HP-UX Reference (11i v1 05/09) - 2 System Calls (vol 5)

s
sigaltstack(2) sigaltstack(2)
NAME
sigaltstack - set and/or get signal alternate stack context.
SYNOPSIS
#include <signal.h>
int sigaltstack(const stack_t *ss, stack_t *oss);
DESCRIPTION
The sigaltstack()
function allows a process to define and examine the state of an alternate stack for
signal handlers. Signals that have been explicitly declared to execute on the alternate stack will be
delivered on the alternate stack.
If ss is not a null pointer, it points to a
stack_t structure that specifies the alternate signal stack that
will take effect upon return from
sigaltstack(). The ss_flags member specifies the new stack state. If
it is set to
SS_DISABLE , the stack is disabled and ss_sp and ss_size are ignored. Otherwise the stack will
be enabled, and the ss_sp and ss_size members specify the new address and size of the stack.
The range of addresses starting at ss_sp, up to but not including ss_sp+ss_size, is available to the imple-
mentation for use as the stack. This interface makes no assumptions regarding which end is the stack base
and in which direction the stack grows as items are pushed.
If oss is not a null pointer, on successful completion it will point to a
stack_t structure that specifies the
alternate signal stack that was in effect prior to the call to
sigaltstack()
. The ss_sp and ss_size
members specify the address and size of that stack. The ss_flags member specifies the stack’s state, and
may contain one of the following values:
SS_ONSTACK The process is currently executing on the alternate signal stack. Attempts
to modify the alternate signal stack while the process is executing on it
fails. This flag must not be modified by processes.
SS_DISABLE The alternate signal stack is currently disabled.
The value
SIGSTKSZ is a system default specifying the number of bytes that would be used to cover the
usual case when manually allocating an alternate stack area. The value MINSIGSTKSZ is defined to be
the minimum stack size for a signal handler. In computing an alternate stack size, a program should add
that amount to its stack requirements to allow for the system implementation overhead. The constants
SS_ONSTACK ,SS_DISABLE ,SIGSTKSZ, and MINSIGSTKSZ are defined in <signal.h> .
After a successful call to one of the
exec functions, there are no alternate signal stacks in the new process
image.
RETURN VALUE
Upon successful completion, sigaltstack()
returns 0. Otherwise, it returns −1 and sets errno to
indicate the error.
ERRORS
The
sigaltstack() function will fail if:
[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 MINSIGSTKSZ .
[EPERM] An attempt was made to modify an active stack.
APPLICATION USAGE
The following code fragment illustrates a method for allocating memory for an alternate stack:
if ((sigstk.ss_sp = malloc(SIGSTKSZ)) == NULL)
/* error return */
sigstk.ss_size = SIGSTKSZ;
sigstk.ss_flags = 0;
if (sigaltstack(&sigstk,(stack_t *)0) < 0)
perror("sigaltstack");
In some implementations, a signal (whether or not indicated to execute on the alternate stack) will always
execute on the alternate stack if it is delivered while another signal is being caught using the alternate
stack.
HP-UX 11i Version 1: September 2005 − 1 − Hewlett-Packard Company Section 2−−363