REGISTER_THREAD_AREA  267 mtcp/NOTES-x86_64/tls-i386.h   REGISTER_THREAD_AREA (32, offsetof (struct user_regs_struct, xgs), 3) \
REGISTER_THREAD_AREA  268 mtcp/NOTES-x86_64/tls-i386.h   REGISTER_THREAD_AREA (64, 26 * 8, 3) /* x86-64's user_regs_struct->gs */