Add stubs and manpage for __{get,set}_tcb

ok deraadt@

1 files changed, 64 insertions, 0 deletions

diff --git a/lib/libc/sys/__get_tcb.2 b/lib/libc/sys/__get_tcb.2
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+.\" $OpenBSD: __get_tcb.2,v 1.1 2011/10/16 06:21:52 guenther Exp $
+.\"
+.\" Copyright (c) 2011 Philip Guenther <guenther@openbsd.org>
+.\"
+.\" Permission to use, copy, modify, and distribute this software for any
+.\" purpose with or without fee is hereby granted, provided that the above
+.\" copyright notice and this permission notice appear in all copies.
+.\"
+.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+.\"
+.Dd $Mdocdate: October 16 2011 $
+.Dt __GET_TCB 2
+.Os
+.Sh NAME
+.Nm __get_tcb ,
+.Nm __set_tcb
+.Nd "get and set the address of the thread-control-block of the current thread"
+.Sh SYNOPSIS
+.Ft void *
+.Fn __get_tcb "void"
+.Ft void
+.Fn __set_tcb "void *"
+.Sh DESCRIPTION
+The
+.Fn __get_tcb
+and
+.Fn __set_tcb
+are for use by librthread and other parts of the system runtime to
+retrieve and set the address of the current thread's TCB
+(thread-control-block).
+This is used to locate per-thread data such as
+.Va 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.
+New threads (including the first thread of a new process) created using
+.Xr fork 2 ,
+.Xr vfork 2 ,
+or
+.Xr rfork 2 ,
+start with this address set to zero.
+Similarly,
+.Xr execve 2
+resets it to zero.
+.Pp
+On some platforms, this address is also directly mapped to a CPU
+register which can be accessed from userspace.
+.Sh RETURN VALUES
+.Fn __get_tcb
+returns the address of the thread-control-block of the current thread.
+.Sh SEE ALSO
+.Xr rfork 2
+.Sh HISTORY
+The
+.Fn __get_tcb
+and
+.Fn __set_tcb
+system calls appeared in
+.Ox 5.1 .