https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81708
--- Comment #8 from H. Peter Anvin <hpa at zytor dot com> --- How about simply letting the user enter an assembly expression of neither of the standard ABI options are suitable? Also, shouldn't the user space default on 64 bits be an offset into the TLS using %fs, or is there something magic about how the kernel is compiled that changes it to %gs:?
