getcontext(2) gets the current context of the calling process, storing it in the ucontext struct pointed to by ucp.
setcontext(2) sets the context of the calling process to the state stored in the ucontext struct pointed to by ucp. The struct must either have been created by getcontext(2) or have been passed as the third parameter of the sigaction(2) signal handler.
The ucontext struct created by getcontext(2) is defined in <ucontext.h> as follows:
typedef struct ucontext
unsigned long int uc_flags;
struct ucontext *uc_link;
struct _fpstate __fpregs_mem;
getcontext(2) returns 0 on success and -1 on failure. setcontext(2) does not return a value on success and returns -1 on failure.
These functions comform to: XPG4-UNIX.
When a signal handler executes, the current user context is saved and a new context is created by the kernel. If the calling process leaves the signal handler using longjmp(2), the original context cannot be restored, and the result of future calls to getcontext(2) are unpredictable. To avoid this problem, use siglongjmp(2) or setcontext(2) in signal handlers instead of longjmp(2).
sigaction(2), sigaltstack(2), sigprocmask(2), sigsetjmp(3), setjmp(3).