sigaltstack(2)

1sigaltstack(2)                   System Calls                   sigaltstack(2)
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NAME

6       sigaltstack - set or get signal alternate stack context
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SYNOPSIS

9       #include <signal.h>
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11       int sigaltstack(const stack_t *restrict ss, stack_t *restrict oss);
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DESCRIPTION

15       The  sigaltstack()  function  allows a thread to define and examine the
16       state of an alternate stack area on which signals are processed. If  ss
17       is  non-zero, it specifies a pointer to and the size of a stack area on
18       which to deliver signals, and informs the system whether the thread  is
19       currently  executing  on  that stack.  When a signal's action indicates
20       its handler should  execute on the alternate  signal  stack  (specified
21       with  a sigaction(2) call), the system checks whether the thread chosen
22       to execute the signal handler is currently executing on that stack.  If
23       the  thread  is not currently executing on the signal stack, the system
24       arranges a switch to the alternate signal stack for the duration of the
25       signal handler's execution.
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28       The  stack_t structure includes the following members:
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30         int   *ss_sp
31         long  ss_size
32         int   ss_flags
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36       If  ss  is  not NULL, it points to a structure specifying the alternate
37       signal stack that will take effect upon successful return from  sigalt‐
38       stack(). The ss_sp and ss_size members specify the new base and size of
39       the stack, which is automatically adjusted for direction of growth  and
40       alignment.   The ss_flags member specifies the new stack state  and may
41       be set to the following:
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43       SS_DISABLE    The stack is to be disabled and  ss_sp  and  ss_size  are
44                     ignored.  If  SS_DISABLE  is  not  set, the stack will be
45                     enabled.
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49       If oss is not NULL, it points to a structure specifying  the  alternate
50       signal stack that was in effect prior to the call to sigaltstack(). The
51       ss_sp and ss_size members specify the base and size of that stack.  The
52       ss_flags  member  specifies the stack's state, and may contain the fol‐
53       lowing values:
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55       SS_ONSTACK    The thread is currently executing on the alternate signal
56                     stack.  Attempts  to  modify  the  alternate signal stack
57                     while the thread is executing on it will fail.
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60       SS_DISABLE    The alternate signal stack is currently disabled.
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RETURN VALUES

64       Upon successful completion, 0 is return. Otherwise, −1 is returned  and
65       errno is set to indicate the error.
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ERRORS

68       The sigaltstack() function will fail if:
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70       EFAULT    The ss or oss argument points to an illegal address.
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73       EINVAL    The  ss argument is not a null pointer, and the ss_flags mem‐
74                 ber pointed to by ss contains flags other than SS_DISABLE.
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77       ENOMEM    The size of the  alternate  stack  area  is  less  than  MIN‐
78                 SIGSTKSZ.
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81       EPERM     An attempt was made to modify an active stack.
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ATTRIBUTES

85       See attributes(5) for descriptions of the following attributes:
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90       ┌─────────────────────────────┬─────────────────────────────┐
91       │      ATTRIBUTE TYPE         │      ATTRIBUTE VALUE        │
92       ├─────────────────────────────┼─────────────────────────────┤
93       │Interface Stability          │Standard                     │
94       ├─────────────────────────────┼─────────────────────────────┤
95       │MT-Level                     │Async-Signal-Safe            │
96       └─────────────────────────────┴─────────────────────────────┘
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NOTES

103       The value SIGSTKSZ is defined to be the number of bytes that  would  be
104       used  to cover the usual case when allocating an alternate  stack area.
105       The value MINSIGSTKSZ is defined to be the minimum  stack  size  for  a
106       signal  handler.   In  computing  an  alternate  stack  size, a program
107       should add that amount to its stack requirements to allow for the oper‐
108       ating system overhead.
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111       The  following code fragment is typically used to allocate an alternate
112       stack with an adjacent red zone (an unmapped  page)  to  guard  against
113       stack overflow, as with default stacks:
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115         #include <signal.h>
116         #include <sys/mman.h>
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118         stack_t sigstk;
119         sigstk.ss_sp = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,
120                 MAP_PRIVATE | MAP_ANON, -1, 0);
121         if (sigstk.ss_sp == MAP_FAILED)
122                 /* error return */;
123         sigstk.ss_size = SIGSTKSZ;
124         sigstk.ss_flags = 0;
125         if (sigaltstack(&sigstk, NULL) < 0)
126                 perror("sigaltstack");
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131SunOS 5.11                        1 Nov 2003                    sigaltstack(2)