The sigsetjmp, setjmp, and _setjmp functions save their calling environment in env. Each of these functions returns 0.
The corresponding longjmp functions restore the environment saved by their most recent respective invocations of the setjmp function. They then return so that program execution continues as if the corresponding invocation of the setjmp call had just returned the value specified by val, instead of 0.
Pairs of calls may be intermixed, i.e., both sigsetjmp and siglongjmp and setjmp and longjmp combinations may be used in the same program, however, individual calls may not, e.g. the env argument to setjmp may not be passed to siglongjmp.
The longjmp routines may not be called after the routine which called the setjmp routines returns.
All accessible objects have values as of the time longjmp routine was called, except that the values of objects of automatic storage invocation duration that do not have the
.Vt volatile type and have been changed between the setjmp invocation and longjmp call are indeterminate.
The setjmp / longjmp pairs save and restore the signal mask while _setjmp / _longjmp pairs save and restore only the register set and the stack. (See sigprocmask 2.)
The sigsetjmp / siglongjmp function pairs save and restore the signal mask if the argument savemask is non-zero, otherwise only the register set and the stack are saved.
If the contents of the env are corrupted, or correspond to an environment that has already returned, the longjmp routine calls the routine longjmperror 3. If longjmperror returns the program is aborted (see abort(3)). The default version of longjmperror prints the message "longjmp botch" to standard error and returns. User programs wishing to exit more gracefully should write their own versions of longjmperror.
sigaction(2), sigaltstack(2), signal(3)