+++ /dev/null
-.\" Copyright (C) 2008, 2014, Michael Kerrisk <mtk.manpages@gmail.com>
-.\"
-.\" %%%LICENSE_START(VERBATIM)
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-.\" manual provided the copyright notice and this permission notice are
-.\" preserved on all copies.
-.\"
-.\" Permission is granted to copy and distribute modified versions of this
-.\" manual under the conditions for verbatim copying, provided that the
-.\" entire resulting derived work is distributed under the terms of a
-.\" permission notice identical to this one.
-.\"
-.\" Since the Linux kernel and libraries are constantly changing, this
-.\" manual page may be incorrect or out-of-date. The author(s) assume no
-.\" responsibility for errors or omissions, or for damages resulting from
-.\" the use of the information contained herein. The author(s) may not
-.\" have taken the same level of care in the production of this manual,
-.\" which is licensed free of charge, as they might when working
-.\" professionally.
-.\"
-.\" Formatted or processed versions of this manual, if unaccompanied by
-.\" the source, must acknowledge the copyright and authors of this work.
-.\" %%%LICENSE_END
-.\"
-.\" Created Sat Aug 21 1995 Thomas K. Dyas <tdyas@eden.rutgers.edu>
-.\" Modified Tue Oct 22 22:09:03 1996 by Eric S. Raymond <esr@thyrsus.com>
-.\" 2008-06-26, mtk, added some more detail on the work done by sigreturn()
-.\" 2014-12-05, mtk, rewrote all of the rest of the original page
-.\"
-.TH SIGRETURN 2 2014-12-31 "Linux" "Linux Programmer's Manual"
-.SH NAME
-sigreturn \- return from signal handler and cleanup stack frame
-.SH SYNOPSIS
-.BI "int sigreturn(...);"
-.SH DESCRIPTION
-If the Linux kernel determines that an unblocked
-signal is pending for a process, then,
-at the next transition back to user mode in that process
-(e.g., upon return from a system call or
-when the process is rescheduled onto the CPU),
-it saves various pieces of process context
-(processor status word, registers, signal mask, and signal stack settings)
-into the user-space stack.
-.\" See arch/x86/kernel/signal.c::__setup_frame() [in 3.17 source code]
-
-The kernel also arranges that, during the transition back to user mode,
-the signal handler is called, and that, upon return from the handler,
-control passes to a piece of user-space code commonly called
-the "signal trampoline".
-The signal trampoline code in turn calls
-.BR sigreturn ().
-
-This
-.BR sigreturn ()
-call undoes everything that was
-done\(emchanging the process's signal mask, switching signal stacks (see
-.BR sigaltstack "(2))\(emin "
-order to invoke the signal handler.
-It restores the process's signal mask, switches stacks,
-and restores the process's context
-(processor flags and registers,
-including the stack pointer and instruction pointer),
-so that the process resumes execution
-at the point where it was interrupted by the signal.
-.SH RETURN VALUE
-.BR sigreturn ()
-never returns.
-.SH CONFORMING TO
-Many UNIX-type systems have a
-.BR sigreturn ()
-system call or near equivalent.
-However, this call is not specified in POSIX,
-and details of its behavior vary across systems.
-.SH NOTES
-.BR sigreturn ()
-exists only to allow the implementation of signal handlers.
-It should
-.B never
-be called directly.
-Details of the arguments (if any) passed to
-.BR sigreturn ()
-vary depending on the architecture.
-
-Once upon a time, UNIX systems placed the signal trampoline code
-onto the user stack.
-Nowadays, pages of the user stack are protected so as to
-disallow code execution.
-Thus, on contemporary Linux systems, depending on the architecture,
-the signal trampoline code lives either in the
-.BR vdso (7)
-or in the C library.
-In the latter case,
-.\" See, for example, sysdeps/unix/sysv/linux/i386/sigaction.c and
-.\" sysdeps/unix/sysv/linux/x86_64/sigaction.c in the glibc (2.20) source.
-the C library supplies the location of the trampoline code using the
-.I sa_restorer
-field of the
-.I sigaction
-structure that is passed to
-.BR sigaction (2),
-and sets the
-.BR SA_RESTORER
-flag in the
-.IR sa_flags
-field.
-
-The saved process context information is placed in a
-.I ucontext_t
-structure (see
-.IR <sys/ucontext.h> ).
-That structure is visible within the signal handler
-as the third argument of a handler established with the
-.BR SA_SIGINFO
-flag.
-
-On some other UNIX systems,
-the operation of the signal trampoline differs a little.
-In particular, on some systems, upon transitioning back to user mode,
-the kernel passes control to the trampoline (rather than the signal handler),
-and the trampoline code calls the signal handler (and then calls
-.BR sigreturn ()
-once the handler returns).
-.SH SEE ALSO
-.BR kill (2),
-.BR restart_syscall (2),
-.BR sigaltstack (2),
-.BR signal (2),
-.BR getcontext (3),
-.BR signal (7)
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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