SIGALTSTACK(2)             Linux Programmer's Manual            SIGALTSTACK(2)
NAME
       sigaltstack - get or set alternate signal stack content

SYNOPSIS
       #include <signal.h>

       int sigaltstack(const stack_t *ss, stack_t *oss);

       where:

       ss     points to a signalstack structure defined in <signal.h> contain-
              ing stack content after the call.

       oss    if not NULL, points to a signalstack structure containing  stack
              content before the call.

DESCRIPTION
       sigaction(2)  may indicate that a signal should execute on an alternate
       stack. Where this is the case, sigaltstack(2) stores the signal  in  an
       alternate stack structure ss where its execution status may be examined
       prior to processing.

       The sigaltstack struct is defined in <signal.h> as follows:

                  void       *ss_sp     /* SVID3 uses caddr_t ss_sp
                  int        ss_flags
                  size_t     ss_size
       where:

       ss_sp  points to the stack structure.

       ss_flags
              specifies the stack state to SS_DISABLE or  SS_ONSTACK  as  fol-
              lows:

              If  ss is not NULL,the new state may be set to SS_DISABLE, which
              specifies that 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, the stack state may be either SS_ONSTACK  or
              SS_DISABLE.  The  value SS_ONSTACK indicates that the process is
              currently executing on the alternate stack and that any  attempt
              to  modify  it during execution will fail.  The value SS_DISABLE
              indicates that the current signal stack is disabled.

       ss_size
              specifies the size of the stack.

       The value SIGSTKSZ defines the average number of bytes used when  allo-
       cating an alternate stack area.  The value MINSIGSTKSZ defines the min-
       imum stack size for a signal handler.   When  processing  an  alternate
       stack  size,  your  program  should  include  these values in the stack
       requirement to plan for the overhead of the operating system.

RETURN VALUES
       sigaltstack(2) returns 0 on success and -1 on failure.

ERRORS
       sigaltstack(2) sets  errno for the following conditions:

       EINVAL ss is not a null pointer 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.

STANDARDS
       This function comforms to: XPG4-UNIX.

SEE ALSO
       getcontext(2), sigaction(2), sigsetjmp(3).

Red Hat Linux 6.1              20 September 1999                SIGALTSTACK(2)