rv[6] &= 0xcf
	rv[6] |= 0x30
	rv[8] &= 0x3f
	rv[8] |= 0xc0

	return rv
}

// machoRewriteUuid copies over the contents of the Macho executable
// exef into the output file outexe, and in the process updates the
// LC_UUID command to a new value recomputed from the Go build id.
func machoRewriteUuid(ctxt *Link, exef *os.File, exem *macho.File, outexe string) error {

		uuidUpdated = true
	}
	if ctxt.IsDarwin() && !uuidUpdated && *flagBuildid != "" {
		updateMachoOutFile("rewriting uuid",
			func(ctxt *Link, exef *os.File, exem *macho.File, outexe string) error {
				return machoRewriteUuid(ctxt, exef, exem, outexe)
			})
	}
	if ctxt.NeedCodeSign() {
		err := machoCodeSign(ctxt, *flagOutfile)
		if err != nil {
			Exitf("%s: code signing failed: %v", os.Args[0], err)
		}
	}