SunOS man pages : sigaltstack (2)
System Calls sigaltstack(2)
NAME
sigaltstack - set or get signal alternate stack context
SYNOPSIS
#include <signal.h>
int sigaltstack(const stack_t *ss, stack_t *oss);
DESCRIPTION
The sigaltstack() function allows an LWP to define and exam-
ine the state of an alternate stack area on which signals
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 LWP is currently execut-
ing on that stack. When a signal's action indicates its
handler should execute on the alternate signal stack
(specified with a sigaction(2) call), the system checks
whether the LWP chosen to execute the signal handler is
currently executing on that stack. If the LWP 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:
SS_ONSTACK
The LWP is currently executing on the alternate signal
stack. Attempts to modify the alternate signal stack
while the LWP is executing on it will fail.
SunOS 5.8 Last change: 10 Jun 1999 1
System Calls sigaltstack(2)
SS_DISABLE
The alternate signal stack is currently disabled.
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 contains flags other
than SS_DISABLE.
ENOMEM
The size of the alternate stack area is less than MIN-
SIGSTKSZ.
EPERM An attempt was made to modify an active stack.
SEE ALSO
getcontext(2), sigaction(2), ucontext(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 sigaltstack() function creates an alternate signal stack
for the calling LWP, with the implication that in a mul-
tithreaded application, only bound threads (or in POSIX ter-
minology, only threads whose scheduling contention scope is
PTHREAD_SCOPE_SYSTEM, see thr_create(3THR) and
pthread_create(3THR)) should call sigaltstack(). The
behavior of an application that calls sigaltstack() from an
unbound thread (that is, a POSIX thread whose scheduling
contention scope is PTHREAD_SCOPE_PROCESS) is undefined. In
a future release, sigaltstack() may return a new error value
if it is called from an unbound thread.
The following code fragment is typically used to allocate an
alternate stack:
SunOS 5.8 Last change: 10 Jun 1999 2
System Calls sigaltstack(2)
if ((sigstk.ss_sp = (char *)malloc(SIGSTKSZ)) == NULL)
/* error return */;
sigstk.ss_size = SIGSTKSZ;
sigstk.ss_flags = 0;
if (sigaltstack(&sigstk, (stack_t *)0) < 0)
perror("sigaltstack");
SunOS 5.8 Last change: 10 Jun 1999 3
|
 |
|
|
