https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77964
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
You don't need it for both.
struct builtin_fw *b_fw = __start_builtin_fw;
asm ("" : "+r" (b_fw));
for (; b_fw != __end_builtin_fw; b_fw++) {
should be enough. And indeed, without that it is undefined behavior.
