cmd/link: pass -no-pie (if supported) when creating a race-enabled executable.

Fixes #15443

Change-Id: Ia3593104fc1a4255926ae5675c25390604b44b7b
Reviewed-on: https://go-review.googlesource.com/22453
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/link/internal/ld/lib.go

@@ -1204,6 +1204,24 @@ func hostlink() {
 
 	argv = append(argv, ldflag...)
 
+	if flag_race != 0 {
+		// On a system where the toolchain creates position independent
+		// executables by default, tsan initialization can fail. So we pass
+		// -no-pie here, but support for that flag is quite new and we test
+		// for its support first.
+		src := filepath.Join(tmpdir, "trivial.c")
+		if err := ioutil.WriteFile(src, []byte{}, 0666); err != nil {
+			Ctxt.Diag("WriteFile trivial.c failed: %v", err)
+		}
+		cmd := exec.Command(argv[0], "-no-pie", "trivial.c")
+		cmd.Dir = tmpdir
+		out, err := cmd.CombinedOutput()
+		supported := err == nil && !bytes.Contains(out, []byte("unrecognized"))
+		if supported {
+			argv = append(argv, "-no-pie")
+		}
+	}
+
 	for _, p := range strings.Fields(extldflags) {
 		argv = append(argv, p)