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System Calls sigaltstack(2)
NAME
sigaltstack - set or get signal alternate stack context
SYNOPSIS
#include <signal.h>
int sigaltstack(const stack_t *restrict ss, stack_t *res-
trict oss);
DESCRIPTION
The sigaltstack() function allows a thread to define and
examine the state of an alternate stack area on which sig-
nals are processed. If ss is non-zero, it specifies a
pointer to and the size of a stack area on which to deliver
signals, and informs the system whether the thread is
currently executing on that stack. When a signal's action
indicates its handler should execute on the alternate sig-
nal stack (specified with a sigaction(2) call), the system
checks whether the thread chosen to execute the signal
handler is currently executing on that stack. If the thread
is not currently executing on the signal stack, the system
arranges a switch to the alternate signal stack for the
duration of the signal handler's execution.
The stack_t structure includes the following members:
int *ss_sp
long ss_size
int ss_flags
If ss is not NULL, it points to a structure specifying the
alternate signal stack that will take effect upon successful
return from sigaltstack(). The ss_sp and ss_size members
specify the new base and size of the stack, which is
automatically adjusted for direction of growth and align-
ment. The ss_flags member specifies the new stack state
and may be set to the following:
SS_DISABLE The stack is to be disabled and ss_sp and
ss_size are ignored. If SS_DISABLE is not
set, the stack will be enabled.
If oss is not NULL, it points to a structure specifying the
alternate signal stack that was in effect prior to the call
to sigaltstack(). The ss_sp and ss_size members specify the
base and size of that stack. The ss_flags member specifies
the stack's state, and may contain the following values:
SunOS 5.10 Last change: 1 Nov 2003 1
System Calls sigaltstack(2)
SS_ONSTACK The thread is currently executing on the
alternate signal stack. Attempts to modify
the alternate signal stack while the thread
is executing on it will fail.
SS_DISABLE The alternate signal stack is currently dis-
abled.
RETURN VALUES
Upon successful completion, 0 is return. Otherwise, -1 is
returned and errno is set to indicate the error.
ERRORS
The sigaltstack() function will fail if:
EFAULT The ss or oss argument points to an illegal
address.
EINVAL The ss argument is not a null pointer, and
the ss_flags member pointed to by ss con-
tains flags other than SS_DISABLE.
ENOMEM The size of the alternate stack area is less
than MINSIGSTKSZ.
EPERM An attempt was made to modify an active
stack.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Standard |
|_____________________________|_____________________________|
| MT-Level | Async-Signal-Safe |
|_____________________________|_____________________________|
SunOS 5.10 Last change: 1 Nov 2003 2
System Calls sigaltstack(2)
SEE ALSO
getcontext(2), mmap(2), sigaction(2), ucontext.h(3HEAD),
attributes(5), standards(5)
NOTES
The value SIGSTKSZ is defined to be the number of bytes that
would be used to cover the usual case when allocating an
alternate stack area. The value MINSIGSTKSZ is defined to
be the minimum stack size for a signal handler. In comput-
ing an alternate stack size, a program should add that
amount to its stack requirements to allow for the operating
system overhead.
The following code fragment is typically used to allocate an
alternate stack with an adjacent red zone (an unmapped page)
to guard against stack overflow, as with default stacks:
#include <signal.h>
#include <sys/mman.h>
stack_t sigstk;
sigstk.ss_sp = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANON, -1, 0);
if (sigstk.ss_sp == MAP_FAILED)
/* error return */;
sigstk.ss_size = SIGSTKSZ;
sigstk.ss_flags = 0;
if (sigaltstack(&sigstk, NULL) < 0)
perror("sigaltstack");
SunOS 5.10 Last change: 1 Nov 2003 3
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This page was generated on Wed Sep 12 11:27:10 GMT 2007
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