1SIGALTSTACK(3P) POSIX Programmer's Manual SIGALTSTACK(3P)
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6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
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13 sigaltstack — set and get signal alternate stack context
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16 #include <signal.h>
17 int sigaltstack(const stack_t *restrict ss, stack_t *restrict oss);
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21 The sigaltstack() function allows a process to define and examine the
22 state of an alternate stack for signal handlers for the current thread.
23 Signals that have been explicitly declared to execute on the alternate
24 stack shall be delivered on the alternate stack.
25 If ss is not a null pointer, it points to a stack_t structure that
27 specifies the alternate signal stack that shall take effect upon return
28 from sigaltstack(). The ss_flags member specifies the new stack state.
29 If it is set to SS_DISABLE, the stack is disabled and ss_sp and ss_size
30 are ignored. Otherwise, the stack shall be enabled, and the ss_sp and
31 ss_size members specify the new address and size of the stack.
32 The range of addresses starting at ss_sp up to but not including
34 ss_sp+ss_size is available to the implementation for use as the stack.
35 This function makes no assumptions regarding which end is the stack
36 base and in which direction the stack grows as items are pushed.
37 If oss is not a null pointer, upon successful completion it shall point
39 to a stack_t structure that specifies the alternate signal stack that
40 was in effect prior to the call to sigaltstack(). The ss_sp and
41 ss_size members specify the address and size of that stack. The
42 ss_flags member specifies the stack's state, and may contain one of the
43 following values:
44 SS_ONSTACK The process is currently executing on the alternate signal
46 stack. Attempts to modify the alternate signal stack while
47 the process is executing on it fail. This flag shall not be
48 modified by processes.
49 SS_DISABLE The alternate signal stack is currently disabled.
51 The value SIGSTKSZ is a system default specifying the number of bytes
53 that would be used to cover the usual case when manually allocating an
54 alternate stack area. The value MINSIGSTKSZ is defined to be the mini‐
55 mum stack size for a signal handler. In computing an alternate stack
56 size, a program should add that amount to its stack requirements to
57 allow for the system implementation overhead. The constants SS_ONSTACK,
58 SS_DISABLE, SIGSTKSZ, and MINSIGSTKSZ are defined in <signal.h>.
59 After a successful call to one of the exec functions, there are no
61 alternate signal stacks in the new process image.
62 In some implementations, a signal (whether or not indicated to execute
64 on the alternate stack) shall always execute on the alternate stack if
65 it is delivered while another signal is being caught using the alter‐
66 nate stack.
67 Use of this function by library threads that are not bound to kernel-
69 scheduled entities results in undefined behavior.
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72 Upon successful completion, sigaltstack() shall return 0; otherwise, it
73 shall return −1 and set errno to indicate the error.
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76 The sigaltstack() function shall fail if:
77 EINVAL The ss argument is not a null pointer, and the ss_flags member
79 pointed to by ss contains flags other than SS_DISABLE.
80 ENOMEM The size of the alternate stack area is less than MINSIGSTKSZ.
82 EPERM An attempt was made to modify an active stack.
84 The following sections are informative.
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88 Allocating Memory for an Alternate Stack
89 The following example illustrates a method for allocating memory for an
90 alternate stack.
91 #include <signal.h>
93 ...
94 if ((sigstk.ss_sp = malloc(SIGSTKSZ)) == NULL)
95 /* Error return. */
96 sigstk.ss_size = SIGSTKSZ;
97 sigstk.ss_flags = 0;
98 if (sigaltstack(&sigstk,(stack_t *)0) < 0)
99 perror("sigaltstack");
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102 On some implementations, stack space is automatically extended as
103 needed. On those implementations, automatic extension is typically not
104 available for an alternate stack. If the stack overflows, the behavior
105 is undefined.
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108 None.
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111 None.
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114 Section 2.4, Signal Concepts, exec, sigaction(), sigsetjmp()
115 The Base Definitions volume of POSIX.1‐2008, <signal.h>
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119 Portions of this text are reprinted and reproduced in electronic form
120 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
121 -- Portable Operating System Interface (POSIX), The Open Group Base
122 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
123 cal and Electronics Engineers, Inc and The Open Group. (This is
124 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
125 event of any discrepancy between this version and the original IEEE and
126 The Open Group Standard, the original IEEE and The Open Group Standard
127 is the referee document. The original Standard can be obtained online
128 at http://www.unix.org/online.html .
129 Any typographical or formatting errors that appear in this page are
131 most likely to have been introduced during the conversion of the source
132 files to man page format. To report such errors, see https://www.ker‐
133 nel.org/doc/man-pages/reporting_bugs.html .
134IEEE/The Open Group 2013 SIGALTSTACK(3P)