicBinary(ctx android.ModuleContext,
 	objFiles, sharedLibs, staticLibs, lateStaticLibs, wholeStaticLibs, deps android.Paths,
-	crtBegin, crtEnd android.OptionalPath, groupLate bool, flags builderFlags, outputFile android.WritablePath) {
+	crtBegin, crtEnd android.OptionalPath, groupLate bool, flags builderFlags, outputFile android.WritablePath, implicitOutputs android.WritablePaths) {
 
 	ldCmd := "${config.ClangBin}/clang++"
 
@@ -634,7 +635,11 @@ func TransformObjToDynamicBinary(ctx android.ModuleContext,
 	}
 
 	for _, lib := range sharedLibs {
-		libFlagsList = append(libFlagsList, lib.String())
+		libFile := lib.String()
+		if ctx.Windows() {
+			libFile = pathtools.ReplaceExtension(libFile, "a")
+		}
+		libFlagsList = append(libFlagsList, libFile)
 	}
 
 	deps = append(deps, staticLibs...)
@@ -648,6 +653,7 @@ func TransformObjToDynamicBinary(ctx android.ModuleContext,
 		Rule:            ld,
 		Description:     "link " + outputFile.Base(),
 		Output:          outputFile,
+		ImplicitOutputs: implicitOutputs,
 		Inputs:          objFiles,
 		Implicits:       deps,
 		Args: map[string]string{

cc/library.go

@@ -347,9 +347,10 @@ func (library *libraryDecorator) linkerFlags(ctx ModuleContext, flags Flags) Fla
 				)
 			}
 		} else {
-			f = append(f,
+			f = append(f, "-shared")
-				"-shared",
+			if !ctx.Windows() {
-				"-Wl,-soname,"+libName+flags.Toolchain.ShlibSuffix())
+				f = append(f, "-Wl,-soname,"+libName+flags.Toolchain.ShlibSuffix())
+			}
 		}
 
 		flags.LdFlags = append(f, flags.LdFlags...)
@@ -673,6 +674,14 @@ func (library *libraryDecorator) linkShared(ctx ModuleContext,
 	outputFile := android.PathForModuleOut(ctx, fileName)
 	ret := outputFile
 
+	var implicitOutputs android.WritablePaths
+	if ctx.Windows() {
+		importLibraryPath := android.PathForModuleOut(ctx, pathtools.ReplaceExtension(fileName, "a"))
+
+		flags.LdFlags = append(flags.LdFlags, "-Wl,--out-implib="+importLibraryPath.String())
+		implicitOutputs = append(implicitOutputs, importLibraryPath)
+	}
+
 	builderFlags := flagsToBuilderFlags(flags)
 
 	// Optimize out relinking against shared libraries whose interface hasn't changed by
@@ -724,7 +733,7 @@ func (library *libraryDecorator) linkShared(ctx ModuleContext,
 
 	TransformObjToDynamicBinary(ctx, objs.objFiles, sharedLibs,
 		deps.StaticLibs, deps.LateStaticLibs, deps.WholeStaticLibs,
-		linkerDeps, deps.CrtBegin, deps.CrtEnd, false, builderFlags, outputFile)
+		linkerDeps, deps.CrtBegin, deps.CrtEnd, false, builderFlags, outputFile, implicitOutputs)
 
 	objs.coverageFiles = append(objs.coverageFiles, deps.StaticLibObjs.coverageFiles...)
 	objs.coverageFiles = append(objs.coverageFiles, deps.WholeStaticLibObjs.coverageFiles...)

cc/linker.go

@@ -290,10 +290,6 @@ func (linker *baseLinker) useClangLld(ctx ModuleContext) bool {
 	if ctx.Darwin() {
 		return false
 	}
-	// http://b/110800681 - lld cannot link Android's Windows modules yet.
-	if ctx.Windows() {
-		return false
-	}
 	if linker.Properties.Use_clang_lld != nil {
 		return Bool(linker.Properties.Use_clang_lld)
 	}
@@ -347,7 +343,7 @@ func (linker *baseLinker) linkerFlags(ctx ModuleContext, flags Flags) Flags {
 			// darwin defaults to treating undefined symbols as errors
 			flags.LdFlags = append(flags.LdFlags, "-Wl,-undefined,dynamic_lookup")
 		}
-	} else if !ctx.Darwin() {
+	} else if !ctx.Darwin() && !ctx.Windows() {
 		flags.LdFlags = append(flags.LdFlags, "-Wl,--no-undefined")
 	}
 
@@ -384,7 +380,7 @@ func (linker *baseLinker) linkerFlags(ctx ModuleContext, flags Flags) Flags {
 
 	flags.LdFlags = append(flags.LdFlags, proptools.NinjaAndShellEscapeList(linker.Properties.Ldflags)...)
 
-	if ctx.Host() {
+	if ctx.Host() && !ctx.Windows() {
 		rpath_prefix := `\$$ORIGIN/`
 		if ctx.Darwin() {
 			rpath_prefix = "@loader_path/"