From: Nick Alcock <nick.alcock@oracle.com>
The address of the stack canary is stored in a per-thread variable,
which means that we must ensure that the TLS area is intialized before
calling any -fstack-protector'ed functions. For dynamically linked
applications, we ensure this (in a later patch) by disabling
-fstack-protector for the whole dynamic linker, but for static
applications the AT_ENTRY address is called directly by the kernel, so
we must deal with the problem differently.
So split out the part of pthread initialization that sets up the TCB
(and, more generally, the TLS area) into a separate function (twice --
there is one implementation in libpthread.a, and another outside it for
programs that do not link with libpthread), then call it at
initialization time. Call that, and move the stack guard initialization
above the DL_SYSDEP_OSCHECK hook, which if set will probably call
functions which are stack-protected (it does on Linux and NaCL too).
We also move apply_irel() up, so that we can still safely call functions
that require ifuncs while in __pthread_initialize_tcb_internal()
(though if stack-protection is enabled we still have to avoid calling
functions that are not stack-protected at this stage).