NAME
sigstack - set and/or get signal stack context

SYNOPSIS
#include <signal.h>

struct sigstack {
caddr_t ss_sp;
int ss_onstack;
};

sigstack(ss, oss);
struct sigstack *ss, *oss;

DESCRIPTION
Sigstack allows users to define an alternate stack on which signals
are to be processed. If ss is non-zero, it specifies a signal
stack on which to deliver signals and tells the system if the
process is currently executing on that stack. When a signal’s
action indicates its handler should execute on the signal stack
(specified with a sigvec(2) call), the system checks to see if the
process is currently executing on that stack. If the process is
not currently executing on the signal stack, the system arranges a
switch to the signal stack for the duration of the signal handler’s
execution. If oss is non-zero, the current signal stack state is
returned.

NOTES
Signal stacks are not "grown" automatically, as is done for the
normal stack. If the stack overflows unpredictable results may
occur.

RETURN VALUE
Upon successful completion, a value of 0 is returned. Otherwise, a
value of -1 is returned and errno is set to indicate the error.

ERRORS
Sigstack will fail and the signal stack context will remain
unchanged if one of the following occurs.

[EFAULT] Either ss or oss points to memory that is not a
valid part of the process address space.

SEE ALSO
sigvec(2), setjmp(3)