These system calls are obsolete. Do not use them; use sigprocmask(2) instead.
sgetmask() returns the signal mask of the calling process.
ssetmask() sets the signal mask of the calling process to the value given in newmask. The previous signal mask is returned.
The signal masks dealt with by these two system calls are plain bit masks (unlike the sigset_t used by sigprocmask(2)); use sigmask(3) to create and inspect these masks.
Glibc does not provide wrappers for these obsolete system calls; in the unlikely event that you want to call them, use syscall(2).
These system calls are unaware of signal numbers greater than 31 (i.e., real-time signals).
These system calls do not exist on x86-64.
It is not possible to block SIGSTOP or SIGKILL.