NAME
__get_tcb,
__set_tcb —
get or set the address of the thread
control block of the current thread
SYNOPSIS
void *
__get_tcb(void);
void
__set_tcb(void
*);
DESCRIPTION
The
__get_tcb()
and
__set_tcb()
functions are for use by libpthread and other parts of the C runtime to
retrieve and set the address of the current thread's thread control block
(TCB). This is used to locate per-thread data such as
errno. Each kernel-level thread in a process has a
separate value for this address, which can be obtained and changed via these
system calls.
The initial thread of a new process created using fork(2) or vfork(2) inherits the TCB address of the thread that created it. A thread created using __tfork(3) starts with the TCB address specified in that call. execve(2) resets the thread's TCB address to zero.
On some platforms, this address is also directly mapped to a CPU register which can be accessed from userspace.
RETURN VALUES
__get_tcb() returns the address of the
thread control block of the current thread.
SEE ALSO
HISTORY
The __get_tcb() and
__set_tcb() system calls appeared in
OpenBSD 5.1.