for help! : two question  about tls
i was puzzle by code in x64tls.c 
i have three question. 
first, tls data access problem.  if a native  lib has some tls data,   and  a  emulated lib access the tls data use fs register, while native lib use arm style access the tls data, how this worked?

second: in setupTlsdata , i saw  index will be set throgh below code:
     *(uint64_t*)((uintptr_t)ptr + context->tlssize + POS_TLS+i*16)) = i;
      i have saw the tcbeader_t in gliibc/sysdeps/x86_64/nptl/tls.h, but i can find the data format behind the tcbheader_t  .
      can you give some url link about the data format about this?

third：
      vsyscall will be copy to tcbheader in function setupTLSData, i want know when it will be used by who?