// the package being tested and the source root.
	pkgpath = ""
	for element := range strings.SplitSeq(finalPkgpath, string(filepath.Separator)) {
		if debug {
			log.Printf("copying %s", pkgpath)
		}
		pkgpath = filepath.Join(pkgpath, element)
		dst := filepath.Join(dstbase, pkgpath)
		src := filepath.Join(cwd, pkgpath)
		if err := copyLocalDir(dst, src); err != nil {
			return "", err
		}
	}

	-e
		No limit on number of errors reported.
	-gensymabis
		Write symbol ABI information to output file. Don't assemble.
	-o file
		Write output to file. The default is foo.o for /a/b/c/foo.s.
	-p pkgpath
		Set expected package import to pkgpath.
	-shared
		Generate code that can be linked into a shared library.
	-spectre list
		Enable spectre mitigations in list (all, ret).
	-trimpath prefix
		Remove prefix from recorded source file paths.