sigstack(S)

sigstack -- set and/or get signal stack context

Syntax

cc . . . -lc

#include <signal.h>

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

Description

sigstack allows users to define an alternate stack, called the ``signal stack,'' on which signals are to be processed. When a signal's action indicates its handler should execute on the signal stack (specified with a sigaction(S) 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.

A signal stack is specified by a sigstack structure, which includes the following members:

   void    *ss_sp;       /* signal stack pointer */
   int	ss_onstack;   /* current status */

ss_sp is the initial value to be assigned to the stack pointer when the system switches the process to the signal stack. Note that this is not the address of the beginning of the signal stack area. The ss_onstack field of oss is non-zero or zero depending on whether the process is currently executing on the alternate signal stack or not.

If ss is not a NULL pointer, sigstack sets the signal stack state to the value in the sigstack structure pointed to by ss.

If ss is a NULL pointer, the signal stack state will be unchanged. If oss is not a NULL pointer, the current signal stack state is stored in the sigstack structure pointed to by oss.

Return values

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

Diagnostics

sigstack will fail and the signal stack context will remain unchanged if the following occurs:

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

Limitations

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

Files

/lib/libc.a: linking library

Standards conformance

sigstack is conformant with:

X/Open Portability Guide Issue 4, Version 2 (Spec-1170).