The sigstack() function allows the calling process to indicate to the system an area of its address space to be used for processing signals received by the process.
If the ss argument is not a null pointer, it must point to a sigstack structure. The length of the application-supplied stack must be at least SIGSTKSZ bytes. If the alternate signal stack overflows, the resulting behavior is undefined. (See USAGE below.)
- The value of the ss_onstack member indicates whether the process wants the system to use an alternate signal stack when delivering signals.
- The value of the ss_sp member indicates the desired location of the alternate signal stack area in the process' address space.
- If the ss argument is a null pointer, the current alternate signal stack context is not changed.
If the oss argument is not a null pointer, it points to a sigstack structure in which the current alternate signal stack context is placed. The value stored
in the ss_onstack member of oss will be non-zero if the process is currently executing on the alternate signal stack. If the oss argument
is a null pointer, the current alternate signal stack context is not returned.
When a signal's action indicates its handler should execute on the alternate signal stack (specified by calling sigaction(2)), sigstack() checks to see if the process is currently executing on that stack. If the process is not currently
executing on the alternate signal stack, the system arranges a switch to the alternate signal stack for the duration of the signal handler's execution.
After a successful call to one of the exec functions, there are no alternate signal stacks in the new process image.