4.4BSD/usr/share/man/cat2/sigaltstack.0

SIGALTSTACK(2)              BSD Programmer's Manual             SIGALTSTACK(2)

NNAAMMEE
     ssiiggaallttssttaacckk - set and/or get signal stack context

SSYYNNOOPPSSIISS
     ##iinncclluuddee <<ssyyss//ttyyppeess..hh>>
     ##iinncclluuddee <<ssiiggnnaall..hh>>
     struct sigaltstack {
             caddr_t ss_sp;
             long    ss_size;
             int     ss_flags;
     };

     _i_n_t
     ssiiggaallttssttaacckk(_c_o_n_s_t _s_t_r_u_c_t _s_i_g_a_l_t_s_t_a_c_k _*_s_s, _s_t_r_u_c_t _s_i_g_a_l_t_s_t_a_c_k _*_o_s_s);

DDEESSCCRRIIPPTTIIOONN
     SSiiggaallttssttaacckk() allows users to define an alternate stack on which signals
     are to be processed.  If _s_s is non-zero, it specifies a pointer to and
     the size of a _s_i_g_n_a_l _s_t_a_c_k on which to deliver signals, and tells the
     system if the process is currently executing on that stack.  When a sig-
     nal's action indicates its handler should execute on the signal stack
     (specified with a sigaction(2) call), the system checks to see if the
     process is currently executing on that stack.  If the process is not cur-
     rently executing on the signal stack, the system arranges a switch to the
     signal stack for the duration of the signal handler's execution.

     If SA_DISABLE is set in _s_s___f_l_a_g_s, _s_s___s_p and _s_s___s_i_z_e are ignored and the
     signal stack will be disabled.  Trying to disable an active stack will
     cause ssiiggaallttssttaacckk to return -1 with _e_r_r_n_o set to EINVAL. A disabled stack
     will cause all signals to be taken on the regular user stack.  If the
     stack is later re-enabled then all signals that were specified to be pro-
     cessed on an alternate stack will resume doing so.

     If _o_s_s is non-zero, the current signal stack state is returned.  The
     _s_s___f_l_a_g_s field will contain the value SA_ONSTACK if the process is cur-
     rently on a signal stack and SA_DISABLE if the signal stack is currently
     disabled.

NNOOTTEESS
     The value SIGSTKSZ is defined to be the number of bytes/chars that would
     be used to cover the usual case when allocating an alternate stack area.
     The following code fragment is typically used to allocate an alternate
     stack.

           if ((sigstk.ss_sp = malloc(SIGSTKSZ)) == NULL)
                   /* error return */
           sigstk.ss_size = SIGSTKSZ;
           sigstk.ss_flags = 0;
           if (sigaltstack(&sigstk,0) < 0)
                   perror("sigaltstack");
     An alternative approach is provided for programs with signal handlers
     that require a specific amount of stack space other than the default
     size.  The value MINSIGSTKSZ is defined to be the number of bytes/chars
     that is required by the operating system to implement the alternate stack
     feature.  In computing an alternate stack size, programs should add
     MINSIGSTKSZ to their stack requirements to allow for the operating system
     overhead.

     Signal stacks are automatically adjusted for the direction of stack
     growth and alignment requirements.  Signal stacks may or may not be pro-
     tected by the hardware and are not ``grown'' automatically as is done for
     the normal stack.  If the stack overflows and this space is not protected
     unpredictable results may occur.

RREETTUURRNN VVAALLUUEESS
     Upon successful completion, a value of 0 is returned.  Otherwise, a value
     of -1 is returned and _e_r_r_n_o is set to indicate the error.

EERRRROORRSS
     SSiiggssttaacckk() will fail and the signal stack context will remain unchanged
     if one of the following occurs.

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

     [EINVAL]  An attempt was made to disable an active stack.

     [ENOMEM]  Size of alternate stack area is less than or equal to
               MINSIGSTKSZ.

SSEEEE AALLSSOO
     sigaction(2),  setjmp(3)

HHIISSTTOORRYY
     The predecessor to ssiiggaallttssttaacckk, the ssiiggssttaacckk() system call, appeared in
     4.2BSD.

4.2 Berkeley Distribution        June 4, 1993                                2