NAME

sigaltstack − set or get signal alternate stack context

SYNOPSIS

#include <signal.h>

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

PARAMETERS

ssIf valid, specifies a pointer to a structure that indicates what will be in effect upon return from the call to the sigaltstack function. 

ossIf not NULL, specifies the pointer to a structure that contains the alternate signal stack that was in effect prior to the call to the sigaltstack function. 

DESCRIPTION

This function enables another stack area to be defined where signals can be examined for their execution status and processed.  If a signal’s action, specified by the sigaction(2) function, indicates that a signal should execute on a different stack, that signal is examined for its processing status.  A signal that is not currently executing on the signal stack is switched to an alternate stack for the duration of the handler’s execution. 

The sigaltstack structure is set up as follows:      caddr_t    ss_sp
     int        ss_flags
     size_t     ss_size
 

The values for each field is as follows:

ss_spSpecifies the new base for the stack. 

ss_flagsSpecifies the new stack state and may be set to either SS_DISABLE or SS_ONSTACK as follows:

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_sizeSpecifies the size of the stack. 

RESTRICTIONS

The value SIGSTKSZ defines the average number of bytes used when allocating an alternate stack area.  The value MINSIGSTKSZ defines the minimum 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

Upon successful completion, zero (0) is returned.  On error, the value -1 is returned and errno is set to indicate the error. 

RELATED INFORMATION

Functions: getcontext(2), sigaction(2). 

Routines: sigsetjmp(3). 

Files: ucontext(5).