4 files changed, 101 insertions, 2 deletions

diff --git a/src/cmd/link/dwarf_test.go b/src/cmd/link/dwarf_test.go
index ecc96019be..e9c9e29301 100644
--- a/src/cmd/link/dwarf_test.go
+++ b/src/cmd/link/dwarf_test.go
@@ -171,3 +171,54 @@ func TestDWARFiOS(t *testing.T) {
 	testDWARF(t, "c-archive", true, cc, "CGO_ENABLED=1", "GOOS=darwin", "GOARCH=arm", "GOARM=7")
 	testDWARF(t, "c-archive", true, cc, "CGO_ENABLED=1", "GOOS=darwin", "GOARCH=arm64")
 }
+
+func TestBuildFortvOS(t *testing.T) {
+	testenv.MustHaveCGO(t)
+	testenv.MustHaveGoBuild(t)
+
+	// Only run this on darwin/amd64, where we can cross build for tvOS.
+	if runtime.GOARCH != "amd64" || runtime.GOOS != "darwin" {
+		t.Skip("skipping on non-darwin/amd64 platform")
+	}
+	if err := exec.Command("xcrun", "--help").Run(); err != nil {
+		t.Skipf("error running xcrun, required for iOS cross build: %v", err)
+	}
+
+	sdkPath, err := exec.Command("xcrun", "--sdk", "appletvos", "--show-sdk-path").Output()
+	if err != nil {
+		t.Fatalf("xcrun --sdk appletvos --show-sdk-path failed: %v", err)
+	}
+	CC := []string{
+		"clang",
+		"-arch",
+		"arm64",
+		"-isysroot", strings.TrimSpace(string(sdkPath)),
+		"-mtvos-version-min=12.0",
+		"-fembed-bitcode",
+		"-framework", "CoreFoundation",
+	}
+	lib := filepath.Join("testdata", "lib.go")
+	tmpDir, err := ioutil.TempDir("", "go-link-TestBuildFortvOS")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	ar := filepath.Join(tmpDir, "lib.a")
+	cmd := exec.Command(testenv.GoToolPath(t), "build", "-buildmode=c-archive", "-o", ar, lib)
+	cmd.Env = append(os.Environ(),
+		"CGO_ENABLED=1",
+		"GOOS=darwin",
+		"GOARCH=arm64",
+		"CC="+strings.Join(CC, " "),
+	)
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Fatalf("%v: %v:\n%s", cmd.Args, err, out)
+	}
+
+	link := exec.Command(CC[0], CC[1:]...)
+	link.Args = append(link.Args, ar, filepath.Join("testdata", "main.m"))
+	if out, err := link.CombinedOutput(); err != nil {
+		t.Fatalf("%v: %v:\n%s", link.Args, err, out)
+	}
+}
diff --git a/src/cmd/link/internal/ld/macho.go b/src/cmd/link/internal/ld/macho.go
index 32b2013059..98359c26fc 100644
--- a/src/cmd/link/internal/ld/macho.go
+++ b/src/cmd/link/internal/ld/macho.go
@@ -11,6 +11,9 @@ import (
 	"cmd/link/internal/sym"
 	"debug/macho"
 	"encoding/binary"
+	"fmt"
+	"io"
+	"os"
 	"sort"
 	"strings"
 )
@@ -691,8 +694,14 @@ func Asmbmacho(ctxt *Link) {
 			}
 		}
 	}
-
-	if ctxt.LinkMode == LinkInternal {
+	load, err := hostobjMachoPlatform(hostobj)
+	if err != nil {
+		Exitf("%v", err)
+	}
+	if load != nil {
+		ml := newMachoLoad(ctxt.Arch, load.cmd.type_, uint32(len(load.cmd.data)))
+		copy(ml.data, load.cmd.data)
+	} else if ctxt.LinkMode == LinkInternal {
 		// For lldb, must say LC_VERSION_MIN_MACOSX or else
 		// it won't know that this Mach-O binary is from OS X
 		// (could be iOS or WatchOS instead).
@@ -1017,6 +1026,32 @@ func Machoemitreloc(ctxt *Link) {
 	}
 }
 
+// hostobjMachoPlatform returns the first platform load command found
+// in the host objects, if any.
+func hostobjMachoPlatform(hostobj []Hostobj) (*MachoPlatformLoad, error) {
+	for _, h := range hostobj {
+		f, err := os.Open(h.file)
+		if err != nil {
+			return nil, fmt.Errorf("%s: failed to open host object: %v\n", h.file, err)
+		}
+		defer f.Close()
+		sr := io.NewSectionReader(f, h.off, h.length)
+		m, err := macho.NewFile(sr)
+		if err != nil {
+			// Not a valid Mach-O file.
+			return nil, nil
+		}
+		load, err := peekMachoPlatform(m)
+		if err != nil {
+			return nil, err
+		}
+		if load != nil {
+			return load, nil
+		}
+	}
+	return nil, nil
+}
+
 // peekMachoPlatform returns the first LC_VERSION_MIN_* or LC_BUILD_VERSION
 // load command found in the Mach-O file, if any.
 func peekMachoPlatform(m *macho.File) (*MachoPlatformLoad, error) {
diff --git a/src/cmd/link/testdata/lib.go b/src/cmd/link/testdata/lib.go
new file mode 100644
index 0000000000..bc6c699440
--- /dev/null
+++ b/src/cmd/link/testdata/lib.go
@@ -0,0 +1,8 @@
+package main
+
+import "C"
+
+//export GoFunc
+func GoFunc() {}
+
+func main() {}
diff --git a/src/cmd/link/testdata/main.m b/src/cmd/link/testdata/main.m
new file mode 100644
index 0000000000..1c8175f6cc
--- /dev/null
+++ b/src/cmd/link/testdata/main.m
@@ -0,0 +1,5 @@
+extern void GoFunc();
+
+int main(int argc, char **argv) {
+	GoFunc();
+}