For a main thread a thread object is created by the CRT0 before _main gets
called so that _main can already run in a generic environment that, e.g.,
catches stack overflows as a page-fault instead of corrupting the BSS.
Additionally dynamic programs have only one CRT0 - the one of the LDSO -
which does the initialization for both LDSO and program.
ref #989
To remap its UTCB to its context area later, a main thread needs
to know the according dataspace capability. This is done through
the start-info it receives from its creator at startup.
ref #989
Every thread receives a startup message from its creator through the initial
state of its userland thread-context. The thread-startup code remembers the
kernel name of the new thread by reading this message before the userland
thread-context gets polluted. This way, Kernel::current_thread_id becomes
unnecessary.
fix#953
Don't set priority and label in platform thread and then communicate this
core object via Kernel::new_thread but communicate priority and label directly.
This way kernel doesn't need to know anymore what a platform thread is.
ref #953
Instead of writing initial thread context to the platform-thread members
and then communicating this core object to kernel, core calls
Kernel::access_thread_regs first to initialize thread context and then
Kernel::start_thread without a platform-thread pointer. This way
the frontend as well as the backend of Kernel::start_thread loose
complexity and it is a first step to remove platform thread from the
vocabulary of the kernel.
ref #953
