1 .\" Copyright (C) 2008, 2014, Michael Kerrisk <mtk.manpages@gmail.com>
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25 .\" Created Sat Aug 21 1995 Thomas K. Dyas <tdyas@eden.rutgers.edu>
26 .\" Modified Tue Oct 22 22:09:03 1996 by Eric S. Raymond <esr@thyrsus.com>
27 .\" 2008-06-26, mtk, added some more detail on the work done by sigreturn()
28 .\" 2014-12-05, mtk, rewrote all of the rest of the original page
30 .TH SIGRETURN 2 2014-12-31 "Linux" "Linux Programmer's Manual"
32 sigreturn \- return from signal handler and cleanup stack frame
34 .BI "int sigreturn(...);"
36 If the Linux kernel determines that an unblocked
37 signal is pending for a process, then,
38 at the next transition back to user mode in that process
39 (e.g., upon return from a system call or
40 when the process is rescheduled onto the CPU),
41 it saves various pieces of process context
42 (processor status word, registers, signal mask, and signal stack settings)
43 into the user-space stack.
44 .\" See arch/x86/kernel/signal.c::__setup_frame() [in 3.17 source code]
46 The kernel also arranges that, during the transition back to user mode,
47 the signal handler is called, and that, upon return from the handler,
48 control passes to a piece of user-space code commonly called
49 the "signal trampoline".
50 The signal trampoline code in turn calls
55 call undoes everything that was
56 done\(emchanging the process's signal mask, switching signal stacks (see
57 .BR sigaltstack "(2))\(emin "
58 order to invoke the signal handler.
59 It restores the process's signal mask, switches stacks,
60 and restores the process's context
61 (processor flags and registers,
62 including the stack pointer and instruction pointer),
63 so that the process resumes execution
64 at the point where it was interrupted by the signal.
69 Many UNIX-type systems have a
71 system call or near equivalent.
72 However, this call is not specified in POSIX,
73 and details of its behavior vary across systems.
76 exists only to allow the implementation of signal handlers.
80 Details of the arguments (if any) passed to
82 vary depending on the architecture.
84 Once upon a time, UNIX systems placed the signal trampoline code
86 Nowadays, pages of the user stack are protected so as to
87 disallow code execution.
88 Thus, on contemporary Linux systems, depending on the architecture,
89 the signal trampoline code lives either in the
93 .\" See, for example, sysdeps/unix/sysv/linux/i386/sigaction.c and
94 .\" sysdeps/unix/sysv/linux/x86_64/sigaction.c in the glibc (2.20) source.
95 the C library supplies the location of the trampoline code using the
99 structure that is passed to
107 The saved process context information is placed in a
110 .IR <sys/ucontext.h> ).
111 That structure is visible within the signal handler
112 as the third argument of a handler established with the
116 On some other UNIX systems,
117 the operation of the signal trampoline differs a little.
118 In particular, on some systems, upon transitioning back to user mode,
119 the kernel passes control to the trampoline (rather than the signal handler),
120 and the trampoline code calls the signal handler (and then calls
122 once the handler returns).
125 .BR restart_syscall (2),
131 This page is part of release 3.79 of the Linux
134 A description of the project,
135 information about reporting bugs,
136 and the latest version of this page,
138 \%http://www.kernel.org/doc/man\-pages/.